Coastal ecosystems provide vital services, including water storage, carbon sequestration, biodiversity, and coastal protection. Human disturbances, however, cause massive losses. The most direct impact is habitat destruction through infrastructure development, restricting the space available to coastal ecosystems and impeding their capacity to adapt to sea level rise by landward retreat – a phenomenon called ‘coastal squeeze’. While shoreline retreat is intensively studied, coastal congestion through infrastructure remains unquantified. Here we calculated the distance to the nearest human-made structure along 263,900 transects worldwide to show that infrastructure occurs at a 560-meter median distance from the shoreline. Moreover, we find that 18% of global sandy shores harbour less than 100 m of infrastructure-free space, and that 14-17% of the unimpacted space may drown by 2100 according to sea level rise projections. Further analyses show that population density and gross domestic product explain 40-44% of observed squeeze variation, emphasizing the intensifying pressure imposed as countries develop and populations expand. Encouragingly, we find that nature reserves relieve squeezing by 3-5 times, illustrating their effectiveness. Yet, at present only 16% of world’s sandy shores has a protected status. We therefore argue that expansion of nature reserves could be key to preserving coastal resilience to sea level rise.

How to cite: Lansu, E., Reijers, V., Höfer, S., Luijendijk, A., Rietkerk, M., Wassen, M., Lammerts, E. J., and van der Heide, T.: A global analysis of how human infrastructure squeezes sandy coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-67, https://doi.org/10.5194/egusphere-egu23-67, 2023.

Coastal ecosystems are vulnerable to climate change, with rising sea levels and increased anthropogenic pressure constraining space for natural processes. Nature based solutions using sediments rather than hard surfaces in coastal defense may offer an alternative that both creates new habitats and offer a flexible protection against flooding.

In contrast to hard infrastructure, the topography of dunes depends on the highly dynamic processes of wind and waves and the resistance to them offered by dune vegetation. Perennial grass species such as marram grass (Ammophila arenaria) and sand couch (Elytrigia juncea) play a key-role for topographic stability and the development and shape of coastal dune forms. This is usually attributed to their dense cover which effectively traps sand as well as their positive growth response to burial by sediments. Therefore, species like marram grass have been used as ecosystem engineers in both past and recent coastal dune restoration projects.

Whether this solution will be applicable in the future depends on climate change. Coastal vegetation is vulnerable to climate change due to its susceptibility to changes in growing conditions (e.g. Temperature, Precipitation). Especially at the dry-beach section where the influence of groundwater is limited, a change in growing season precipitation could potentially affect the cover of dune grasses. Past research was already able to establish a general link between dune development and growth in function of precipitation. However, to this date direct responses of dune vegetation to precipitation has not been quantified.

We explored the response of dune building grasses to summer precipitation and its implication for the future dune building in a two-step approach. We used a greenhouse-experiment to derive species growth relationships with water availability for marram grass and sand couch. In a second step we used these relationships to explore the impact of potential changes in summer precipitation on the growth of these species. We found that both marram grass and sand couch were equally sensitive to changes in water availability and responded positively to an increase in it. Comparing soil moisture from the field to the greenhouse, showed that field water availability tended to be on the lower end of ranges in the greenhouse. This suggests that dune vegetation in the field is susceptible to drought effects. Exploring these results further using climate scenarios, we found that plant growth was increased by 1.3 % (experimental period) – 1.8 % (extrapolated) under the most recent RCP 4.5 IPCC projection and by 9.6 – 13 % for an extremely wet year. In contrast, for an extremely dry year plant growth could decrease by 6.2 – 8.2 %.

While changes of < 2 % in plant growth might have limited implications for dune development and stability, years of extreme climate conditions show a bigger range in plant growth (- 8 % - + 13 %) which is more likely to also have direct consequences for dune growth and development. Incorporating these relationships between plant growth and climate in models of coastal dune development should improve predictions of climate change impacts.

How to cite: Homberger, J.-M., Lynch, A., Limpens, J., and Riksen, M.: Response of dune-building grasses to summer precipitation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1076, https://doi.org/10.5194/egusphere-egu23-1076, 2023.

Around the Arctic Ocean there are many stretches of coastline composed of ice-rich sediments. With the dramatic climatic, oceanic and terrestrial changes that are currently underway, there is considerable concern over the stability of these coasts and how they impact coastal communities. Unfortunately, there is still relatively little research that has been done the processes at work in these environments. Being able to effectively model coastal erosion in a permafrost setting is highly desirable. With the complexity that ice-rich permafrost conditions add to the coastal setting, modelling erosion involves a more detailed understanding of the physical and thermal conditions as well as the sedimentological and wave action processes. This research examines the rate and character of coastal erosion of ice-rich terrain and role that re-sedimentation has on the shallow water energy balance in preserving sub-bottom massive ice. It also addresses it implications to secondary sea bottom disturbance as the water depth increases.

The study area was Peninsula Point which is approximately 10 km west of Tuktoyaktuk, Northwest Territories, Canada. The massive ice and retrogressive thaw flows at this location are some of the more dramatic examples of the impact of ice-rich permafrost on coastal processes in the Arctic. Through a three decade long program of remote sensing, geophysical and ground-based monitoring, long-term changes were investigated. The character of coastal retreat above, and below, the waterline in an area where a massive ice body extends to depths below sea level were revealed. Airphoto, satellite imagery and drone data revealed the complexity of erosion with the retreating headwall of retrogressive thaw flow more rapidly eroding the landscape than the observed lateral changes of the waterline. Ground-penetrating radar (GPR) imaged the top and base of the massive ice body as well as providing a delineation of the subsurface sedimentary architecture. In winter, the GPR was pulled behind a snowmobile along transects on land, across the shoreline and out onto the near shore area of the Beaufort Sea. This provided the stratigraphic continuity between the terrestrial and sub-sea settings. The roles of erosion, re-sedimentation and shallow-water thermodynamics in the degradation and preservation of massive ground ice were revealed. The results of this study demonstrate how coastal erosion is much more complex that just the inland movement of the waterline.

How to cite: Moorman, B., Clark, A., and Whalen, D.: Ice-rich permafrost coastline erosion processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1493, https://doi.org/10.5194/egusphere-egu23-1493, 2023.

How to cite: van Rosmalen, S., Homberger, J.-M., Riksen, M., and Limpens, J.: Recreation impact on establishment of dune building species, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2771, https://doi.org/10.5194/egusphere-egu23-2771, 2023.

In front of the traditional dike at Oosteroever, Belgium, a new 120x20 m² artificial dune with planted marram grass of different densities and patterns was built in January 2021. This man-made dune was constructed to reduce the local aeolian sand nuisance on the dike. The complex interaction between aeolian sand transport and vegetation will ensure future morphological development of a dune body strengthening the local coastal protection. For an optimal design of these planted dunes, a fundamental knowledge of morphological changes is required. This study is twofold: 1) Investigate dune growth by exploring a multi-monthly field dataset of wind characteristics and high-resolution topographic data, 2) Development and assessment of the AeoLiS model for simulation of this new planted coastal dune field. The performance of AeoLiS is analyzed by comparing observed and simulated results of erosion and deposition patterns and cross-shore bed level changes. The total volume of sand in the dune has increased significantly since the plantation of marram grass, resulting in 15 m³ m^-1 due to aeolian sand transport from the surrounding beach. Most dune growth occurred during the first year. Dune growth during the second year was less pronounced and was attributed to the influence of supply limitations, vegetation characteristics, and sediment erosion by wind and storm events. The results of the model simulations demonstrate that AeoLiS can replicate the spatial patterns and profile development inside the artificial dune area to some extent. However, to adequately account for the interaction between vegetation and aeolian sand transport, the model's treatment of vegetation dynamics needs to be improved.

How to cite: Strypsteen, G. and Rauwoens, P.: Morphological changes in a planted coastal dune field: measurements and modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4119, https://doi.org/10.5194/egusphere-egu23-4119, 2023.

How to cite: Choi, K., Kim, D., Jo, J., Sohn, S., and Nam, S.-I.: Morphodynamic evolution of paraglacial spit complexes on a tide-influenced Arctic fjord delta (Dicksonfjorden, Svalbard), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4579, https://doi.org/10.5194/egusphere-egu23-4579, 2023.

Located in north-eastern Canada near Shippagan, New Brunswick, the Shippagan Gully Conservation Offsetting Project is leveraging salt marsh creation and sand motor techniques to create Piping Plover habitat while increasing resiliency of the Chaisson Office Spit and surrounding communities to climate change. The spit has been altered by more than a century of human activity and is increasingly impacted by climate change and sea-level rise. The project, which employs a holistic approach to improve marine navigation through the Gully and install nature-based solutions for coastal protection and habitat creation, is the first sand motor in Atlantic Canada and the most northern created marsh with sill to date. Extensive modeling was undertaken by NRC prior to the commencement of baseline data collection and design in 2017. Several monitoring and research initiatives are associated with the project, including a fifteen-year monitoring program (regulatory requirement), five-year post-graduate scientific research program, and a 3-year research project which will augment and build on the NRC-led Nature-Based Infrastructure for Coastal Resilience project. Construction began on the sand motor in 2020, with the marsh and marsh sill scheduled to be built in winter 2023 from on-site materials and planted in  spring 2023. The final stages of the implementation will include dune and wetland restoration following the removal of old infrastructure, returning nearly the entire spit to a more natural state and restoring natural processes. The first two years of monitoring following the sand motor implementation have shown a shift in conditions to those more closely matching a nearby control site, as well as the first successful nesting and fledging of Piping Plover (Federally Endangered Species) on the site in over 20 years. The project is the result of a collaborative effort that includes federal and provincial government departments, private industry, academia, and environmental NGOs.

How to cite: Graham, J., vanProosdij, D., Ellis, K., Bowron, T., and Thomas, J.: Restoring Piping Plover Habitat and Building Coastal Resilience with Nature-based Solutions in Atlantic Canada, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4673, https://doi.org/10.5194/egusphere-egu23-4673, 2023.

The Bering and Chukchi Seas are important oceanic regions of carbon sequestration, owing to enhanced gas solubility in cold surface waters and the rapid uptake of carbon dioxide (CO₂) during intense spring blooms. The biogeochemical impacts of decreasing sea ice extent and earlier onset of spring ice melt in this region are yet uncertain. As these marginal seas of the western Arctic Ocean are quite shallow, mostly <60m depth, there is extensive interaction across air-sea-sediment boundaries, but the transformations and fluxes of inorganic carbon in Bering and Chukchi Sea sediments have not been directly quantified. In May-June 2021, we collected water column samples at 14 stations and sediment cores at 5 stations spanning the eastern Bering Sea and southern and eastern Chukchi Sea. Duplicate cores were incubated for several days at in situ temperature, and core-top water was sampled to estimate inorganic carbon and nutrient fluxes. The stations spanned a range of surface ice coverage history, from greater than one month to less than one day of ice-free conditions. In the Chukchi Sea, salinity-normalized bottom water nutrient and dissolved inorganic carbon (DIC) concentrations increased northward, indicating a net input of remineralization products, although effluxes of these parameters from the sediments decreased northward. Moving northward in the Chukchi Sea, the surface water had greater sea ice concentrations, inhibiting surface productivity and air-sea exchange. This may have reduced the rain of labile carbon to the seafloor, resulting in the decreased benthic remineralization. The combination of increasing northward ice coverage and the northward flow of nutrient and IC-rich Pacific-sourced waters influences the bottom-water concentration of remineralization products and sediment-water fluxes. We expect our northeastern Chukchi Sea flux observations are representative of baseline low wintertime sediment-water flux conditions, while the more southerly stations represent at least one month post-ice melt benthic fluxes when surface water productivity is high and the air-water-sediment system openly interacts. We note that some duplicate core measurements were highly heterogeneous, especially in the Bering Sea, illustrating the dynamic nature of this macrofauna-dominated benthic environment and the range of possible fluxes under different rates of bioturbation. While these observations may serve as a seasonal reference, they may also demonstrate how sedimentary fluxes will evolve under future conditions that are expected when sea ice retreats earlier in the season. Here we present our sediment-water flux and water column DIC and nutrient measurements and place them in context with previous work in the region.

How to cite: Barrett, L., Vlahos, P., and Hammond, D.: Early melt-season nutrient and inorganic carbon sediment-water fluxes in the Bering and Chukchi Seas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7877, https://doi.org/10.5194/egusphere-egu23-7877, 2023.

While most global coasts suffer from a loss of landmass due to sea-level rise and coastal transgression, the Arctic and Sub-Arctic coastlines of Hudson Bay and James Bay witness a reverse phenomenon due to post-glacial rebound. The carbon-rich peatlands Hudson Bay Lowland, that emerged from the retraction of the Tyrell Sea, are witnessing the highest rate of vertical upliftment on the planet. The continual reshaping of the coastline by multiple physical forcings is readily visible by the contiguous and recurrent pattern of raised beach ridges imprinted on the rising land far from the present-day coastline. These beach ridges, formed through the interplay of coastal sea ice dynamics and then preserved above sea-level by uplift, hold back terrestrial runoff and are thus critical to the extensive wetland-saltmarsh ecosystems that provide important habitats for waterfowl and wildlife. This study examines the intricate process behind the formation and modification of these geomorphological units using remote sensing techniques. The study includes the use of various remote sensing products to determine ice duration (Canadian Ice Service- Ice Charts), change detection of ridge dimensions and vectors (Landsat Images), elevation (SRTM and ICESat-2), rate of vertical upliftment (glacial isostasy models) and ice motion in the nearshore zone (GOES). Remote sensing observations reveal that the beach ridges originate offshore on mudflats due to ice scouring and gradually, pushed by sea ice, move shoreward, and often merge and build up existing ridges but sometimes initiating a new beach ridge sequence. The current study documents the impact of changing ice regime on the landward movement of beach ridges on the tidal flats. We find that the seaward point of origin on the tidal flats, and the rate at which the ridges expand and finally merge with the coastline vary greatly across the coastline. The slope of the coast and the dynamics of the sea ice in the nearshore zone are key factors leading to this variability.

How to cite: Ehn, J., Gupta, K., Reeves, A., and Mukhodpadhyay, A.: Beach ridge formation and landward migration along the isostatically rising coastlines of Hudson Bay, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9832, https://doi.org/10.5194/egusphere-egu23-9832, 2023.

The Arctic coast is facing rapid, irreversible changes mainly caused by Climate Warming, e.g., melting sea ice, permafrost thaw, glacial retreat, land uplift and sea level rise. These processes are leading to fundamental changes in the ecosystem structure and functioning, negatively impacting biological and human communities. Under this complex setting, more knowledge is needed to identify the hotspots of shoreline displacement at an Arctic scale. Thus, the goal of this study was to develop and describe a procedure for mapping long-term shoreline displacement in the Arctic that can provide local communities and environmental managers better opportunities to adapt to further coastal changes. Therefore, the procedure will need to be transferrable to diverse environments and able to handle pan-Arctic analyses at a 30-meter spatial resolution. In this study, the procedure was developed using two test areas: Tanafjorden in the low Arctic mainland Norway and Kongsfjorden in the high Arctic Svalbard. The presentation introduces the final procedure and validation results, and discusses its applicability to pan-Arctic shoreline displacement analyses.

The procedure was calibrated in the surroundings of Tanafjorden. It was built on a 40-year time-series of open Landsat and Sentinel multispectral satellite images, taken during the Arctic summer. Supervised random forest classification was used to identify land and water pixels, utilizing information from multiple infrared bands and spectral indices. Mountain shadow pixels were treated as their own class and then merged to the land class. Open spatial data were used for limiting the area-of-interest and for automated creation of training data. In total over 700 individual images were first classified separately to account for local environmental conditions and transient illumination conditions. Images were then summarized over 5-year time-steps. The classification results were examined against an independent validation dataset of 2000 land cover observations and manually digitized shoreline, and the supervised classification results were compared to single-band classifications based on Otsu’s thresholding. The final procedure was then validated in the Kongsfjorden environment. The process was built on Google Earth Engine’s image collections and cloud computing infrastructure to minimize computing times.

The results indicate that it is possible to transform open satellite imagery into 40-year pan-Arctic shoreline displacement information, with a 30-meter resolution and an overall accuracy of more than 95 %. Data fusion is needed in most processing steps: to limit the area-of-interest, save computing power and reduce errors, provide information that complements multispectral satellite data and reduce the impact of short-term atmospheric and water-level effects. Summarizing dozens of images efficiently removes data gaps and the impact of noise, but this efficiency is sensitive to the number of summarized images. The single-image classification approach is flexible and seems to make the procedure transferable to different locations. Cloud image collections are needed to remove the bottleneck of reading and writing satellite data, and potentially allows the promising procedure to be applied at a pan-Arctic scale in the future.

How to cite: Nylén, T., Gonzales-Inca, C., and Calle Navarro, M.: Procedure for examining long-term Arctic shoreline displacement from multispectral satellite data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11651, https://doi.org/10.5194/egusphere-egu23-11651, 2023.

The consequences of accelerating climatic warming on Arctic landscape evolution are far-reaching. In Svalbard, glaciers are rapidly retreating after the Little Ice Age, which leads to exposing new coastal landscapes from marine-terminating glaciers. Precise quantification of these changes was limited until the complete dataset of Svalbard glacier outlines from 1930’s was made available. Here, we analyse the new Svalbard glacier change inventory data and demonstrate that glacier retreat was responsible for a major shift from marine-terminating towards land-terminating glaciers in the last century. This retreat also led to the formation of 922.9 km of new coastline since 1930’s (representing increase of 16.37% in coastline length) creating pristine landscapes governed by paraglacial processes and sediment-rich nearshore fjord environments. Recent palaeogeographical reconstructions suggest that such a mode of coastal evolution was dominant over the extended periods of the Holocene. Transitions from marine-terminating to land-based glaciers had significant implications for fjord circulation, biological production, state of marine ecosystems, biogeochemical cycles between land and seas, and CO₂ budget in coastal waters. Still ongoing climate warming with associated further glacier retreat may lead to more coasts to be exposed in the future. Moreover, glacier retreat will likely cause collapse of Hornbreen-Hambergbreen glacier bridge leading to separation of Sørkappland and rest of Spitsbergen with severe consequences for regional ocean circulation and climate dynamics.

New bays, new straits, new peninsulas and new islands, that have appeared in the last decades of unprecedented warming and associated decay of marine-terminating glaciers in the Arctic are predominantely uncharted and unexplored territories which foreshadow ice-free Arctic and other cold regions of the warmer future. The importance of transdisciplinary research exploring those deglaciated oases has never been more important than at present.

Acknowledgement: The research leading to these results has received funding from the Norwegian Financial Mechanism  2014-2021: SVELTA - Svalbard Delta Systems Under Warming Climate (UMO-2020/37/K/ST10/02852) based at the University of Wroclaw.

How to cite: Kavan, J. and Strzelecki, M.: Glacier decay boosts formation of new Arctic coastal environments – lessons learned from Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12412, https://doi.org/10.5194/egusphere-egu23-12412, 2023.

Increasing water levels at the shore can cause coastal erosion, wave overtopping and flooding that threaten communities and infrastructure. More frequent, longer and more severe storm events observed in the North Atlantic sector of the Arctic bring more energetic waves to beaches of western Svalbard. Decreasing extent and duration of the sea ice cover increases potential fetch which makes the waves higher and longer. At the shore, the number of ice-free days per year has increased and coasts that were protected from waves by ice are becoming exposed perennially or over longer time. Modelling suggests that in future the sea ice will continue to decrease while the storminess will further increase. Better understanding the role of sea ice conditions and nearshore wave transformations on wave energy at the Arctic shores is needed to predict coastal hazards under changing climate.

In this study we focus on wave energy delivery to the shores of Hornsund, a ~300 km² fjord of south-western Spitsbergen, Svalbard, and particularly to Isbjornhamna bay in northern Hornsund, where the Polish Polar Station infrastructure is located. We monitor continuously nearshore wind wave conditions and the state of the shore ice, and seasonally the wave run-up and beach morphology. We use three nested SWAN (Simulating WAves Nearshore) models that take low-resolution global wind and wave models and nearshore bathymetry to reconstruct wind wave conditions in the nearshore (~15 m depth) Isbjornhamna. Finally, we use Sentinel-1 SAR data to reconstruct sea ice conditions in Hornsund area which need be incorporated into the wave model. Here we show how our monitoring and modelling scheme facilitates the comprehensive understanding of the nearshore and coastal processes in Isbjornhamna.

How to cite: Swirad, Z., Moskalik, M., Herman, A., Johansson, M., and Rees, G.: Sea ice, wind waves and coastal erosion in Hornsund, Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13052, https://doi.org/10.5194/egusphere-egu23-13052, 2023.

Rapid and unprecedented warming of high latitudes exposes Arctic coastal communities to greater vulnerability as they observe their territory changing through general permafrost degradation, episodes of flooding and accelerated coastal erosion threatening their infrastructure and livelihood. Local information is known for infrastructures mapping and coastal changes but consistency in the measurement is lacking as well as spatial coverage for large coastal areas. The need of a consistent circumpolar dataset is primordial in order to map risks and mitigate impacts for arctic coastal communities. Machine learning methods with Sentinel 1/2 imagery allow the circumpolar mapping of arctic coastal settlements (Bartsch et al. 2021a). Validation of recent updates are supported by high-resolution data from the Pleiades satellites, aerial and drone imagery. 

This study is part of the ESA EO4PAC project which aims to provide a range of satellite derived information, including coastal erosion/accretion and infrastructure in the proximity, for the next generation of the Arctic Coastal Dynamic Database (ACD; Lantuit, et al. 2012).  Previous results highlight the detection of 50% more human presence information than in OpenStreetMap especially in Russia with recent expansion of infrastructures related to expanding oil and gas industry. Recent updates of the SACHI dataset (Bartsch et al. 2021b) will be presented including additional attributes for roads and their validation. A preliminary categorization of settlements with respect to permafrost degradation (based on Permafrost_cci records) and coastal erosion based on the current ACD will be presented.

Bartsch, A., G. Pointner, I. Nitze, A. Efimova, D. Jakober, S. Ley, E. Högström, G. Grosse, P. Schweitzer (2021a): Expanding infrastructure and growing anthropogenic impacts along Arctic coasts. Environmental Research Letters. https://doi.org/10.1088/1748-9326/ac3176

Bartsch, Annett, Pointner, Georg, & Nitze, Ingmar. (2021b). Sentinel-1/2 derived Arctic Coastal Human Impact dataset (SACHI) (Version 1) [Data set]. Zenodo. https://doi.org/10.5281/zenodo.4925911

Lantuit, Hugues; Overduin, Pier Paul; Couture, Nicole; Wetterich, Sebastian; Are, Felix; Atkinson, David; Brown, Jerry; Cherkashov, Georgy A; Drozdov, Dimitry S; Forbes, Donald Lawrence; Graves-Gaylord, Allison; Grigoriev, Mikhail N; Hubberten, Hans-Wolfgang; Jordan, James; Jorgenson, M Torre; Ødegård, Rune Strand; Ogorodov, Stanislav; Pollard, Wayne H; Rachold, Volker; Sedenko, Sergey; Solomon, Steve; Steenhuisen, Frits; Streletskaya, Irina; Vasiliev, Alexander (2012): The Arctic Coastal Dynamics Database: A New Classification Scheme and Statistics on Arctic Permafrost Coastlines. Estuaries and Coasts, 35(2), 383-400, https://doi.org/10.1007/s12237-010-9362-6

How to cite: Tanguy, R., Bartsch, A., Widhalm, B., von Baeckmann, C., Efimova, A., and Vieira, G.: Pan-Arctic remotely sensed observation of coastal settlements - recent updates, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14578, https://doi.org/10.5194/egusphere-egu23-14578, 2023.

Under current conditions, the Spanish Mediterranean coast is already presenting hotspots of extreme exposure to coastal hazards and recurrent damage, making it necessary to adopt disruptive adaptation strategies as opposed to the classic expectation of full protection. This situation is expected to worsen under the effect of sea level rise, which will increase existing erosion rates, with some areas being fully eroded due to the lack of accommodation space to allow natural adaptation to the new conditions.

In this context, nature-based solutions (NBS) are becoming one of the main type of measures to be favored in order to be more climate-resilient and thus support EU policy priorities. Although research on the effectiveness of most nature-based coastal protection methods is still limited, some of them such as dune systems and sand banks have been classified as essential for future coastal defense.

In highly-developed coastal zones, which are the most at risk, the lack of the sufficient space limits the viability of using NBS as they cannot be accommodated. Thus, the existence of accommodation space is the required condition to permit the beach migration and rebuilding under SLR, otherwise will progressively decline and ultimately disappear. It has to be stressed that the accommodation space is a relative concept, being related to the expected magnitude of the shoreline retreat at a given time horizon under a given climate forcing scenario. 

Within this context, this work presents a regional-scale framework to assess the accommodation space needed to adopt dune-based NBS planning as a coastal adaptation strategy, by integrating predictions of accommodation space needed to cope with coastal hazards under current and IPCC AR6 climate scenarios and for different time horizons relevant for planning purposes (up to 2100), and to enable dune development. The hazards considered are (i) long-term (decadal scale) coastline evolution; (ii) storm-induced erosion; (iii) SLR-induced erosion; (iv) permanent inundation due to SLR; and (v) storm-induced flooding. The framework applies to the Catalan coast, a 600 km long stretch of the Spanish Mediterranean coastline.

This work was supported by the Spanish Agency of Research in the framework of the CoastSpace project, TED2021-130001B-C21 (MCIN/AEI/10.13039/501100011033).

How to cite: Romero-Martín, R., Valdemoro, H., Ranasinghe, R., and Jiménez, J. A.: A framework for assessing the space needed for dune-based coastal adaption at multiple time scales., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14844, https://doi.org/10.5194/egusphere-egu23-14844, 2023.

The ongoing rise of atmospheric temperatures and sea level is exacerbating Arctic coastal permafrost thaw which leads to increased coastal erosion and input of permafrost soils into the Arctic Ocean. Permafrost soils hold vast amounts of organic carbon (OC) which is released into the coastal waters upon thawing. The fate of this OC with regards to its transport and degradation pathways is not yet fully understood - it could either be degraded within the water column and released into the atmosphere as CO2 or it could be buried at the sea floor. When settling onto the seafloor sediment-water interactions become crucial in the OC degradation process. These so-called flocculation layers at the sediment-water interface hold a high potential for sediment re-suspension and therefore represent an environment favouring the degradation of OC thus preventing burial. Yet, there is little data available from these flocculation (i.e. nepheloid) layers, particularly in the Arctic shelf seas.

To improve our understanding of OC degradation within these flocculation layers, we analysed samples from the flocculation layer and from the underlying surface sediments for organic geochemical parameters (TOC, C/N values, δ13C, Δ14C, sediment surface area). Samples within this study were collected along two cross-shelf transects in the Laptev and in the East Siberian Sea during ISSS-2020 expedition in late summer (Sept-Oct) of 2020 onboard R/V Akademik Msistlav Keldysh. First results show variations in OC composition in both shelf seas between the flocculation and surface sediment layers and also with increasing water depth and distance from shore, further emphasizing the degradation potential of this particular layer. With the collected data, we want to gain new insights into how transport and degradation processes of terrestrial OC vary across the vast Siberian shelves.

How to cite: Madaj, L., Keskitalo, K., Gustafsson, Ö., Tesi, T., Semiletov, I., Dudarev, O., Martens, J., Haghipour, N., Bröder, L., and Vonk, J.: Cross-Shelf Transport, Composition and Degradation of Terrestrial Permafrost Organic Matter at the Sediment-Water Interface in the Laptev and East Siberian Seas, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14978, https://doi.org/10.5194/egusphere-egu23-14978, 2023.

Nature-based solutions (NbS) are fast becoming the norm for multifunctional climate adaptation to the combined challenges of increased sea-level rise, coastal population densities, and erosion of sandy shores worldwide, delivering functions such as flood prevention, recreation, and biodiversity benefits. However, it remains a challenge to the research field to inform decision-makers well on the outcomes and trade-offs of designing, planning, and managing the multifunctional NbS. This study set out to identify the information requirements by decision-makers on NbS for coastal climate adaptation. Using the Sand Motor in The Netherlands as a case study, we applied a policy science framework to distinguish four stages of decision-making to quantitatively analyse the content of functions and indicators utilized per stage in public policy documents. These stages are the ambition, political, bureaucratic, and provisioning processes. This study is the first comprehensive empirical investigation distinguishing these crucial stages of decision-making to analyse NbS information requirements. Our results show, most notably, that as the project developed through the decision-making stages, the content of the functions and indicators changed from abstract to concrete. And, with it, the content of the information required shifted significantly. These results suggest that it is crucial for academic researchers to recognize the decision-making process their information will be used in and adapt its content and level of abstraction accordingly to increase its uptake in decision-making. This study lays the groundwork for future research into the multiple dimensions of NbS decision-making and for the increased understanding of the information requirements on evaluation and trade-offs in planning, designing, and managing NbS, to increase the ability of NbS to deliver multifunctional coastal climate adaptation for sandy shores worldwide.

How to cite: Geukes, H., Van Oudenhoven, A., and Van Bodegom, P.: Decision-Making on Nature-Based Solutions for Multifunctional Coastal Climate Adaptation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15297, https://doi.org/10.5194/egusphere-egu23-15297, 2023.

Nature-based solutions (NBS) are promising methods to enhance biodiversity and adapt to climate change in coastal areas. However, upscaling NBS to replace conventional methods requires knowledge about their performance from multiple perspectives, e.g., biodiversity, coastal safety, and economy. In recent years, great efforts have been put into researching NBS pilots of sandy solutions. Some of the most prominent examples are found in the Netherlands, e.g., the Sandmotor, the Hondsbossche Dunes, and the Prince Hendrik Sand dike. These are examples of large-scale interventions with nourished sand volumes of hundreds of thousands to millions of cubic meters. In contrast, this study focuses on small-scale NBS pilots of sandy solutions with nourishment volumes of hundreds to thousands of cubic meters. Two NBS pilots in Sweden are described and analysed, and the advantages and disadvantages of small-scale NBS are discussed in relation to larger-scale interventions.

The first pilot was installed in 2018 in the Furusund navigational fairway in the Stockholm Archipelago. A few hundred cubic meters of sand was nourished to a beach subject to erosion due to ship-generated waves. The nourishment protects an eroding bluff and prevents the loss of forest areas with high nature values. Compared to hard solutions, e.g., a rock revetment, the small-scale beach nourishment supplies sand to a small sandy beach down-drift used for recreational purposes. Since the implementation, a significant part of the nourishment has already been eroded, and the expected lifetime of this intervention is in the order of a few years.

The second pilot was installed at Fortuna beach, located in the narrow sound between Sweden and Denmark. The area has a low-energy wave climate, and the nourishment was designed to protect a beach in front of a residential area from storm erosion recurring with decadal frequency. The beach and dune area were nourished with approximately 3000 m³ of sediment. The area has limited offshore sand resources that can be extracted without adverse environmental impact. Therefore, the beneficial use of sediment dredged from local marinas and a mixture of sand and seaweed from nearby beach clean-ups was used to carry out the project. Within a year after the nourishment, a storm with a recurrence period of approximately 5-20 years hit the coast, but the dune volume still exceeded the volume before the measures.

Experiences from the small-scale sandy solutions are that the limited extent of the interventions facilitates financing and permitting processes, which can be a bottleneck in upscaling NBS. The limited volume of nourishments makes it easier for beneficial use of dredged material, which in many cases is viewed as a waste rather than a resource. Both the volume and timing can be adapted to nearby dredging operations, thus reducing the cost of maintenance of small marinas with a high cultural value. The short lifetime and low safety level of small-scale NBS can be a disadvantage but allow for more flexibility, and no-regret solutions compatible with adaptive pathway approaches to climate change adaptation.

How to cite: Hallin, C., Schmidt, E., and Almström, B.: Small-scale nature-based solutions for protection of sandy coasts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15893, https://doi.org/10.5194/egusphere-egu23-15893, 2023.

Martian gullies are kilometre-scale landforms consisting of an alcove, channel and depositional fan. They are among the youngest landforms that may have formed by liquid water and are active today. Understanding their formation is thus critical for resolving Mars’ most recent climatic history and potential to sustain life. Gullies on Mars have been hypothesized to have formed by either the action of liquid water and brines or the action of sublimating carbon-dioxide (CO₂) ice. They strongly resemble terrestrial systems formed by aqueous debris flows, having similar sedimentology, morphology, and morphometry. Yet, new deposits have formed within multiple gullies across Mars over the past decade, and we cannot reconcile these flows with the low availability of atmospheric water and the triple point of water under present martian conditions. These flows do, however, occur in winter when temperatures are below the CO₂ condensation point, and CO₂-ice has been observed in many gullies during time of activity. But can CO₂ sublimation support and fluidize mass flow on Mars and form deposits similar to terrestrial debris flows? Here, I present novel experiments where we operate small-scale mass-flow flumes inside Mars chambers at Aarhus University (Denmark) and the Open University (UK). In these chambers Martian atmospheric conditions can be simulated, which is crucial for fluidization of mass flows since volume expansion, and therefore gas flow rate, by CO₂-ice sublimation is much larger under the low atmospheric pressure of Mars (8 mbar) than under the atmospheric pressure of Earth (1000 mbar). These experiments reveal that CO₂ sublimation under martian atmospheric conditions can fluidize mass flows by generating elevated pore pressures reducing intergranular friction, resulting in lobate deposits with levees, as observed in martian gullies. These findings show that CO₂-sublimation processes can explain our observations in active Martian gully systems today, which has far-reaching implications for the search for potential liquid water on Mars as well as the interpretation of planetary landforms on other planetary bodies. In particular, they show that on planetary bodies unlike Earth, landforms may be created that look similar to those found on Earth but are actually produced by disparate and so-far unknown processes.

How to cite: de Haas, T., Roelofs, L., Conway, S., McElwaine, J., Merrison, J., Patel, M., and Sylvest, M.: Sublimation-driven formation of recent mass flows on Mars: experimental tests in low-pressure environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1451, https://doi.org/10.5194/egusphere-egu23-1451, 2023.

Since the end of the 19th century, geomorphologists have been on a relentless quest to unravel the mysteries of landscape evolution and explain the diversity of the resulting forms. However, a quantitative model of landscape morphodynamics that is relatively universal and applicable at various time scales still eludes us. This raises an important question: are we, geomorphologists, dumber than the average scientist, or is landscape evolution particularly complex to decipher? ChatGPT tells us that, indeed, landscape evolution is complex. 

As for many natural phenomena, the complexity of landscape evolution results from 3 elementary components: processes, stochasticity, and heterogeneity. Process geomorphology tackles the complex morphodynamics emerging from the diversity and interactions of physical, chemical, and biological processes that shape the Earth. Stochastic geomorphology addresses the role of fluctuations in the drivers of landscape evolution, such as the frequency-magnitude distribution of precipitation events, landslides, earthquakes, or fires. Heterogeneous geomorphology embraces the variable nature of the properties of landscape elements on which geomorphic processes operate or that they create. This includes, for instance, the distribution of grain sizes, the diversity of rock type, the fractal nature of rock fractures, or the spatial variations in vegetation size and type.

Accounting for all these sources of complexity, inasmuch as they can be quantified, is an untractable problem resulting in models of little explainability. Therefore, hypotheses had been and must be formulated to simplify the problem of landscape evolution comprehension and modeling. There is, arguably, a long tradition of emphasizing process complexity to explain landscape dynamics, neglecting or simplifying both stochastic fluctuations and heterogeneity. In this lecture, I shall discuss this view, emphasizing the now well-established importance of stochastic fluctuations, and how little we know of the role of heterogeneity.

On this latter topic, I shall illustrate with a variety of examples how time series of high-resolution and high-precision topographic data (4D data) offers unprecedented insights into landscape morphodynamics. Beyond quantifying and detecting a variety of processes and their temporal fluctuations, 4D data allow a systematic quantification of the heterogeneity (e.g., vegetation, grain size, ...) of landscape elements, and spatial variability of geomorphic rates, thus bringing us closer to formulating the role of heterogeneity in landscape dynamics. Yet, this goal can only be achieved if tools to harness the complexity and richness of high-resolution topographic data are developed and made available.

Keywords: fluvial incision, landslides, floods, salt marshes, topo-(bathymetric) LiDAR, numerical modeling, machine learning.

How to cite: Lague, D.: Coping with the complexity of landscape evolution and how high-resolution topography can help, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10371, https://doi.org/10.5194/egusphere-egu23-10371, 2023.

Martian gullies are kilometre-scale landforms consisting of an alcove, channel and depositional fan. They are among the youngest landforms that may have formed by liquid water and are active today. Understanding their formation is thus critical for resolving Mars’ most recent climatic history and potential to sustain life. Gullies on Mars have been hypothesized to have formed by either the action of liquid water and brines or the action of sublimating carbon-dioxide (CO₂) ice. They strongly resemble terrestrial systems formed by aqueous debris flows, having similar sedimentology, morphology, and morphometry. Yet, new deposits have formed within multiple gullies across Mars over the past decade, and we cannot reconcile these flows with the low availability of atmospheric water and the triple point of water under present martian conditions. These flows do, however, occur in winter when temperatures are below the CO₂ condensation point, and CO₂-ice has been observed in many gullies during time of activity. But can CO₂ sublimation support and fluidize mass flow on Mars and form deposits similar to terrestrial debris flows? Here, I present novel experiments where we operate small-scale mass-flow flumes inside Mars chambers at Aarhus University (Denmark) and the Open University (UK). In these chambers Martian atmospheric conditions can be simulated, which is crucial for fluidization of mass flows since volume expansion, and therefore gas flow rate, by CO₂-ice sublimation is much larger under the low atmospheric pressure of Mars (8 mbar) than under the atmospheric pressure of Earth (1000 mbar). These experiments reveal that CO₂ sublimation under martian atmospheric conditions can fluidize mass flows by generating elevated pore pressures reducing intergranular friction, resulting in lobate deposits with levees, as observed in martian gullies. These findings show that CO₂-sublimation processes can explain our observations in active Martian gully systems today, which has far-reaching implications for the search for potential liquid water on Mars as well as the interpretation of planetary landforms on other planetary bodies. In particular, they show that on planetary bodies unlike Earth, landforms may be created that look similar to those found on Earth but are actually produced by disparate and so-far unknown processes.

How to cite: de Haas, T., Roelofs, L., Conway, S., McElwaine, J., Merrison, J., Patel, M., and Sylvest, M.: Sublimation-driven formation of recent mass flows on Mars: experimental tests in low-pressure environments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1451, https://doi.org/10.5194/egusphere-egu23-1451, 2023.

As detailed in a recent journal publication by the authors of this abstract, women have made significant contributions in the fluvial, aeolian, and (cryo)volcanic subdisciplines of planetary geomorphology, despite undeserved challenges to their participation. Some women—in particular, women of color—are highlighted in this work to show a part of these foundational contributions. As the latter half of the 20th century was a revolutionary time for terrestrial geomorphology and the inception of the discipline of planetary geomorphology, we focused our research into these contributions on women scientists who were working during this time. We also focused on women working in our scientific subdisciplines so that we could provide proper context for their work. These contributions have occurred both as discoveries in terrestrial geomorphology leading to follow-on discoveries in planetary geomorphology and through serving as educators and role models. With women increasingly achieving positions of influence both in the geo- and planetary sciences as in American society, this research allows us to celebrate these contributions of women and particularly women of color while looking forward to a more complete record of their past contributions and greater future achievements.

How to cite: Burr, D., Diniega, S., Quick, L., Gardner-Vandy, K., and Rivera-Hernandez, F.: Foundational women in planetary geomorphology: Some contributions in fluvial, aeolian, and (cryo)volcanic subdisciplines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2912, https://doi.org/10.5194/egusphere-egu23-2912, 2023.

Debris flows are extremely rapid, flow-like landslides composed of fine and coarser-grained components, boulders, woody debris as well as water. They are characterized by large impact forces as well as long runout distances and are one of the most dangerous types of mass movements in mountainous regions. More detailed field-scale measurements of hazard-related parameters in natural debris flows are required to better understand the fundamental mechanisms governing their motion and, ultimately, reduce the associated risks.

In the present work, we analyzed two debris-flow events using timelapse point clouds from a high-resolution, high-frequency 3D LiDAR sensor (Ouster OS1), which we installed at the WSL debris-flow monitoring station in the Illgraben catchment (Valais, Switzerland). We developed and applied both manual and automated algorithms to derive critical hazard-related parameters – including front and surface velocities, cross-sectional area, discharge and event volume – at an unprecedented level of detail.

In both events, we observed that surface velocities measured directly behind the front exceeded the front velocity (by a factor of 1.75x on average), which likely led to the formation of the bouldery front. We further found that different objects traveled at systematically different velocities: large, rolling boulders were moving at 0.6–0.8 the velocity of floating woody debris during both analyzed events. This observation was likely caused by these different objects sampling the vertical velocity profile at different depths, and thus provided quantitative information about the shape of the velocity profile.

We further applied automated surface velocity estimation techniques as well as automated cross-sectional area measurements to derive the discharge over time and in space at three different, closely spaced channel sections upstream of a check dam. We accounted for potential changes in the shape of the channel bed by considering different “channel geometry scenarios” (based on pre-event and post-event scans) and included presumed changes in the vertical velocity profile – based on our findings mentioned above – in our discharge derivation. We assessed the reliability of these different scenarios by comparing the discharge values at different sections, which allowed us to infer potential changes in the channel bed geometry.

The LiDAR data analyzed in this work is unique because it allows for a truly 3D, high-resolution investigation of moving debris flows at sub-second intervals. The developed methods will be applied to LiDAR data from additional monitoring stations and events at the Illgraben, which should allow for further inference into the internal dynamics of debris flows. Eventually, this might enhance our understanding of the fundamental debris-flow mechanisms, help to optimize numerical as well as empirical modeling approaches, improve hazard mitigation in general and reduce the risk posed by flow-like landslides in the future.

How to cite: Spielmann, R. and Aaron, J.: High-resolution 3D LiDAR measurements of natural debris flows at sub-second intervals; Illgraben, Switzerland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5357, https://doi.org/10.5194/egusphere-egu23-5357, 2023.

Preserved geomorphological landforms on the surface of Mars indicate the presence of abundant liquid water in the early history of Mars. Many of these geomorphic features were developed by erosion and deposition of sediments by water. It is therefore important to understand how fluvial sediment transport works on Mars and how it is different from Earth. Due to the lower gravity on Mars water flows down slope with less energy, resulting in lower bed shear stresses and flow velocities. Nonetheless, fluvial sediment transport is more efficient. Due to the lower gravity the mobility of the sediment is higher. Larger grains are brought into motion and suspension (Komar, 1980; Burr et al., 2006) and the magnitude of suspended transport is significantly higher (Amy and Dorrell, 2021), as is the total transport flux (Braat et al., 2022). In addition, the settling of sediment is slower, resulting in larger transport distances on Mars compared to Earth. Based on the differences in entrainment due to gravity, different grain size mixtures are transported and settle out in a different manner (Braat et al., 2022). Therefore, the geomorphology and stratigraphy of geomorphic landforms might be different than we expect from Earth observations. In this study, we investigate how fluvial geomorphology differs on Mars through sediment transport calculations on Mars and our terrestrial knowledge and experience.

We use two methods: 1) We use standard hydraulic equations to calculate hydrodynamic conditions based on a slope, channel width and discharge. From these conditions we calculate sediment transport fluxes using multiple sediment transport predictors for both bedload and suspended load. Total load predictors are not suitable for Mars, as they do not account for a variable gravity effect with grain size. 2) We also run numerical hydro-morphodynamic model scenarios to compare the evolution of fluvial geomorphic features with Earth and Mars gravity. We use the software package Delft3D (Lesser et al., 2004), and amended the code to work on Mars.

Simple sediment transport calculations indicate that the sediment fraction at the bedload-suspended load boundary is most affected by gravity. In our examples transport could be up to 6 times higher for this fraction. Overall, the magnitude of the total transport flux on Mars is also bigger, predominantly because of increased suspended transport. As the bedload fraction is the ‘channel-building’ fractions and suspended transport determined channel-floodplain interaction, we hypothesise that floodplain deposition will increase. Additionally, with more sediment entering the floodplain levee accretion will increase, as will cut-off infilling and crevasse splays. We also hypothesise that increased suspension will reduce channel migration, reduce branching, increase the avulsion rate, and create more sinuous, narrow channels (Nicholas, 2013). The preliminary model outcomes confirm our hypothesis that depositional slopes are lower due to longer advections lengths related to lower settling velocities. For example, this will transport more sediment to the delta front and pro-delta, impacting deltas foresets (van der Vegt et al., 2016). Finally, the models agree that geomorphic features develop faster on Mars.

How to cite: Braat, L., Brückner, M., Baar, A., Lamb, M., and Sefton-Nash, E.: Differences in Fluvial Geomorphology between Earth and Mars, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8070, https://doi.org/10.5194/egusphere-egu23-8070, 2023.

Nowadays, the majority of detailed information about groundwater is acquired by wells that provide limited insight in time and especially space. Therefore, it would be interesting to monitor groundwater by continuously measuring seismic velocity changes in the subsurface. The shallow soil is affected by environmental influences like temperature, rainfall or drought, which in turn changes the seismic velocity in the subsurface.

In this study, we use three-component seismometers, which are placed next to an in-situ measurement station of soil conditions (moisture and temperature at different depths) and a meteorological station in the city of Hamburg, Germany. We investigate the sensitivity of high-frequency (> 1 Hz) seismic waves with an anthropogenic origin to ground moisture changes in the uppermost layers of soil. To monitor velocity changes, Passive Image Interferometry is applied. Using the three-component data, we are able to retrieve Rayleigh and Love waves. Relative velocity changes are retrieved using the stretching method. A comparison of seasonal seismic velocity changes and environmental changes shows a positive correlation between velocity and temperature, as well as a negative correlation between velocity and groundwater content. Freezing events are exceptions, as they cause relative velocity increases twice as high as seasonal changes.

The aim of this work is to eliminate temperature effects to work towards inferring water content directly from seismic velocity changes. To eliminate the contribution of temperature, its relation to seismic velocity changes and water content is quantified using regression. Since the relative velocity change is influenced by both temperature and water content, a time period of stable water content is used to quantify the relation between velocity change and temperature. As a result, the residual relative velocity change reproduces the residual water content.

How to cite: Kiel, A., Steinmann, R., Larose, E., and Hadziioannou, C.: Can we monitor shallow groundwater using ambient seismic noise?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-675, https://doi.org/10.5194/egusphere-egu23-675, 2023.

Located in the southern Aegean Sea, the Christiana-Santorini-Kolumbo volcanic field is one of the most hazardous volcanic regions in the world and lies in an active continental rift zone. Northeast of Santorini lies the Kolumbo Volcanic Chain (KVC), which comprises more than 20 submarine volcanic cones, with the Kolumbo volcano representing the most prominent edifice of this chain. However, due to their inaccessibility, little is known about the spatio-temporal evolution and tectonic control of these submarine volcanoes and their link to the volcanic plumbing system of Santorini. We will present multichannel reflection seismic data that allow us to image the internal architecture of the KVC and study its link to Santorini. Using a seismostratigraphic framework, we are able to show the KVC evolved during two episodes, which initiated at approx. 1 Ma with the formation of mainly effusive volcanic edifices along a NE-SW trending zone. Most of the cones of the second episode represent submarine pumice cones that were formed by submarine explosive eruptions between 0.7 and 0.3 Ma and partly developed on top of volcanic edifices from the first episode. Our data show that two prominent normal faults underlie the KVC, indicating a direct link between tectonics and volcanism. In addition, we are able to reveal several buried volcanic centers and a distinct volcanic ridge connecting the KVC with Santorini, suggesting a connection between the two volcanic centers in the past. We argue that this connection was interrupted by a major tectonic event and, as a result, the two volcanic systems now have separate, largely independent plumbing systems despite their proximity.

How to cite: Preine, J., Hübscher, C., Karstens, J., Crutchley, G., and Nomikou, P.: Seismic imaging of the submarine Kolumbo Volcanic Chain reveals its volcano-tectonic evolution and link to Santorini, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-714, https://doi.org/10.5194/egusphere-egu23-714, 2023.

The need to better predict how the great ice sheets will respond to continued atmospheric and ocean warming is paramount. Ice deformation and mechanisms for ice sliding across the bedrock underneath are both key considerations. Constraints of this critical ice-bedrock interface zone, particularly over extensive inland areas of Antarctica and Greenland, remain a major hurdle in ice-sheet modeling and estimations of future sea level rise.

Passive seismology offers a logistically-efficient avenue for such investigations, with improvements in sensor technologies, autonomous power solutions and telemetry systems encouraging the deployment of temporary arrays for subglacial mapping and real-time monitoring. Previous experiments have demonstrated the potential of techniques such as receiver functions, horizontal-to-vertical spectral ratios (HVSR) and ambient noise interferometry for characterising the depth and nature of the ice-bedrock zone. This research looks to fully explore the sensitivity range of available passive seismic methods for the ice-bedrock interface, with a view towards optimising data collection and array geometries for future applications. In this contribution, we present an optimised workflow making use of HVSR analysis and the spatial autocorrelation (SPAC) technique using numerical simulations and field data collected from East Antarctica. The results from this study provide a benchmark to guide future deployments in the polar regions.

How to cite: Kelly, I., Reading, A., Staal, T., and Bassom, A.: Optimising passive seismic investigations of the ice-bedrock interface zone for the great ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-900, https://doi.org/10.5194/egusphere-egu23-900, 2023.

Karst is a landscape with distinctive hydrology and landforms that arise when the underlying rock is soluble. Locating the flowing conduits and pathways in karst is important in terms of water resource management, groundwater flooding, geotechnical and engineering projects. Understanding flow pathways is particularly important for road and railway construction, so as not to adversely affect hydrological networks, in particular those associated with Turloughs.

The aim of this study was to develop methods for directly detecting energetic groundwater flow in sub-surface conduits through passive seismic applications, by detecting the small ground vibrations (seismic microtremor) that flowing water in the sub-surface may generate. This is in contrast to the current ‘traditional’ approach of attempting to actively image the conduits using geophysical and other methods, in order to determine the geometry of flow paths. The imagery of conduits in karst is a very difficult problem and determining if they contain flowing structures is also a very significant challenge using traditional methods, which is the motivation for developing a new approach to the problem.

We undertook experiments at two sites on karst in Ireland; one gently-sloping shallow conduit and one relatively deep and complex-structured conduit. We chose these sites as the caves had previously been dived and we had access to the shapefiles of these caves to ground-truth our findings.

We observed that subterranean flow-related micro-tremor in karst appears as persistent frequency bands on the spectrograms that vary with time and seismic station location with respect to the conduit. This persistent frequency is different than the soil resonating frequency and relates to the subterranean water flow in the conduits. Application of an Amplitude Location Method (ALM)  clearly delineated the conduit as the source of the micro-tremor.

We also conducted an active Airgun experiment at the second site to locate the conduit by tracking a pressure wave, using two arrays of surface seismic stations, as it propagated into the conduit. This combination of detecting and locating seismic microtremor generated by water flow in the conduits and the use of seismic array analysis to track active Airgun source pressure waves propagating at depth in conduits offers a new tool kit for karst hydrology determination. In the next step, we will assess the applicability of Distributed Acoustic Sensing (DAS) using fiber optic cables as sensors for detecting sub-surface water flow, where we expect unrivaled spatial resolution of the flow-induced seismic wavefield. Such a study would be the first attempt to fill the current gap regarding an understanding of karst groundwater dynamics along the entire conduit pathway, at an exceptionally high spatial scale.

How to cite: Karbala Ali, H., Bean, C. J., and Chalari, A.: Detection and source location of the groundwater-induced seismic signal in karst using a combination of passive and active seismic approaches, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1046, https://doi.org/10.5194/egusphere-egu23-1046, 2023.

Unlike surface water reservoirs, that can be easily quantified and monitored, underground conduits in karst systems are often inaccessible, hence challenging to monitor. Seismic noise analysis was proved to be a reliable tool to monitor ground water storage in a fractured rock aquifer (Lecocq et al. 2017). In underground karstic environments, seismic noise monitoring was able to detect hydrological cycles and monitor the groundwater-content variations (Almagro Vidal et al. 2021). The following approach relies on coupling passive seismic wavefield with hydrological data in a machine learning algorithm in order to monitor underground water heights. The studied site is the Fourbanne karst aquifer (Jura Mountains, Eastern France, Jurassic Karst observatory). The underground conduit is accessible through a drilled shaft and instrumented by two 3-component seismological stations, one located underground and the other one at the surface, and a water height probe. We applied a new approach based on the machine learning random forest (RF) algorithm and continuous seismic records (Hibert et al., 2017), to find characteristic signals to predict the underground river water height. The method consists on the computation on a sliding window of seismic signal features (waveform, spectral and spectrogram features) and using the corresponding water height at the same time window to train the algorithm, and then apply it on new data. The RF algorithm is capable of accurately detecting flooding periods and reproduce the groundwater heights with an efficiency exceeding 95% and 53% using the Nash-Sutcliffe criterion for the seismic stations located in the underground conduit and at the surface respectively. The obtained results are a first promising outcome for the remote study of water circulation in karst aquifers using seismic noise.

How to cite: Abi Nader, A., Albaric, J., Steinmann, M., Hibert, C., Malet, J.-P., Pohl, B., and Sue, C.: Groundwater Heights Prediction from Seismic Waves with Machine Learning, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1601, https://doi.org/10.5194/egusphere-egu23-1601, 2023.

Basal icequakes are generated as a glacier slides over its underlying bedrock, and the stick-slip motion of constant loading and unloading releases shear stresses that produce these very small magnitude (ML < 0) glacial microseisms. Detecting and locating nucleation of these fine-scale icequakes can provide highly useful insights into the deformation processes occurring at the bed and consequently the mechanisms governing glacier flow. We present icequake data derived from a seismic array installed at the grounding line of the Rutford Ice Stream in West Antarctica by Penn State University and the British Antarctic Survey during the 2018/19 austral summer. The region’s natural source seismicity was first processed using the earthquake detection and location software QuakeMigrate and the events were relatively relocated using HypoDD/GrowClust. We then clustered the events into sticky spot clusters using the unsupervised clustering algorithm DBSCAN, and finally from the clusters we selected “model” waveforms to perform template matching on the original seismic traces to create methodically comprehensive high-resolution icequake catalogs at the grounding line of Rutford. We present our methodology including the complete processing pipeline (supplemented by developed supporting open-source scripts) along with key tuning parameters, and describe how our catalogs were used to resolve glacier sliding patterns and key topographical features and characteristics of the bed like sticky spots. We additionally explore the effects of tidal modulation and Rutford ice flow motion on icequake occurrences. Our seismic traces primarily contain icequake signals that derive from stick-slip sliding, but also unique waveforms that might be derived from crevassing and teleseisms that we will also explore. Our results show that stick-slip basal icequakes and these resultant icequake catalogs are valuable data-rich resources that help improve our understanding of glacier flow dynamics and will be important toward improving glacier flow models used for constraining global mean sea level rise.

How to cite: Lee, I., Anandakrishnan, S., Alley, R., Brisbourne, A., and Smith, A.: Event Relations and Sources of Icequakes at the Grounding Line of Rutford Ice Stream, West Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1677, https://doi.org/10.5194/egusphere-egu23-1677, 2023.

Rainfalls and freeze-thaw cycles are well known to largely contribute to rock slopes erosion, including chemical processes (dissolution, alteration) together with mechanical action (stress change in fractures due to water freezing). The role of heat waves and thermal cycles is less studied in dry conditions. Here we present a thermo-acousto-elastic (TAE) model for rock volumes exposed to cyclic (daily to seasonal) thermal forcings, as an application of environmental seismology (1).

In our model, we assume that the rock temperature is constant at depth (a few meters in general), and that the free surface is exposed to heat fluxes (radiative and convective ones). In practice, these heat fluxes can be respectively derived from solar radiation normal to the rock surface and from the air temperature, both parameters are easily measured in the field. We then develop a numerical model based on a) thermal diffusion (heat propagation in the rock in 2D or 3D models, including complex geometries as cracks, rock columns…), b) thermal expansion relating temperature to strain, and c) acousto-elasticity relating the elastic parameters to the state of stress, (2). Such a model is run, for example, with COMSOL Multiphysics with a finite element scheme. We end up with a 2D or 3D numerical model of stress and deformation of the rock volume evolving over time ranging from sub-daily to yearly time scales.

As an application we test this model on various rock columns and observe that the developed model properly reproduces field observations, including daily and seasonal cycles: the natural resonance frequency of the rock column, a proxy for its rigidity, increases with increasing heat flux (3) and the rear crack closes up. As a result of fitting our numerical model to natural rock columns, we can evaluate the acousto-elastic constant that relates the rigidity to the state of stress, a parameter that is known to mainly depend on the state of damage of the material, opening the route for rockfall risk assessment, monitoring and early warning systems. Our model also allows to shed new light into fatigue and cyclic damage process of rock slopes and cliffs, a key to rock erosion.

References:

• (1) Guillemot, L. Baillet, E. Larose, P. Bottelin : Changes in resonance frequency of rock columns due to thermoelastic effects on a daily scale : observations, modeling and insights to improve monitoring, Geoph. J. Int. 231, 894-906 (2022).
• (2) Larose, E. & Hall, S.: Monitoring stress related velocity variation in concrete with a 2.10−5 relative resolution using diffuse ultrasound, J. acoust. Soc. Am., 125, 1853–1856 (2009).
• (3) Bottelin, P., Levy, C., Baillet, L., Jongmans, D. & Gueguen, P.: Modal and thermal analysis of Les Arches unstable rock column (Vercors massif, French Alps), Geophys. J. Int., 194, 849–858 (2013).

How to cite: Larose, E., Guillemot, A., Baillet, L., and Bottelin, P.: Thermo-Acousto-Elasticity (TAE) of natural rock cliffs: toward better understanding and monitoring damage and erosion process, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2707, https://doi.org/10.5194/egusphere-egu23-2707, 2023.

Many deep faults do not reach the earth’s surface and thus are not recognized. Such faults are rarely mapped by standard surface geological mapping. This seriously hinders seismic risk mitigation efforts. In this study, we applied the horizontal-to-vertical spectral ratio (HVSR) method to identify blind faults invisible at the surface. Despite its simplicity and low-cost implementation, we noticed that HVSR results were unstable using data collected by exposed seismometers or under higher wind speeds. Therefore, three-component seismic sensors for ambient noise observations were buried at different depths to examine the effects of ground coupling, wind speeds, and precipitations. Results from a series of field tests under diverse conditions guided us to establish data selection criteria. The first required condition is that seismic sensors should be buried (>0.3 meters) to secure ground coupling and to avoid any direct exposure to wind or precipitations. The other is that data should be collected at low wind speeds (< 3 m/s). The requirements were applied to ambient noise data along two profiles traversing unnamed and inferred faults in Pohang, Korea. We initially estimated the resonance frequencies for each site, which varied from 0.41 to 2.52 Hz. They were then converted to bedrock depths using an empirical relationship between the resonance frequency and depth to bedrock observed at boreholes in the area. The estimated depths to bedrock along profiles ranged from 8.0 to -472.0 meters. The resulting depth profiles show significant lateral variations in the bedrock depth, including the one near the Gokgang fault at which the thickness to the major impedance contrasts decreased from 196 to 20 meters. Sudden variations were also observed at unexpected locations along the profile. We examined the details, especially for sites of apparent changes in bedrock depth, and compared their characteristics with other geophysical studies, including Vs30, MASW, Bouguer gravity anomaly, and adjacent stations correlation. Their results are all well correlated to each other and indicate rapid changes in bedrock depth. We attribute the rapid changes to vertical displacements by ancient faulting activity.

How to cite: Kang, S. Y., Kim, K.-H., Kim, D., Kim, B., Liu, L., and Lee, Y.: Identification of bedrock depth and blind fault by HVSR analysis along two profiles in Pohang, South Korea considering optimal weather environment and seismometer burial depth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3010, https://doi.org/10.5194/egusphere-egu23-3010, 2023.

Weather conditions are an important driver of Earth surface dynamics, such as gravitational mass wasting, flood propagation, biological activity events and physical interactions within the critical zone. While there are dedicated sensors to capture meteorological parameters, these sensors are comparably expensive, have a small spatial footprint and often lack the temporal resolution needed to constrain high frequency meteorological dynamics. We introduce the concept of meteo-seismology, i.e. the measurement of first-order ground motion signatures of weather conditions by decisively installed seismic sensors. While meteorological manifestations are generally considered seismic noise and it may seem odd to use seismometers instead of weather stations, geophysical sensors circumvent or complement the above caveats and add further important data to a comprehensive picture of the rapidly changing state of the atmosphere and its interaction with the landscape we live in. Based on examples from prototype forested landscapes in Central Europe and Chilean Patagonia, we demonstrate how seismic stations can be used to infer properties of the pressure and wind field and its coupling to the biosphere, constrain rain intensity and drop properties, yield temperature proxies and their propagation into the ground, and survey ground moisture trends and discharge patterns. Understanding the seismic signatures of a meteorological origin also allows to, vice versa, better handle the contaminating side of these seismic sources in records, where high frequency signals are to be used for other than meteo-seismological studies. Our approach offers an alternative and complementary way to non-invasively monitor hydrometeorological energy and matter fluxes at high temporal and spatial resolution.

How to cite: Dietze, M., Mohr, C., Tolorza, V. A., Sotomayor, B., and Gonzalez, E.: Meteo-Seismology: Harvesting the Seismic Signals of Weather Dynamics in the Critical Zone, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3593, https://doi.org/10.5194/egusphere-egu23-3593, 2023.

Large rockfalls often cause huge economic losses and casualties in densely populated mountain areas. Timely acquiring information on a large rockfall can help promptly assess the damage and residual risks and guide the emergency response. Recent works suggest that the seismic signals generated by large rockfalls can provide these key information, but most of them focused on exploring seismic signatures to understand rockfall dynamics, lacking a rapid disaster assessing scheme. Here, we establish a seismic signal-based assessment scheme and demonstrate its capability by taking a large event – the 5 April 2021 Hongya rockfall (Sichuan, China) – as a case study. This scheme consists of three components, which are rockfall identification, detection and location, and characterization. In the rockfall identification module, we show how a rockfall can be distinguished from an earthquake and a rockslide by analyzing its seismic signatures. In the detection and location module, we demonstrate how the kurtosis-based method can be used to rapidly detect the initiation of a rockfall and determine the seismic wave velocity accordingly, and how the arrival-time-based location method can be used to locate a rockfall event. In the rockfall characterization module, we show how rockfall volume can be estimated from the magnitude of radiated seismic energy and how to characterize the dynamic process of a rockfall by the signatures of seismogram, spectrum and recorded seismic energy. Our results show that the seismic signal-based scheme presented here is suitable to characterize large rockfalls and has certain potential for rapid and effective emergency management.

How to cite: Li, W., Wang, D., and Zhang, Z.: Large rockfall detection, location and characterization using broadband seismic records: A case study of Hongya rockfall, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3773, https://doi.org/10.5194/egusphere-egu23-3773, 2023.

The collapse at depth of a cavern on the side of the Napoleonville salt dome, Assumption Parish, Louisiana, led to the formation of a large sinkhole at the surface. Besides surficial evidence from direct observations, the precise timeline of the evolution of the sinkhole is poorly known.  Here, we used two years of continuous ambient seismic vibrations recorded at 11 3-component seismic stations located around the Bayou Corne sinkhole to monitor the daily relative seismic velocity changes associated with the sinkhole activity. The sinkhole started to form in 2012 and had several phases of activity. The seismic network was installed in early 2013 and recorded the last major collapses before settling in 2014. Following standard seismic interferometry processing, we computed the full 9-component tensors of ambient vibrations cross-correlations between each pair of sensors. After a drastic quality check of the correlations, we rejected several components for which we did not have enough data or for which the data were corrupted in a way that was difficult to correct. We monitored the relative velocity variations (dv/v) during the studied period using the stretching method in the 0.9-3 Hz frequency band within the early coda of the correlations. We employed a reference-less inversion procedure to obtain a dv/v time series for each component and each pair of stations. The multi-component pairs curves are averaged to get the final time series. The results show significant velocity changes in early 2013 associated with the collapse phases of the sinkhole. The velocity recovers steadily after the second half of 2013 and all of 2014. Two seismically active periods generate smaller velocity drops. In agreement with the spatial extension of the sinkhole toward the southwest seen from the surface, the pairs of stations the most affected by large velocity drops are the ones located along the southwestern shore of the lake.
Our monitoring allows for refining the timeline of the events affecting the sinkhole and its overall activity with a daily temporal resolution. From the analysis of these two years of data, the sinkhole stabilized after intense activity in early 2013. The large velocity variations indicate a strong destructuring of the ground, with potential fracturing and water invasion.

How to cite: Mordret, A., Lavoué, A., Witten, B., Baig, A., Beaupretre, S., Courbis, R., and Gradon, C.: Ambient noise monitoring of the Bayou Corne sinkhole evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4500, https://doi.org/10.5194/egusphere-egu23-4500, 2023.

Data acquired by a dense seismic network deployed in the Cerdanya basin (Eastern Pyrenees) is used to track the temporal and spatial evolution of meteorological events such as rainfall episodes or thunderstorms. Comparing seismic and meteorological data, we show that for frequencies above 40 Hz, the dominant source of seismic noise is rainfall and hence the amplitude of the seismic data can be used as a proxy of rainfall. The interstation distance of 1.5 km provides an unprecedented spatial resolution of the evolution of rainfall episodes along the basin. Two specific episodes, one dominated by stratiform rain and the second one dominated by convective rain, are analyzed in detail, using high resolution disdrometer data from a meteorological site near one of the seismic instruments.

Seismic amplitude variations follow a similar evolution to radar reflectivity values, but in some stratiform precipitation cases, it differs from the radar-derived precipitation estimates in this region of abrupt topography where radar may suffer antenna beam blockage. Hence, we demonstrate the added value of seismic data to complement other sources of information such as rain-gauge or weather radar observations to describe the evolution of ground-level rainfall fields at high spatial and temporal resolution. The seismic power and the rainfall intensity have and exponential relationship and the periods with larger seismic power are coincident. The time periods with rain drops diameters exceeding 3.5 mm do not result in increased seismic amplitudes, suggesting that there is a threshold value from which seismic data are no longer proportional to the size of the drops.

Thunderstorms can be identified by the recording of the sonic waves generated by thunders. We show that single thunders can be recorded to distances of a few tens of kilometers. As the propagation of these acoustic waves is expected to be strongly affected by parameters as air humidity, temperature variations or wind, the seismic data could provide an excellent tool to investigate atmospheric properties variations during thunderstorms.

How to cite: Diaz, J., Ruiz, M., Udina, M., Polls, F., Martí, D., and Bech, J.: Tracking storms in the Pyrenees using a dense seismic network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5344, https://doi.org/10.5194/egusphere-egu23-5344, 2023.

Karst aquifers are characterized by their heterogeneity and complex underground geometry. A great part of the world relies on karst resources for drinkable water and understanding the functioning of karst systems is essential to assess their vulnerability and response to rainfall. Relevant continuous parameters to quantify the underground flow dynamics are still required for these studies as direct underground measurements are not possible. We used surface ambient noise measurements to estimate the seismic signature and amplitude associated with the water flow within an underground karst conduit. We combined geophysical measurements with hydro-chemical and hydrogeological data to build a multidisciplinary approach. The experimental site is the Glane spring, in Dordogne (France). The hydrogeological catchment of this Vauclusian-type spring is 75 km² and consists of upper Jurassic carbonate rocks. The Glane spring shows rapid and intense variations of discharge following rainfall events, ranging from 0.1 to 4 m³/s in 2021. Ambient noise has been continuously recorded since December 2021 using four seismic stations deployed upstream of the source and above the well-known karst terminal conduit. Hydro-chemical parameters and water level have been continuously monitored during a full hydrological cycle and a rain gauge was installed on site to monitor rainfall. During the first year of monitoring, we identified six flooding events. Each event was characterized by an increase in water flow associated with an increase in the seismic signal amplitude. We observed that the seismic amplitude standard level is higher during the high-water period than during the low water period suggesting a larger base water flow. We also observed hysteresis between the seismic power and hydro-chemical parameters. Correlations between the seismic recordings and hydrochemistry might suggest a change in water flow regime within the conduit prior to the flood. Seismic power variations associated with discharge variations are similar to what was already observed for sub-glacial melting flow. Other springs and swallow holes are currently instrumented to validate the approach in the field.

How to cite: Pantiga, A., Allègre, V., Lastennet, R., Houillon, N., Mateo, S., Naessens, F., and Denis, A.: Evidence of sub-surface water flow dynamics within a karst conduit from ambient noise monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5610, https://doi.org/10.5194/egusphere-egu23-5610, 2023.

Historically, there is one larger quick clay landslide in Norway every year. Since 80 percent of those happen in known quick clay risk areas, it is important to monitor these sites continuously. Alna, a busy, urban area in Oslo, is an example of such a location where a quick clay slide could lead to substantial human and economical losses.

In this study we use ambient noise methods to monitor changes in the subsurface at Alna using a small array of three-component seismic sensors. To retrieve small velocity changes, we apply coda wave interferometry using 12 months of urban seismic noise (above 1 Hz).

We compare the observed day-to-day changes to air temperature, precipitation, and water levels in a nearby river, and observe environmental velocity fluctuations well correlated with air temperature and precipitation. In particular, freezing and thawing produces strong changes in seismic velocity (up to 4 percent). The surface wave-coda used here is sensitive to changes in shear wave velocity, which in turn can be used to detect changes of the sub-surface properties. Therefore, observed velocity variations at Alna could have potential for monitoring and early warning of quick clay instabilities.

How to cite: Bruland, C., Köhler, A., and Oye, V.: Towards quick clay monitoring in the city of Oslo, Norway with urban seismic noise, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6049, https://doi.org/10.5194/egusphere-egu23-6049, 2023.

Karstic zones are numerous on Earth and offer a particular field of study to evaluate the ground motion levels that occurred in the past in support of regional seismic hazard assessment. Indeed, some fine and slender candlestick stalagmites are intact and therefore indicate that a certain level of ground motion has not been exceeded since they exist. Many parameters must be considered in the behaviour of stalagmites to earthquakes such as their shape, their mechanical properties and their natural frequency. A good way to better understand and characterize the reaction of these stalagmites to earthquakes is to study their reaction to the current permanent ground motion. To do this, a study based on the measurement of ambient seismic noise is underway in the cave of Han-sur-Lesse (Ardenne, Belgium). The ambient seismic noise is measured both at the surface (above the limestone massif and in the nearest village), on the floor of the cave and on the stalagmites themselves. Different three-component seismic sensors are used in parallel: three SmartSolo IGU-16HR 3C and two Raspberry Shake 3D Personal Seismographs, one of which has been adapted to be easily attached to the stalagmites. This parallel configuration during two-week recording periods made it possible to determine the eigenfrequencies and the polarization of the associated movements of 16 stalagmites. In addition, daily and weekly variations in ambient noise and transient events are measured such as earthquakes, quarry explosions or flooding in the cave. The presence of sensors in different places over the same period also makes it possible to study the possible impact of the cave's local characteristics on these measurements.

How to cite: Martin, A., Lecocq, T., Lannoy, A., Quinif, Y., Camelbeeck, T., and Fagel, N.: Stalagmites' reactions to ground motion studied using modified Raspberry Shake and nodal sensors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6264, https://doi.org/10.5194/egusphere-egu23-6264, 2023.

Hazardous mass-movements pose a great danger to the population and critical infrastructure, especially in alpine areas. Monitoring and early-warning systems can potentially save many lives and improve the resilience of mountain communities to catastrophic events. Increasing coverage of seismic networks recording hazardous mass-movements opens up new warning perspectives as long as efficient algorithms screening the seismic data streams in real-time are available.

We propose to combine physical and statistical properties of seismic ground velocity recordings from geophones and seismometers as a foundation for an unsupervised workflow for mass movement detection. We evaluate the performance, consistency, and generalizability of unsupervised clustering algorithms like K-means and Bayesian Gaussian Mixture Models against supervised methods like the Random Forest classifier. Focusing on debris-flow records at the Illgraben torrent in Switzerland, we present a generic mass-movement detector with high accuracy and early-warning capability. We apply this detector to other datasets form other sites to investigate its transferability.

Since our results aim to enable mass-movement monitoring and early-warning worldwide, Open Research Data principles like Findability, Accessibility, Interoperability and Reusability (FAIR) are of high importance for this project. We discuss how using the Renku (renkulab.io) platform of the Swiss Data Science Center ensures FAIR data science principles in our investigation. This is a key step towards our ultimate goal to enable seismology-based early warning of mass-movements wherever it may be required.

How to cite: Paitz, P., Chmiel, M., Husmann, L., Volpi, M., Kamper, F., and Walter, F.: Towards an unsupervised generic seismic detector for hazardous mass-movements: a data-driven approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6300, https://doi.org/10.5194/egusphere-egu23-6300, 2023.

In this study, we used coda wave interferometry to investigate four years of continuous data from AlpArray and other locations throughout Europe. We estimate the hourly Green’s function by cross-correlating ambient seismic noise recorded at pairs of stations. The results indicate short and long-term variations of the seismic velocities and show the feasibility of large-scale monitoring with ambient seismic noise at high temporal resolution. The relative seismic velocities (dv/v) show temporal variations on the order of 10^-3 in a frequency band around 1 Hz. Spectra of the velocity time series contain strong daily and sub-daily behaviour, which are primarily caused by the coupling of atmospheric processes and solid Earth. The explanatory model focuses on depth variations of the groundwater table, linking atmospheric pressure (loading and unloading the Earth's surface) to variations in seismic velocity. This study aims to understand and explain differences in daily and sub-daily behaviour across Europe. This may contribute to the hydrological characterization of the near-subsurface in central Europe. 

How to cite: Kramer, R., Lu, Y., and Bokelmann, G.: Can we characterize groundwater reservoirs in central Europe from air-pressure-induced seismic velocity changes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6321, https://doi.org/10.5194/egusphere-egu23-6321, 2023.

In the context of climate change, the occurrence of geohazards such as landslides or rockfalls might increase. Therefore, it is important to have the ability to characterise their (spatial and temporal) occurrences in order to implement protection measures for the potential impacted populations and infrastructures. Nowadays, several methods including Machine Learning algorithms are used to study landslides-triggered micro-seismicity and the associated seismic sources (eg. rockfalls and  slopequakes). Those innovative algorithms allow the automation of the processing chains used to build micro-seismicity catalogues, leading to the understanding of the landslide deformation pattern and internal structure. Unfortunately, each landslide context has its own seismic signature which requires the use of the most complete and handmade training samples to train a Machine Learning algorithm. This is highly time consuming because it involves an expert that needs to manually check every seismic signal recorded by the seismic network, which can be thousands per day.

The aim of this study is to develop semi-supervised and unsupervised clustering methods to characterise the micro-seismicity of landslides in near real time. Here, we present the preliminary results obtained for creating a landslide micro-seismicity catalogue from the analysis of a dense network of 50 seismic stations deployed temporarily at the Super-Sauze landslide (French Alps). First, we present the performance of supervised Random Forest and XGBoost trained models on the event signals. Then, an approach aimed at processing streams of raw seismic data based on 18s-length windows is explored. Finally, we discuss the clustering results and the transferability possibilities of the approach to other landslides and even environments (glaciers, volcanoes).

How to cite: Rimpot, J., Hibert, C., Malet, J.-P., Forestier, G., and Weber, J.: Towards a generic clustering approach for building seismic catalogues from dense sensor networks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7136, https://doi.org/10.5194/egusphere-egu23-7136, 2023.

In coastal Antarctica, outlet glaciers exhibit complex dynamics materialized by intense internal deformation, enhanced basal sliding and strong thermo-mechanical interactions with the ocean. Here we aim to use seismic observations to unravel these various processes and their link with glacier and ocean dynamics. As part of the SEIS-ADELICE project (2020-2024) supported by the French Polar Institute IPEV, in January 2022 we deployed four permanent and six temporary (1 month long) broadband seismic stations on and around the Astrolabe Glacier (Terre Adélie, East Antarctica), as well as four ocean-bottom seismometers at sea near the terminus of the floating tongue. In January 2023 we will be supplementing this setup by a temporary network of 50 seismic nodes above the grounding line of the glacier.

Preliminary detection and classification of seismic events reveals a wide variety of cryo-seismic signals. The most pervasive events correspond to icequakes, are located close to the surface, and exhibit clear tidal modulation. We interpret these events as being generated by the brittle fracturing of ice associated with crevasse opening. We also observe numerous short and similar repetitive events of much lower amplitude that are located at few restricted locations near the ice-bedrock interface. These events are likely produced by basal stick-slip over punctual bedrock asperities. Finally, we observe glacial tremors which could result from hydraulic sources at the ice-bedrock interface, although further analysis is required to confirm this hypothesis.

This preliminary work provides useful grounds for deeper analysis to be done in the future on source characteristics and their more quantitative links with glacier dynamics.

How to cite: Le Bris, T., Barruol, G., Le Meur, E., Gimbert, F., and Zigone, D.: Monitoring the cryoseismic activity of the Astrolabe glacier, Terre Adélie, Antarctica, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7489, https://doi.org/10.5194/egusphere-egu23-7489, 2023.

Seafloor sediment flows (turbidity currents) form some of the largest sediment accumulations on Earth, carry globally significant volumes of organic carbon, and can damage critical seafloor infrastructure. These fast and destructive events are notoriously challenging to measure in action, as they often damage any instruments anchored within the flow. We present the first direct evidence that turbidity currents generate seismic signals which can be remotely sensed (~1-3 km away), revealing the internal structure and remarkably prolonged duration of the longest runout sediment flows on Earth. Passive Ocean Bottom Seismograph (OBS) sensors, located on terraces of the Congo Canyon, offshore West Africa, recorded thirteen turbidity currents over an 8-month period. The occurrence and timing of these turbidity currents was confirmed by nearby moorings with acoustic Doppler current profilers.

Results show that turbidity currents travelling over ~1.5 m/s produce a seismic signal concentrated below 10 Hz with a sudden onset and more gentle decay. Comparison of the seismic signals with information on flow velocities from the acoustic Doppler current profilers demonstrates that the seismic signal is generated by the fast-moving front of the flow (frontal cell), which contains higher sediment concentrations compared to the slower-moving body. Long runout flows travelling >1000 km have a fast (3.7-7.6 m s^-1) frontal cell, which can be 14 hours, and ~350 km long, with individual flows lasting >3 weeks. Flows travelling >1000 km eroded >1300 Mt of sediment in one year, yet had near-constant front speeds, contrary to past theory. The seismic dataset allows us to propose a fundamental new model for how turbidity currents self-sustain, where sediment fluxes into and from a dense frontal layer are near-balanced.

Seismic monitoring of turbidity currents provides a new method to record these hazardous submarine flows, safely, over large areas, continuously for years yet at sub-second temporal resolution. Monitoring these processes from land would considerably ease deployment efforts and costs. Thus, work is underway investigating if terrestrial seismic stations can record submarine seafloor processes in Bute Inlet, a fjord in western Canada where independent measurement of delta-lip failures and turbidity currents can be compared to a passive seismic dataset.

How to cite: Baker, M., Talling, P., Burnett, R., Pope, E., Ruffell, S., Cartigny, M., Dietze, M., Urlaub, M., Clare, M., Neasham, J., Silva Jacinto, R., Kunath, P., and Peirce, C.: Seabed seismometers reveal duration and structure of longest runout sediment flows on Earth, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7549, https://doi.org/10.5194/egusphere-egu23-7549, 2023.

Use of seismic monitoring and data analysis techniques in recent years have allowed for improved understanding of several shallow earth processes, such as glacial motion, subsurface water flow, and bedload transport. Early applications using seismic data collected at high energy alpine rivers suggest that seismic energy within certain frequency bands is linked to bedload discharge.  However, study of other river systems have been more limited, even though some of these systems, such as ephemeral streams in arid environments, transport large quantities of sediment during short-lived flash flood events.  Here we present seismic and hydrologic data collected in a unique sediment observatory within an ephemeral tributary to the Rio Grande River, in the desert southwest of the U.S., combining dense seismic observations with a variety of in-channel bedload and water monitoring measurements. We have seismic records for more than a dozen floods ranging in depth from a few centimeters to over one meter, encompassing bedload flux as high as 12 kg s^-1 m^-1, two orders of magnitude higher than in most perennial settings. Our efforts to date focus on identifying the noise sources within the seismic record, characterization of the seismic properties of the site, and determining the seismic frequency ranges best correlated with the automatically measured bedload flux. Within the 30-80 Hz frequency range, we find a linear relationship between seismic power and bedload flux. We hypothesize that variations in linear fit statistics between flood events are due to varying bedload grain size distributions and in-channel morphological changes.

How to cite: Bilek, S., McLaughlin, J. M., Cadol, D., and Laronne, J.: Using Seismic Methods to Monitor Bedload Transport Along a Desert Environment Ephemeral Tributary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7727, https://doi.org/10.5194/egusphere-egu23-7727, 2023.

Rapid mass movements are a major threat in populated landscapes, as they can cause significant loss of life and damage civil infrastructure. Previous work has shown that using environmental seismology methods to monitor such mass movements and establish monitoring systems offers advantages over existing approaches. The first important step in developing an early warning system for rapid mass movements based on seismic signals is automatically detecting events of interest. Though the approach, such as short-term average to long-term average ratio (STA/LTA) and machine learning model, was introduced to detect events (e.g., debris flow and rockfall), it is still challenging to calibrate input parameters and migrate existing methods to other catchments. Detection of debris flows, for instance, is similar to anomaly detection if we consider the seismic stations recording background signals as an overwhelming majority condition. 
Benford's law describes the probability distribution of the first non-zero digits in numerical datasets, which provides a functional, computationally cheap approach to anomaly detection, such as fraud detection in financial data or earthquake detection in seismic signals. In this study, seismic signals generated by rapid mass movements were collected to check the agreement of the distribution of the first digit with Benford's law. Subsequently, we develop a computationally efficient and non-site-specific model to detect events based on Benford's law using debris flows from the Illgraben, a Swiss torrent, as an example. Our results show that seismic signals generated by high-energy mass movements, such as debris flows, landslides, and lahars, follow Benford's law, while those generated by rockfall and background signals do not. Furthermore, our detector performance in picking debris-flow events is comparable to a published random forest and seismic network-based approach. Our method can be applied at other sites to detect debris-flow events without additional calibration and offers the potential for real-time warnings.

How to cite: Zhou, Q., Tang, H., Turowski, J. M., Braun, J., Dietze, M., Walter, F., Yang, C.-J., Lagarde, S., and Abdelwahab, A.: Benford's law in detecting rapid mass movements with seismic signals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8127, https://doi.org/10.5194/egusphere-egu23-8127, 2023.

Landslides are a major natural hazard that can cause significant loss of life and property damage around the world. As global temperatures rise and weather extremes become more frequent, we can expect an increase in the hazard emanating from landslides too. In order to better understand and mitigate landslide risks, a variety of strategies have been developed to characterize and monitor landslide activity. Many established approaches provide valuable information about surface displacement and surface properties, but are not suited to inspect the subsurface parts of a landslide body. In contrast, seismic imaging and monitoring methods allow us to study subsurface structures, properties, and internal processes that control landslide behaviour.

In our project, we develop novel seismic data acquisition and interpretation approaches to characterize and monitor one of the largest active unstable slopes in the Alps, the Cuolm da Vi landslide, with an unprecedented spatial resolution. We achieve this by combining an array of over 1’000 seismic nodes with fiber-optic based monitoring techniques such as Distributed Acoustic (DAS) and Strain Sensing (DSS).

The deep-seated Cuolm da Vi landslide is located near Sedrun (Central Switzerland) and consists of approximately 100-200 million m³ of unstable rock reaching displacement rates up to 10-20 cm/yr with clear seasonal cycles. In summer 2022, we buried over 6 kilometres of fiber-optic cable in this alpine environment covering the most active part of the landslide with multiple cable orientations. Additionally, we deployed a nodal array of 1046 accelerometers in a hexagonal grid covering around 1km² with a nominal spacing of 28 meters. Seismic data were acquired with the nodes and the DAS system continuously for four weeks. This time period included the blasting of 163 dynamite shots for calibration and active-source imaging purposes. In 2023, we plan to conduct data acquisition for longer periods using primarily fibre-optic based techniques with a focus on the temporal evolution of the landslide dynamics.

Our first goal is to resolve the internal structure of the landslide based on the controlled-source data acquired in summer 2022 to construct, for example, a seismic velocity model. Based on the models derived from the active-source seismic data, we plan to exploit the continuous seismic recordings of ambient vibrations and potential seismic signals produced by the landslide activity to complement structural models and study the landslide dynamics. We will present our current results and discuss their implications for the next steps towards monitoring this landslide over time.

How to cite: Kiers, T., Schmelzbach, C., Edme, P., Paitz, P., Amann, F., Maurer, H., and Robertsson, J.: Monitoring of an Alpine landslide using dense seismic observations: combining Distributed Acoustic Sensing and 1000 autonomous seismic nodes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8986, https://doi.org/10.5194/egusphere-egu23-8986, 2023.

Alpine glaciers have been rapidly retreating and at increasing rates in recent decades due to climate warming. As a consequence, large amounts of suspended- and bed-load flux are being released to proglacial environments, such as proglacial forefields. These regions are among the most unstable geomorphic systems of the Earth because they rapidly respond to changing discharge and sediment conditions. Given this, it might be hypothesized that their intense morphodynamic activity, being a complex and non-linear process, could “shred” the sediment transport signal itself, and especially that related to subglacial sediment export.

To date, our knowledge on subglacial sediment export by subglacial streams is essentially dominated by suspended sediment dynamics recorded in front of shrinking glaciers because of the limitations in measuring bedload transport. The latter is usually monitored far downstream from glacier termini by permanent stations (e.g. water intakes, geophone systems) leaving major uncertainties in the absolute amounts and temporal patterns of transport in both glacial and proglacial environments, as well as the relative importance compared to suspended sediment in case of morphodynamic filtering. Thus, the aim of this project was to investigate the evolution of the both suspended- and bedload subglacial export signals within the proglacial forefield to quantify the extent and the timescale over which proglacial morphodynamics filter them.

This work focuses on a large Alpine glacial forefield, almost 2 km in length, that has formed since the early 1980s at the Glacier d’Otemma (southern-western Swiss Alps, Valais). Data were collected over two entire melt seasons (June-September 2020 and 2021) experiencing different climatic conditions, the first year warm and relatively dry and the second cold and relatively wet. Suspended transport was recorded using conventional turbidity-suspended sediment concentration relationship, bedload transport was monitored seismically, while the morphodynamic filtering was determined using signal post-processing techniques. At present, there are no studies combining continuous measurements of both suspended- and bed-loads in such environments.

Results show that the signal of subglacial bedload export, unlike suspended load export, is rapidly shredded by proglacial stream morphodynamics, which we show is due to a particle-size dependent autogenic sorting of sediment transport at both daily and seasonal time-scales. The result is that over very short distances, the signal of subglacial bedload sediment export is lost and replaced by a signal dominated by morphodynamic reworking of the proglacial braidplain. The suspended signal is less impeded but significant floodplain storage and release of suspended sediment was observed. These results question the reliability of current inferences of glacial erosion rates from sediment transport rates often measured some way downstream of glacier margins.

How to cite: Mancini, D., Dietze, M., Müller, T., Jenkin, M., Miesen, F. M., Roncoroni, M., Nicholas, A., and Lane, S. N.: Rapid shredding of the subglacial sediment export signal by proglacial forefields, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11404, https://doi.org/10.5194/egusphere-egu23-11404, 2023.

As observed elsewhere on a global scale, mountain permafrost at the Zugspitze (German/Austrian Alps) is degrading in response to climate change, which affects the rock slope stability and thus the hazard potential. Recent studies suggest that passive seismology is a promising and emerging tool to monitor permafrost changes as the seismic velocity of rocks strongly decreases/increases upon thawing/freezing. Compared to other, more classical methods like borehole temperature logging or electrical resistivity tomography (ERT), seismology is less laborious and costly, non-invasive and allows continuous monitoring. At Mt. Zugspitze, we exploit these advantages using a permanent seismic station (installed in 2006) as well as three small seismic arrays and Distributed Acoustic Sensing (DAS; both available since summer/fall 2021), to infer permafrost dynamics with high spatio-temporal resolution. The seismic data show repeating diurnal noise generated by the operation of cable cars, which we leverage for cross-correlation analysis. Our results suggest that the dominant signal in the retrieved seismic velocity change time series is caused by the seasonal freeze-thaw cycles associated with permafrost bodies on the northern side of the mountain ridge. On the long-term, the time series show a gradual velocity decrease associated with permafrost degradation due to atmospheric warming and compare well with modeled velocity change time series using rock temperature data from a nearby borehole, which intersects the mountain ridge. We discuss differences in our seismic analysis results obtained from direct and coda waves as well as from single station to station pairs and DAS and interpret the results in the light of other measurements including ERT, rock temperature logging and meteorological parameters.

How to cite: Lindner, F., Smolinski, K., Scandroglio, R., Fichtner, A., and Wassermann, J.: Seismic Monitoring of Permafrost Dynamics at Mt. Zugspitze (German/Austrian Alps), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12107, https://doi.org/10.5194/egusphere-egu23-12107, 2023.

Monitoring temporal and spatial changes in sediment volume in the upstream reservoir is one of the important indicators for evaluating the reservoir project life, especially the information carried by bedload and suspended load. According to field condition, direct bedload monitoring is often difficult. Thus, bedload usually can be estimated by a specific proportion of suspended load depended on the flooding magnitude, which can cause a large uncertainty in estimates of total sediment load. In recent years, riverine micro-seismic signals have been applied to study bedload transport. Our study chose the Da-Pu Dam (location: 23.296500°N, 120.644611°E), located at the upstream of the Zeng-Wen Reservoir and the junction of the Zeng-Wen river and Cao-Lan river, which is the last check dam before entering the reservoir area. Its upstream catchment area is 30,312 hectares that comprise approximately 63% of the Zeng-Wen Reservoir catchment area (48,100 hectares). The length of the monitoring section of the Da Pu Dam is 1,100 meters, with an average width of 121 meters and an average slope of 0.36 degrees. With the available data composed of riverbed cross-section survey, sediment particle size distribution, fluvial measurements (water depth, surface flow velocity), orthoimagery, and suspended load measurement, our study applies seismic saltation model to estimate the bedload flux and compares the results with the measured suspended load. Results showed that there are different ratios between bedload and suspended load under similar hydrological condition during the plum rain season(May-June) and typhoon period(July-September). In a case of flooding event considering the flow stage from medium to high discharge, significant temporal changes in the ratio between bedload and suspended load can also be observed, which imply a complex transition process between the bedload and suspension particles. The temporal changes in sediment ratio obtained in this study can be applied to estimate the total volume of sediment load entering the reservoir. Our estimated results are consistent with the survey of sediment accumulation at the end of each year in the reservoir area.

How to cite: Meng, C. T., Chao, W. A., and Chen, Y. S.: Probing temporal variation of suspended load to bedload ratio using seismic saltation model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12128, https://doi.org/10.5194/egusphere-egu23-12128, 2023.

Understanding the spatiotemporal details in the occurrence of jökulhlaups, also referred to as glacier lake outburst floods (GLOFs), is important for improving early warning and forecasting future events. Jökulhlaups occur in many different glacier-related settings and differ in their characteristics depending on the natural conditions: From very rapid floods (minutes-hours) originating from moraine dammed lakes in steep valleys to gradual floods (days-weeks) from subglacial lakes such as the ones beneath Vatnajökull ice cap, in Iceland. Previous studies of the October 2015 Skaftá jökulhlaup suggested that several hours of early-warning is possible based on the generated seismic tremor. Here, for the first time, we looked into all three spatial components of GNSS and seismic array data, respectively. Previous studies have already analysed the seismic events (icequakes, tremor, other migrating transient events) in detail, yet only on the z component. We reprocessed all three components of the seismic array data using frequency-wavenumber -analysis (fk-analysis) and match field processing (MFP). Both techniques allow to locate distant signal sources, either by direction only (fk) or actual location (MFP). We specifically focused on the time period when the tremor source is moving with the flood front and found two unexplained seismic signals:

• A second migrating signal is visible on the lowermost part of the flood path 6 hours later than the passing of the first flood front.

  We compared this with a GNSS observations on top of the subglacial flood path and a hydrometric station 25 km downstream from the glacier margin in the affected Skaftá-river.

  After aligning the time series by the arrival of the pressure wave, the timing of the second seismic signal fits well with a 10 cm uplift of the glacier at the GNSS station; but also with a change in the rate of water level rise at the hydrometric station.

  We discuss this in the context of either explaining GNSS, hydrometric and seismological data individually or giving a hypothetical process that explains all three together. That could be a second intraglacial water lense draining, after the emptying of the lake deformed the overlaying glacier and connected the two water bodies. However, radio echo sounding survey over the source area in spring 2015 did not indicate a significant intraglacal water lense above the subglacial lake. The GNSS data may be cleared as noise artifact and the hydrometric data explained by flow of water out of the river course of Skaftá and onto porous lava fields between Sveinstindur, where the discharge of Skaftá is measured, and the glacier. Yet: The seismic signal then is left unexplained and open for discussion.

• Finally, 18 hours after the first pulse, we found a sudden deceleration in horizontal motion on the GNSS that coincided with a sudden increase in seismic signals originating at the glacier terminus. We discuss if what we see is actually the glacier stopping, after losing the flood lubrication.

How to cite: Dietrich, T., Eibl, E. P. S., Magnússon, E., Binder, D., Heimann, S., and Roessner, S.: Surprising seismological signals during the October 2015 Skaftá jökulhlaup, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12687, https://doi.org/10.5194/egusphere-egu23-12687, 2023.

One major challenge in Environmental Seismology is that signals of interest are often buried within the high noise level emitted by a multitude of environmental processes. Those signals potentially stay unnoticed and thus, might not be analyzed further.

Distributed acoustic sensing (DAS) is an emerging technology for measuring strain rate data by using common fiber-optic cables in combination with an interrogation unit. This technology enables researchers to acquire seismic monitoring data on poorly accessible terrain with great spatial and temporal resolution. We utilized a DAS unit in a cryospheric environment on a temperate glacier. The data collection took place in July 2020 on Rhonegletscher, Switzerland, where a 9 km long fiber-optic cable was installed, covering the entire glacier from its accumulation to its ablation zone. During one month 17 TB of data were acquired. Due to the highly active and dynamic cryospheric environment, our collected DAS data are characterized by a low signal to noise ratio compared to classical point sensors. Therefore, new techniques are required to denoise the data efficiently and to unmask the signals of interest. 

Here we propose an autoencoder, which is a deep neural network, as a denoising tool for the analysis of our cryospheric seismic data. An autoencoder can potentially separate the incoherent noise (such as wind or water flow) from the temporally and spatially coherent signals of interest (e.g., stick-slip event or crevasse formation). We test this approach on the continuous microseismic Rhonegletscher DAS records. To investigate the autoencoder’s general suitability and performance, three different types of training data are tested: purely synthetic data, original data from on-site seismometers, and original data from the DAS recordings themselves. Finally, suitability, performance as well as advantages and disadvantages of the different types of training data are discussed.

How to cite: Zitt, J., Paitz, P., Walter, F., and Umlauft, J.: Denoising Cryoseismological Distributed Acoustic Sensing Data Using a Deep Neural Network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13269, https://doi.org/10.5194/egusphere-egu23-13269, 2023.

Climate change is causing major shifts in the dynamics of the cryosphere, leading to sea-level rise, glacier break-off events, flooding, and landslides. Geological, thermodynamic and hydraulic processes at the base of an ice mass play a central role in ice flow dynamics, and understanding these is imperative for predicting ice body behavior in a changing climate. To this end, sustained ambient vibrations in glaciated environments can be used to monitor subglacial conditions over significant spatial extent with relatively low-cost acquisition.

In earthquake seismology, a well-established methodology to investigate subsurface properties is the horizontal-to-vertical spectral ratio (H/V) of ambient seismic ground unrest. In cryoseismology, the H/V approach is already used to invert for velocity profiles of ice or firn, to obtain bedrock topography and to identify the presence of basal sediments. To date, only a few hours of seismic vibration records are typically used. Yet in such short time records, biases may arise because of the dynamic character of the glacier. Seismic resonances within the soft ice layer and resulting H/V ratios are expected to vary with changes in subglacial hydraulic conditions.

We propose to leverage temporal variations in H/V spectra to investigate subglacial processes. As a case study, we first focus on the Glacier de la Plaine Morte (Switzerland), where a seismic array was deployed for four months in summer of 2016. During this time, an ice-marginal lake formed and suddenly drained through and under the glacier, making this seismic record ideal for our purposes. This drainage event is well recorded and strongly influences the H/V in terms of amplitude and resonance frequency. We next present ambient H/V measurements of the Sermeq Kujalleq in Kangia (also known as Jakobshavn Isbræ), one of Greenland’s largest outlet glaciers. Here, the H/V spectra show multiple resonances over time, whose origin we discuss in more detail. For both our study cases, separating variations in source and medium properties is pivotal. Tackling this challenge provides glaciologists with a valuable tool to investigate the poorly accessible subglacial environment, which holds the key to our understanding of ice flow and eustatic sea level rise.

How to cite: van Ginkel, J., Walter, F., Nap, A., Häusler, M., and Lüthi, M.: Ambient H/V sensitivity to the dynamics of glaciers and ice sheets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13334, https://doi.org/10.5194/egusphere-egu23-13334, 2023.

Increased glacier melt leads to a change in sediment transport capacity below glaciers, which impacts the sediment transport within proglacial areas as well as downstream ecosystems and geomorphology. Previous work on Alpine glaciers shows that strong diurnal discharge variations lead to fluctuations in sediment transport capacity such that deposition and erosion can occur in the proglacial area over the course of the melt season. However, the exact processes controlling sediment transport at the outlet glaciers of ice sheet margins and in their proglacial areas remain uncertain. Data suggest that the diurnal discharge variations are substantially reduced and baseflow discharge is much greater, likely capable of maintaining significant sediment transport throughout the melt season. This difference in the hydrological regime as compared with Alpine glacial systems may drive different rates and variations in sediment transport and, ultimately, in proglacial braid plain morphodynamics.

We measure proglacial sediment transport at Leverett glacier, a land-terminating glacier located at the western margin of the Greenland Ice Sheet. As bedload transport is exceptionally difficult to measure in situ, two seismic stations were installed to evaluate bedload transport in the glacial meltwater stream in the summer of 2022. The first station is located close to the current glacier terminus, and the second one is about 2 km from the current glacier terminus. These two stations allow for the examination of the sediment transport processes within the proglacial area. By using a Fluvial Inversion Model the recorded seismic data is converted into bedload flux. The model is calibrated using active seismic surveys and statistical approaches to evaluate the physical parameters. Outputs of the Fluvial Inversion Model are validated with available water stage data.  The results provide insight as to whether the proglacial area is aggrading or eroding as sediment transport in the two locations at Leverett glacier evolves over the summer season. We discuss the relationship between bedload transport and level of the proglacial river, as well as the seasonal variations in proglacial sediment transport and deposition in Leverett glacier’s proglacial area.

How to cite: Gevers, M., Mancini, D., Lane, S., and Delaney, I.: Using a record of bedload transport from Leverett glacier in western Greenland to understand proglacial sediment transport processes from the ice sheet  , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13383, https://doi.org/10.5194/egusphere-egu23-13383, 2023.

Outlet glaciers and ice streams are the main channels through which ice sheets transport their mass towards the ocean. One of Greenland’s largest outlet glaciers Sermeq Kujalleq in Kangia (Jakobshavn Isbrae) has been broadly researched after experiencing a rapid retreat of the terminus and accompanying speedup to up to 40 m/day in the early 2000’s. However, such short-term ice dynamic variations remain poorly understood making numerical models difficult to constrain and predictions on future sea-level rise uncertain.

The short-term ice dynamics of Sermeq Kujalleq consists in transient states and can only be captured by in-situ measurements of high spatial and temporal resolution. Glacier seismology has proven to be a valuable tool to study these dynamics, it provides data with a high temporal resolution and can provide information on processes happening below the ice surface. Within the COEBELI project we combine passive glacier seismology with global navigation satellite system (GNSS) receivers, long-range drones, time-lapse cameras and terrestrial radar interferometry to capture processes such as calving and basal sliding at their respective timescales.

Here, we present results from a multi-array seismic deployment at Sermeq Kujalleq in Summer 2022. From May until September two arrays were deployed in the upstream part of the fast-flowing ice stream (>22 km from calving front) and one array on slower moving ice North of the main trunk. For a 3-week period in July, four more arrays were deployed on the fast-flowing ice stream closer to the calving front (<15 km). In the severely crevassed areas near the calving front (<15 km), the arrays consisted of custom-made autonomous seismic boxes whereas at more accessible upstream areas we installed borehole instruments. During the deployment we recorded multiple large calving events, glacier speedups and periodic multi-hour tremors accompanied by bursts of short-term high frequency (>50 Hz) icequakes. By studying these different signals, we are able to better constrain the processes and forces that control fluctuating ice-flow velocity and calving events.

How to cite: Nap, A., Walter, F., Wehrlé, A., Kneib-Walter, A., Jouvet, G., and Lüthi, M. P.: Short-term fast ice dynamics derived from passive seismic data at a large Greenland outlet glacier, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16008, https://doi.org/10.5194/egusphere-egu23-16008, 2023.

High-melt areas of glaciers generate a rich spectrum of ambient seismicity. These signals do not only contain information about the source mechanisms (e.g. englacial fracturing, water flow, iceberg detachment, basal stick-slip motion) but also carry information about seismic wave propagation within the glacier ice and, therefore, the mechanical properties of the ice. In the summer of 2021 two seismic arrays were deployed in Southern Spitsbergen at the vicinity of Hansbreen’s terminus, one being placed directly on the glacial ice, yielding an 8-days long time series of glacial seismicity.

The direct and scattered wave fields from tens of thousands of icequake records (few thousands per day) were used to determine seismic velocities and monitor structural changes within the ice, while the analysis of the ambient noise was leveraged to constrain the ice thickness. The surface icequakes dominate the seismograms due to an abundance of englacial fracturing. Hence, Rayleigh waves and beam-based techniques were employed to characterise the patterns of microseismicity at the transform junction of two glaciers (Tuvbreen and Hansbreen). Several clusters of various-origin seismicity being active at certain times are identified with a majority of them located on stagnant, fast-melting Tuvabreen.

How to cite: Gajek, W.: Rayleigh wave is the coolest – resolving microseismicity of a tidewater glacier in Svalbard, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16346, https://doi.org/10.5194/egusphere-egu23-16346, 2023.

Glaciers or ice-streams have many common points with tectonic faults. Glaciers can move by

stable or unstable slip or by creep within the glacier thickness. Like faults, glacier sliding can

produce “icequake” signals over a huge range of frequencies, rupture length and signal

duration, as well as tremor. But because glaciers are shallower, the sliding interface can be

accessed directly much more easily, by boreholes or cavities. And they move much faster than

tectonic faults, so that deformation is easier to estimate and icequake inter-event times are

much shorter than for earthquakes.

Here I present some observations of high- and low-frequencies repeaters of basal icequakes

in the Mont-Blanc areas. Both types of events occur as bursts lasting for a few days or weeks,

with quasi-regularly inter-events times of the order of a few minutes or hours, and progressive

changes in amplitude and inter-event times. High-frequency events (around 50 Hz) occur all

over the year, with no clear triggering mechanism, and are located on the lower-part of

glaciers, where ice is at the melting point temperature and the glacier mainly moves by stable

sliding. Low frequency events (around 5 Hz) are mainly located at higher elevations (mainly

above 3000 m asl), on steeper slopes, and have larger magnitudes (-2<m<0). They are mainly

observed during or shortly after snowfalls. At these elevations, glaciers are possibly coldbased,

or close to the melting-point temperature, so that they are stuck to their bed and

mainly deform by creep within the ice. We observe progressive changes in waveforms that

suggest slow and evolving rupture velocities. These low-frequency icequakes may be the

analog of low-frequency earthquakes, which also occur near the transition between stable and

unstable slip.

How to cite: helmstetter, A.: Clusters of low- and high-frequency repeating icequakes in the Mont-Blanc massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16571, https://doi.org/10.5194/egusphere-egu23-16571, 2023.

Changes in glacier area, snow, ice, debris cover, and other geomorphological features such as debris cones have a significant impact on the glacial dynamics, are a direct measure of glacier advance and retreat, form a critical input for measuring glacier mass balance, help identify the location of equilibrium line altitude, contribute to the global sea-level rise, and are a good index for understanding local climatic changes. Formation of glacial lakes enhance the rate of glacial melting and catastrophic events arising out of the outburst of glacial lakes can have serious impacts on the human life and economy. So, monitoring the spatial and temporal changes of glacier surface as well as non-surface features is imperative for assessing the health of glaciers and their behavior toward the climate change. The availability of high spatial resolution remote sensing images, has made precise mapping and monitoring of the changes in the glacier surface features and geomorphological features viable at a local level using object-based change detection (OBCD) rather than traditional pixel-based change detection (PBCD). OBCD has been used in numerous applications however, it has received little attention within the glaciological community. Advantage of using OBCD over PBCD is that the object-based paradigm enables the characterization of different land cover classes within the same image, using different object sizes. Further, in OBCD, each image object is considered as a single entity and hence, the small spurious changes and misregistration errors that occur due to high spectral variability are reduced because segmentation generates image objects which are less sensitive to the small spurious changes and misregistration respectively. Furthermore, a comprehensive literature survey on the Gangotri Glacier, Indian Himalayas uncovered that so far, no work has been done linking the variation of glacier surface and non-surface features with the important climate variables that is, temperature and precipitation. Therefore, this study has evaluated the changes in the Gangotri Glacier features at a large scale using class OBCD approach from high spatial resolution WorldView-2 and LISS-4 images for a three-year period from 2011-2014. The meteorological data of Gangotri Glacier was obtained from Climate Research Unit Time Series v.4.06 dataset. A surge in the annual mean temperature and decline in the annual precipitation caused snow/ice area reduction by ~52%. This is accompanied by an increase in the ice-mixed debris (IMD) area by ~11%. The increase in IMD may lead to enhanced ice melting as it could reflect less incoming solar radiations. This further should have revealed expansion in supraglacial debris (SGD) area, however, it has minimized by ~0.4% which is justified with a rise in the periglacial debris (PGD) and debris cones by ~21% and ~9% respectively. Ascend in the annual mean temperature has also shown an increase of ~70% in the area of supraglacial lakes (SGLs), though the number of SGLs decreased; decrease in the number of SGLs suggests widening of SGLs in area. Thus, the dynamics of the glacier features is greatly affected by the yearly temperature and precipitation alterations in the area.

How to cite: Mitkari, K. V., Sofat, S., Arora, M. K., and Tiwari, R. K.: Linking Changes in Gangotri Glacier Features Derived at a Large-Scale with Climate Variability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-252, https://doi.org/10.5194/egusphere-egu23-252, 2023.

The Çukurova Delta Complex, which is located in the south of Turkey along the northeastern corner of the Mediterranean Sea, is the second-largest delta system in the Mediterranean. The Seyhan River flowed 10 km east from its current course until at least the 16^th Century, and shifted to its current course in the west and began to build the modern delta and the youngest foredune ridges were formed by a combination of aeolian and littoral processes. Morphometrics of foredunes greatly contributes to understanding the relationship between aeolian and marine dynamics. High-resolution digital elevation models (DEMs) are important in examining the geomorphic features of foredune ridges because the low-relief delta environment makes it difficult to use standard topographic maps. Therefore, in the study, the morphometric features, including foredune height, foredune slope, foredune width, the space between foredune ridges, and beach width of the ridges within the study area were extracted from the DEM and orthophotograph of historical and recent aerial photographs. Structure from Motion (SfM) techniques allow for the reconstruction of present and past landforms, and to detect long-term topographic changes in the low-relief areas using historical and modern aerial images. A total of 27 aerial photographs were acquired from flights in AD 2016 covering the study area with a ground sampling distance of 0.3 m, while 13 archive analog aerial photographs with a ground sampling distance of 0.7 m were available from flights in AD 1950. Analysis of SfM-derived high-resolution DEM for the Seyhan Delta shows at least 25 foredune ridges inland for 4 km. It is very important to know the origin and morphodynamics of ridges in terms of revealing the coastal evolution of the Seyhan Delta. Since these ridges preserve past shoreline positions Holocene foredune ridges in the study area can be used to help reconstruct the nature of paleoenvironmental change.

How to cite: Özcan, O., Özpolat, E., Akay, S., Özcan, O., and Görüm, T.: Reconstruction of landforms using historical and recent aerial photographs for landscape evolution of coastal dune dynamics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1852, https://doi.org/10.5194/egusphere-egu23-1852, 2023.

Since the end of the Little Ice Age around 1850, global warming has led to rapid landscape changes, especially in high mountain areas. The ongoing glacier melt leads to an expansion of the LIA glacier forefields, so-called proglacial areas. The exposed lateral moraines often show increased sediment activity over decades and centuries, which is generally described as the paraglacial adjustment process. Slope instabilities are caused, for example, by the loss of the support from the melting glaciers, which can lead to large landslides and thus heavy deformations. In order to understand corresponding geomorphological processes, it is important that surface changes can be reconstructed and analysed in high spatial and temporal resolution. However, aerial photographs of the European Alps, which are well suited for observing proglacial areas, only extend to the middle of the 20th century, thus resulting in a temporal limitation.

Therefore, in this work we show a nearly 100-year quantitative monitoring of a large-scale deformation of a LIA lateral moraine in the glacier forefield of the Gepatschferner in the upper Kaunertal (Tyrol, Austria). We achieve this long-term (1922 to 2021) observation by combining different topographic data sets based on different remote sensing methods and techniques. The reconstructed earth surfaces are based on airborne LiDAR data (2006 to 2021) and photogrammetric DEMs (1953 to 2003) as well as a historical stereophotogrammetric map from 1922, which was also generated into a DEM. In total, eight DEMs were generated and corresponding DoDs calculated.

Different landslides within the first three epochs (1922 to 1953, 1953 to 1971 and 1971 to 1983) could be determined on the slope, which can be directly linked to the corresponding glacier melt. Even after the landslide processes (from 1983 onwards), continuous geomorphological activity could be observed until today (2021), whereby the total volume of net erosion of all epochs (from 1922 to 2021) added up to approx. 486,000 m³.

How to cite: Altmann, M., Haas, F., Rom, J., Fleischer, F., Heckmann, T., Ressl, C., and Becht, M.: Long-term reconstruction of a large-scale landslide of a LIA  lateral moraine in the Upper Kaunertal in Tyrol, Austria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2715, https://doi.org/10.5194/egusphere-egu23-2715, 2023.

Information regarding the spatial arrangement and extent of habitats in the past is highly important for understanding present biodiversity patterns, assessing restoration potential and fighting extinction-debt effects. Due to increasing intensity of land use, European landscapes have changed profoundly over recent decades, with the trend accelerating following World War 2. Here, we explore the feasibility of deriving a 1946 habitat map for Switzerland compatible and hence comparable with the present-day area-wide habitat map. We take advantage of the newly available orthorectified composite of aerial photographs taken in summer 1946 by the US-Army and provided by swisstopo. The ortho imagery (1 m resolution) is segmented into image objects based on spectral and shape homogeneity for 7 case study areas (320 -508 km²), which represent the main biogeographical regions of Switzerland. Initial training data is derived by manual aerial orthoimage interpretation differentiating 16 habitat classes including wetland, grassland, arable land, hedges, orchard meadows and open forest. A random forest model is trained to classify the segments using variables describing spectral information, image texture, segment shape, topography and climate. To increase the accuracy of the classification, an iterative and semi-automated active learning technique is applied. This technique complements the initial training data with new data for segments with high classification uncertainty. With this contribution, we demonstrate the potential and challenges of object-based image analysis, machine learning and active learning to derive habitat maps from historical black-and-white aerial photography.

How to cite: Huber, N., Price, B., Ginzler, C., Holderegger, R., and Bürgi, M.: Historical habitat mapping based on black-and-white aerial photography, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6092, https://doi.org/10.5194/egusphere-egu23-6092, 2023.

Historical images are an important resource for documenting the early states of our environment after the last little ice age. To extract a feature (e.g. glacier outline) from a single historical oblique image in a global coordinate system monoplotting is commonly used: Rays originating from the projection center passing through the pixel vertices, which represent the considered feature, in the image are intersected with a reference terrain model. A subsequent spatial analysis not only requires the 3D position of these vertices as result of monoplotting but also their positional accuracy. The derivation of the latter has not been properly addressed so far.

Existing approaches for assessing the monoplotting accuracy are either based on i) reference data or ii) selected ground control points (GCPs). The first approach is generally not suitable for historical images as reference data is mostly not available. Evaluation based on GCPs is only a rough measure for the potentially achievable accuracy as the monoplotting accuracy varies strongly within an image and the number of GCPs is usually limited. 

Hence, we propose a new approach based on variance propagation. Formulating the monoplotting principle using projective geometry both the accuracy of the estimated camera parameters as well as the reference terrain are considered within the estimation of the uncertainty for the 3D position of each vertex. Estimating the uncertainty for each vertex of the monoplotted feature further allows to derive a differentiated analysis of the results. Furthermore, being independent from necessary reference data our approach is well suited for historical images. Hence, with the developed approach it becomes possible to consider the uncertainty of monoplotted features in subsequent spatial analyses which is especially important when comparing these features with modern reference datasets; e.g. in order to judge the significance of possible changes or deformations.

How to cite: Mikolka-Flöry, S., Ressl, C., and Pfeifer, N.: Uncertainty of monoplotted features from historical single oblique images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6469, https://doi.org/10.5194/egusphere-egu23-6469, 2023.

Point clouds can be acquired by different sensor types and methods, such as lidar (light detection and ranging), radar (radio detection and ranging), RGB-D (red, green, blue, depth) cameras, SfM (structure from motion), etc. 

In many cases multiple point clouds are recorded over time, sometimes also referred to as 4D point clouds. For example, automotive lidars from Ouster or Velodyne record point clouds at around 10-20Hz resulting in millions of points per second. In addition, monitoring with terrestrial laser scanners is becoming used more often. Producing similar datasets than the automotive lidars, although with larger individual point clouds at a lower frame rate.

Analyzing such a large collection of point clouds is a big challenge due the size and unstructured nature of the data. The Python package "pointcloudset" provides a way to store, analyze, and visualize large datasets consisting of multiple point clouds recorded over time. Pointcloudset features lazy evaluation, parallel processing and is designed to enable the development of new point cloud algorithms and their application on big datasets. The package is based on the Python packages pandas, pytncloud, dask and open3D. Its API is easy to use and high level and the package is open source and available on GitHub. 

How to cite: Goelles, T., Schlager, B., and Muckenhuber, S.: pointcloudset - A Python package to analyze large datasets of point clouds recorded over time, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6554, https://doi.org/10.5194/egusphere-egu23-6554, 2023.

In recent years, photogrammetric models have gained widespread use in geosciences due to their ability to reproduce natural surfaces. These models offer a cost-effective and user-friendly alternative to other systems, such as LiDAR, for creating 3D point clouds. On the other hand, rockfalls pose a significant risk to society, as they are the most common natural hazard in mountainous areas and can occur with great speed, resulting in high levels of danger. The aim of this communication is to show results on the development of new algorithms and time-lapse photogrammetric systems for automatic rockfall monitoring (Blanch, 2022).

To acquire the data, a photogrammetric system consisting of different photographic modules and a data transmission module has been developed. This system uses conventional cameras (24Mpx-48Mpx) powered by solar panels and it is controlled by a Raspberry Pi. The system captures time-lapse images, can be programmed, configured flexibly, and it can send images remotely for near real-time processing. The system has been installed at two sites with rockfall activity. One in the Puigcercós cliff, located in the Origens UNESCO Gobal Geopark (Spain), and the other in the Tajo de San Pedro cliff located in the Alhambra de Granada - UNESCO World Heritage Site (Spain).

Data processing comprises two main steps. The first step involves the automatic photogrammetric process using SfM-MVS algorithms. Thereby, the MEMI workflow is applied to improve the level of detection in the change-detection comparison (Blanch et al., 2021). Afterwards, a workflow based on M3C2 (Lague et al., 2013) comparison and DBSCAN clustering is applied to identify possible rockfall clusters. The resulting clusters are processed via a machine learning approach to automatically discriminate the true rockfall events from the candidate clusters . To perform this task, various metric parameters, i.e. features, of the candidate clusters are calculated, and a Random Forest machine learning model is used to perform the classification.

The presented approach facilitates the automated monitoring of rockfalls in near-real time, while improving the detection threshold in the 3D change-detection models, resulting in a more detailed characterisation of active zones and defining the framework that allows for automated 4D rockfall monitoring in high temporal frequency.

Blanch, X., 2022.  Developing Advanced Photogrammetric Methods for Automated Rockfall Monitoring. Doctoral dissertation. http://hdl.handle.net/10803/675397

Blanch, X.; Eltner, A.; Guinau, M.; Abellan, A., 2021. Multi-Epoch and Multi-Imagery (MEMI) Photogrammetric Workflow for Enhanced Change Detection Using Time-Lapse Cameras. Remote Sens. , 13, 1460. https://doi.org/10.3390/rs13081460

Lague, D., Brodu, N., Leroux, J., 2013. Accurate 3D comparison of complex topography with terrestrial laser scanner: Application to the Rangitikei canyon (N-Z). ISPRS Journal of Photogrammetry and Remote Sensing 82, 10–26. https://doi.org/10.1016/j.isprsjprs.2013.04.009

How to cite: Blanch, X., Eltner, A., Guinau, M., and Abellán, A.: Photogrammetric time-lapse workflow for automated rockfall monitoring, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7007, https://doi.org/10.5194/egusphere-egu23-7007, 2023.

Three-dimensional data have become increasingly present in earth observation over the last decades and, more recently, with the development of accessible 3D sensing technologies. However, many 3D surveys are still underexploited due to the lack of accessible and explainable automatic classification methods. In this work, we introduce explainable machine learning for 3D data classification using Multiple Attributes, Scales, and Clouds under 3DMASC, a new workflow. It handles multiple clouds at once, including or not spectral and multiple returns attributes. Through 3DMASC, we use classical 3D data multi-scale descriptors and new ones based on the spatial variations of geometrical, spectral and height-based features of the local point cloud. We also introduce dual-cloud features, encrypting local spectral and geometrical ratios and differences, which improve the interpretation of multi-cloud surveys. 3DMASC thus offers new possibilities for point cloud classification, namely for the interpretation of bi-spectral lidar data. Here, we experiment on topo-bathymetric lidar data, which are acquired using two lasers at infrared and green wavelengths, and feature two irregular point clouds characterized by different samplings of vegetated and flooded areas, that 3DMASC can harvest. By exploring the contributions of 88 features and 30 scales – including two types of neighborhoods – we identify a core set of features and scales particularly relevant for coastal and riverine scenes description, and give indications on how to build an optimal predictor vector to train 3D data classifiers. Our findings highlight the predominance of lidar return-based attributes over classical features based on dimensionality or eigenvalues, and the significant contribution of spectral information to the detection of more than a dozen of land and sea covers – artificial/vegetated/rocky/bare ground, rocky/sandy seabed, intermediate/high vegetation, buildings, vehicles, power lines. The experimental results show that 3DMASC competes with state-of-the-art methods in terms of classification performances while demanding lower complexity and thus remaining accessible to non-specialist users. Relying on a random forest algorithm, it generalizes and applies quickly to large datasets, and offers the possibility to filter out misclassified points depending on their prediction confidence. Classification accuracies between 91% for complex scene classifications and 98% for lower-level processing are observed, with average prediction confidences above 90% and models relying on less than 2000 samples per class and at most 30 descriptors – including both features and scales. Though dual-cloud features systematically outperform their single cloud equivalents, 3DMASC also performs on single cloud lidar data, or structure from motion point clouds. Our contributions are made available through a self-contained plugin in CloudCompare allowing non-specialist users to create a classifier and apply it, and an opensource labelled dataset of topo-bathymetric data.

How to cite: Letard, M., Lague, D., Le Guennec, A., Lefevre, S., Feldmann, B., Leroy, P., Girardeau-Montaut, D., and Corpetti, T.: 3DMASC: accessible, explainable 3D point clouds classification. Application to bi-spectral topo-bathymetric LiDAR data., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7115, https://doi.org/10.5194/egusphere-egu23-7115, 2023.

The digital elevation model (DEM) is an important basic data tool applied in geoscience applications. Because of its high cost and long development cycle of enhancing hardware performance, designing the related models and algorithms to improve the resolution of DEM is of considerable significance. At present, Neural networks (NNs) have demonstrated the potential to recover finer textural details from lower-resolution images by super-resolution (SR). Given similar grid-based data structures, some researchers have transferred image SR methods to DEM. These efforts have yielded better results than traditional spatial interpolation methods. However, the deep learning(DL) models need a lot of training data, and the model is difficult to converge, resulting in high training costs, which can be challenging. Therefore, in order to reduce the difficulty and cost of DL method training, we detrend the DEM data to decompose the target DEM into a deterministic low frequency trend part and a high frequency residual part. In the process of DL training, focus on the high-frequency part. We use multiple DL models and DEM data of various landforms to verify, and the experimental results show that our proposed method can indeed reduce the difficulty and cost of DL training. At the same time, our method can also be extended to other DL models.

How to cite: Wang, H.: Super-resolution of digital elevation models using deep learning methods based on detrending, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7311, https://doi.org/10.5194/egusphere-egu23-7311, 2023.

Surface processes in topographic data are typically extracted either as local surface changes with static spatial extent between multiple acquisitions, or by tracking features or objects with more or less rigid properties which are re-identified in each epoch. Such approaches are challenged when surface processes are highly dynamic, such as material transport of sand or snow as moving and deforming forms. For the observation of dynamic surface processes, strategies of near-continuous 3D acquisition, e.g. permanent laser scanning or time-lapse photogrammetry, capture dense time series of point clouds of a scene. To extract surface processes as moving spatiotemporal objects from these datasets, we propose a time-extended approach to the extraction of 4D objects-by-change [1]. These objects are automatically identified in their spatial and temporal extent in 3D time series by first detecting surface activities in the time series at a location, and then spatially delineating them based on similar change histories (i.e. surface behavior in time) throughout their duration. So far, this method was temporally static, meaning that the timing and duration was fixed for each 4D object-by-change. By extending the search for similar change histories along the time domain, we enable to trace a moving object through the space-time coverage of a dataset. We demonstrate the method using simulated 3D time series and present first results for real-world near-continuous 3D data of sediment transport. The method will be openly accessible in py4dgeo [2], an open source Python library for change analysis in 4D point clouds. Advantages over existing methods are that no a-priori information on specific processes are required, and no definition of distinct features to be tracked is needed. A major strength is the novel possibility to delineate surface processes as intangible objects in space and time, which holds potential to provide completely new information on surface dynamics in topographic scenes.

References:

[1] https://doi.org/10.1016/j.isprsjprs.2021.01.015

[2] https://github.com/3dgeo-heidelberg/py4dgeo

How to cite: Anders, K. and Höfle, B.: Spatiotemporal tracking of surface processes through their change histories in dense 3D time series by implementing a time-extension on the 4D objects-by-change method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8158, https://doi.org/10.5194/egusphere-egu23-8158, 2023.

High-frequency monitoring of hardly-accessible glaciers is usually challenging. Though, it is critical for understanding and modeling infra-seasonal glacier dynamics. Fixed time-lapse camera are often used for retrieving high-frequency qualitative and quantitative information on glaciers' evolution. Nevertheless, only one camera is usually employed for estimating glacier surface velocity by Digital Image Correlation (DIC) techniques and an approximate DSM is required [1]. Using multiple cameras can step up in-situ glacial monitoring, as 3D scene reconstruction can be obtained by photogrammetry and Structure-from-Motion (SfM). Indeed, two (or more) cameras allows for estimating glacier surface flow velocity in a 3D world, volume variations, ablation and glacier terminus retreat.

This work presents a pilot study for implementing a low-cost image-based stereoscopic system for automatic high-frequency monitoring of an alpine glacier. Each hand-made monitoring station includes a DSLR camera, an Arduino microcontroller for camera triggering, a Raspberry Pi Zero with a SIM card for sending images to a remote server. The two cameras were installed in summer 2021 on each side of the Belvedere Glacier north-west terminus (Italian Alps), with a wide baseline (i.e., ∼260 m). The cameras have been operating taking daily images for one and a half year. Every day, the acquired stereo-pair was processed by SfM. Due to the wide baseline, which is typical of complex mountain environments, finding corresponding points across different viewpoints was troublesome [2]. Commercial SfM software packages based on traditional feature matching (e.g., Agisoft Metashape) failed to find enough and well distributed matches, while state-of-the-art deep learning-based algorithms for wide-baseline matching, such as SuperGlue [3], outperformed traditional feature matching. Therefore, an automatic open-source Python pipeline for finding matches, orienting image-pairs, solving Bundle Adjustment with Ground Control Points (GCPs) and building 3D point clouds was developed from scratch. Although alternative open-source solutions are under study, dense 3D reconstruction is currently carried out at every epoch by Agisoft Metashape, exploiting Python API to fully integrate dense matching in the processing pipeline. Results were validated at three epochs by UAV-based ground truth, obtaining RMSE of point clouds of ∼15 cm.

Overall, the monitoring system is simple and low-cost (less than €2000 per camera), requires minimum in-situ operations (limited to cameras’ installation and materialization of few GCPs), and an automatic 3D processing of stereo-pairs can improve in-situ glacier monitoring. Indeed, from daily point clouds, glacier volume reduction and retreat speed can be estimated by computing cloud-to-cloud distances. This, combined with surface velocities estimated by DIC, may help glaciologists to better understand glacier dynamics and quantify mass balances. The full Python pipeline will be released as open-source code, together with a documentation to make it reproducible for other study cases.

[1] Messerli, A., & Grinsted, A. (2015). Image georectification and feature tracking toolbox: ImGRAFT. Geosci. Instrum. Meth., 4(1), 23–34.

[2] Yao, G., Yilmaz, A., Meng, F., & Zhang, L. (2021). Review of Wide-Baseline Stereo Image Matching Based on Deep Learning. Remote Sens., 13(16)

[3] Sarlin, P. E., Detone, D., Malisiewicz, T., & Rabinovich, A. (2020). SuperGlue: Learning Feature Matching with Graph Neural Networks. Proc. CVPR IEEE, 4937–4946.

How to cite: Ioli, F., Nex, F., and Pinto, L.: High-frequency automatic 3D glacier monitoring using low-cost time-lapse cameras and Deep Learning algorithms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10018, https://doi.org/10.5194/egusphere-egu23-10018, 2023.

Accurate estimation of surficial sediment size in alpine landforms such as talus slopes, rock glaciers, and moraines is crucial for understanding geomorphologic processes and predicting the potential impact of natural hazards. Traditional methods for measuring sediment size in these environments can be time-consuming and labor-intensive. Additionally, they are usually applied to selected areas and are rarely used to cover larger areas, making the development of more efficient approaches essential. This study presents a new method for estimating large-scale surficial sediment size based on unmanned aerial vehicle (UAV) photogrammetry and combining SediNet and PebbleCountAuto image analysis methods. SediNet is a configurable machine-learning framework for estimating either (or both) continuous and categorical variables from a photographic image of clastic sediment. SediNet can achieve subpixel resolutions because the dimensions of the grains aren't being measured directly. However, site-specific sediment sizes are necessary to train this model. On the other hand, PebbleCountAuto does not require any site calibration by using segmentation methods to delimitate the grains automatically and provide a full grain-size distribution. Our proposed methodology trains the SediNet model using the sediment sizes outputs of the PebbleCountAuto method. Our study area is the upper part of the Lake O'Hara watershed in the Canadian Rockies, composed of talus slopes and a large ice-cored moraine. We performed two types of UAV flights; high-altitude flights (~100 m height) to cover the whole study area with medium-to-high resolution orthomosaic (pixel resolution 3 cm) and low-altitude flights (~25 m height) at smaller patches to achieve high-resolution orthomosaic (pixel resolution 5-8 mm). First, the sediment size was estimated in the high-resolution patches with the PebbleCountAuto method. Then, these results were used to train the SediNet model and generate a large-scale sediment size estimation. Our results show that this combination of methods is a reliable and efficient approach for accurately estimating sediment sizes in alpine landforms. The use of UAV photogrammetry allows for the rapid and cost-effective collection of high-resolution imagery, while the combination of SediNet and PebbleCountAuto provides robust estimates of sediment size over large areas. This new method can improve our understanding of geomorphologic processes and hazard assessment in these environments.

How to cite: Zegers, G., Garces, A., and Hayashi, M.: Large-scale estimation of surficial sediment size in alpine landforms using UAV photogrammetry and machine learning., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10162, https://doi.org/10.5194/egusphere-egu23-10162, 2023.

Accurate measurements of geomorphic change are necessary to improve quantitative and conceptual models in geomorphology. New generation high-resolution topography (HRT) is enabling increasingly accurate quantification of surface change via differencing of fine scale (<1 m) multi-temporal digital elevation models (DEMs). The resulting DEMs of difference (DoDs) provide spatially continuous estimates of surface change. However, harnessing the information contained in HRT DoDs requires progressively sophisticated methods for handling the error propagated into a DoD from each DEM. As HRT acquisition increases, and technology to host and distribute the data improves, there is increasing need for reliable and repeatable error handling procedures. We investigate the potential for satellite-borne optical and radar data to improve DEM-based geomorphic change detection in semi-arid landscapes. The primary motivation for this work is to enable improved geomorphic change detection in semi-arid landscapes affected by extensive erosion. We apply the methodology to a ~15 km² catchment adjacent to the Great Barrier Reef, Australia, where independent end-of-catchment sediment load data is available for comparison. Our goal is to enable improved geomorphic change detection over relatively large areas (>1 km²) by minimising systematic error propagated into a DoD, particularly from DEMs with sparse ground control networks.

We find the methodology reliably decreases the systematic error in our DoD and improves the separation of real geomorphic change from noise. However, the presence of grass and consequent point misclassification remains a key challenge even with a relatively high point density (~48 pts·m²) airborne-lidar dataset. This is the first time optical and radar remote sensing have been used alongside airborne-lidar for improved DEM-based geomorphic change detection in semi-arid landscapes.

How to cite: Walker, S., Wilkinson, S., Bartley, R., Levick, S., Kinsey-Henderson, A., Khan, S., and Castellazzi, P.: Optical and radar remote sensing improve DEM-based geomorphic change detection in semi-arid landscapes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10244, https://doi.org/10.5194/egusphere-egu23-10244, 2023.

Tree-line shifts are evident signs of various aspects of global climatic changes. Remote sensing techniques and aerial imageries are typically used to assess the changes of tree-line in mountainous areas over the past years mostly based on field survey and repeat photography work. The extraction of tree-lines was either done by visual image interpretation or low spatial resolution satellite images. (Bolton et al., 2018)

In Switzerland, the earliest available historical black and white (B&W) images are from the 1920s, and in the other European countries, there is such abundant data as well. Nevertheless, these data sources are currently insufficiently used and there is only limited use of historical aerial images in the analysis of past vegetation. Therefore their automatic and accurate processing still remains challenging. In our previous studies (Wang et al., 2022) covering parts of the Swiss Alps we obtained promising classification results using a deep learning approach. However, difficulties were related to weak and time consuming labeling efforts. In addition, unclear interclass differences between dense forest and group of trees had a negative effect on model accuracies.

In this study, we proposed a BWForest-Unet based on semantic segmentation to access tree cover in Swiss mountain areas. Images from 2019 and labeled tree images using a countrywide canopy height model (CHM) were used in the model. The main advantage of this net is that features from different spatial regions of the image are combined and thus enabling the localization of more precisely regions of interest. The designed BWForest-Unet tries to learn the spatial interdependencies of features by adding an attention model in the decoder processing. Furthermore, suitable data augmentations, e.g., thickness, local elastic, pinch, scratch and grid distortion were applied as an effective method of supplementing the training samples, which intend to efficiently simulate 1980s images by using current 2019 images. The test area consists of 170 1km*1km sample plots distributed over the whole of Switzerland in 1980s.

The study reveals that 1) suitability of semantic segmentation based on BWForest-Unet in combination with B&W aerial images are superior to previous work and therefore promisingto map mountain tree-line change over 35 years in upper tree-line ecotones of the Alps 2) the usese of existing CHMs substantially reduced the labelling workload. 3) The combination of suitable data augmentations simulates the 1980s image to a certain extent.

Bolton, D.K., Coops, N.C., Hermosilla, T., Wulder, M.A., White, J.C., 2018. Evidence of vegetation greening at alpine treeline ecotones: three decades of Landsat spectral trends informed by lidar-derived vertical structure. Environmental Research Letters 13, 084022.

Wang, Z., Ginzler, C., Eben, B., Rehush, N., Waser, L.T., 2022. Assessing Changes in Mountain Treeline Ecotones over 30 Years Using CNNs and Historical Aerial Images. Remote Sensing 14, 2135.

How to cite: Wang, Z., Gui, Y., Li, W., Eben, B., Waser, L. T., and Ginzler, C.: Can historical black and white images be used to map changes of tree-line?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12274, https://doi.org/10.5194/egusphere-egu23-12274, 2023.

Between June and August 2022, the European Forest Fire Information System (EFFIS) reported more fires in Europe than in any other recent summer season. This is particularly true for Central Europe, where the largest forest fire in recent Czech history occurred in the German-Czech border region. With global warming and resulting longer dry periods, the length and severity of wildfire seasons in central Europe will likely increase. Therefore, easy to implement and cost-effective methods to assess wildfire damage and regeneration of the ecosystems are getting increasingly important. In this study we evaluated how different datasets obtained by uncrewed aerial system (UAS) can be incorporated with datasets obtained from the ground to describe the fire affected landscape. Thereby, multi-spectral 3D point clouds were derived from low-cost UAV laser scanning and using structure from motion (SfM) photogrammetry applied to RGB and multi-spectral imagery. The aerial datasets were combined with ground-based terrestrial and mobile laser scanning. The datasets were acquired in several surveys following the forest fire event in the German part of the National park Saxonian/Bohemian Switzerland.

Initial results show the potential of UAS-based sensing for efficient mapping of a burned area with a high resolution (600-1000 pts/m²). The combination of point clouds from UAS-based laser scanning and photogrammetry enables a detailed representation of the burned forest with different levels of fire damage (e.g., in still present canopy) when compared to the single datasets. The UAS based laser scanning data reveals higher noise compared to the SfM-based point clouds. However, the accuracy is still sufficient to improve the quality of orthomosaics in densely vegetated areas. In a next step, further investigations on data accuracy are conducted and automated point cloud fusion algorithms based on classified points are considered.

How to cite: Krüger, R., Blanch Gorriz, X., Grothum, O., and Eltner, A.: Using multi-scale and multi-model datasets for post-event assessment of wildfires, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13008, https://doi.org/10.5194/egusphere-egu23-13008, 2023.

Dolines are concave circular karst landforms that are clearly presented by topography data (topographic maps), especially on high-resolution LiDAR digital terrain models (DTM). In the karst landscape, man has reshaped natural dolines through centuries by collecting rocks and soil to increase the flat area of tillable (cultivated) land at the bottom of the doline. By this human-induced process, the natural doline was reshaped into a cultivated doline. Cultivated dolines have a rich historical legacy of use for local agricultural production, high geomorphological value for geodiversity and present an important habitat supporting biodiversity. They are an element of agro-karstic landscape (paysage agro-karstiques) and are distinctive of Mediterranean karst landscapes like Dinaric karst, Central massive, Apulia etc. Most of the cultivated dolines have been recently abandoned, and covered by forest, thus the human impact is not evident anymore so clearly.

In most studies on natural characteristics and processes in dolines, there is no distinct separation between natural and cultivated dolines and no consideration of past agricultural land use. Thus, the main goal of this study/presentation is to provide a geoinformatics methodology to separate cultivated dolines from natural dolines based on differences in micro-topography by using recent very high-resolution LiDAR topography data and historical cadastral maps (19^th century).

Using visualized LiDAR DTM the most evident morphometric differences between the natural and cultivated doline landforms were recognized. Cultivated dolines were characterized by (1) a circular concave landform with a flat bottom (2) the presence of anthropogenic elements, such as circular stonewalls at the upper doline edge, which provides evidence of stone-removal from the doline slopes (smooth surface). Additionally, in the 19th-century cadastral maps, only individual dolines with important land use were marked as special lots. Given the rural character of the landscape during that time, the only land use recorded in the concentric lots of the dolines was agricultural use (arable fields, gardens, meadows, and pastures). As a result, the number, location and surface coverage of cultivated dolines were precisely defined for classical karst regions in SW Slovenia. Based on Lidar data, bowl-shaped cultivated dolines with flat bottoms were separated from non-cultivated funnel-shaped dolines.

How to cite: Breg Valjavec, M., Ciglič, R., Geršič, M., and Čonč, Š.: Application of historical cadastral maps and high resolution airborne LiDAR topography to distinguish anthropogenic from natural karst landforms: case study of karst dolines, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13315, https://doi.org/10.5194/egusphere-egu23-13315, 2023.

Karst is a geomorphological system that covers almost 50% of the area of Slovenia and is mainly characterised by circular concave and convex landforms such as conical hills, dolines, uvalas and poljes. These large landforms can be easily detected with a number of already developed (semi-)automatic detection methods. In addition to these large landforms, the karst surface is dissected by smaller scale features consisting mainly of numerous rocks of different shapes and sizes. Due to the different lithology that makes up the Slovenian karst (e.g., limestone, dolomite), rocky outcrops have different morphographic and morphometric characteristics due to the different dynamics of the mechanical weathering of the bedrock. The variety in shapes and sizes of rocky outcrops makes their detection by automatic or semi-automatic methods difficult. In our study area in the Dinaric Karst in Slovenia, they reach heights of up to several metres and lengths of about 10 metres.

Field mapping or digitizing such landforms would be time-consuming, labour-intensive, and costly. The combination of high-resolution LiDAR-derived DEMs (digital elevation models) and (semi-)automatic landform detection and delineation methods in GIS environments enables remote and low-cost mapping, which has an outstanding potential for large-scale spatial analysis and mapping in remote, forested, and difficult-to-access areas such as the Dinaric Karst.

The main objective of this study was to develop an approach for quantitative identification and detection of rocky outcrops. The approach is based on spatial analysis of high-resolution (1 m × 1 m) LiDAR DEM and field analysis of outcrop morphography and morphometry. The study was conducted in the Dinaric Karst area in Slovenia, which consists mainly of Cretaceous and Jurassic limestones and dolomites. First, we calculated the values of TPI (Topographic Position Index) to identify all convex shapes (i.e., ridges) within a search radius of 10 m around each cell. Slope was used as an additional criterion for defining rocky outcrops. Based on field measurements, we found that bedrock in areas with limestone (30°) outcrop at a lower surface slope than in areas with dolomite (50°).

The study has shown that the different spatial distribution, shape and size of the rocky outcrops are related to the geological structure. In the limestones they are much denser and more numerous than in the dolomites. In average, the dimensions of the outcrops are also much larger. This is due to the porosity of the dolomites, which causes greater mechanical weathering. We have also found that rocky outcrops often occur on certain landforms, e.g. on the slopes of dolines and other karst depressions or fluviokarst valleys.

Airborne LiDAR DEMs can be a useful source of information for detecting and studying the spatial patterns and morphometric settings of rocky outcrops. The number of landforms detected indicates that, in addition to dolines, rocky outcrops are one of the most common landforms in the Dinaric Karst.

Key words: Rocky outcrops, karst landform, GIS, LiDAR, (semi-)automatic methods, geomorphology, Dinaric mountains

How to cite: Čonč, Š. and Breg Valjavec, M.: Detection of rocky outcrops from LiDAR-derived DEM in Dinaric Karst, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13606, https://doi.org/10.5194/egusphere-egu23-13606, 2023.

Glacier surface velocity is a crucial information to assess the impact of global warming on glaciers, since it is related to the ice thickness; its variations provide information on mass balance and, in general, on the current state of glacier “health”. Moreover, velocity anomalies are often an indicator of glacier instabilities. Therefore, attention has been dedicated to surveying glacier velocity. Historically, surface velocity was the first quantitative variable measured on glaciers since the 19^th century, using phototheodolites. In the last decades, terrestrial monoscopic digital time-lapse cameras (TLC) have permitted to conduct automatic surveying for long periods at high spatial and temporal resolutions using digital image correlation. Even though terrestrial time-lapse imagery is currently a consolidated technique in glacier monitoring, the number of dedicated publications is relatively small. In particular, possible strategies, limitations and potentialities have never been systematically reviewed.

This work aims to illustrate the typical procedures required to monitor glacier surface velocity using terrestrial monoscopic TLC, which can be synthetically listed as: 1) correct deployment of the equipment and image acquisition; 2) data pre-processing: 2.1) image selection, 2.2) colour/feature enhancement and 2.3) image registration; 3) data processing: displacement measurement using image correlation; 4) data post-processing: 4.1) outlier correction, 4.2) image geocoding and 4.3) time-series extraction. We describe possible inconveniences that can arise during the survey – e.g., image misregistration, distortion and defocusing, illumination and chromatic variation (shadows, snow patches), presence of outliers, and geocoding issues – and provide some guide lines to minimise such problematics. We present six study cases in the European Alps – Planpincieux, Grandes Jorasses, Freney and Brenva glaciers in the Mont Blanc massif, and Western and Eastern Fellaria glaciers in the Bernina massif – that feature different monitoring equipment, site geometry and glacier morphodynamics to illustrate possible solutions for terrestrial imagery monitoring.

The results revealed that terrestrial TLC provided high spatial resolution and acquisition frequency to detect small kinematic sectors and fast-occurring velocity anomalies, which would be difficult to identify using alternative approaches (e.g., satellites or topographic). However, like other passive optical sensors, the principal limitation is that they are affected by poor visibility and cannot acquire during the night. This study highlighted the great potentiality of TLC in glacier kinematics surveying, which can be conducted using either professional cameras or low-cost webcam and IP cameras, according to the scope and financial availability. The contained costs and ease of installation make TLC a very high benefit-to-cost tool and permit the development of strategies for widespread glacier monitoring at a regional scale with relatively low financial efforts.

How to cite: Dematteis, N., Troilo, F., Scotti, R., Colombarolli, D., Giordan, D., and Maggi, V.: Monoscopic terrestrial time-lapse cameras: an effective tool for surveying glacier surface velocity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13783, https://doi.org/10.5194/egusphere-egu23-13783, 2023.

This work is on the automated, photogrammetric orientation of World War II aerial reconnaissance images. For these near-nadir images, the footprint centers are known beforehand with an accuracy of a few hundred meters, together with coarse image scales and nominal focal lengths, but without image rotations. Since their overlap is typically small or absent, the approach orients the images one after another. A novel rotation-invariant, end-to-end CNN image feature matcher finds homologous points both in an aerial image and in an iteratively refined detail of a present-day orthophoto map, initially extracted according to the given metadata. This results in automatically determined ground control points whose heights are interpolated in a likewise present-day terrain model, and which serve to estimate image orientations in a bundle adjustment. The image orientation quality is assessed by projecting manually observed ground control points into image space and comparing them to their likewise manually observed image positions. Hundreds of images of various scales are evaluated, featuring cloud and snow cover, long cast shadows, dust, and scratches. Despite the large gap in time between the aerial and reference data sets and respectively large changes on the ground and in appearance, the approach results in an RMSE of manual ground control points of less than 1mm for over 60% of the images.

How to cite: Karel, W.: Deep Georeferencing of WWII Aerial Reconnaissance Images, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17437, https://doi.org/10.5194/egusphere-egu23-17437, 2023.

Compared to the Western European Alps, the ice extent during the Last Glacial Maximum (LGM) and the subsequent deglaciation history of the Eastern Alps east of the Tauern Window remains less well constrained. Also, considerable discrepancies exist between the mapped LGM ice margin (Ehlers and Gibbard, 2011; van Husen, 2004, 2011) and the ice extent predicted by ice-sheet models (Seguinot et al., 2018). Here we present the first ¹⁰Be surface exposures ages from two regions east of the Tauern window (Gurktal and Lavantal Alps), which provide constraints on the LGM ice extent and the deglaciation history (Wölfler et al., 2022). Our results show that the deglaciation of the Gurktal Alps occurred between 16-14 ka, which agrees with the predictions from ice-sheet models and implies that the LGM ice cover was greater than mapped. This finding also supported by our analysis of high-resolution DEMs that revealed glacially streamlined ridges and macroscale glacial striations consistent with modelled ice flow directions (Seguinot et al., 2018). In contrast, the ¹⁰Be ages from the Lavantal Alps located farther east are either LGM in age or pre-date the LGM, indicating that these regions were ice-free or only partially covered by LGM ice. Based on these results, our future investigations will aim at obtaining more age data from the Eastern Alps to refine the location of the LGM ice margin and the deglaciation history, which is also crucial for climate-evolution and postglacial-rebound models.

References

Ehlers J, Gibbard PL, Hughes PD (2011) Quaternary glaciations - Extent and chronology. A closer look. Developments in Quaternary Science 15.

Seguinot J., Ivy-Ochs S, Jouvet G, Huss M, Funk M, Preusser F. (2018) Modelling last glacial cycle ice dynamics in the Alps. The Cryosphere 12: 3265–3285.

van Husen D. (2004) Quaternary glaciations in Austria. In: Quaternary Glaciations: Extent and Chronology Part I: Europe, Ehlers J, Gibbard PL (eds). Elsevier: London: 1–13.

van Husen D (2011) Quaternary Glaciations in Austria. In Quaternary Glaciations – Extent and Chronology: A Closer Look, Ehlers J, Gibbard PL, Hughes PD (eds). 15: 15–28.

Wölfler A, Hampel A, Dielforder A, Hetzel R, Glotzbach C (2022) LGM ice extent and deglaciation history in the Gurktal and Lavantal Alps (eastern European Alps): first constraints from ¹⁰Be surface exposure dating of glacially polished quartz veins, Journal of Quaternary Science  37: 677-687. https:// doi.org/10.1002/jqs.3399

How to cite: Hampel, A., Wölfler, A., Dielforder, A., Hetzel, R., and Glotzbach, C.: LGM ice extent and deglaciation history in the Gurktal and Lavantal Alps (Eastern European Alps): first constraints from 10Be surface exposure dating of glacially polished quartz veins, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1380, https://doi.org/10.5194/egusphere-egu23-1380, 2023.

The Bohemian Massif is the relic of a major Paleozoic mountain range that is known to have exhumed and its surface levelled in the Permian. The southern part of the Bohemian Massif with high grade metamorphic rocks and magmatic intrusions dips towards the south under the weakly consolidated Neogene sediments of the Molasse Basin. However, Neogene landscape evolution is largely unconstrained, but the occurrence of marine sediments several hundred meters above sea level is a clear indication of significant surface uplift during the last few million years. The landscape is characterized by rolling hills and extended planation surfaces above an elevation of about 500 m. However, at lower elevations deeply incised gorges confined by steep hillslopes are abundant and contrast impressively with the low relief landscapes above. A continental drainage divide follows the central ridge of the Bohemian Massif with the Vlatava (Moldau) and the Danube (Donau) draining the regions north and south of the drainage divide. In this study we aim quantifying spatial and temporal variations of landscape change in the Bohemian Massif during the last few million years. To characterize the two contrasting landscape states, we computed landscape metrics based on digital elevation models (e.g. normalized steepness index, geophysical relief). To determine the rate landscape change we determined catchment-wide erosion rates from the concentration of cosmogenic ¹⁰Be in river sands.

Results show that the landscape is characterized by out-of-equilibrium river profiles with knickpoints abundantly occurring at elevations between 450 m and 550 m separating steep channel segments at lower elevations from less steep channels at higher elevations. Hypsometric maxima at or close above knickpoint elevations along with high and low values in geophysical relief downstream and upstream of major knickpoints support the idea of landscape bimodality. Furthermore, we found a strong drainage divide asymmetry, which evidences for the reorganization of the drainage network of the region. Across-divide gradients in channel steepness predict the northward migration of the Danube-Vltava drainage divide including growth and shrinkage of tributary catchments. Erosion rates of the 20 investigated catchments are very low (20 – 50 m per million year) compared to the Alps or other active mountain ranges. The lowest erosion rates occur in catchments with a large fraction of planation surfaces at mid-altitudes. Highest erosion rates occur in elongated catchments of Danube tributaries. Based on our results we suggest that the occurrence of contrasting bedrock properties between Molasse sediments and the crystalline basement represents a superior control on the topographic evolution of the entire region. The transition from soft sediments of the Molasse basin to much less erodible basement rocks during progressive river incision in a setting of low but long last uplift distinctly changes the channel steepness and relief, the course of the receiving streams, and their susceptibility to sudden changes in flow direction (river capture) of the million years’ time scale.

How to cite: Robl, J., Stüwe, K., Dremel, F., Liebl, M., von Hagke, C., and Fabel, D.: Old orogen - young topography: Landscape Rejuvenation in the Bohemian Massif, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2068, https://doi.org/10.5194/egusphere-egu23-2068, 2023.

We present cosmogenic nucleide data that help to understand the ill-constrained  uplift history of the Eastern Aps. Well accepted, but indirect evidence  for this uplift history includes: (a) the onset of flexural subsidence of the foreland basins, or (b) the formation of the Periadriatic line (recording the onset of continent-continent collision in the Alps). Both are often used to suggest about 30 Ma as the starting date for the surface uplift of the range. Since this time the fine interplay of many kilometres of upwards rock uplift and downwards erosion resulted in net surface uplift of some 2-3 kilometres but reference frames that allow to discern between rock uplift and surface uplift are often hard to identify. One way of measuring surface uplift rates is through the study of areas where erosion did not occur. That is, dating and identifying relicts of ancient base levels for example in caves, sediments or paleosurfaces.

In this contribution we present ¹⁰Be, ²¹Ne, ²⁶Al cosmogenic nucleide data of fluvial sediments sampled in some 50 caves across the Eastern Alps from elevations between 300 and 2500 m surface elevation. We collected samples that were interpreted to have been deposited during cave formation at the vadose-phreatic transition. As such, they form markers for base level and  the age of their burial into the cave may be interpreted as the time the cave was at base level some few hundreds of meters above sea level. Interpretation of our data indicates that the uplift rate of the Eastern Alps may be in the order of 200 m – 500 m per Million years for much of the Pliocene. As such, much of the observed surface uplift of the Eastern Alps may have occurred since the late Miocene and surface uplift is thus much faster than previously thought.

How to cite: Stüwe, K., Gradwohl, G., Robl, J., Plan, L., Fabel, D., and Stuart, F.: Surface uplift of the Eastern Alps. Much faster than we thought?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2346, https://doi.org/10.5194/egusphere-egu23-2346, 2023.

Soil loss is one of the major environmental threats the world is facing due to horizontal expansion of cities and increasing land abuse. It has been previously shown by workers that the abuse or improper use of land and soil had adversely affected early civilisations. Keeping into consideration the imminent threat, a number of methods have been proposed to estimate soil loss e.g. numerical models, monitoring-based field methods. However, these are either time-consuming or inherently carry a degree of uncertainty.

One method involves using environmental fallout nuclides as tracers of soil erosion and mapping areas of soil loss and accumulation. The commonly used nuclides in this technique are ¹³⁷Cs and ⁷Be. ¹³⁷Cs is a nuclear fission product and cannot be used to track soil dynamics older than 1940s, while ⁷Be has a very short half-life and is used to study soil dynamics in a seasonal scale.

In this study, we have proposed a method of using meteoric ¹⁰Be to trace long-term soil redistribution in a landscape. This cosmogenic nuclide is produced in the atmosphere and reaches the land surface by dry and wet fallout. Once it reaches the surface, it is adsorbed by the soil particles and it mobilizes along with the soil. Thus, higher concentrations indicate net soil accumulation, whereas, lower concentrations are due to net soil loss. The rate of delivery of ¹⁰Be flux estimated from global circulation models (GCMs) has been used to calculate rates of erosion.

We tested our method in Pranmati catchment, a small river catchment (~93 km²) in Uttarakhand, India and validated by comparing our findings with previously proposed geomorphic transport laws. Our results show that soil erodes from the high lying divergent (convex) topography and accumulates in the low lying convergent (concave) topography. The rates of erosion are also influenced by land cover – erosion in forests is much slower compared to grassland.

How to cite: Sarkar, A., Singh, V., Kumar, P., Kumar, P. V., and Sharma, R.: Inferring Long Term Averaged Soil Redistribution Pattern using Meteoric 10Be, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4811, https://doi.org/10.5194/egusphere-egu23-4811, 2023.

Erosion rates are commonly used to study tectonic uplift and sediment export from mountain ranges. However, the scarcity of erosion rate data often hinders detailed tectonic interpretations. Here, we present 25 new erosion rates from the Northern Andes of Colombia, determined from cosmogenic ¹⁰Be measurements, to study spatial and temporal patterns of uplift along the Central and Eastern Cordillera. These rates, along with published data and precipitation-corrected normalized channel steepness measurements, were used to create high-resolution erosion rate maps. The results show that the southern Central Cordillera has relatively uniform erosion rates, averaging around 0.3 mm/a, while the northern Central Cordillera exhibits rapidly eroding canyons dissecting slowly eroding low-relief surfaces. We interpret that long-term, steep slab subduction has led to an erosional steady-state in the southern Cordillera Central, while Late Miocene slab flattening caused an acceleration in uplift in the northern Cordillera Central which the landscape has not yet adjusted to. The Eastern Cordillera also displays pronounced erosional disequilibrium, with a slowly eroding central plateau rimmed by faster eroding western and eastern flanks. Our maps suggest recent topographic growth of the Eastern Cordillera, with deformation focused along the eastern flank, which is also supported by balanced cross-sections and thermochronologic data. Spatial gradients in predicted erosion rates along the eastern flank of the Eastern Cordillera suggest transient basin-ward migration of thrusts. By using our erosion maps to estimate sediment fluxes, we find that the Eastern Cordillera exports nearly four times more sediment than the Central Cordillera. Our analysis shows that accounting for spatial variations in erosion parameters and climate gradients reveals important variations in tectonic forcing that would otherwise be obscured in traditional river profile analyses. Moreover, given relationships between tectonic, and topographic evolution, we propose that the dynamic landscape evolution of the Northern Andes, as revealed by our erosion maps, is primarily linked to spatial and temporal variations in slab dip, with potentially additional influences from inherited Mesozoic rift structures.

How to cite: Ott, R., Perez-Consuegra, N., Scherler, D., Mora, A., Huppert, K., Braun, J., and Hoke, G.: Erosion rate maps of the Northern Andes highlight spatio-temporal patterns of uplift and quantify sediment export, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5206, https://doi.org/10.5194/egusphere-egu23-5206, 2023.

The aim of this study is to test the Holocene relative sea-level (RSL) curve (or shoreline displacement curve) for east central Sweden using ¹⁴C produced in situ in quartz-bearing bedrock (in-situ ¹⁴C). The original RSL curve is instead based on radiocarbon dating of organic material from isolation basins. Having an accurate RSL curve is crucial from at least two aspects. In Sweden’s safety assessments for a planned spent nuclear fuel repository and for the existing repository for low- and intermediate level waste, the RSL curve is used to constrain the emergence above sea level in landscape development models. Also, the RSL is used to constrain model estimates of rates and depths of glacial and subaerial erosion from cosmogenic ¹⁰Be and ²⁶Al produced in situ in quartz in bedrock surfaces.

Avoiding vein quartz and hydrothermally altered bedrock, five samples of granitoid bedrock were taken along an elevation transect extending southwards from Forsmark, the location of the planned spent nuclear fuel repository. Because all samples derive from bedrock outcrops positioned below the highest postglacial shoreline, they target the timing of progressive landscape emergence above sea level. To further assess the accuracy of in-situ ¹⁴C dating, we took an additional five samples from bedrock outcrops 100 km west of Forsmark, above the highest postglacial shoreline. The in-situ ¹⁴C concentrations in these samples should reflect local deglaciation ages.

The ten new in-situ ¹⁴C measurements provide robust age constraints that compare favorably with the original RSL curve derived from radiocarbon dating of organic material in isolation basins and with the regional deglaciation chronology. Inferences of limited rates and depths of bedrock erosion over the past 1 Myr, inferred from ¹⁰Be and ²⁶Al inheritance and which are critically dependent on the RSL curve, therefore glean strong support from these new in-situ ¹⁴C measurements.

How to cite: Goodfellow, B. W., Stroeven, A. P., Lewerentz, A., Hippe, K., Heyman, J., Lifton, N. A., Caffee, M. W., and Näslund, J.-O.: Last ice sheet recession and landscape emergence above sea level in east central Sweden, evaluated using 14C produced in situ in quartz, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6006, https://doi.org/10.5194/egusphere-egu23-6006, 2023.

The Vogelsberg area in Hessen, Germany, comprises the largest contiguous volcanic complex in Central Europe, covering an area of about 2300 km². After volcanic activity ceased during the mid-Miocene, the complex was subject to extensive erosion and weathering. Fluvial erosion has shaped the area, which is now characterised by Pleistocene valleys and a radial river system exposing primitive alkali basalts and basanites. However, the inference of catchment-wide weathering and erosion rates from the most commonly used cosmogenic nuclide – mineral pair (e.g. ¹⁰Be from quartz) remains challenging in such an environment due to the mafic nature and nominally quartz-free composition of the local bedrock. Due to these method-related obstacles only few cosmogenic studies have focused on basaltic regions until now, even though basalt weathering is globally an important CO₂ sink.

The development and establishment of the novel method using terrestrial cosmogenic krypton (Kr) in the weathering-resistant mineral zircon (Dunai et al. 2022) allows quantification of denudation on quartz-poor lithologies over hundreds of kyr timescales. We exploit the method’s advantage and sampled zircons from sediments of streams radially draining the Vogelsberg and measured Kr isotope abundances to assess the time-integrated erosion patterns shaping the volcanic complex. Integrating over millennial timescales, the ¹⁰Be(meteoric)/⁹Be system will be applied to the same catchments. The ¹⁰Be/⁹Be system can be measured on sediment of any type of lithology including mafic rock (Dannhaus et al. 2018), and thus presents an inter-method validation of the Kr method. We will present the krypton results and discuss basalt weathering in a currently temperate climate through the lens of the different methodological approaches applied.

Dunai et al. (2022) Geochronology, https://doi.org/10.5194/gchron-4-65-2022

Dannhaus et al. (2018) GCA, https://doi.org/10.1016/j.gca.2017.11.005

How to cite: Niemeyer, S., Wittmann, H., and Dunai, T. J.: Deriving basin-wide denudation rates of basaltic rocks using cosmogenic Kr isotopes, vulcanic complex Vogelsberg, Germany, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6902, https://doi.org/10.5194/egusphere-egu23-6902, 2023.

Inferring erosion rates from ¹⁰Be or ²⁶Al concentrations in stream sediments has become standard practice in geomorphology. In formerly glaciated landscapes, however, this technique is problematic because repeated phases of shielding and exposure during the past glacial and interglacial periods can lead to ¹⁰Be or ²⁶Al concentrations that are difficult to interpret. Cosmogenic in-situ ¹⁴C has a short half-life (~5,730 years) that means ¹⁴C atoms in stream sediments cannot be inherited from before the glacial period and inferred erosion rates will reflect post-glacial, Holocene erosion. Using cosmogenic in-situ ¹⁴C, we report the first millennial-scale erosion rates in the post-glacial landscapes of Glen Feshie, within the Cairngorm mountains of Scotland.

The River Feshie contains active gravel reaches that cut through glacial outwash terraces. We counterintuitively find the lowest inferred erosion rates (0.06 mm/yr) in the steepest side tributary and the highest inferred erosion rates at the low-relief outlet of Glen Feshie near the confluence with the River Spey (0.21 mm/yr). Based on field observations, we interpret that hillslopes have been largely inactive and contributed limited sediment fluxes. To provide further insight into the highest erosion rate documented furthest downstream, we consider the hypothesis that sediment from the hillslopes with higher concentrations of ¹⁴C has been diluted with lower concentration material from the terraces. Further, we hypothesise that if terraces that border the channel increase in height downstream, their incision could have remobilised an increasing amount of sediment with lower ¹⁴C concentrations downstream, leading to increased dilution and the observed concentrations. Results show terrace height above the channels does not increase downstream and averages approximately 2 meters. We therefore suggest terrace height does not account for higher erosion rates, and present a cosmogenic-nuclide mixing model to explore the degree to which the input of sediment that has been shielded from cosmic rays in terraces can explain the observed concentrations in stream sediments.   

How to cite: Towers, A., Mudd, S., Attal, M., Binnie, S., Clubb, F., and Dunai, T.: Post-glacial catchment denudation rates from 14C concentrations in Glen Feshie, Scotland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6922, https://doi.org/10.5194/egusphere-egu23-6922, 2023.

The Early to Mid-Pleistocene Transition (MPT) between ~ 1.2 Ma to ~500 ka (also termed as ‘900 ka event’) marks a change in climatic periodicity, from 41 ka cycles to 100 ka cycles of increased intensity. In non-glaciated areas of Europe this climatic shift has been associated with pronounced acceleration of river incision, in part driven by increased sediment loads from periglacial hillslope processes. Until the Pleistocene, low-relief landscapes are thought to have dominated throughout Europe. Utilizing novel in-situ cosmogenic Krypton in zircon methodology (Dunai et al. 2022), we find direct evidence that this was indeed the case, and that these landscapes were profoundly transformed during the MPT.

Our study area (Vogtland, Saxony, Germany) was never glaciated but was within 50 km of the ice margins during the largest Quaternary glaciations. For our study, we utilize a unique source of megacryst zircons (Ebersbrunn diatreme), whose exhumation, dispersal and burial history is recorded by cosmogenic Krypton. The megacryst zircons are found in the fluvial sediments of the current catchments downstream of the source (Raumbach, Göltzsch, Weiße Elster), however, also in a distal catchment (Weida), now disconnected from the source due to late Pleistocene superimposed drainage (Weiße Elster valley).

The cosmogenic Krypton data from the megacryst zircons is commensurate with a long (1 to 3 Myr) exposure at or near the surface, or exhumation at a very low rate (<0.1 mMyr^-1), followed by a period of burial of 600 to 900 kyr and a recent re-emergence in the active fluvial system. Samples collected further from the source (≥15 vs. 5 km) have longer burial histories. The extremely low erosion rates inferred prior to burial (<0.1 mMyr^-1) are unprecedented for temperate regions in Europe, and late Quaternary erosion rates of landscapes with similarly moderate relief are two orders of magnitude faster. In situ cosmogenic ¹⁰Be and ²⁶Al results on vein-quartz from the region address the latter findings.

Based on our data and external constraints on climate and landscape evolution in Europe, the most likely scenario is that of a formerly stable, low-relief Plio-Pleistocene landscape whose transformation in response to periglacial processes commenced during marine isotope stage (MIS) 22 and was largely concluded by MIS 16. Incision of drainage that developed during and after the MPT formed the current moderate relief landscape.

Dunai et al. (2022) Geochronology, https://doi.org/10.5194/gchron-4-65-2022

How to cite: Dunai, T. J. and Binnie, S. A.: Transformation of a low-relief periglacial landscape during the Mid Pleistocene Transition revealed by cosmogenic Krypton, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7262, https://doi.org/10.5194/egusphere-egu23-7262, 2023.

Two published cosmogenic radionuclide (CRN) ²⁶Al/¹⁰Be burial age calculation methods developed to correct for post-depositional production of nuclides in settings with low sediment overburden are compared. The advantages and limitations of simple (ISO; [1], [2]) and inverse modelling (INV, [3]) isochrons are investigated.

The studied dataset originates from the gravel of a Danube terrace in the Central Vienna Basin (Austria) [4]., where two horizons (5.5 m and at 11.8 m subsurface depth) were sampled. Each sample set contained 6 quartz or quartzite cobbles.

The advantage of ISO is that it is uninfluenced by changes in sample depth over time. However, the initial ²⁶Al/¹⁰Be ratio is fixed and no pre- and post-burial denudation rates can be calculated. In addition to age, INV models source and sink denudation rates, but assumes constant depth over burial time.

For correct application of ISO and INV outliers, must be excluded. The robustness of both methods is tested by systematically including or excluding data points (bootstrapping) to estimate the dependence of numerical ages on sample selection either in the field, or during outlier identification.

For outlier identification the traditional method of data exclusion of points above or below the isochron line is used. In addition, a new way is introduced here: the post-burial production is calculated using the modelled burial age and denudation rate and compared to the measured inventories of ¹⁰Be and ²⁶Al. If the fraction of post-burial production is equal or higher compared to the measured inventory and its ratio is considerably different for the two isotopes from the same sample, the datapoint is invalid.

In addition, the influence of each sample on the modelled burial age, tested by bootsrapping, is used to exclude samples with a large effect on the age.

The resulting ages at both levels using ISO and INV agree within errors with ISO being systematically slightly younger. The importance of outlier removal is stressed by the fact that inclusion of all samples results in a considerably older age of the stratigraphically higher level compared to the underlying one.   When outliers are excluded, burial ages of the two sampled horizons overlap within uncertainty, suggesting one single deposition event for the whole sediment package.

Interestingly, when the entire dataset is merged, both methods provide similar ages regardless of the outliers being excluded or kept in. This demonstrates that a larger sample number increases the robustness of a dataset considerably and decreases the sensitivity of either method to potential outliers.

In summary, both ISO and INV are robust ways of CRN burial age determination, provided that model presumptions are not violated and outliers are excluded or the sample number large enough to overprint the influence of outliers.

Funding: NKFIH FK124807; OMAA 90ou17; OMAA 98ou17.

References

[1] Balco, G., Rovey, C.W., 2008. American Journal of Science 308(10), 1083-1114.

[2] Erlanger, E.D., et al., 2012. Geology 40(11), 1019-1022.

[3] Pappu, S. et al., 2011. Science, 331(6024), 1596-1599.

[4] Ruszkiczay-Rüdiger, Zs. et al., 2021. Journal of Radioanalytical and Nuclear Chemistry, 329(3), 1523-1536.

How to cite: Ruszkiczay-Rüdiger, Z., Neuhuber, S., Hintersberger, E., Nørgaard, J., and Braucher, R.: Calculation of cosmogenic radionuclide burial ages: a comparison of two models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7899, https://doi.org/10.5194/egusphere-egu23-7899, 2023.

In recent decades, most mountain glaciers have been losing mass in response to climate change, and the area of the ablation zone covered by rock debris is expanding. Debris-covered glaciers are expected to have a longer life expectancy than climatically equivalent clean-ice glaciers because supraglacial debris insulates the underlying ice surface and reduces ablation. In order to accurately predict how debris-covered glaciers will evolve under a changing climate it is essential to quantify the processes controlling their behaviour. We used luminescence rock surface burial dating to constrain the englacial transport time of debris within an alpine debris-covered glacier. We collected 24 samples embedded in the ice in the ablation zone of the Miage Glacier, in the Mont-Blanc Massif (Italy). The natural luminescence signal of rock slices was measured from the surface to a depth of ~10 mm using a protocol comprising IRSL50, IRSL225 and OSL125 measurements. Nine of our samples showed a plateau within the first 2 to 3 discs suggesting that the luminescence signal has the potential to be used to date the burial duration of debris. Among them, 5 and 7 samples passed the dose recovery test for the IR50 signal within 10% and 20% of unity respectively. Only 3 samples passed the dose recovery test for the IR225 signal within 10% of unity. After 24h bleaching in the solar simulator, typical residual doses are as high as 20-40% of the natural equivalent dose measured. We obtained preliminary non fading corrected ages for 5 samples in the range from ~0.8 to ~11 ka. Glacier model estimated englacial rock debris transport times are an order of magnitude lower than the oldest ages obtained suggesting either that some clasts were stored on hillslopes or within moraines prior to englacial transport or that calibration issues may have contributed to age overestimation. Further luminescence signal processing quality checks are required to assess the quality of our ages. If ultimately successful, our results, and the application of luminescence rock surface burial dating to englacially transported debris, will enhance understanding of the dynamics of debris-covered glaciers and inform the use of glacier models for debris covered glaciers, which will improve projections of the contribution of mountain glaciers to the sustainability of water resources in vulnerable catchments such as those in High Mountain Asia and South America.

How to cite: Margirier, A., King, G., Schmidt, C., Brondex, J., and Rowan, A.: Englacial transport time of rock debris: new constraints from luminescence rock surface burial dating, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8283, https://doi.org/10.5194/egusphere-egu23-8283, 2023.

Constraining the impact of Quaternary glaciations on landscape dynamics is required to better understand the interaction between tectonics, climate, and erosion. Over the years, low-temperature thermochronology such as apatite (U-Th)/He (AHe) has been used to quantify glacial erosion in different climatic and tectonic settings. However, in some contexts, AHe records lack temporal resolution because of limited exhumation due to glacial incision and/or low geothermal gradients. In addition, significant spatial variability in erosion can affect the quality of thermal-kinematic inversions when combining spatially distributed AHe data. This effect may be significant in glacial settings where a switch from a fluvial to a glacial landscape induced a significant change in the spatial distribution of erosion.

However, the ⁴He/³He thermochronology can extract lower-temperature and higher-resolution thermal histories from an AHe dataset. The method uses the spatial distribution of natural ⁴He in an apatite crystal, which reflects the rate of cooling through the AHe partial retention zone. It has been successfully applied to track glacial incision and relief-development histories that would have been untraceable with conventional AHe thermochronology. Consequently, thermochronology data can now provide more detailed and localized thermal history. While ⁴He/³He thermochronology has been successfully used in settings where background exhumation rates are moderate, the sensitivity of the technique remains untested in settings with notably low exhumation-rates, such as at passive margins.

Here, we couple a glacial landscape-evolution model (iSOSIA) with a new version of a thermo-kinematic model (PecubeGUI), incorporating radiation-damage effects on helium diffusion, to explore the ability of apatite (U-Th)/He and ⁴He/³He thermochronometers to record glacial incision. To do so, we model a range of synthetic glacial scenarios in different tectonic, climatic, and thermal settings.  Our landscape-evolution models include glacial, fluvial and hillslope erosion, as well as sediment transport. We assess model predictions of thermochronologic parameters, including age-elevation relationships and ⁴He/³He spectra, and their evolution when switching from a steady-state fluvial to a glacial topography. This modelling exercise aims to provide a guide for sampling strategies and interpretations for both conventional apatite (U-Th)/He and ⁴He/³He thermochronology when working in glacial settings, considering their particular tectonic and climatic context.

How to cite: Bernard, M., van der Beek, P., Colleps, C., and amalberti, J.: Spatial and temporal distribution of glacial erosion as recorded by apatite (U-Th)/He and 4He/3He thermochronology., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8714, https://doi.org/10.5194/egusphere-egu23-8714, 2023.

Cosmogenic nuclides have become a well-established tool in geomorphology for quantifying surface process rates and for dating landforms and sedimentary deposits such as terraces, alluvial fans, lakes, and cave infills.  In many cases, these sedimentary deposits can tell us not only about landscape evolution, but if they contain artifacts or fossils, they can also inform us about human evolution, migration, and the development of stone tool technology.   

Burial dating with ²⁶Al and ¹⁰Be is becoming increasingly important in archaeology and paleoanthropology, particularly in areas that lack volcanic rocks suitable for dating. The development of isochron methods has improved both the precision and reliability of dating results, lending confidence to the age interpretations.  However, because cosmogenic nuclides reflect the exposure and burial history of rocks near the ground surface, it is important to recognize that properly interpreting the depositional age requires understanding the surface processes responsible for sediment erosion and deposition. 

Cosmogenic nuclides have now been applied to archaeology and human evolution at a variety of sites across Africa, Asia, and Europe.  In most cases, the new dates conform to pre-existing models and provide a fuller picture of human occupation of the landscape.  However, a few sites have challenged current paradigms.  I will present recent studies from caves and terraces in South Africa and China that have produced surprising results, pushing the boundaries of where early humans were found. 

How to cite: Granger, D.: Cosmogenic nuclide dating applied to human evolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9975, https://doi.org/10.5194/egusphere-egu23-9975, 2023.

Surface exposure ages of marine and fluvial terraces based on in situ ¹⁰Be dating were determined to estimate formation ages and long-term rates of coastal uplift along the northern Pacific coast of Northeastern Japan. Surface rock samples were collected along the northern and southern coasts of Sanriku based on a reinterpretation of dispersed marine and fluvial terraces using DEM and aerial photographs. We collected three samples at the Samuraihama site from outcrops of pairs of marine and fluvial terraces distributed over the east-facing flank of the Kitakami Mountains. At the Yoshihama site, in contrast, where bedrock surfaces could be better exposed, we took vertical samples from weathered granite rocks on small trench walls dug on the middle marine terrace at Yoshihama Bay. Surface exposure ages from ¹⁰Be concentrations in quartz calculated from the measured ¹⁰Be/⁹Be ratios commonly suggest slow in both sites, whereas steep (~ 10°) dip domains on the marine terraces along the northern Sanriku coast may imply localized permanent strain accumulation.

How to cite: Wakasa, S., Ishiyama, T., Hirouchi, D., Matta, N., Fujita, N., and Echigo, T.: 10Be dating of middle-late Pleistocene uplifted marine terraces in northern Pacific coast of Northeastern Japan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10655, https://doi.org/10.5194/egusphere-egu23-10655, 2023.

Transient topography represents an opportunity for extracting information on the combined effect of tectonics, mantle-driven processes, lithology and climate across different temporal and spatial scales. The geomorphic signature of transient conditions can be used to unravel the landscape evolution and to assess perturbations in uplift rates, especially in areas devoid of stratigraphic constraints. The Atlas-Meseta system experienced a large scale topographic rejuvenation during the Cenozoic through a combination of different processes. Despite the uplift, the Western Moroccan Meseta (WMM) represents a quiescent tectonic domain with deeply incised valleys and high-standing erosional surfaces (relict landscape). This topography is characterized by elevated non-lithological knickpoints, that delimit an uplifted relict landscape, implying a transient response to a change in uplift rates. Here, we determine denudation rates of selected watersheds and bedrock outcrops from cosmogenic nuclides and perform stream profile, regional and basin-scale geomorphic analysis. Denudation rates of the relict and the rejuvenated landscape range from 15 to 20 m/Myr and from 30 to 40 m/Myr, respectively. These results allow estimating the erodibility parameter for performing river-profile inversions and hence extracting rock uplift rates through time. Inverted rock uplift rates are 10-25 m/Myr from 45 to 22 Ma and 30-55 m/Myr from 22 to 10 Ma. Despite the different time scales, the inverted rates are consistent with ¹⁰Be averaged denudation rates (15-20 and 30-40 m/Myr) and river incision values from Pleistocene lava flows (<10 and ~50 m/Myr) for the rejuvenated and relict regions of the WMM. These results agree with geological data and indicate that the observed 400 m of surface uplift in the WMM started to develop at ~22-20 Ma. Given the wavelength of the topographic swell forming the topography of the WMM, uplift is here interpreted to reflect localized crustal thickening through magma addition or lithospheric thinning through mantle delamination. This event, however, represents only a first episode of uplift. The occurrence of ~7-Myr-old marine sediments at ~1200 m of elevation indicates that the adjacent Folded Middle Atlas experienced a more recent surface uplift at ~170 m/Myr. Considering the cumulative amount of surface uplift that varies eastward from 400 to 800 and 1200 m from the Meseta to the Tabular and the Folded Middle Atlas, as well as the spatio-temporal pattern of alkaline volcanism (middle Miocene and Pliocene to Present), we suggest that the most recent episode (second phase) of surface uplift was induced by a larger-scale process that most likely included upwelling of asthenospheric mantle and to a lesser extent crustal shortening and thickening in the Folded Middle Atlas.

How to cite: Clementucci, R., Ballato, P., Siame, L., Claudio, F., Simone, R., Giacomo, T., Riccardo, L., Laetitia, L., and Guillou, V.: Cenozoic uplift history and topographic rejuvenation of the northern Atlas-Meseta system (Morocco), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11243, https://doi.org/10.5194/egusphere-egu23-11243, 2023.

The interactions between Earth surface processes, climate and tectonics determine the landscape in mountain regions. The Japanese Alps uplifted throughout the Quaternary and now reach elevations of up to 3,000 m. However, quantifying relief changes in response to tectonic activity, magmatism and Late Quaternary glaciation is challenging due to the young age of the Japanese Alps and the difficulty of measuring surface processes at the timescale of glacial-interglacial cycles. Here, we use ultra-low temperature thermochronometers based on the luminescence of feldspar minerals and the electron spin resonance (ESR) of quartz minerals, in combination with inverse modelling to derive rock cooling rates and exhumation rates histories at 10⁴-10⁶ years timescales. We focus on the Tateyama region in the Hida range of the Japanese Alps, which was glaciated during the late Quaternary period. In total, 19 new samples were analyzed by luminescence and ESR thermochronometry. While most luminescence signals have already reached their upper dating limit, ESR signals (Al and Ti centres) yielded ESR ages of between 0.5-0.9 Ma. In general, thermal stability is lower for the Al centre compared to that of the Ti centre, but both centres constrain similar exhumation rates. Inversions reveal rock cooling rates on the order of 30-80 °C/Ma, which can be inverted to erosion rates of <1 mm/a within the past 1 Ma. In the next step, we will relate these rates to the climate and tectonic history of the Tateyama region.

How to cite: Bartz, M., King, G. E., Herman, F., Anderson, L. S., Sueoka, S., Tsukamoto, S., and Tagami, T.: High-relief exhumation history in the Japanese Alps within the past 1 Ma inferred from trapped charge thermochronometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11600, https://doi.org/10.5194/egusphere-egu23-11600, 2023.

The impact of Quaternary climate change on landscape evolution, and more specifically the timing of incision of the overdeepened Alpine valleys, remains difficult to quantify with existing thermochronometric methods. Thermochronometers are used to determine rates of rock cooling, however most techniques are insensitive to temperature changes <60 °C that occur within the last kms of Earth’s crust. Recording cooling rates within this temperature range is essential if the impact of glacial-interglacial cycles on rock exhumation is to be resolved.

Electron spin resonance (ESR) thermochronometry applied to quartz minerals has the potential to span this thermal (and temporal) gap. We are developing this method by building upon previous studies (e.g. Scherrer, 1993) with the ultimate aim of constraining the timing of incision of the Rhône valley. Preliminary data from the Japanese Alps (King et al., 2020) indicate that ESR thermochronometry could resolve rates of <1 mm/yr over Quaternary timescales.

To determine a rock cooling history using ESR thermochronometry, signal accumulation and signal thermal loss must be robustly determined within the laboratory. We have collected a series of geological samples including rocks from boreholes that have known isothermal histories to investigate the potential of this technique. Our objective is to use the latter rocks to confirm the validity of our laboratory measurements and data-fitting/numerical models. Specifically, we have investigated known-thermal history samples from the MIZ1 borehole (Japan) and the KTB borehole (Germany) as well as samples from Sion in the Western European Alps.

Preliminary data reveal that the ESR dose response and thermal decay of different quartz samples is highly variable. Whereas the Al-centre of some samples exhibits linear dose response to laboratory irradiation up to 15 kGy, the Al-centre of other samples exhibits exponential, or double-exponential growth and saturates at doses of 3-4 kGy. The Ti-centre of most samples is well described by a single saturating exponential function, however samples from the MIZ1 borehole exhibit pronounced sub-linearity in the low-dose response region. Furthermore, whereas for some samples the Al-centre is less thermally stable than the Ti-centre, for other samples the inverse is observed. These observations suggest that a uniform measurement protocol and data-fitting approach may not be appropriate for quartz ESR data.

Inversion of two KTB samples yielded temperatures within uncertainty of borehole temperature, however results for the MIZ1 borehole are more variable and can only recover temperature at best within ~10%. Investigations into the cause of the poor results for the MIZ1 borehole are ongoing (i.e. measurement protocol, data-fitting/numerical model) and will be discussed. Preliminary data from Sion are promising and reveal consistent cooling rates.

Scherer, T., Agel, A., and Hafner S. S.: Determination of uplift rates using ESR investigations of quartz, KTB Rep. 93-2. Kontinentales Tiefbohrprogram der Bundesrepublic Deutschland Niedersächs. Landesamt Bodenforsch., Hannover, 121–124, 1993.

King, G.E., Tsukamoto, S., Herman, F., Biswas, R.H., Sueoka, S., Tagami, T. Electron spin resonance (ESR) thermochronometry of the Hida range of the Japanese Alps: validation and future potential. Geochronology 2, no. 1 (2020): 1-15.

How to cite: King, G., Wen, X., Bartz, M., Anderson, L., Bossin, L., Tsukamoto, S., Li, Y., Herman, F., Ogata, M., and Sueoka, S.: Will ESR thermochronometry reveal the timing of Rhône valley incision?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11839, https://doi.org/10.5194/egusphere-egu23-11839, 2023.

Understanding topographic relief evolution and its changes over hundreds of thousands to million-year timescales remains challenging. Recent approaches usually combine numerical modelling of terrestrial cosmogenic nuclide (TCN) exposure ages on strath terraces, exhumation histories based on thermochronology, drainage basin evolution, and basin stratigraphy. However, even when combined, these methods are unable to measure the rate changes with precisions needed to differentiate climate from tectonic drivers over multiple glacial cycles and longer timescales.

Muon-paleotopometry is a new approach that may address the methodological gap in determining relief generation. Muon-paleotopometry utilizes the dependence of cosmic ray muon flux on crustal shielding depth. The spatial pattern of concentrations of multiple muon-induced TCN measured along a near-horizontal transect under valleys and peaks relates directly to the history of changes (positive or negative) in crustal thickness. It enables paleotopometry above the sample datum over an isotope-specific monitoring duration. By sampling at depths of hectametres, long-lived TCNs are not sensitive to minor short-term (<10⁵-yr) changes owing to cut and fill terraces or transgressions for instance, but short-lived isotopes may provide constraints on this. The method uses concentration differences among samples, so is not significantly impacted by limitations in knowledge of muon flux and interactions at those depths. Early proof-of-concept investigations at Dalhousie (M. Soukup, Hon. Thesis, 2017) provided encouraging results to allow for the current large-scale relief investigation of the European Alps.

How to cite: Raab, G., Gosse, J., and Hidy, A.: Muon Paleotopometry – Measuring crustal thickness variations with muons?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17271, https://doi.org/10.5194/egusphere-egu23-17271, 2023.

How to cite: Wang, X., Campmans, G., Weinhart, T., Thornton, A., Luding, S., and Wijnberg, K.: Discrete element modelling of grain-scale aeolian sediment transport on moist beach surface, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-385, https://doi.org/10.5194/egusphere-egu23-385, 2023.

As different from traditional large dams, the hydraulic lifting dam is a kind of low-head movable weir, which can be partly lifted to impede water while the rest part of the weir collapsed to surpass water, resulting in a rather complicated terrain. Therefore, the flow structure around a hydraulic lifting dam might become complex and highly three-dimensional (3D). Generally, depth-averaged two-dimensional (2D) models are employed in the prediction of riverine morphodynamic processes. However, in the vicinity of a hydraulic lifting dam, the 2D models not only lose the turbulence details, but also neglect the impacts of turbulence on sediment transport and hence bed deformation. Here, a comparison study is conducted by using a 2D and a 3D model, respectively. The 2D model is a validated depth-averaged hydro-sediment-morphodynamic model using Finite Volume Method on unstructured meshes. The 3D model adopts a Reynolds-averaged Navier-Stokes (RANS) based turbulence model or a delay detached eddy simulation (DDES) model under the framework of OpenFOAM. The results show that the flow details, which cannot be reproduced by a 2D model, have a great potential of modifying the morphodynamic processes, so a 3D model is desperately required for resolving flow structure as well as sediment transport and morphological changes in the vicinity of a hydraulic lifting dam.

How to cite: Ni, Y.: Flow structure around a hydraulic lifting dam and its implication for sediment transport and morphological changes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2197, https://doi.org/10.5194/egusphere-egu23-2197, 2023.

Debris flows are the common gravity-driven mass flows in mountain areas that have high sediment concentration, wide grain sizes, and strong impact force.  Erosion or entrainment is the main mechanism by which the flows significantly increase their volume and destructive potential when they progressively move down over colluvial or alluvial beds. However, the scale and mechanism of erosion are poorly understood due to scarcity of field data. We present on-site data of a rare event in which three consolidated landslide dams were incised deeply by debris flows in a small catchment, southwestern China. The highest erosion rate was up to 1.3 m/min or 568 m³ per unit channel length. The channel topographical condition controls transition from erosion to deposition and the locations of local erosion maxima. An outburst-flood erosion model incorporating flow discharge, channel slope and erodibility is adopted to simulate the progressive erosion of these dams. The infrequent case confirms the key role of debris flows in alpine landscape evolution and provides field data (case data) for developing advanced erosion models. This work provides new insights into the role and scale of debris-flow erosion in catchment evolution.

How to cite: Hu, K., Ning, L., Wei, L., and Zhang, Q.: Progressive channel erosional processes of the 2020 Heixiluo debris flow in Dadu River, southwestern China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2278, https://doi.org/10.5194/egusphere-egu23-2278, 2023.

This paper investigates effect of scour adjacent to the bridge piers with installed riprap as the scour countermeasure. A riprap sloping structure is a conical placement of launchable stones around the bridge pier commonly used as erosion protection. Riprap sloping structure affects the flow in similar manner to groynes, shifting the scour hole downstream of the toe of the structure. Assuming that the installation of the riprap erosion protection deflects the scour hole development downstream of the bridge, experimental model is developed to represent natural environment under different flow scenarios. The 3D model requires calibration of numerical parameters to accurately simulate the prototype conditions – e.g. cell mesh size, turbulence model, and roughness associated with natural riverbed and the riprap sloping structure. Calibration of the Flow-3D numerical model was performed against the flow measurements conducted during field campaign. Flow measurements were collected using Acoustic Doppler current profiler on 20 transects along the river section adjacent to the bridge. Two independent surveys were conducted: for 30 % flow duration and 60 % flow duration (mean flow conditions). After obtaining the results, cross-sectional velocities were analyzed in 3 characteristic transects (upstream, downstream and at the bridge opening). Finally, good agreement was achieved between the model and measured flow field across all transects, enabling numerical setup to be reliable for simulating rare flood events, and associated scour development.

Acknowledgments:

This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046).

How to cite: Harasti, A. and Gilja, G.: Simulation of equilibrium scour hole development around riprap sloping structure using the numerical model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6811, https://doi.org/10.5194/egusphere-egu23-6811, 2023.

Floods cause severe natural disasters over the world generating property and infrastructures damages, poverty and loss of human life, among others. Mediterranean watersheds are especially sensible to floods due to their typical drainage basin features (steep slopes, short concentration times, complex orography, etc.) and the high rainfall intensity typical of convective systems. Knowing channel dimensions and other fluvial morphological features is key to (i) understanding the morphological evolution of the fluvial system in response to changes in land use and climate, and (ii) as an input for hydrological and erosion modelling. The objective of this study is to develop a simple method to obtain reliable estimates of channel dimensions and granulometry of bed material, based on statistical relations with catchment characteristics (e.g. topography, land use, soil properties, lithology, precipitation, connectivity indicators).

First, channel dimensions were estimated based on GIS analysis using a high resolution digital elevation model (2x2m) and ortophotos (50 cm resolution) for the Upper Segura River catchment, a Mediterranean catchment of 2,592 km² located in the southeast of Spain. These estimates were validated with field measurements of depth and width of bankfull channels in the catchment headwaters. This comparison revealed that there was generally good agreement between channel dimensions obtained with the GIS method and those observed in the field for all evaluated channels (depth: RMSE=0.06; R²=0.93; width: RMSE=0.59, R²=0.45), although with better results for dry channels than for channels with continuous water flow. At each field observation, we also took sediment samples and characterised the granulometry of the channel bed material in the laboratory through dry sieving. Preliminary results show that bed material is composed mainly by gravels (67.8%), followed by sands (31.1%) and clays and silts (1.1%).    

Next, channel dimensions, obtained using GIS analysis across the entire catchment, and granulometry of bed material were used as dependent variables in advanced statistical analyses (such as machine learning algorithms) at sub-basin scale, with catchment characteristics as independent variables. The outcome of this analysis is now being used to make spatially continuous predictions of channel dimensions and granulometry of bed material at the catchment scale. This information will then ultimately serve as input for a coupled model that simulates channel hydraulics and morphodynamics at the catchment level.

Keywords: geomorphology; sediment yield; depth and width of bankfull channels; Mediterranean environment; GIS based tools; southeast of Spain.

We acknowledge funding from the Spanish Ministry of Science and Innovation and ‘Agencia Estatal de Investigación’ (PID2019-109381RB-I00/AEI/10.13039/501100011033).

How to cite: Jodar-Abellan, A., Carrillo-López, E., Eekhout, J., Boix-Fayos, C., Pérez-Cutillas, P., and de Vente, J.: Predicting channel dimensions and bed materials in intermittent Mediterranean rivers., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7170, https://doi.org/10.5194/egusphere-egu23-7170, 2023.

When it comes to plastic manufacturing worldwide, more than half of what is produced gets dumped into the world's oceans and rivers. The rivers are the primary pathways for plastics to reach the seas. The infiltration behavior of plastic particles into mobile sediment beds (coarse sand) with median diameters (d50) between 0.4 and 0.8 mm was studied using flume experiments with varying plastic particle parameters (such as density and size) under a variety of controlled hydraulic settings.

The results are thought to be very useful for improving our understanding of and research into how microplastic particles with different characteristics infiltrate into rivers and streams (in mobile beds) with different bedload rates and stay there. The findings showed that microplastic particles were present in both the stationary and mobile sediment layers of the moving sandy bedforms. The number of particles that infiltrate into the sediment is influenced by particle sizes, densities, and bedform characteristics. In general, it was found that the distributions of microplastic particles of different types and sizes in migrating sandy sediment were heterogeneous, although certain trends could be seen, such as a reduction in infiltration rate and average infiltration depth with increasing bedform celerity. Higher infiltration depths and infiltration percentages are also seen for denser and smaller particles. Additionally, the ratio of infiltrated particles in stationary layers of bedforms to total infiltrated (%) decreases as bedform celerity increases. Using the project's findings, future research and numerical modeling studies on plastic particles' accumulation, distribution, and pathways will be able to inform better decisions about how to clean up future microplastic sediment pollution, as well.

How to cite: Alhusban, Z., rovelli, L., and Lorke, A.: Studying the effect of moving sandy bedforms on the infiltration behavior of microplastic particles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9197, https://doi.org/10.5194/egusphere-egu23-9197, 2023.

Particle size segregation is a phenomenon that generates preferential sorting of particles, based on size, in material flows of non-uniform size distribution. Landslide hazards, such as debris flows, involve materials of non-uniform particle sizes and therefore generate flow structures which arise from particle size segregation. The mobility, distal reach and impact forces associated with these natural hazards are influenced by these processes. Understanding the mechanisms of this phenomenon is essential for acquiring accurate input parameters that are needed to model these flows and properly design debris flow barriers and retaining structures. While the dynamics of particle size segregation in flow and deposition have been furthered through studying granular flows, studies to date have had several limitations. They primarily examine flows of bidispersed material, are small in scale, and rely on observations from flume sidewalls, precluding the study of dynamics along the centreline of flows. In this study, a large scale 6.8 m long and 2.1 m wide slope inclined at 30 degrees was used to generate dry tridispersed granular flows with 0.6 m³ of material. The tridisperse mixture consisted of even proportions by mass of 3 mm, 6 mm and 12 mm diameter spherical particles. Replicate tests were conducted to observe flow dynamics and assess methods for sampling along the internal plane of the test deposit. Image analysis techniques were developed to quantify particle size distributions within the deposit. Flume sidewall and internal observations were found to differ significantly from each other, in that side wall observations contained significantly higher proportions of the largest particle size. Additional replicate tests were conducted with saturated material to further examine the impact of pore fluid on segregation. This work will allow for future calibration of both numerical and theoretical models of particle size segregation and ultimately enable better debris flow modelling and mitigation practices.

How to cite: Kimball, J., Bowman, E., Gray, N., and Take, A.: Assessing Experimental Methods for the Quantification of Particle Size Segregation in Large Scale Flume Tests using Image Analysis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10517, https://doi.org/10.5194/egusphere-egu23-10517, 2023.

Dam breach is a large-scale, highly unsteady, and complex water-sediment flow. Dam breach events span scenarios involving natural dams (created following valley blocking landslides) to scenarios involving anthropogenic structures such as water-retaining dams and dams designed specifically to store mine waste (e.g. tailings). Management of the risk posed by a potential breach of a dam structure requires a careful analysis of the consequences of failure. These analyses, often called dam breach studies, aim to improve safety and risk management through the prediction of travel time, flow velocity, and spatial extent of the hazard (e.g. map of depth of inundation) in the event of a breach. These factors in turn define the consequence classification of a dam and guide the development of emergency preparedness plans. The key boundary condition required for flood routing numerical simulations often conducted for dam breach studies is the outflow hydrograph which describes the relationship between outflow of the retained volume with time. In this study we explore the effect of failure mechanism on the characteristics of the outflow hydrograph of otherwise identical physical model dams. Physical model dams of 1 m in height were constructed of fine sand near the midspan of the 36 m long, 2.1 m wide, and 1.2 m high large landslide flume facility at Queen’s University Coastal Engineering Laboratory. Three failure mechanisms are explored; a) notch overtopping, initiated by incising a v-notch into the dam crest and allowing the impounded reservoir to intersect this local low point; b) wide-width overtopping, where a retaining wall placed along the crest of the dam allows for an additional reservoir capacity above the height of the crest that when rapidly removed a full width sheet of water cascades over the dam; and c) geotechnical seepage failure, where closing the toe drain allows a seepage face to develop that causes a failure in the downstream face of the dam. The reservoir surface elevation during breach was monitored with a series of five Akamina AWP-24 wave capacitance height gauges distributed centerline in the upstream reservoir. The evolution of breach shape is captured every 3 s using five Canon EOS Rebel T5 Digital Single-lens Reflex (DSLR) that capture a plan view area of the entire 2.1 m width of the dam and a combined upstream and downstream length of 4.3 m. To further capture the evolution of failure a Blickfeld LiDAR sensor was positioned oblique to the downstream slope to capture a point cloud scan ever 1.4 s. These data sets are then used to compare the physical characteristics of each breach process and the resulting implications for the observed outflow hydrographs for each failure mechanism.

How to cite: McKellar, M., McDougall, S., Evans, S., and Take, A.: Comparison of outflow hydrographs following dam breach arising from overtopping, wide-width overtopping, and geotechnical seepage failure mechanisms., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10650, https://doi.org/10.5194/egusphere-egu23-10650, 2023.

Bridges with elements interacting the flow, such as piers constructed in the main river channel or approach embankments blocking the overbanks, alter the flow conditions and initiate local and contraction scour in the bridge profile. Scour countermeasures are often placed around the bridge piers with goal to scour and associated risk of bridge failure. Effectiveness of scour countermeasures depend on its influence on the surrounding riverbed – in case that countermeasures obstruct significant area, flow can be concentrated and accelerated, inducing scour of the banks. Long-term effects of the scour countermeasures on the river morphology can lead to flow redistribution and lateral shifting of the river cross-section, altering the design conditions in the bridge vicinity. Aim of this work is to compare the flow environment at 4 distinctive bridge locations simulated in HEC-RAS model under characteristic hydraulic scenarios that induce scour. Results show that for all bridges current flow environment differs from the design state, so that additional intervention in the riverbed geometry doesn’t significantly change the flow conditions. Flow environment was simulated with sill placed on different distances downstream or excavation of the riverbed to reduce flow velocity. In all scenarios main flow remain concentrated similar to the current state, showing that countermeasures have to be substantial in order to be effective.

Acknowledgments

This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046).

How to cite: Cibaric, A., Troskot, N., Veseljak, M., Vukovac, M., and Gilja, G.: Flow pattern around the bridge piers with installed scour countermeasures, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11405, https://doi.org/10.5194/egusphere-egu23-11405, 2023.

Rapid development of the instantaneous flow velocity instruments allows for high frequency measurement of turbulent flow field in the hydraulic flume. To obtain accurate and reliable flow measurement it is necessary to correctly configure the instrument using the manufacturer’s general guidelines. When instruments are used in highly turbulent flows, such as flows around bridge piers, selection of parameters is not straightforward and it generally requires validation against known data. In this study, experimental flow velocity data was collected in the hydraulic flume at three characteristic cross-sections – bridge profile, and upstream, and downstream profile. Velocity was measured on 10 points for each cross-section using Nortek Vectrino Profiler. Velocity measurements were processed to calculate turbulent kinetic energy at discrete points, after which TKE map was interpolated over the entire cross-section using QGIS. Results of TKE maps are compared for two characteristic flow rates and changes in TKE distribution respective to the flow downstream analyzed to quantify influence of the bridge pier and scour protection on the flow in the bridge vicinity.

Acknowledgments

This work has been supported in part by Croatian Science Foundation under the project R3PEAT (UIP-2019-04-4046)

How to cite: Gilja, G., Drandić, L., Fliszar, R., and Harasti, A.: Experimental study of turbulent kinetic energy of flow over scoured riverbed, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11685, https://doi.org/10.5194/egusphere-egu23-11685, 2023.

Bedload transport has major consequences for public safety, water resources and environmental sustainability. In mountains, steep slopes drive an intense transport of a wide range of grain sizes implying size sorting or segregation largely responsible for our limited ability to predict sediment flux and river morphology. Size segregation can lead to very complex and varied morphologies of bed surface and subsurface, including armouring, and can drastically modify the fluvial morphology equilibrium.

In this work, the mobility of bidisperse beds is studied with coupled fluid-Discrete Element Method (DEM) simulations of bedload transport. Initially, a large particle layer is deposited over a 10% slope bed made of small particles. A gravity-driven water free surface flow induces a downslope shear-driven granular flow of the erodible bed. It is observed that, for the same water flow conditions, the bedload transport rate is higher in the bidisperse configuration than in the monodisperse one. Depending on the Shields number and on the depth of the interface between small and large particles, different transport phenomenologies are observed, ranging from no influence of the small particles to small particles reaching the bed surface due to diffusive remixing. In cases where the small particles hardly mix with the overlying large particles and for the range of studied size ratios (r < 4), it is shown that the increase of mobility of the sediment bed is a granular effect, which can be explained within the mu(I) rheology framework. The buried small particles are more mobile than larger particles and play the role of a “conveyor belt” for the large particles at the surface. Based on rheological arguments, a simple predictive model is proposed for the additional transport in the bidisperse case. It reproduces quantitatively the DEM results for a large range of Shields numbers and for size ratios smaller than 4.

Finally, a phenomenological map is proposed. It presents the different transport regimes of bidisperse mixtures, depending on the mechanism responsible for the mobility of the small particles.

How to cite: Chassagne, R., Maurin, R., Chauchat, J., and Frey, P.: Mobility of bi-disperse sediment beds in bedload transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11802, https://doi.org/10.5194/egusphere-egu23-11802, 2023.

Abstract: A very common engineering task we encounter in practice is calculating the annual balance of sediments on some watercourse. This is particularly challenging when assessing the backfilling of river reservoirs that have a multifunctional function.

Trakošćan Lake was built in the period from 1850 to 1862 as a pond and landscape addition to the park and Trakošćan castle. The topographic catchment area of the lake is 10.7 km², it is about 1.5 km long, and its area is about 17 hectares, with an average depth of about 2.5 meters. The lake's total volume was originally 400,000 cubic meters, and downstream from the dam, the water of the Čemernica stream flows into the Bednja River.

After 61 years, the lake was drained, and in 2022, work began on sediment excavation to improve the lake's ecological condition due to about 200,000 cubic meters of deposited silt in the lake. The projected depth of the lake after cleaning would be about 6 meters.

In the example of this artificial lake, an estimate of the annual sediment spread by empirical parametric methods was carried out. Furthermore, the results were compared with the results of previous analysis obtained based on geotechnical sediment investigation at Lake Trakošćan.

How to cite: Oskoruš, D., Leskovar, K., and Pavlić, K.: Parametric methods for assessing the production of suspended sediment and its deposition in artificial lakes - an example of Lake Trakošćan, Croatia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13546, https://doi.org/10.5194/egusphere-egu23-13546, 2023.

The risk of scour of hydraulic infrastructure, such as bridge piers and abutments, may considerably rise during extreme weather events. The removal of coarse bed material and consequent critical failure of the riverbed surface layer's protective layer against scour can result from sufficiently energetic flow structures, which normally scale with their cross-sectional lengthscale [1] (typically a naturally formed armour layer or implemented rip-rap protection, comprising of cobbles and rocks). This study intends to directly monitor the likelihood of entrainment of an instrumented particle [2] that is properly positioned on the riverbed surface near a bridge pier, in order to evaluate the probability of critical failure of the scour protection layer. By directly observing (visually with an underwater camera) as well as monitoring with inertial sensors within the instrumented particle its likelihood of being entrained, this study seeks to evaluate and validate the risk of a critical failure of the scour protection layer close to build hydraulic infrastructure (here, a model bridge pier). As the physical model of a bridge pier is laid downstream, a series of flume experiments (four flow rates) are conducted under carefully controlled flow conditions to evaluate the change in entrainment frequencies of the instrumented particle. The experimentally obtained highly resolved (at 200Hz) time series of the instrumented particle's entrainment, are validated with the camera placed underwater, for the various flow conditions. The instances of instrumented particle entrainment - from which the rate of entrainment is found (matching the probability of bed surface destabilization [3]) - are derived from the analysis of fused raw data from the calibrated embedded sensors (accelerometer, magnetometer, and gyroscope) to identify entrainment events. Acoustic Doppler velocimetry (ADV) under proper configurations [4], is used to collect flow profiles at various distances downstream of the model pier in an initial effort to connect the local and dynamic driving processes for particle entrainment to the phenomenologically significant bulk flow and pier characteristics (such as pier lengthscale, average flow velocity and depth, the median size of armour layer particles). In order to examine the incipient destabilization of riverbed material, typically leading to the disruption of the bed surface protective layer and catastrophic scour, this research effectively demonstrates the employment of purpose designed instrumented particles, showcasing it as a method that is affordable, non-intrusive, long-lasting, and with readily accessible results.

References

• 1. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
• 2. AlObaidi, K., Valyrakis, M. (2021). A sensory instrumented particle for environmental monitoring applications: development and calibration, IEEE Sensors, 21(8), pp.10153-10166, DOI: 10.1109/JSEN.2021.3056041.
• 3. AlObaidi, K., Valyrakis, M. (2021). Linking the explicit probability of entrainment of instrumented particles to flow hydrodynamics, Earth Surface Processes and Landforms, 46(12), pp. 2448-2465 DOI: 10.1002/esp.5188.
• 4. Liu, D., AlObaidi, K., Valyrakis, M. (2022). The assessment of an Acoustic Doppler Velocimetry profiler from a user’s perspective, Acta Geophysica, 70, pp. 2297-2310. DOI: 10.1007/s11600-022-00896-3.

How to cite: Valyrakis, M. and Xu, Y.: Using instrumented particles for monitoring the likelihood of bridge scour protection destabilization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14619, https://doi.org/10.5194/egusphere-egu23-14619, 2023.

Most aeolian sand transport models incorporate a so-called “splash function” that describes the number and velocity of particles ejected by the splash of an impacting particle. It is usually obtained from experiments or simulations in which an incident grain is shot onto a static granular packing. However, it has recently been discovered that, during aeolian sand transport, the bed cannot be considered as static, since it cannot completely recover between successive impacts. This leads to a correction of the splash function accounting for cooperative effects, which is responsible for an anomalous third-root scaling of the sand flux with the particle-fluid density ratio s [1]. Here, we present a two-species saltation model that incorporates this correction. In contrast to the model by [1], it does not only quantitatively reproduce sand fluxes but also transport thresholds from measurements and discrete element method-based sand transport simulations across several orders of magnitude of s.

[1] Tholen, Pähtz, Kamath, Parteli, Kroy, Anomalous scaling of aeolian sand transport reveals coupling to bed rheology, Physical Review Letters, accepted.

How to cite: Chen, Y., Pähtz, T., and Tholen, K.: A two-species model of aeolian saltation incorporating cooperative splash, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14688, https://doi.org/10.5194/egusphere-egu23-14688, 2023.

ABSTRACT: Gravity currents are flows generated by density differences within two contacting fluids. In this work the interaction between lock-release gravity currents propagating over a horizontal rectangular channel and an emergent cylinder is analyzed through velocity measurements obtained through PIV. Two-dimensional instantaneous velocity fields are measured in a plane perpendicular to the bottom along the center axis of the channel upstream of the obstacle. The experiments were also conducted without the cylinder for comparison purposes and ten repetitions were carried out for each configuration. The analyses focus on the effects that the presence of an adverse pressure gradient has on both the mean velocity field and the turbulence of the leading part of the current, the head, before the impact. The mean velocity field is not affected by the presence of the obstacle and since no differences were found in the spatial distribution of the mean velocity components, the necessary cylinder-induced deceleration occurs uniformly. Turbulence is studied through the components of the Reynolds stress tensor and their fluxes within the head. In the configuration with the cylinder, there are no fluxes of Reynolds stresses in the inner part of the section. Consequently, the Reynolds stress intensity decreases inside the head compared to the configuration without the obstacle. In conclusion, the presence of an adverse pressure gradient stops the mechanism of Reynolds stress distribution from the main source of production, i.e. the front region, to the inner region of the flow. This leads to a decrease in Reynolds stresses in the inner part of the head and an increase in the frontal region.

Acknowledgements: This work was partially supported by Foundation for Science and Technology's through funding UIDB/04625/2020 (CERIS research unit).

Keywords: Gravity currents, lock release, Particle Image Velocimetry, adverse pressure gradient, Reynolds stress.

How to cite: Di Lollo, G., Adduce, C., Brito, M., Ferreira, R. M. L., and Ricardo, A.: Reynolds stresses in gravity currents approaching an obstacle, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15236, https://doi.org/10.5194/egusphere-egu23-15236, 2023.

One of the main causes of destabilizing bridge piers has been identified as the process of scour due to the action of the turbulent flows around them, rendering it as one of the most frequent and costly infrastructure failure events all around the world. The challenge of scour-induced catastrophes will keep increasing, affecting the resilience of our society, as extreme weather intensifies affecting the exposed hydraulic infrastructure, such as bridge piers, abutments and spur dikes [1], and aquatic vegetation [2, 3]. Therefore, research into the highly dynamic scour processes that surround hydraulic infrastructure is becoming increasingly valuable. Researchers have investigated maximum scour depth estimation extensively over the past few decades, combining mean flow parameters, bridge pier, and riverbed materials characteristics using phenomenological or empirical methodologies. The precise cause of the formation and amplification of scour-holes that result in bridge pier failure are yet unknown. This study's main goal is to offer new insights on the dynamical interactions of flow structures shed downstream model bridge piers with bed surface particles, that are strong enough to remove them, thus causing the formation of scour holes. This study specifically intends to better understand the interactions between the coarse bed surface particles and the energetic events of the turbulent flow field, as modified by a cylindrical bridge pier. Extreme impulses (flow impulses above a critical impulse level [4]), are modelled using appropriately fitted probability density functions in order to generate new scour depth predictive equations. The tests are carried out in a research flume that circulates water under the same flow conditions using model bridge piers of various model pier diameters. High-resolution acoustic Doppler velocimetry is used to gather flow velocity profiles downstream of the bridge pier. The patterns of flow structures will change as the morphology of the riverbed next to a pier changes. Based on the velocity profiles captured by ADV, the study presents the variation in flow structures, including velocity (U), turbulence intensity, and turbulent kinetic energy (TKE), downstream of the four bridge pier diameters used in the experiments.

References

• 1. Pandey, M., Valyrakis, M., Qi, M., Sharma, A., Lodhi, A.S. (2020). Experimental assessment and prediction of temporal scour depth around a spur dike, International Journal of Sediment Research, 36(1), pp.17-28, DOI: 10.1016/j.ijsrc.2020.03.015.
• 2. Yagci O., Celik, F., Kitsikoudis, V., Ozgur Kirca, V.S., Hodoglu, C., Valyrakis, M., Duran, Z., Kaya S. (2016). Scour patterns around individual vegetation elements, Advances in Water Resources, 97, pp.251-265, DOI: 10.1016/j.advwatres.2016.10.002.
• 3. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
• 4. Valyrakis, M., Diplas, P., Dancey C.L. (2011). Entrainment of coarse grains in turbulent flows: an extreme value theory approach, Water Resources Research, 47(9), W09512, pp.1-17, DOI:10.1029/2010WR010236.

How to cite: Xu, Y. and Valyrakis, M.: Stochastic modelling of the extreme flow impulses leading to bridge pier scour, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15846, https://doi.org/10.5194/egusphere-egu23-15846, 2023.

Scour monitoring in experimental environments relies primarily on visual point-wise measurements that may provide less accurate estimates of scour and its effects. To fulfil these issues many studies and methods has been developed to analyse scour surfaces. Recently, the use of 3D point clouds and digital elevation models has proven to be an effective method for describing scour around bridge foundations with a high degree of accuracy. This is especially true under drained conditions. Therefore, it has become necessary to develop a system that can continuously monitor the development of scour at bridge foundations without interrupting the flow. 

Few studies have addressed continuous monitoring of the scouring process. These include: (i) photogrammetry-based methods using two cameras and algorithms for image calibration, rectification, and stereo-triangulation, and (ii) a laser-based approach using both a laser source and a camera. As a result of these studies, further researches need to be developed in order to effectively monitor scouring process by using the increasing technology of submersible cameras and underwater processing capabilities. In this study, a novel method for acquiring 2D scour profiles was developed to enable continuous monitoring of the scour phenomenon. The developed technique uses a computer vision technique, namely homography transformation, which relates the coordinates of points in one image to the coordinates of corresponding points in another image through a Python routine. This algorithm also considered the critical issues inherent in any underwater image processing technique, such as correcting for perspective, distortion, scaling, and camera lens rotation. 

In the laboratory, four cameras were used to collect synchronized underwater images of the scour holes formed and the affected surrounding areas around an oblong bridge pier model due to the local scour phenomenon. By processing each image sequence and running the Python code to measure the depth of the border line between the sand and the bridge foundation model at specific times during the scouring experiment, it was possible to obtain the evolution of the scour holes in the form of 2D bed profiles. The accuracy of the developed algorithm to study the bed morphology in the vicinity of bridge piers during the scouring process showed promising results compared to point-wise scour depth measurements.

This work was partially funded by the Portuguese Foundation for Science and Technology (FCT) through Project DikesFPro PTDC/ECI-EGC/7739/2020 and through CERIS funding UIDB/04625/2020.

How to cite: Bento, A. M., Mendes, L., and Ferreira, R.: Homography-based continuous bridge scour depth estimation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16037, https://doi.org/10.5194/egusphere-egu23-16037, 2023.

Authors: Thomas Pähtz, Katharina Tholen, Sandesh Kamath, Eric Parteli, Klaus Kroy

Title: Anomalous scaling of aeolian sand transport reveals coupling to bed rheology

Predicting transport rates of windblown sand is a central problem in aeolian research, with implications for climate, environmental, and planetary sciences. Though studied since the 1930s, the underlying many-body dynamics is still incompletely understood, as underscored by the recent empirical discovery of an unexpected third-root scaling in the particle-fluid density ratio [1]. Here, by means of grain-scale simulations and analytical modeling, we elucidate how a complex coupling between grain-bed collisions and granular creep within the sand bed yields a dilatancy-enhanced bed erodibility. Our minimal saltation model robustly predicts both the observed scaling and a new undersaturated steady transport state that we confirm by simulations for rarefied atmospheres [2].

[1] Pähtz, Durán, Scaling laws for planetary sediment transport from DEM-RANS numerical simulations, https://arxiv.org/abs/2203.00562

[2] Tholen, Pähtz, Kamath, Parteli, Kroy, Anomalous scaling of aeolian sand transport reveals coupling to bed rheology , Physical Review Letters, accepted.

How to cite: Pähtz, T., Tholen, K., Kamath, S., Parteli, E., and Kroy, K.: Anomalous scaling of aeolian sand transport reveals coupling to bed rheology, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16245, https://doi.org/10.5194/egusphere-egu23-16245, 2023.

Large lacustrine mass movements and delta collapses are increasingly being considered as potential tsunamigenic sources. They are therefore hazardous for the population and infrastructure along lakeshores. In most studies of slope stability and triggered tsunamis, however, subaqueous deltas have largely been excluded as we lack information on their morphodynamic evolution. Thus, a holistic assessment of tsunami hazards in the lacustrine environment is required for a better understanding of how delta lakes evolve through time and space.
Within a study funded by the Federal Office of the Environment, we aim to understand what types of deltas are susceptible to slope failure within the perilapine Swiss lakes. To achieve our goal, we primarily focus on those deltas that present an increased potential for subaqueous erosion and analyse their morphological, morphometric and sedimentological characteristics taking advantage of the existing and publically available datasets. In this contribution, we present the designed approach and preliminary results, using Lake Lucerne as a case study. This approach will then be applied to all lakes with a surface area > 1 km², for which high-resolution bathymetric data are available. The outcomes of such a study will be summarized in a geodatabase of the different delta-types for the perilpine Swiss lakes and it represents an important milestone for the assessment of tsunami hazard with regard to the lakes of Switzerland.

How to cite: Vendettuoli, D., Strupler, M., Anselmetti, F. S., Fabbri, S. C., Shynkarenko, A., and Kremer, K.: What controls deltas failure in the Swiss perialpine lakes?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-966, https://doi.org/10.5194/egusphere-egu23-966, 2023.

It is now well established that many lansdcapes are organized to be close to the threshold of sediment motion: rivers, wind-blown dunes and hillslopes. 

Whether explicitly or implicitly, this threshold is almost universally treated as a Mohr-Coulomb failure criterion, which is an opaque barrier that prevents us from viewing and understanding motion beneath the yield point. Below-threshold motion is creep, and the dynamics are creepy indeed: typical continuum descriptions break down, and observed behaviors can be counterintuitive. 

In this talk I present two experiments, using two different optical techniques, that study very slow particle motions below the threshold of motion. Experiments in a scaled-down river use refractive-index matched scanning to image the interior of a sediment bed sheared by a fluid, and track particles over many orders of magnitude in velocity to show that creep is activated deep into the sediment bed. This creep hardens the bed and drives segregation. Tracking creeping grains becomes impractical, however, as it takes several months to measure the slowest particle motions. 

To overcome these simplifications and expand our study of creep, we examine an apparently static sandpile that is isolated from external disturbance. Instead of particle tracking, we use an optical interferometry technique called Diffusive Wave Spectroscopy (DWS) that allows us to measure creep rates as low as nanometers/second. Viewed through the lens of DWS, the model hillslope is alive with motion as internal avalanches of grain rearrangements flicker throughout the pile. We observe similar dynamics to those observed in the river experiment -- albeit over much shorter timescales -- even though the only significant stress is gravity. What causes these grains to creep below their angle of repose? Observations suggest that minute mechanical noise may play a role, but reducing the noise floor beyond our fairly quiescent conditions is very challenging. Instead, we raise the driving stresses through heating, tapping and flow. 

The observations lead to new view of sediment creep as relaxation and rejuvenation of a glassy material, where mechanical noise plays a role akin to thermal fluctuations in traditional glass materials. Sub-yield deformation is a new world to explore, for those patient enough to look for it. 

How to cite: Jerolmack, D. and Deshpande, N.: The seedy underbelly of yield: how measuring verrrrrry slow grain motion changes our view of landscapes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1787, https://doi.org/10.5194/egusphere-egu23-1787, 2023.

We study the effect of an increase in flow discharge on the shape and growth of an experimental alluvial fan. The fan is built by a single-thread channel in which the flow occurs near the threshold of sediment motion. We first define a criterion that predicts the conditions under which a change in discharge leaves an inprint on the morphology of a fan. We then report on experimental runs which allow us to establish the relevance of this criterion. Experiments are carried out during which climatic changes are applied to the feeding channel of a fan. By playing on the initiation time of climate change, on the duration of the rise in flow, or on the total variation in discharge, we scan a range of configurations that allow us to qualitatively and quantitatively test our incision criterion. Qualitatively, we note that the dynamics of the fan seems altered only for values of the criterion which exceed the critical value of 1.5. In these situations, the channel stops moving and entranches. Quantitatively, we extract a characteristic time by autocorrelating spatio-temporal channel migration diagrams and show that this time correlates with the value of the incision criterion.

How to cite: Metivier, F., Devauchelle, O., and Delorme, P.: Adaptation of an experimental alluvial fan to climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2362, https://doi.org/10.5194/egusphere-egu23-2362, 2023.

Most gravitational currents occur on sloping topographies, often in the presence of particles that can settle during the current propagation. Yet, an exhaustive exploration of associated parameters in experimental devices is still lacking. Here, we present an extensive experimental investigation on the slumping regime of turbidity (particle-laden) currents in two lock-release (dam-break) systems with inclined bottoms. We identify 3 regimes controlled by the ratio between settling and current inertia. (i) For negligible settling, the turbidity current morphodynamics correspond to those of saline homogeneous gravity currents, in terms of velocity, slumping (constant-velocity) regime duration and current morphology. (ii) For intermediate settling, the slumping regime duration decreases to become fully controlled by a particle settling characteristic time. (iii) When settling overcomes the current initial inertia, the slumping (constant-velocity) regime is not detected anymore. In the first two regimes, the current velocity increases with the bottom slope, of about 35% between 0° and 15°. Finally, our experiments show that the current propagates during the slumping regime with the same shape in the frame of the moving front. Strikingly, the current head (first 10 centimeters behind the nose) is found to be independent of all experimental parameters covered in the present study. We also quantify water entrainment coefficients E, and compare them with previous literature, hence finding them proportional to the current Reynolds numbers.

How to cite: Gadal, C., Mercier, M., and Lacaze, L.: Slumping regime in lock-release turbidity currents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2733, https://doi.org/10.5194/egusphere-egu23-2733, 2023.

River flows and associated suspended sediment (SS) transport are intermittent processes possessing fluctuations over a large range of time scales and space, making it challenging to develop predictive models that are applicable across timescales and rivers. A concept of “effective timescales of connectivity” has been used to define the timeframe over which sediment (dis)connectivity occurs, whereby parts of the catchment are “switched on and off” as a response of events with varying frequency-magnitude relationships and antecedent soil moisture. These concepts provide excellent frameworks to understand temporal variability and identify relevant timescales for sediment transport, but do not help in the knowledge of mechanisms for temporal variability in SS transport. The complexity and scale dependency of processes driving SS transport stress the need to detect how sediment generation, storage, and transport are linked across different timescales. Furthermore, the mechanisms that produce travel time distributions over many orders of magnitude are not known precisely. To this end, in this study we have considered SS transport as a fractal system. By approaching SS transport dynamics as a fractal system, it is assumed that patterns of variation in SS transport exist over different timescales, while linkages across those temporal scales are expressed as fractal power-laws.

This work aims to defines the link between (i) sediment transport and deposition and (ii) fractal geometry and fractal storage time distributions in streams.

Here, we present case study where fractals are used to describe and predict patterns over different spatial or temporal scales of dynamics in SSCs. We have considered in these studies the statistics and the dynamics of streamflow, SSCs and associated grain size distribution at event based by considering respectively their probability distribution function and Fourier power spectra.

We set up a natural experiment site of a first-order mixed bedrock and alluvial stream channel by using LISST instrument coupling with LIDAR remote sensing measurement. Here we obtain high-resolution observations of streambed topography and continuously long-term measurements of suspended sediment in natural experimental site located in an agricultural watershed of a Chianti area (Florence, Italy).

The LISST is a submersible laser diffraction particle size analyzer for measuring suspended particle size (range from 2.50 µm to 500 µm), its volume concentration at different time step and depth. We set up at time interval equal to 5 minutes of sample rate.

Preliminary results obtained indicate large fluctuations with heavy tails, and long-range properties, characterized by extreme events much more frequent than what is found for a Gaussian process.

Hence, insights into the degree of fractal power of a SS transport system may provide a useful basis to evaluate and develop the most appropriate predictive models and management strategies.

How to cite: Pelacani, S., Barbadori, F., Raspini, F., Schmitt, F. G., and Moretti, S.: Fractal characteristics of suspended sediment transport in rivers: natural experiment site, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2913, https://doi.org/10.5194/egusphere-egu23-2913, 2023.

In some landslides, collapse is accompanied by the upslope retreat of a well-defined scarp whose speed controls the rate of mobilization of debris. Here we examine the evolution of such scarps in an idealized laboratory setting. We conduct tilted channel experiments involving retrogressive dry granular landslides over an erodible substrate. After first tilting up a deep sand layer to close to the angle of repose, then imposing an abrupt base-level drop, granular flow is induced at the downstream outlet. This flow generates an upstream-traveling wave with a well-defined scarp at the upstream tip. Downstream of the moving scarp, sand flows as an avalanching layer of finite depth over the erodible but stationary substrate, and outflows over the lowered outlet sill. A series of such experiments were conducted to determine the influence of channel width and base-level drop height on the speed of scarp retreat and other flow properties. Measurements included the time-evolving profile of the free surface, surface velocities acquired using particle tracking velocimetry, and the time-evolving mass outflow rate at the downstream outlet. Dimensional analysis clarifies the physical mechanisms governing the rate of scarp retreat. These results will help guide and validate numerical models of granular landsliding over erodible substrates.

How to cite: Hung, Y.-F., Capart, H., and Stark, C. P.: Kinematics of scarp retreat in idealized tilted channel experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3735, https://doi.org/10.5194/egusphere-egu23-3735, 2023.

Prior to earthquake ruptures and slope failures, accelerated surface deformations can sometimes be observed. To anticipate rupture processes, these deformations are interpreted in terms of a strain budget and its stressors. If the budget exceeds an assumed critical value, rupture happens. But not all components of the budget can readily be inferred from the bulk deformation. For example, elastic strain build-up and other ‘silent’ contributions challenge the predictability of these potential natural hazards. We present preliminary experimental results, focussing on deformation by compaction. We report an analogous experiment of loading and unloading to constrain compaction behaviour, elastic strain-build up, and release to understand their ‘silent’ contributions to the strain budget. As analogue material, we use sand to assess emergent bulk behaviour. Using natural quartz crystals allows to apply in-situ neutron diffraction to measure elastic strain during loading and unloading stages. We find that while compaction and remnant compaction scale linearly with load magnitudes, elastic strain build-up seems to be independent of stresses ≥60 MPa. In addition to the in-situ neutron diffraction experiments, we conducted mechanical compaction tests at ramped load stages and analysed the post-compaction changes of the grain size distribution. With increased loading, the mean grain size decreased, leading to increased bulk density in the compacted portion. Based on these observations, we reason that the linear elastic bulk compaction of our samples is due to non-linear local brittle deformation. There is only limited elastic strain built up during the compaction, which is likely released due to local crushing. Localized failure produces a denser material in which strain can build up more homogeneously, causing rupture at its bulk elastic limit. Our experiments show that deducing or simply converting loading and displacement to stress-strain relationships to establish a strain budget may be inadequate. Silent components that are likely due to non-linear and emergent processes can in the short term lead to local elastic strain energy release or bulk dynamic ruptures. Conceptually, to especially anticipate the timing of slope failures and the magnitude of earthquake ruptures, the hidden costs, e.g. due to localized failure, and internal changes, concerning density or elastic properties, are crucial components that need to be constrained while compiling a strain or energy budget of these processes.

How to cite: Voigtländer, A., Sikolenko, V., Turowski, J. M., Illien, L., Bedford, J., and Pruß, G.: Tales of compacting sand to anticipate strain budget of rupture processes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6809, https://doi.org/10.5194/egusphere-egu23-6809, 2023.

Geomaterial are complex porous material presenting a wide diversity of structures, which set how a fluid will flow through it. The understanding of the mechanisms controlling the flow kinematics at the pore scale is however decisive to predict and control transport processes (dispersion and mixing) and to relate them to the macroscale behaviour of porous materials. Because of the opaque nature of porous media, the flow visualization and characterization of the velocity fields within a porous media is particularly challenging in three-dimensional (3-D) porous media. However, recent development of experimental techniques including index matching, allow to develop transparent porous media to perform direct visualization of the flow in these artificial material.

I will here discuss about how such approach have already been successfully implemented to study porous media composed of randomly packed solid monodisperse spheres, allowing to directly visualize the flow within the bulk of the 3-D media, and to investigate how a blob of dye stretches and get mixed when injected within such 3-D porous media. Using Particle Image Velocimetry techniques (PIV), these promising techniques also allow to perform successive scans of the velocity field, providing highly resolved experimental reconstruction of the 3-D Eulerian fluid velocity field in the bulk of the porous media. This approach is therefore promising to further investigate flow kinematic in more complex porous media, or to directly visualize other crucial mechanisms in such media, like for instance erosion, clogging, or the effect of strong heterogeneities on the overall flow behavior.

How to cite: Souzy, M.: Direct flow visualization and transport processes in transparent 3D porous media, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7051, https://doi.org/10.5194/egusphere-egu23-7051, 2023.

Sediment gravity flows are common processes in the submarine environment. They are important for the global sediment transport, but can destroy offshore infrastructure and may even contribute to tsunami generation. These flows, however, remain poorly understood. There is a lack of direct observations due to difficulties with deploying appropriate instruments and predicting the occurrence and route of these flows, especially on open continental slopes. Deployed instruments are further often destroyed as a result of the gravity flows. Submarine fibre cables are present along almost all continental margins worldwide. They are economically important for telecommunication and internet data transfer. Historic records, however, have shown that submarine gravity flows affect and even severe these cables. 

Recent studies successfully tested the usage of fibre optic cables to detect earthquakes and other processes such changes in the wave height associated with storm events. The aim of this study will be to test whether fibre optic cables can also detect submarine gravity flows using laser interferometry. The study is based on a cooperation between the University of Malta and the Istituto Nazionale di Ricerca Metrologica (INRiM) in Italy and is part of the European funded project “Modern and recent sediment gravity flows offshore eastern Sicily, western Ionian Basin (MARGRAF, ID 101038070)”. The University of Malta has been granted permission to collect data from a 260-km long optical fibre cable that connects Malta and Sicily through the western Ionian Basin. INRiM provided the measurement system and technical support needed to carry out the experiment. The western Ionian Basin is an ideal study site, as it is characterised by many earthquakes, tsunamis and submarine sediment gravity flows. The cable crosses known pathways of these gravity flows and thus provides a high possibility to detect modern sediment flows. The laser interferometry data will be analysed to detect disturbances (e.g., twists, expansions, contractions) on the cable. Any detected disturbances will be compared with oceanographic and seismometer data, both from onshore stations and Ocean Bottom Seismometers (OBS). This comparison will allow us to infer the source of the cable disturbance. In addition, we plan to collect gravity cores in vicinity of the event to assess whether the event was based on a gravity flow or not. Initial results showed earthquakes and various storm events recorded by the cable. 

The findings are expected to improve our current understanding of gravity flows in the region in terms of potential trigger mechanisms and reoccurrence rate. Eastern Sicily is densely populated and hosts touristic and industrial infrastructure, which makes it important to constrain the geohazard implication of these flows. A successful test will further allow to use this application on cables in other regions worldwide. 

How to cite: Schulten, I., Clivati, C., Micallef, A., Donadello, S., Calonico, D., Xuereb, A., Mura, A., and Levi, F.: Testing the potential of a submarine fibre optic cable to detect sediment gravity flows using laser interferometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7709, https://doi.org/10.5194/egusphere-egu23-7709, 2023.

When rivers with high suspended sediment load plunge into lakes and reservoirs, the resulting density currents often cause the formation and progradation of hyperpycnal deltas. Suspended load can contribute to delta progradation through two different mechanisms: (1) indirectly, by increasing the excess density of the underflows, thus enhancing the basal shear stresses that drive along-bed transport; (2) directly, by settling out of suspension onto the evolving bed. In this work, we conducted laboratory experiments designed to investigate the relative importance of these two mechanisms, aided by a conceptual model that includes both processes. The experiments are conducted in a narrow tank of constant slope, supplied with prescribed water, sediment, and/or saline influxes. Both suspended sediment load and salinity can therefore contribute independently to the excess density of the inflow. Simultaneous measurements of delta profile evolution and suspended sediment concentration are then acquired using imaging methods. To interpret the results, we construct a simplified one-dimensional model of delta progradation in which along-bed transport is modelled as a diffusion process, and suspended sediment settling as an advection-deposition process. We then examine the influence of process coefficients on the morphology and rate of evolution of the delta fronts and compare simulations with the experiments. It is found that the evolution of the bed profile alone is not sufficient to distinguish between the two mechanisms, hence the importance of simultaneously measuring suspended sediment concentration. Although obtained in a simplified setting and at reduced scale, the results should provide useful guidance for the modeling and monitoring of reservoir sedimentation at field scales.

How to cite: Liang, Y.-Y., Su, C.-C., and Capart, H.: Influence of suspended sediment concentration on hyperpycnal delta progradation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7952, https://doi.org/10.5194/egusphere-egu23-7952, 2023.

Vertical size segregation or sorting of particles in bedload transport, strongly impacts the sediment rate and the river bed morphology. To better account for this process in sediment transport models, it is essential to understand the mechanisms acting at the grain scale (Frey, 2009). Following the work of Rousseau (2021), focus is made on the behaviour of a single large particle segregating upwards in a monodisperse mixture of smaller beads during bedload transport. Experiments are carried out in a narrow flume and the bead dynamics is recovered through image analysis. A great number of repetition is performed for different size ratios (large to small bead diameter) in order to conduct statistical analysis. This work confirms the measurements from Rousseau (2021) and suggests that the time for the large particle to reach the bed surface is minimum for a size ratio of 2. This result supports previous research which, using simpler granular configurations, evidenced a similar tendency in terms of segregation force (Guillard, 2016, Jing, 2020) or segregation velocity (Golick, 2009). Other observations are made on the spatial trajectory of the intruder, which have been previously reported to be linear with a repeatable slope independent of the size ratio. These observations offer interesting insights to understand the mechanisms governing size segregation and could provide new closures to upscale the phenomenon at the continum scale.

Illustration: A 5 mm intruder in a 2 mm bed (size ratio = 2.5), flow from right to left, dimensionless bed shear stress (Shields number) = 0.25.

Frey, P. and Church, M. (2009). “How River Beds Move”. Science, 325(5947), pp. 1509–1510.
Golick, L. A. and Daniels, K. E. (2009). “Mixing and Segregation Rates in Sheared Granular Materials”. Physical Review E, 80(4), p. 042301.
Guillard, F., Forterre, Y., and Pouliquen, O. (2016). “Scaling Laws for Segregation Forces in Dense Sheared Granular Flows”. Journal of Fluid Mechanics, 807.
Jing, L., Ottino, J. M., Lueptow, R. M., and Umbanhowar, P. B. (2020). “Rising and Sinking Intruders in Dense Granular Flows”. Physical Review Research, 2(2), p. 022069.
Rousseau, H. (2021). “From Particle Scale to Continuum Modeling of Size Segregation in Bedload Transport : A Theoretical and Experimental Study.” PhD thesis. Université Grenoble Alpes.
Rousseau, H., Frey, P., and Chauchat, J. (2022). “Experiments on a single large particle segregating in bedload transport”. Physical Review Fluids, 7(6), p. 064305.

How to cite: Dedieu, B., Frey, P., and Chauchat, J.: Experimental investigation of the segregation of a large intruder in bedload sediment transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8385, https://doi.org/10.5194/egusphere-egu23-8385, 2023.

Granular material is nearly ubiquitous in nature.  Some examples include sand, soil, snow, rocks; even the interactions of ice burgs and floes can reasonably be considered as large-scale particle interactions.  It is well accepted that continuum-scale behaviour of a granular body is determined by the grain-scale interactions of its constituent particles, but there is still much to learn regarding those grain-scale interactions and their relationship with continuum-scale inputs.  Vibrating granular beds are a good case study for examining this, since differing flow regions generally form within the bed – depending on both the nature of the vibrations and granular material – and the test conditions can be repeated accurately in a laboratory. 

In this experimental study, various beds of spherical glass beads were subjected to sinusoidal horizontal vibrations of various amplitude and frequency combinations.  The granular beds were framed as quasi two-dimensional: the particles were three-dimensional, contained within a thin transparent tank such that phenomena could only occur in two dimensions.  The tests were designed to provide insight into the grain-scale interactions within granular materials.  That is: how do various load inputs and granular compositions affect general grain-scale response, and in turn, how does this grain-scale response affect the continuum-scale behaviour of the material?

Grain-scale interactions were compared between differing granular beds undergoing equivalent vibrations.  The results are used to discuss how behavioural response of granular material to macro-scale inputs is ultimately tied to the geometric complexity of the internal packing structure and the corresponding network of contact forces that packing structure lends itself to.  The concept of ‘geometric compatibility’ between particles within any granular medium is discussed as an explanation for large behavioural differences between grain-scale, and by extension continuum-scale, responses to vibration – or indeed any mechanical work a granular material is subjected to.

How to cite: Moss, J. and Glovnea, R.: Grain-scale geometry and force networks in general granular materials, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8707, https://doi.org/10.5194/egusphere-egu23-8707, 2023.

Sediment transport in rivers and estuaries is typically monitored infrequently and discontinuously, which is a key reason why sediment budget estimations are often poor. On the contrary, water discharge is often monitored with high accuracy, and continuously, which requires periodic ship measurements for recalibration of rating curves. Even in tidal rivers, continuous flow measurements can be obtained by upscaling transect flow measurements to cover the entire cross-section, which rarely occurs for sediment transport (Kästner et al., 2018). This contribution discusses how existing discharge measurement schemes can be extended to yield continuous measurements of sediment transport, separating between suspended load and bedload sediment fluxes. A new approach is outlined, which relies on repeated cross-river transect measurements, using multiple acoustical and optical instruments. Innovative suspended load measurements make use of acoustic profilers with multiple sound frequencies and a spectrometer, which can measure suspended sediment mean particle size and carbon content from light absorbance (Sehgal et al., 2022). Inference of bedload transport from bedform tracking improves when taking secondary bedforms into account, which can migrate fast and persist in the lee of primary dunes, contributing significantly to the total bedload transport (Zomer et al., 2021). For sand-bed rivers in particular, a generic approach to upgrade existing discharge monitoring programmes to include continuous sediment transport may be feasible with limited additional ship survey time.

Kästner, K., Hoitink, A. J. F., Torfs, P. J. J. F., Vermeulen, B., Ningsih, N. S., & Pramulya, M. (2018). Prerequisites for accurate monitoring of river discharge based on fixed‐location velocity measurements. Water resources research, 54(2), 1058-1076.

Sehgal, D., Martínez‐Carreras, N., Hissler, C., Bense, V. F., & Hoitink, A. J. F. (2022). Inferring suspended sediment carbon content and particle size at high frequency from the optical response of a submerged spectrometer. Water Resources Research, 58(5), e2021WR030624.

Zomer, J. Y., Naqshband, S., Vermeulen, B., & Hoitink, A. J. F. (2021). Rapidly migrating secondary bedforms can persist on the lee of slowly migrating primary river dunes. Journal of Geophysical Research: Earth Surface, 126(3), e2020JF005918.

How to cite: Hoitink, T. (A. J. F. ).: Quantifying sediment transport from periodic transect measurements in rivers and estuaries, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9236, https://doi.org/10.5194/egusphere-egu23-9236, 2023.

During calm cooling periods, differential cooling can induce winter cascading which is an important process for littoral-pelagic exchange and deep water renewal in large, deep lakes (Fer et al., 2001; Peeters et al., 2003). Generated in the shallow near-shore regions, such cold-water density currents travel down the sloping lakebed until they reach their depth of neutral buoyancy. The latter is strongly dependent on the entrainment of warmer ambient water, often expressed by the entrainment coefficient (i.e., the ratio of the entrainment velocity to the bulk velocity of the density current, e.g., Legg, 2012). Fer et al. (2001, 2002) studied density currents in Lake Geneva and showed that they occur in the form of cold-water pulses that last 1-2 hours, with a typical thickness of 10 m, a mean velocity of ~5 cm s^-1 and an entrainment coefficient of ~0.03.

With recent advances in instrument capabilities, our recent investigations in Lake Geneva reveal also the presence of shorter, but still strong, temperature fluctuations of O(10) min in those density currents. To investigate further the mechanisms of entrainment in cascading flows, we designed a turbulence platform that was deployed on the sloping bed of Lake Geneva at 25-m depth. The platform is equipped with (high frequency) temperature and current velocity sensors which collect data over 3 meters vertically. A connection to the shore via a cable laid on the lakebed enables to control the platform’s vertical position and ensures continuous long-term measurements at high frequency. The background variables, such as velocity and temperature profiles, characterizing the nearshore zone in the surrounding of the platform are measured continuously using lower resolution sensors.

Here, we briefly expose the design of the platform, present a case of cascading flow and give small-scale hydrodynamic details of eddies that are observed intermittently within the density currents. Indeed, instantaneous unstable profiles (warm water intruding below cold water) within the dense cold flow show the presence of large eddies with spatial scales similar to the thickness of the mean current. The preliminary results shed light on the mechanism of warm ambient water entrainment into the cold-water density current. The high intermittency of occurrence of large eddies, i.e., those that contribute the most to entrainment, contrasts with the classic concept of a bulk entrainment coefficient.

Fer, I., Lemmin, U., & Thorpe, S. A. (2001). Cascading of water down the sloping sides of a deep lake in winter. Geophysical Research Letters, 28(10), 2093–2096. https://doi.org/10.1029/2000GL012599

Fer, I., Lemmin, U., & Thorpe, S. A. (2002). Winter cascading of cold water in Lake Geneva. Journal of Geophysical Research: Oceans, 107(C6), 13-1-13–16. https://doi.org/10.1029/2001JC000828

Legg, S. (2012). Overflows and convectively driven flows. In E. Chassignet, C. Cenedese, & J. Verron (Eds.), Buoyancy-Driven Flows (pp. 203-239). Cambridge: Cambridge University Press. doi:10.1017/CBO9780511920196.006

Peeters, F., Finger, D., Hofer, M., Brennwald, M., Livingstone, D. M., & Kipfer, R. (2003). Deep-water renewal in Lake Issyk-Kul driven by differential cooling. Limnology and Oceanography, 48(4), 1419–1431. https://doi.org/10.4319/lo.2003.48.4.1419

How to cite: Mettra, F., Reiss, R. S., Lemmin, U., Kindschi, V., Graf, B., and Barry, D. A.: A moored profiling platform to study turbulent mixing in density currents in a large lake, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9662, https://doi.org/10.5194/egusphere-egu23-9662, 2023.

Predictions of bed load sediment flux are notoriously imprecise despite widespread occurrence and importance in contexts ranging from river restoration to planetary exploration. Natural variations in grain size, shape and density are possible sources of inaccuracy in sediment transport, as well as mixtures of different grain sizesand time-dependent bed structure. While many of these effects have been studied in depth, the effects of grain shape have rarely been quantified, even though shape has long been hypothesized to influence sediment transport.

During bed load transport, the granular bed is sheared by the flow passing over it. Aspherical grains and rough surfaces generally increase the resistance to such shearing, enhancing frictional resistance, and reducing the efficiency of bed load transport. However, aspherical grains also experience higher fluid drag force than spherical grains of the same volume, enhancing transport efficiency under the same flow conditions. These two competing effects generally get stronger as grain shape deviates from spherical, making it challenging to predict the net effect of grain shape on sediment transport. We disentangle these competing effects by formulating a theory that accounts for the influence of grain shape on both fluid-grain and grain-grain interactions. It predicts that the onset and efficiency of transport depend on the average coefficients of drag and bulk friction of the transported grains. Because we use the average statistics of drag and friction to characterize the effect of grain shape, our approach is also applicable to materials like natural gravel that have many different shapes in the same sample.

Using a series of flume experiments with different granular materials of distinct shapes, we show that grain shape can modify bed load transport rates by an amount comparable to the scatter in many sediment transport data sets. Our data also demonstrates that, although bed load transport of aspherical grains is generally inhibited by higher bulk friction and enhanced by higher fluid drag, these two effects do not simply cancel each other. This means that the effect of grain shape on sediment transport can be difficult to intuit from the appearance of grains, with the possibility for grain shape changes to lead to either a reduction or an enhancement of sediment transport efficiency.

How to cite: Deal, E., Venditti, J., Benavides, S., Bradley, R., Zhang, Q., Kamrin, K., and Perron, T.: Grain shape effects in bed load sediment transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12076, https://doi.org/10.5194/egusphere-egu23-12076, 2023.

Deltas represent transfer zones where sediment is moved from terrestrial to the subaquatic domains. They are depositional areas and a source for sediments simultaneously. One of the aspects in this highly dynamic environment that has experienced so far little attention are slope failures in deltas. Such failures are, however, mentioned as potential cause for large (up to m-scale), graded deposits in the sedimentary record, often referred to as megaturbidites or homogenites. In some cases, they may have generated tsunamis in the near-shore area. These delta failures can be triggered, amongst other causes, by spontaneous slope collapses (e.g. Muota delta 1687 in Lake Lucerne, Switzerland). To better understand the controlling factors of slope stability in deltas, we need to comprehend the interplay between deltaic deposition and erosion through time and monitor their evolution.

Repeated bathymetric mapping has been used as powerful tool to better understand the short-term processes occurring in deltas. In this contribution, repeated bathymetric mapping is used to better characterize, which short-term processes may shape subaqueous delta fronts. Using the dataset acquired in recent years in Swiss lakes, we seek to answer (1) what processes can be visualized based on repeated bathymetric mapping?; (2) which areas are prone to depositional/erosion processes?; and (3) what type of delta is more prone to slope failures? We present the first datasets of differential maps from four deltas in Switzerland that show different processes of erosion and deposition on short and long time scales. In addition, we will present the design of a planned multi-method monitoring campaign for delta processes in a sublacustrine delta in a peri-alpine lake in Switzerland. 

How to cite: Kremer, K., Fabbri, S. C., Vendettuoli, D., Affentranger, C., Girardclos, S., and Anselmetti, F. S.: Monitoring sediment processes in different delta systems in Swiss peri-alpine lakes through 4D bathymetric mapping, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12918, https://doi.org/10.5194/egusphere-egu23-12918, 2023.

There is now a clear consensus that climate change will lead to an increase in the frequency and intensity of extreme rainfall events in many parts of the world, which, in turn, will lead to increased flood flows and thus flooding of large areas. Numerical simulation is one way to improve our understanding of flooding processes, especially through Global Flood Modelling (GFM). Current GFMs represent the morphology of river channels and floodplains in a very simplified way. In particular, GFM assumes that the channel morphology remains unchanged over time. However, rivers are dynamic, their morphology evolves by erosion and deposition of sediments carried by the flow. These morphological changes can radically alter the conveyance capacity of the channel and therefore the flood risk. Integrate these morphological changes in the new GFM framework is one of the main objectives of the NERC-funded EVOFLOOD project. 

Here we present the results of the experimental part of the project. We designed a controlled laboratory experiment to identify the factors controlling the morphodynamic response within river channel. In this experiment, we generate a succession of flood events characterised by different magnitudes and durations, and we quantify the evolution of the flooded area and channel width as a function of the duration, intensity and flood history. 
We find that the main parameters controlling morphological changes are flood intensity and flood history. The duration of the flood does not have a significant impact on the morphological changes because the main changes occur during the first period of the flood event. Finally, we show the importance of the upstream sediment discharge on the modification of the conveyance capacity.

How to cite: Delorme, P., McLelland, S., Murphy, B., and Parsons, D. and the EvoFlood Team: Experimental evidences of the influence of flood magnitude and duration on the morphological evolution of a river: Initial results from the EVOFLOOD project, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14185, https://doi.org/10.5194/egusphere-egu23-14185, 2023.

At present, SSC fluxes in rivers are typically estimated by multiplying the river discharge with the
average suspended sediment concentration (SSC). The latter is typically obtained from optical turbidity
measurements in one single point of the river cross‐section. The optical turbidity is converted in
average SSC based on a relation that is derived from the laboratory analysis of regular SSC samples.
This method has the disadvantages that it is based on a one‐point measurement and that it is
expensive.

The SSC distribution in an entire profile – vertical or horizontal – can also be derived from the
backscatter of single‐frequency echosounders. The disadvantage of this method is that the particle size
of the suspended sediment needs to be known in order to convert the profile of backscatter into a
profile of SSC.

Here we present a hydro‐acoustic method based on multi‐frequency echosounding. Operating on
multiple acoustic frequencies allows estimating the mean particle size directly from the backscatter at
the different frequencies. The method based on multi‐frequency echosounding is illustrated with
measurements on the Rhône River just upstream of Lake Geneva in Switzerland. The results are
compared to measurements based on optical turbidity measurements and to measurements based on
single‐frequency echosounding.

How to cite: Höllrigl, J., Blanckaert, K., Hurther, D., Fromant, G., and Storck, F. R.: Measurements of sediment flux in rivers with a multi-frequency echosounder, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14356, https://doi.org/10.5194/egusphere-egu23-14356, 2023.

A centrifuge model test platform was designed and developed to verify the critical continuous rainfalls triggering shallow landslides in natural slopes. Based on literature reviews, in-situ dimensions of shallow landslides on natural slopes were determined to 40 m (Length) × 16 m (Width) × 2 m (Depth) on average. In consequence, considering the model mounting space of the centrifuge test facility, a gravity level was decided (N = 40g) so that the length of a model slope equals 1 m according to scaling law. The width and depth of the model slope were hence determined to 0.4 m and 0.05 m, respectively. On the other hand, a rainfall simulator comprised of a series of air-atomizing spray nozzles was designed and developed considering scaling laws of rainfall infiltration and subsurface water flows. As a simulation result in a 40g condition, rainfall dispersions reduced and its trajectory bending induced by Coriolis’ force was almost vanished. After the development of centrifuge model test platform, several 1g performance tests of the rainfall simulator were conducted to test the spatial uniformity of rainfall distributions and fit the conditions of applying water and air pressures to rainfall intensities. The study also presents preliminary test results of shallow landslides in a 1g condition conducted to find and solve errors and unexpected problems before mounting the platform to the centrifuge test facility.

How to cite: Park, J.-Y., Cheon, E., Lee, S.-R., Choo, J., Lim, H., and Nam, Y.: Centrifuge model test platform for rainfall simulation triggering shallow landslides, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15044, https://doi.org/10.5194/egusphere-egu23-15044, 2023.

Impulse waves are waves generated by subaerial landlsides impacting the free surface of a lake or a sea. These waves differs from earthquake tsunami, even if often associated, as the generation mechanism and the scale of influence are not the same. Although they can travel over much shorter distance than other tsunamis, waves generated by landslides can be locally more dangerous [1]. Consequently, predicting the wave amplitude, and particularly its maximum during the generation remain crucial. Even if several studies have been devoted to the prediction of the wave amplitude at the laboratory scale, the mechanisms involved during the generation and particularly the role of the granular material to mimic landslide are still poorly understood [2, 3]. In this context, the presented study aims to better understand the interaction between the landslide and the generated waves, by understanding the physical mechanisms at the origin of the deformation of the free surface and the dry-wet transition of the granular flow. A laboratory model is used consisting of a 2m long chute of varying slope angle ending in a 4m long water tank. More specifically, the landslide is modelled by a monodisperse granular flow of 1mm spherical glass beads.
A picture of the experiment is represented in Figure 1a. The dynamic of the slide when crossing the air/water interface as well as the spatio-temporal structure of the wave are caracterised as a function of the properties of the impacting granular flow. Figure 1b shows the spatial and temporal evolution of the water free surface elevation during the wave generation process. This figure also highlights that the wave crest is stronlgy correlated to the granular front at early stages, while freely propagates in the far field. Based on physical mecanisms during generation, this study allows to discuss existing models relating the maximum wave amplitude to a so-called impulse parameter [4].