Content:

GM – Geomorphology

GM1.1 – Geomorphology Frontiers: Earth Surface Dynamics in an era of extremes

EGU2020-4726 | Displays | GM1.1 | Highlight | GM Division Outstanding ECS Lecture

Sliding, flowing, rocking and rolling: Sediment and hazard cascades through mountain landscapes

Georgina Bennett

Mountain landscapes are beautiful, yet hazardous, and vulnerable to climate change and population growth. Not only is the study of these landscapes geomorphically captivating, but it is increasingly relevant to society. Three Grand Challenges in the study of processes, landscapes and hazards in mountain regions are (1) Understanding and predicting the response of earth surface processes to climate (2) Monitoring and early warning of extreme events such as landslides and floods and (3) Accounting for connectivity and feedbacks between hillslopes and channels in landscape evolution and hazards. We need a suite of tools and approaches to address these challenges. Harnessing the growing archive of satellite and aerial photography helps us to study landscape dynamics and response to drivers such as climate over large regions. Innovative sensor technology is needed to understand landscape dynamics at a finer scale and to develop real time warning of extreme events. Finally, we need conceptual models that capture the essence of landscape dynamics and help to forecast hazards as they slide, flow, rock and roll through the landscape.

How to cite: Bennett, G.: Sliding, flowing, rocking and rolling: Sediment and hazard cascades through mountain landscapes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4726, https://doi.org/10.5194/egusphere-egu2020-4726, 2020.

The Anthropocene is widely described as producing a rupture in the global stratigraphic signature, attributable to human activities. There is no doubt that human activities have introduced new products into the stratigraphic record; and that humans are modifying the geomorphic processes that produce the sediment which then becomes incorporated into that record. The stratigraphic literature is replete with simplistic generalisations of how sediment flux to the continental shelf is changing, such as increasing due to soil erosion or decreasing due to hydropower related sediment flux disconnection. Here we argue that human impacts on geomorphic processes in the Anthropocene are unlikely to be stationary for long enough for them to be seen consistently across the depositional record of many different environments. Illustrating this for a major inner-Alpine drainage basin, the Swiss Rhône, we show that human-driven global climate-change is indeed dramatically altering the geomorphic process regimes of Alpine environments. However, there are three broad reasons why this is unlikely to be seen in the future geological record. First, the geomorphic response that drives increased sediment delivery is transient because of the significant regime changes associated with global climate change impacts. Second, such increases are countered by other human impacts, notably those on sediment flux, which are tending to reduce the connectivity of sediment sources to downstream sediment sinks. Third, human impacts on both sediment sources and connectivity are nonstationary, driven by both exogenous factors (here illustrated by the worldwide economic shock of 2008) and endogenous ones, notably human response to the perceived problems caused by both sediment starvation and sediment over-supply. In geomorphic terms, then, there is a difference between the pervasive nature of Earth system shifts that we see in the pre-Holocene depositional record and the more ephemeral impacts of the Earth system – human coupling associated with the Anthropocene. The extent to which this is the case is likely to vary geographically and temporally as a function of the degree and nature of human impacts on geomorphic processes. Thus, the primary challenge for future prediction will be as much the prediction of the complex and reflexive nature of human response as it will be geomorphic processes themselves.

How to cite: Lane, S.: Will human impacts on Alpine geomorphic processes scale up to the depositional record?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13018, https://doi.org/10.5194/egusphere-egu2020-13018, 2020.

EGU2020-20334 | Displays | GM1.1

Re-imagining urban coasts: a socio-geomorphology lens to enhance life in an era of extremes

Larissa Naylor, Jim Hansom, Douglas Mitchell, James Fitton, Freya Muir, Martin Hurst, and Alastair Rennie

Geomorphology has much to contribute to the understanding of how geomorphic landscapes have responded to climatological extremes and will likely respond in the future. These contributions can be in terms of systems dynamics and their past, present and likely future responses to sudden events, tipping points or more gradual changes to natural landforms and anthropogenic structures. However, equally importantly, geomorphic contributions also include making proactive resilience and climate change adaptation decisions in order to create physical space for geomorphic systems to respond more naturally and dynamically to extremes – now or in the near (100 year) future. The choices society makes in the present – such as planning, infrastructure and engineering decisions – have a strong bearing on the physical space left to allow natural landforms to adjust to extreme events while minimizing social and economic impacts. This creates a new frontier for geomorphology science at the social, political and policy interface.  Interesting questions arise in this space, such as: How much do we expect a geomorphic system to respond dynamically to extreme forcing? i.e. How much physical space do we [planners] need for the system to respond to an extreme event? Should society see storms as catalysts for proactive adaptation? How much (physical space, i.e. geomorphic accommodation space) can we allow when realigning road or rail inland to reduce risk in future storm events? How do complex physical geomorphic systems interact with complex urban systems? Can we work with artists, landscape architects, geo-spatial, urban and social scientists to create transformative, systems-based adaptation scenarios to allow us to better live in an era of extremes? Geomorphologists are usefully contributing to improving the resilience and/or limiting deterioration or habitat loss (e.g. habitat squeeze due to sea level rise) in urban ecosystems and anthropogenic structures.  This includes geomorphic contributions to nature-based solutions, green infrastructure and the resilience of traditional engineering to extreme events.  This paper highlights some of the opportunities we have to influence and shape our future resilience to extreme events – in the present day – through interdisciplinary research and socio-geomorphology practice. We need to create windows of opportunity now for more dynamic and resilient geomorphic futures.  

How to cite: Naylor, L., Hansom, J., Mitchell, D., Fitton, J., Muir, F., Hurst, M., and Rennie, A.: Re-imagining urban coasts: a socio-geomorphology lens to enhance life in an era of extremes , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20334, https://doi.org/10.5194/egusphere-egu2020-20334, 2020.

EGU2020-11772 | Displays | GM1.1

Gradual and Abrupt Permafrost Thaw as Drivers of Rapid Geomorphic Change in Arctic Permafrost Regions

Guido Grosse, Julia Boike, Louise Farquharson, Benjamin M. Jones, Moritz Langer, Hugues Lantuit, Anna Liljedahl, Ingmar Nitze, Alexandra Runge, Vladimir E. Romanovsky, Thomas Schneider von Deimling, Warwick F. Vincent, and Donald A. (Skip) Walker

In this presentation, we will highlight some of the overarching geomorphic dynamics of gradual and abrupt permafrost thaw using examples from Siberia, Alaska, and Canada, their role in Arctic landscapes transitioning to a warmer world, and implications for the Earth System. Northern high latitude regions are particularly vulnerable to warming and changes in climatic patterns, which leads to the thaw of ice-rich permafrost across vast Arctic and sub-Arctic landscapes. Permafrost thaw and subsequent geomorphological change directly interact with hydrology, biogeochemistry, and biology and thus have been major agents of Arctic ecosystem change since the last deglaciation. The changes are also important contributors to cumulative impacts associated with historic and current development of the Arctic, including in association with infrastructure. Today, in a rapidly warming Arctic, permafrost thaw processes, both gradual and abrupt, are accelerating in a manner comparable to the Holocene Thermal Maximum. At the same time, other environmental forcing factors, such as wildfires, precipitation, and hydrological processes, are also changing, either further reinforcing thaw dynamics or enhancing drainage and stabilizing the ground. Many of the resulting gradual and abrupt thaw processes are non-linear. Their dynamics are still poorly understood and insufficiently quantified in large-scale models due to lacking or limited representation of water-ice phase transitions during freeze-thaw cycles, ground ice distribution and loss, and challenging implementation of sub-gridcell scale interactions between frozen ground and hydrology. Gradual thaw impacts are especially pronounced in regions with an abundance of ice wedge polygons, and include changes in microtopography and extensive ponding in natural landscapes and those adjacent to infrastructure, where soils are warmed due to increased dust, flooding, snowdrifts, and altered vegetation. Abrupt thaw processes such as thermokarst and thermo-erosion represent rapid dynamics that are widespread in Arctic lowlands but poorly represented in observations and models. Characteristic landforms that result from abrupt thaw include thermokarst lakes and basins, retrogressive thaw slumps, and steep coastal bluffs. These landscape changes may be triggered by climate-driven press disturbances such as sea ice loss or increases in precipitation, pulse disturbances such as wildfires, or by anthropogenic disturbances such as road construction. When loss of excess ground ice is involved, positive feedbacks can result in a decoupling of further geomorphological change from climate. Once initiated, this may lead to continued or even accelerated growth of such features under a wide range of climate conditions, including in the high Arctic. Most abrupt thaw processes produce lasting impacts on northern permafrost landscapes that are irreversible over millennial timescales and result in the short-term mobilization of large amounts of permafrost carbon that may further contribute to climate warming.

How to cite: Grosse, G., Boike, J., Farquharson, L., Jones, B. M., Langer, M., Lantuit, H., Liljedahl, A., Nitze, I., Runge, A., Romanovsky, V. E., Schneider von Deimling, T., Vincent, W. F., and Walker, D. A. (.: Gradual and Abrupt Permafrost Thaw as Drivers of Rapid Geomorphic Change in Arctic Permafrost Regions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11772, https://doi.org/10.5194/egusphere-egu2020-11772, 2020.

Global climate change is driving rapid changes in polar region, and significant attention has been given to predicting changes in precipitation and hydrology. However, warming will also alter sediment dynamics and drive morphological change as the melting of river and ground ice will mobilise floodplain and river channel sediments. The transport of this additional sediment can have a number of direct and indirect impacts on societies and ecosystems with yet unpredictable magnitude. There is a significant knowledge gap concerning how material is transported seasonally across such zones, and how the frozen season at present and its possible future changes affect the hydro- and morphodynamics of these northern rivers.

Therefore, it is needed 1: To determine the impacts of varying river ice processes on seasonal hydrodynamics, sediment transport, and flood hazards in the high north; 2: To define the seasonal interlinkages and combined effects of sub-aerial (e.g., freeze-thaw, mass movements) and fluvial processes (e.g., ice-covered/open-channel flow) on morphodynamics, sediment transport and its origin in these seasonally ice-covered river systems. 3: To upscale reach scale seasonally-driven river morphodynamics to the watershed scale and simulate changes into the future, whilst defining the feedbacks between defrosting watersheds and total sediment load transported to the oceans.

This work is yet to be done, however, preliminary results are presented based on gathered pilot data and studies. Recent results have revealed that river ice can have the most significant role, greater than that of flowing water, in erosion and transport of coarse sediment from a sub-arctic river channel bed and its gently sloping banks. In addition, the findings from sandy meandering river suggest that certain ice cover conditions cause the vertical and lateral flow distribution to be opposite to the open channel situation. Thus, future changed river ice cover characteristics are expected to change these transport mechanisms and velocity distribution. This emphasizes that future predictions of river ice are needed, before predicting the changes in river morphology. However, it has been recently shown that thermal ice growth equation is not expected to work in the polar region in the future, as there is expected to be less snow and a higher number of freeze-thaw days in the future. In addition, adjustments to the ice decay equation and the applied parameter values would be needed for predicting ice decay processes in future. Under fast climatic warming of the arctic and subarctic, the shortening frozen period may also induce an earlier and prolonged season of bank erosion in meandering rivers, which further complicates the predictions of river morphodynamics. Thus, the use of improved hydro- and morphodynamic models and high-accuracy spatial and temporal data for better calibrating these models, are essential for detecting seasonally varying feedback effects of different interacting processes on river hydro-morphodynamics at present and in the future.

How to cite: Lotsari, E.: Impacts of frozen season and its possible future changes on the hydro- and morphodynamics of northern rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5719, https://doi.org/10.5194/egusphere-egu2020-5719, 2020.

Climate change is expected to alter fire regimes but also rainfall patterns. Fire is a natural process that removes vegetation and may affect soil properties, resulting in changes in overland flow and streamflow generation. Some fires cause erosion and may even cause destructive debris flow and other events, which can not only threaten lives and property but also leave lasting imprints in landscapes. The geomorphological response after fire events is a complex function of pre-fire landscape and vegetation properties, fire behavior and effects, and post-fire rainfall timing, duration and intensity. In this talk, I highlight these processes using examples of past events, and explore geomorphological response to fires in a future where both fire and rainfall may be be rather different.

 

How to cite: Stoof, C.: Fire effects on geomorphology: what can we expect with climate change?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18260, https://doi.org/10.5194/egusphere-egu2020-18260, 2020.

GM2.1 – Advances in geomorphometry and landform mapping: possibilities, challenges and perspectives

Science progresses when we are afforded with a ‘better look’ at nature. For geomorphology, the production over the last 100 years of an ever-increasingly resolved view of landscapes with topographic maps, DEMs, remote-sensing images, etc. has always been accompanied by new geomorphologic discoveries. LiDAR images of formerly glaciated landscapes reveal glacial landforms in extraordinary detail, showing previously mapped landforms in exquisite new detail (for example, end moraines, drumlins, eskers, ice-walled-lake plains etc.). Particularly important are a range of ‘mesoscale’ landforms that are better seen with LiDAR: De Geer moraines, crag-and-tail ridges, low-relief lineations, post-glacial faults, glacial hummocks, and raised shorelines to name a few. A spate of research has come out recently on such features. LiDAR images also have the potential of revealing landforms new to glacier science, of which ‘murtoos’ are an example. But LiDAR also raises the challenge of geomorphic classification. For example, glacial hummocks and glacial hummocky topography are a mesoscale landform that is known for its high variability. This variability, made more dramatic with new LiDAR images, along with the polygenetic origin of landforms called ‘hummocks’ reveals a weakness in our terminology that needs to be acknowledged and dealt with.

How to cite: Johnson, M.: The LiDAR revolution in glacial geomorphology: its gifts and challenges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7953, https://doi.org/10.5194/egusphere-egu2020-7953, 2020.

EGU2020-2985 | Displays | GM2.1

Tectonics from topography : insights from high-resolution hillslope morphology analysis

Vincent Godard, Jean-Claude Hippolyte, Edward Cushing, Nicolas Espurt, Jules Fleury, Olivier Bellier, Vincent Ollivier, and Aster Team

The spatial distribution of tectonic uplift is often investigated using river profiles, as fluvial gradient is predicted to be strongly dependent on rock uplift. A similar response is expected from hillslope morphology which is also dependent on the relative base-level lowering rate. However, the reduced sensitivity of near-threshold hillslopes and the limited availability of high resolution topographic data has often been a major limitation for their use to investigate the distribution of tectonic activity.

Here we combined high-resolution analysis of hillslope morphology and cosmogenic nuclide-derived denudation rates to constrain the distribution of rock uplift across a thrust system at the Southwestern Alpine front in France. Our study is located in the Valensole Mio-Pliocene basin, where a series of folds and thrusts has deformed a plateau surface. Using a 1-m LiDAR Digital Terrain Model, we analyzed the morphology of hillslopes and extracted proxies for the relative spatial variations in denudation such as hilltop curvature (CHT) and non-dimensional erosion rates (E*). We observed systematic variation of these metrics coincident with the location of a major underlying thrust system identified by seismic surveys. Using a simple deformation model, the inversion of the E* pattern allows us to constrain the geometry of a blind thrust, which is consistent with available geological and geophysical data.

We also sampled clasts from eroding conglomerate at several hilltop locations for 10Be and 26Al concentration measurements. Calculated hilltop denudation rates range from 40 to 120 mm/ka. These denudation rates appear to be correlated with E* and CHT extracted from the morphological analysis, and are used to derive absolute estimates for the fault slip rate. This high resolution hillslope analysis allows us to resolve short wavelength variations in rock uplift that would not be possible to unravel using commonly used channel profile-based methods.

How to cite: Godard, V., Hippolyte, J.-C., Cushing, E., Espurt, N., Fleury, J., Bellier, O., Ollivier, V., and Team, A.: Tectonics from topography : insights from high-resolution hillslope morphology analysis , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2985, https://doi.org/10.5194/egusphere-egu2020-2985, 2020.

EGU2020-503 | Displays | GM2.1

Importance of concavity for interpreting rates and patterns of landscape evolution from river profiles

Boris Gailleton, Simon Mudd, Fiona Clubb, Martin Hurst, and Stuart Grieve

The analysis of river profiles is a fundamental tool in modern quantitative geomorphology. Since the 1960's, workers have demonstrated a systematic power-law relationship between river gradient and discharge, or its proxy drainage area, predicting a steepening of rivers towards the headwaters. This relationship provides means of quantitatively describing river profiles by extracting a concavity index (θ), the rate at which slope decreases as a function of drainage area, and steepness index (ks), the steepness of river reaches independent of changes in drainage area. Recent developments have provided an alternative representation of the slope-area relationship, aiming to circumvent its high sensitivity to topographic noise and to the branching nature of fluvial networks by directly integrating drainage area normalised to a concavity index into a transformed coordinate (χ). These parameters can be easily extracted from digital elevation models, resulting in their widespread application to detect tectonic, climatic, and autogenic signals from landscape morphology, such as active faulting, stream piracy, drainage divide migration or sea-level changes.

River profile concavity, or θ, is an essential metric to constrain, as it is necessary to fix a reference value θref in order to compare χ or ks values between different drainage basins. This exposes a key problem with the slope-area relationship: the watersheds within a study area do not necessarily all have the same optimal θ, potentially leading to incorrect interpretations of the relative distribution of χ and ks within a landscape. This problem is enhanced over large spatial scales, such as over the width of an orogen, where the probability of θ heterogeneity increases drastically. However, the distortion of χ and ks linked to a θref being different than the local best-fit has been poorly explored: we currently do not know how much these concavity variations influence channel steepness interpretations.

In this contribution, we explore the extent of the effect of varying concavity on channel steepness using analytical and numerical methods both on landscape evolution models and real landscapes. We show that (i) relative values of χ and ks, i.e location of local maxima, minima and variations, can be significantly and non-linearly impacted as a function of their Δθ from optimal θ and drainage area; (ii) we identify cases where asymmetries in θ can cause incorrect interpretations of changes in channel steepness (iii) present tools to quantify the extent and therefore the risk of misinterpretation.

How to cite: Gailleton, B., Mudd, S., Clubb, F., Hurst, M., and Grieve, S.: Importance of concavity for interpreting rates and patterns of landscape evolution from river profiles, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-503, https://doi.org/10.5194/egusphere-egu2020-503, 2020.

Digital elevation models (DEM) are mathematical representations of the Earth's bare surface in computer-readable format. The underlying measurements are often obtained by remote sensing and photogrammetry methods and processed into continuous raster data. Each of these data sources, however, provides imperfect information, and further processing steps often increase the degree of imperfection. Consequently, the process of DEM generation cumulates in uncertainty, which affects subsequent hydro- and geomorphological analyses and modelling (e.g., stream network delineation, flowpath distribution, erosion modelling).

In many DEM-based studies, however, the aspect of uncertainty related to the DEM data source has been neglected. Therefore, we propose a new approach for quantifying the effects of DEM uncertainty on hydro-geomorphological modelling based on Gaussian white noise, a concept widely used in signal processing to map noise in signals and extract the actual message context. The basic idea is to add noise to the original DEM values by means of a Gaussian distribution whose parameters are determined from the mean value of the elevation values in a moving window and the device-specific properties (precision and accuracy).

We postulate that such an approach can be used to determine uncertainties and their effect on subsequent analysis steps of hydro-geomorphological modelling. It is conceivable to create DEM ensembles depending on known parameters such as the accuracy and precision of the measuring instrument, as is used operationally in weather forecasting. Using such ensembles, probability ranges for terrain and catchment hydro-geomorphological properties can be determined and uncertainty ranges can be specified. Thus, the currently mostly deterministic approach of digital terrain modelling will be replaced by a more probabilistic understanding. Overall, our approach will help decision-makers and scientists to better assess the results of digital terrain analysis. Furthermore, it will also facilitate determining whether a result of DEM-based hydro-geomorphological analysis is sufficiently certain to answer specific research questions.

How to cite: Graf, L., Moreno-de-las-Heras, M., and Estrany, J.: Assessing the Impact of Uncertainties of Digital Elevation Models on Hydro-Geomorphological Analysis Using Gaussian White Noise, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1347, https://doi.org/10.5194/egusphere-egu2020-1347, 2020.

EGU2020-2079 | Displays | GM2.1

Interaction and Reorganization of Loess Gully Network Evolution

Siming Chen and Liyang Xiong

Loess gully is the most active and changeable landform unit in the Loess Plateau of China, whose morphology has been shaped under various formation processes. During the evolution process, gullies in the Loess Plateau interacted with each other and formed an intricate network system, which was the channel for material transportation and energy transmission in this area. From the perspective of the gully evolution process, the development of gully network is dynamic because such a network gradually tends to equilibrium through continuous reorganization. During the evolutionary process, stream capture occurs when a stream or watershed is diverted from its own bed, and flows instead down the bed of a neighboring stream. The stronger and more powerful streams (in terms of channel gradient, stream velocity, discharge and kinetic energy) capture the upstream of weak streams. In the process of dynamic reorganization, the loess gullies formed different shapes and gradually evolved into a stable network structure. In this paper, several gully areas in the Loess Plateau were selected. Based on the geological background, 5 m horizontal-resolution DEM data were used to analyze these areas. The χ index was used to describe the dynamic characteristics of the gully network, which could characterize the evolution trend of the gully. Finally, the author reveals the evolution and reorganization process of the loess gully networks by comparing the χ index diagrams of different areas in different developmental stages. The results show that the area with the stable geological background is closer to the equilibrium state than the area with the complicated geological structure. In other regions, networks composed of gullies in the middle development stage are more stable than networks in the early development stage. More importantly, for two adjacent mature gully networks, the developmental trends at different locations on their watershed boundaries may be different. The results provide for an understanding of gully network evolution and reorganization process in the Loess Plateau, which also contribute to the development of a process-based gully evolution model.

Key words: Loess Plateau ; Gully Network ; Geomorphologic Evolution ; Digital Terrain Analysis

How to cite: Chen, S. and Xiong, L.: Interaction and Reorganization of Loess Gully Network Evolution, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2079, https://doi.org/10.5194/egusphere-egu2020-2079, 2020.

EGU2020-3015 | Displays | GM2.1

River profiles from digital elevation models – limitations and new ideas

Stefan Hergarten and Jörg Robl

Longitudinal river profiles have been a central if not even the most important subject in tectonic geomorphology since the 1950s. During the last decades, considerable progress has been made in unraveling the tectonic history from river profiles. Going along with the rapidly increasing availability of DEMs, however, scientists try to derive more and more information from the topography. So the quality of the DEM is still a limiting factor in many studies. In particular, local channel slopes are strongly affected by the DEM. Several approaches have been proposed in order to reduce the errors and to distinguish specific features such as knickpoints from noise of the DEM.

In this study we use DEMs with a mesh width of 1 m obtained from airborne laser scans and reduce their resolution artificially in order to analyze the effect of the mesh width on the accuracy of river profiles systematically. Based on the results, we present an idea how the errors in channel slope could be reduced with focus on narrow valleys. Going beyond the majority of the previously published approaches, our idea does not only take into account the elevation along the river profile, but also the curvature of the topography in direction normal to the valley floor.

 

How to cite: Hergarten, S. and Robl, J.: River profiles from digital elevation models – limitations and new ideas, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3015, https://doi.org/10.5194/egusphere-egu2020-3015, 2020.

EGU2020-4068 | Displays | GM2.1

3D Mapping of Rock Formations from Oblique and Nadir Viewing UAV Imagery

Kasper Johansen, Yu-Hsuan Tu, Matteo Ziliani, Bruno Aragon, Yoseline Angel, Bonny Stutsel, Samir Al-Mashharawi, Oliver Lopez, and Matthew McCabe

Detailed information on rock formations and assessment of their geological structures, such as joints, faults, shears and bedding planes, are required for evaluation of rock integrity and stability. Our research demonstrates a comprehensive approach for producing high spatial resolution 3D information of rock formations from unmanned aerial vehicle (UAV) imagery for rock joint identification, and presents an innovative technique for using Terrestrial Laser Scanning (TLS) data to derive ground control points (GCPs) for geo-referencing of UAV imagery of vertical rock walls. UAV imagery was collected from a freestanding 90 m tall rock formation with a 3.5 km perimeter, via oblique rock façade scans and also at-nadir, covering a ground and rock facade area of approximately 0.32 and 0.25 km2, respectively. Seventy-two GCPs were distributed around the rock for geo-referencing of the UAV imagery. As GCPs could not be deployed on vertical rock walls, a TLS system was used for identification of 93 distinct natural features as pseudo-GCPs on the rock walls. Forty scans were collected and geo-referenced from triplets of GCPs placed on the ground near the TLS system for each scan. A Real-Time Kinematic (RTK) Global Navigation Satellite System (GNSS) survey was performed on the GCPs, using a base station and a rover. Continuously Operating Reference Stations (CORS) data were used to fix the position of the base station and improve the absolute geometric position to an average and lowest accuracy of 3.3 and 18.6 mm for 177 GCPs. A total of 44 façade scans, as well as 14 low and 5 high altitude nadir-viewing UAV flights, were undertaken with a Zenmuse X3 RGB camera mounted to a DJI Matrice 100 platform, resulting in a collection of nearly 17,000 photos. The five high altitude flights were designed to include a larger area around the rock to incorporate additional GCPs, while the low altitude flights were to increase the spatial resolution of the imaged rock. Flight planning was undertaken with the Universal Ground Control Station Client application. Façade scans were flown horizontally and parallel to the rock walls at a distance of 20-30 m and at heights between 10-80 m with sidelaps >70% between horizontal flight lines and >80% forward overlap along flight lines. Façade scans were collected with a 4° viewing angle to ensure the base of the rock was included. The Agisoft MetaShape software was initially used to generate a sparse point cloud using all façade scans and nadir-viewing imagery. Geo-referencing of the UAV imagery was based on 136 GCPs, which produced an accuracy of 0.1558 m, with an addition 100 control points kept aside for independent evaluation, yielding an accuracy of 0.2018 m. Subsequent image processing was split into 14 evenly sized “chunks” to enable more efficient processing of a dense point cloud (4.33 billion points) and 3D model (mesh with 129.5 million faces and texture layer) for the entire area. The produced 3D model was found suitable for identification of rock joints larger than 1 m in length.

How to cite: Johansen, K., Tu, Y.-H., Ziliani, M., Aragon, B., Angel, Y., Stutsel, B., Al-Mashharawi, S., Lopez, O., and McCabe, M.: 3D Mapping of Rock Formations from Oblique and Nadir Viewing UAV Imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4068, https://doi.org/10.5194/egusphere-egu2020-4068, 2020.

EGU2020-656 | Displays | GM2.1

Multidisciplinary approach to assess landslide hazards in alpine environment: the geomorphological map of the upper Maira Valley (Western Alps, Italy).

Mauro Bonasera, Alessandro Petroccia, Fabiola Caso, Sara Nerone, and Michele Morelli

The landscape evolution of the U-shaped Maira Valley was mainly led by glacial dynamics during Pleistocene. The Holocene linear fluvial erosion creates higher steepness slopes in a narrow valley in which gravitational phenomena involves buildings and facilities of Acceglio municipality (Piedmont, Italy). A geomorphological survey in an unmapped area of about 12 km2 has been carried out and a new map at scale 1:10000 has been realised. In order to improve the accuracy of fieldwork data, several multidisciplinary techniques have been investigated. The landforms and slope evolution were analysed by using a 5-meters resolution ARPA Digital Elevation Model (DEM) in GIS environment. Discontinuities and geomorphological features were recognized and mapped observing aerial-photos provided by Regione Piemonte. Multi-temporal dataset of orthophotos were useful to examine the river pattern behaviour coupled with interdigitating polygenic fan deposition. The stratigraphic sequence knowledge was achieved using boreholes, inclinometers and piezometers evaluating eventual detrital cover thickness. Detailed field investigations allowed to understand the relationship between structural geology and landslide evolution, in particular concerning several detachment zones characterising the slope overlooking Acceglio town. In the uppermost range of that slope, the fracturation is intense and influences the rock-falls and rock avalanches trigger, whilst debris flows were identified throughout the detected area associated with a homogeneous presence of weathered cover. Widespread accumulation bodies suggest how avalanche and debris flow occurrences have affected Acceglio human activities, testified by historical archives documents as well. In the past, several trial to mitigate these risks were performed through engineering activities which could be refined and implemented with further local analysis on landslide susceptibility. Research on this issue, in addition to having a great scientific interest, can provide essential tools for upper Maira Valley Administrations, being the main available support for an appropriate urban planning.

How to cite: Bonasera, M., Petroccia, A., Caso, F., Nerone, S., and Morelli, M.: Multidisciplinary approach to assess landslide hazards in alpine environment: the geomorphological map of the upper Maira Valley (Western Alps, Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-656, https://doi.org/10.5194/egusphere-egu2020-656, 2020.

EGU2020-5272 | Displays | GM2.1

Geomorphometric characteristics of major badland landscapes of Turkey

Aydogan Avcioglu, Tolga Görüm, Omer Yetemen, and Mariano Moreno de las Heras

Badlands are unique landscapes that are extensively developed on unconsolidated sediments or poorly consolidated bedrocks that are covered by little or no vegetation. They are widely observed landscapes in Turkey similar to arid and semi-arid regions of the world. Turkish badlands are commonly formed on Miocene and Plio-Quaternary deposits, especially in the inner parts of Anatolia. Additionally, these erosional landscapes are also characteristic in the volcanic provinces of Central Anatolia and Eastern Anatolia. Unlike the cognatic badland landscapes in the different arid and semi-arid sections of the world, we have very limited information about the geomorphological characteristics of Turkish badlands.

In this study, we present results from a quantitative analysis of a new inventory of badland areas (~756 km2) at six major badland landscapes in Turkey. Previously partly known but not documented badland geomorphological units were expanded by mapping badland forms from aerial photos and high-resolution multispectral image interpretations focused on the Western and Central Anatolia. The geomorphometric data on badland units, associated structures, and catchment characteristics were extracted from a 5-m Digital Elevation Model (DEM) and compiled in a GIS environment. In total 53 badland geomorphologic units, having a size from 0.15 to 89.2 km2, were analyzed by comparing their topographic dissection, roughness, texture, channel density, slope height and curvature, and lithological variations to characterize their morphology further.

The regional comparison results display statistically significant topographic differences concerning their proportions of morphometric classes. The geomorphometric regional comparisons indicate that the standard deviation and modal values of slope height, topographic dissection, roughness, and curvature vary with a significant fraction in badlands formed in the terrigenous clastic and volcano-sedimentary lithological units. Moreover, the geomorphometric comparison results demonstrate that the skewness of the standard deviation of elevation and hillslope steepness varies in badland landscapes across the semi-arid Western and arid Central Anatolia, and further point out the significance of climatic conditions (i.e., amount of rainfall and evaporation) on geomorphic diversities.  

How to cite: Avcioglu, A., Görüm, T., Yetemen, O., and Moreno de las Heras, M.: Geomorphometric characteristics of major badland landscapes of Turkey, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5272, https://doi.org/10.5194/egusphere-egu2020-5272, 2020.

EGU2020-580 | Displays | GM2.1

Comparative analysis of watershed basins landscape structure in Southwest Asia region based on remote sensing data.

Victoria Milichenkova, Tatiana Trifonova, and Artem Lebedev

In recent years it has become evident that techniques implemented while studying landscape structure of a large geographical area should be comprehensive and consider both endogenous and exogenous factors affecting its formation.

Owing to a specific location in the active zone at the junction between three tectonic plates — the African, the Arabian and the Eurasian - Southwest Asia region, which is subdivided into the Anatolian plateau, the Armenian plateau and the Iranian plateau, was chosen as a target territory. To conduct a further landscape analysis three above-mentioned geographical subregions were segmented into 9 marine basins, with the largest - the Persian Gulf basin, the Caspian sea basin, the Mediterranean sea basin, and the Black sea basin - occupying areas of 1710000, 250000, 330000, 710000 sq.km respectively. In our view, these basins are stated to be isolated macro-geosystems with directed substance and energy flow, where rivers and streams play an essential role in their functioning.

 Thus, according to data obtained from segmentation we can also claim that the target territory is located at the intersection of large watersheds, which is reflected in the basin landscape structure.

Bearing in mind these separate geographical units and taking into account the classification we built up, dominant folded, volcanic and depressive morphostructures were distinguished within each basin. As a result, the Caspian sea basin was represented by all the morphostructures present in the classification with folded and depressive occupying virtually equal areas, whereas the Black sea, the Mediterranean sea and the Persian gulf basins were dominated by folded morphostructures.

Depressive morphostructures in foregoing units appeared in large river valleys and intermontane areas, while volcanic morphostructures were not significant, but they expanded impressively on the Armenian plateau.

Moreover, each morphostructure type represents characteristic landscape patterns according to natural areas and altitudinal zonality concepts, the latter applied to mountain ranges. So, using remote sensing datasets and ArcGIS software general sequence of landscapes in the main mountain ranges, such as Pontic ridge in the Black sea basin, Taurus mountains in the Meditteranean sea basin, Elburz in the Caspian sea basin and Zagros in the Persian Gulf basin were visually interpreted.  Then, a comparative analysis of the interrelation between landscapes in watersheds  was conducted.

Eventually, the obtained data could be applied to further studying and mapping of Southwest Asia region landscape structure formation and, subsequently, refreshing soil cover maps using remote sensing data.

 

How to cite: Milichenkova, V., Trifonova, T., and Lebedev, A.: Comparative analysis of watershed basins landscape structure in Southwest Asia region based on remote sensing data., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-580, https://doi.org/10.5194/egusphere-egu2020-580, 2020.

EGU2020-6498 | Displays | GM2.1

Combination of Web Programming and DAN3D to Generate Interactive Plots for Debris Flow Hazard Assessment

Enok Cheon, Seung Rae Lee, Deuk Hwan Lee, Hwan Hui Lim, and Seung Min Lee

In order to mitigate the potential damage from debris-flow hazards, the debris-flow hazard assessment is conducted to quantify the risk of landslide occurrence and assign potential levels of damage to surrounding buildings. DAN3D (Three-Dimensional Dynamic Analysis), a 3D numerical model for debris-flow simulation, has been widely used to conduct the debris-flow hazard assessment by computing the magnitudes of debris-flow characteristics, such as the velocity, depth, and volume. DAN3D software presents the results on a map plot that shows the magnitude of debris-flow characteristics over the inundated areas at a particular simulation time. These plots neither provide the exact values of debris-flow characteristics at a specific location nor compute the area and the width of debris-flow. Furthermore, a static image can be inconvenient for visualizing the changes in the debris-flow characteristics through time. Therefore, the present study created a program to interprets the DAN3D simulation results and to generate interactive plots using web programming. The interactive plots represent the position of a debris-flow cluster with a centroid location and show debris-flow characteristics, including the area and width of debris-flow, with a color scale. Additionally, the generated plots provide a graphical-user-interface to extract more details or change the plot. The accessibility and customization provided by the generated plots can be very useful for the design of the protection measures and evaluation of the effectiveness of them. A case study of the debris-flow at Sindonga watersheds, Mt. Umyeon, Korea, in 2011, was used to generate several interactive plots and their usefulness in designing barriers as mitigation against debris-flow.

How to cite: Cheon, E., Lee, S. R., Lee, D. H., Lim, H. H., and Lee, S. M.: Combination of Web Programming and DAN3D to Generate Interactive Plots for Debris Flow Hazard Assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6498, https://doi.org/10.5194/egusphere-egu2020-6498, 2020.

In 2020 we celebrate the 40th anniversary of the seminal works of Wood (1980a,b) who was one of the first researchers who considered the shapes of volcanoes in a global point of view. These four decades have seen a number of new approaches that were made possible by the ever increasing computer power and the improvements in Digital Terrain Model (DTM) production. The improving resolution and accuracy of the DTMs of various volcanic fields (VF) opened the way of wide variations of volcanic geomorphometric considerations. However, the differences in approach and, even more importantly, the differences in DTM production technology and resolution make the comparative studies and especially global considerations very difficult.

We have envisioned a global geomorphometric analytical methodology to analyse cinder cone morphometry in terms of shape versus age: The aim is to establish a relationship between the age of scoria cones age and their morphometry. This is knowingly a rather difficult undertaking and we have made only the first steps yet, but our methodological advancements are always developed with this demand in mind.

For the sake of diversity, in the current study four volcanic areas were considered with different age ranges, four different resolution DEMs and different number of cones:  San Francisco Volcanic Field, Arizona, USA (SFVF, 30 m horizontal resolution, 313 pcs), the Chaîne des Puys, France (CdP,  0.5 m, 26 pcs), the central-eastern part of the Sierra Chichinautzin, Mexico (SCVF, 5 m, 152 pcs) and Kula Volcanic Field, Turkey (KVF, 12.5 m, 64 pcs). As age data we had either age ranges or measured ages of the individual cones.

A great number of derivatives (mostly related to slope angles) have been calculated for the individual cones. Their most important statistics and their distribution were computed. Irregularities and, especially, cone degradation modify the original statistical distribution; these distributions can be compared in statistical way. A quantitative distance (metric) has been introduced to study the similarity or dissimilarity of the cones.

For the comparison, we have grouped the cones in several ways – they have been observed individually, by areas and by age groups (based on previous researches). For every cone boxplot diagrams, histograms and cumulative histograms were made to detect differences together with average and median values. These age groups were subjects of the Mann – Whitney statistical test to discriminate statistically independent or dependent samples in the populations. The test showed some clear relations between erosion (shape) and age.

We created a cinder cone viewer for visualization purposes. This tool can display the aforementioned distributions and helps in picking pairs or groups of cinder cones to compare. As expected, the intra-VF comparisons are typically more successful as inter-VF comparisons. However, promising new morphometric derivatives (e.g., sectorial distributions) are under development.

Wood, C. A.: Morphometric evolution of cinder cones, J. Volcanol. Geoth. Res., 7, 387–413, 1980a.

Wood, C. A.: Morphometric analysis of cinder cone degradation, J. Volcanol. Geoth. Res., 8, 137–160, 1980b.

How to cite: Székely, B. and Vörös, F.: Studying the distributions of DTM derivatives of cinder cones: a statistical approach in volcanic morphometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10465, https://doi.org/10.5194/egusphere-egu2020-10465, 2020.

EGU2020-11161 | Displays | GM2.1

Geology mapping with an emphasis on the Quaternary in the Swiss Prealps and Molasse Plateau

Valérie Baumann, Marc-Henri Derron, Jean-Luc Epard, and Michel Jaboyedoff

The main goal of this project is to harmonise the different geological maps (scale 1:25.000) and to improve the Quaternary mapping of the region of “canton de Vaud” in Switzerland using a high resolution LiDAR digital elevation model, and geophysical or boreholes data. We present here the results for the geologic mapping of two test areas: one in the Prealps and the second in the Molasse Plateau.

Detailed geological maps (scale 1:25.000) have been produced during the XX century for the whole region. During the last Late Glacial Maximum (LGM) the canton de Vaud area was covered by ice sheets, then soils and loose rock deposits were formed toward the end of ice age, however the Quaternary formations are sometimes not represented especially when their thickness is only of a few meters and the interpretation of geomorphologic features with aerial photographs was difficult in areas covered by forest.  

In recent years, the high-resolution digital elevation model derived from high resolution LiDAR data with the possibility to remove the trees in the forested areas offers the possibility to detect and interpret new morphologies.

In this study, different LIDAR-derived hillshade maps have been used to improve the delimitation of bedrock and Quaternary formation through morphological feature analyse. Borehole data gave us fundamental data about geology and stratigraphy and field surveys were performed for selected places. Additionally, a terrain classification system first developed in Canada (Cruden and Thomson, 1987) was used to add information for each polygon like genetic material, surface expression, modifying processes and stratigraphic data. All the mapping was performed in a GIS (Geographic system information) environment.

Detailed bedrock and Quaternary mapping will provide very good information for the management of the resources, land planning and geo-hazards. The additional information (terrain classification) for each polygon allow us to create different thematic maps starting from the geological map.

 

Reference:

 Cruden, D. M., and S. Thomson. Exercises in terrain analysis. Pica Pica Press, 1987.

 

How to cite: Baumann, V., Derron, M.-H., Epard, J.-L., and Jaboyedoff, M.: Geology mapping with an emphasis on the Quaternary in the Swiss Prealps and Molasse Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11161, https://doi.org/10.5194/egusphere-egu2020-11161, 2020.

Homogeneous topography pattern - can be an indicator of similar Earth's surfaces genesis and age. It is difficult to automatically formally describe these features and map the terrain. To describe the Earth's surface periodicity, we developing spectral terrain characteristics (STC). Their calculation consists of the following: a sliding window of different sizes decomposes the DEM into a Fourier row from which it is extracted:  1) amplitude of the main harmonic wave; 2) its length; 3) dispersion of heights given by 5% of the most important waves in relation to the general dispersion of heights; 4) general direction of oscillations of the height field; 5) unidirectionality / expression of this direction, etc. Areas with similar values of these parameters have visually homogeneous topographic pattern. We have calculated the above mentioned and some more complicated parameters for the whole territory of the Russian Arctic on a shallow scale: according to GMTED 2010 30" (1000 m per cell) on moving windows with sizes from 40 to 100 km and with the step of 10 km. Fifty-six raster models of SRC were obtained - 8 parameters at 7 scales each. Using them, a map of topographic dissection types in the Russian part of the Arctic was created with the help of self-organizing Kohonen neural networks and subsequent hierarchical clustering of individual neurons. 10 clusters have been identified related to geostructural, geological and geomorphological differences. 

This study was funded by the Russian Science Foundation, project no. 19-77-10036.

How to cite: Kharchenko, S.: Small-scale clustering of the Russian part of Arctic by periodicity type of the topographic patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19509, https://doi.org/10.5194/egusphere-egu2020-19509, 2020.

Landform classification is one of the most important aspects in geomorphological research, dividing the Earth’s surface into diverse geomorphological types. Thus, an accurate classification of landforms is a key procedure in describing the topographic characteristics of a given area and understanding their inner geomorphological formation processes. However, landform types are not always independent of one another due to the complexity and dynamics of interior and external forces. Furthermore, transitional landforms with gradually changing surface morphologies are widely distributed on the Earth’s surface. With this situation, classifying these complex and transitional landforms with traditional landform classification methods is hard. In this study, a deep learning (DL) algorithm was introduced, aiming at automatically classifying complex and transitional landforms. This algorithm was trained to learn and extract landform features from integrated data sources. These integrated data sources contain different combinations of imagery, digital elevation models (DEMs), and terrain derivatives. The Loess Plateau in China, which contains complex and transitional loess landforms, was selected as the study area for data training. In addition, two sample areas in the Loess Plateau with complex and transitional loess hill and ridge landforms were used to validate the classified landform types by using the proposed DL method. Meanwhile, a comparative analysis between the proposed DL and random forest (RF) methods was also conducted to investigate their capabilities in landform classification. The proposed DL approach can achieve the highest landform classification accuracy of 87% in the transitional area with data combination of DEMs and images. In addition, the proposed DL method can achieve a higher accuracy of landform classification with better defined landform boundaries compared to the RF method. The classified loess landforms indicate the different landform development stages in this area. Finally, the proposed DL method can be extended to other landform areas for classifying their complex and transitional landforms.

How to cite: Li, S., Xiong, L., Tang, G., and Strobl, J.: Deep learning-based approach for landform classification from integrated data sources of digital elevation model and imagery, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22334, https://doi.org/10.5194/egusphere-egu2020-22334, 2020.

GM2.5 – Novel Approaches in Geochronology: Quantifying Geomorphological Processes and Landscape Dynamics

EGU2020-2911 | Displays | GM2.5

Surface denudation and soil erosion over 300 ka at the Otago upland (New Zealand) using 10Be and 239+240Pu

Gerald Raab, Fabio Scarciglia, Kevin Norton, Adam Martin, Marcus Christl, Michael Ketterer, and Markus Egli

The Tor Exhumation Approach (TEA) traditionally uses large residual granitic landforms as indicators for surface lowering over time of their surrounding landscape. This study challenged the broad applicability of this approach by using large metamorphic residual landforms instead of the traditional plutonic rock formations. We applied in-situ cosmogenic nuclide techniques (10Be) along vertical landforms (schist-tors) on the Otago upland in southern New Zealand to investigate the capabilities of the TEA within another major rock type. The aim of the investigation was to decipher surface denudation models for the last ~100 ka. The experiment was coupled with fallout radionuclides (239+240Pu) in nearby soils to compare the Pleistocene / Holocene surface denudation rates with the Anthropocene (last ~60 years).

The surface ages of the eight investigated schist-tors was between ~20 ka and ~300 ka. This allowed the numerical modeling of continuous surface denudation rates with highest values near 0.16-0.20 [mm year-1] (about 140–180 [t km-2year-1]), and over a period that has not yet been achieved. The fallout radionuclide study resulted in two different mass redistribution rates. Average soil erosion along a ridge was ~400 to ~850 [t km-2year-1], whereas in an adjacent valley soil deposition rates reached ~130 to ~1,500 [t km-2year-1]. In conclusion, this study provides a new basis on how schist-tors emerge at two different landscape positions (ridges and valleys). In addition, differences between past surface denudation rates and modern ones could be revealed.

How to cite: Raab, G., Scarciglia, F., Norton, K., Martin, A., Christl, M., Ketterer, M., and Egli, M.: Surface denudation and soil erosion over 300 ka at the Otago upland (New Zealand) using 10Be and 239+240Pu, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2911, https://doi.org/10.5194/egusphere-egu2020-2911, 2020.

EGU2020-9990 | Displays | GM2.5

Landscape evolution of the southeastern Tibetan Plateau – Temporal and spatial relationships between glacial and fluvial landforms

Ramona A.A. Schneider, Arjen P. Stroeven, Robin Blomdin, Natacha Gribenski, Marc W. Caffee, Chaolu Yi, Xiangke Xu, Xuezhen Zeng, Martina Hättestrand, Ping Fu, and Lewis A. Owen

Landscape system components interact in ways which are not yet fully understood, and in tectonically active regions it is of particular interest whether endogenic or exogenic factors are the main drivers of landscape evolution. For example, fluvial terraces may form in response to exogenic disturbances like climatic changes or to endogenic forces like tectonic uplift. This study explores how temporal and spatial correlations between end moraines (denoting the advance of glaciers due to climate change) and fluvial terraces can yield insights about exogenic-endogenic processes determining landscape evolution during the Quaternary on the southern margin of the Shaluli Shan plateau, SE Tibet, a formerly glaciated and tectonically active region. A high-resolution TanDEM-X Digital Elevation Model (12 m) was used to produce detailed geomorphological maps of glacial valleys, marginal moraines, glacial lineations, and fluvial terraces. The geomorphological mapping was complemented with geomorphological and sedimentological field observations. Samples for Optically Stimulated Luminescence dating were taken from extensive and distinct terraces located in pull-apart basins bordering the plateau and samples for cosmogenic nuclide exposure dating were collected from selected boulders on end moraines formed by valley glaciers draining the Mt Genie massif on the Shaluli Shan plateau. Infrared stimulated luminescence (IRSL) signals from feldspar multi grains aliquots, and 10Be and 26Al concentrations from quartz, were used to determine depositional ages of terraces and moraines, respectively. In combining both dating techniques, we compare the timing of glacial expansions with the depositonal ages of the terraces to tease out the effects of exogenic and endogenic drivers on terrace formation and to formulate a conceptual model of landscape evolution.

How to cite: Schneider, R. A. A., Stroeven, A. P., Blomdin, R., Gribenski, N., Caffee, M. W., Yi, C., Xu, X., Zeng, X., Hättestrand, M., Fu, P., and Owen, L. A.: Landscape evolution of the southeastern Tibetan Plateau – Temporal and spatial relationships between glacial and fluvial landforms, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9990, https://doi.org/10.5194/egusphere-egu2020-9990, 2020.

EGU2020-4595 | Displays | GM2.5

How to reconcile OSL and TCN data: the potential of high-resolution sampling on the Choushui Tableland (West Central Taiwan)

Magali Rizza, Brice Lebrun, Lionel Siame, and Valéry Guillou

The determination of fault slip rate is often inferred from dating of Quaternary, deformed geomorphological surfaces affected by fault activity. For this reason, cosmogenic and luminescence methods now are widely applied to date the emplacement of geomorphic markers, but each method relates to different geomorphic processes. While the Terrestrial Cosmogenic Nuclides (TCN) method generally dates the exposure duration of the rock surface to cosmic rays, the Optically Stimulated Luminescence (OSL) method provides burial duration of the sediment after deposition. Age differences between these two methods may relate to the erosion-transport-deposition and aggradation processes experienced by the sediment prior its final deposition but combined may provide new insights into the processes affecting alluvial landforms.

Our case study is located in the Western Foothills, south of the Choushui River (Central Taiwan). There, slip on the Changhua blind thrust fault has caused the eastward tilt of a wide flight of fluvial terraces but slip rates on frontal faults are still debated due to large epistemic uncertainties in dating alluvial surfaces with OSL and TCN methods. To achieve a finer chronology of the deposits, a high-resolution sampling strategy has been deployed leading to a direct and unique comparison between OSL and TCN dating methods. Taking advantage of a natural exposure, we collected 10 samples for 10Be dating completed by 5 OSL samples along a 7 m depth profile. The depth distribution of 10Be concentrations show a complex depositional history with at least two depositional sequences, modelled to be older than ~38.7 ka.

As previous work has shown the difficulties of OSL dating in Taiwan, particular attention has been paid to luminescence characteristics of quartz and potential dosimetry issues. Our OSL analysis are in good agreement with 10Be and previous 14C dating and also reveal three depositional units, dated between ~9 ka and ~66 ka, that are evidenced by different OSL signal characteristics and variations in dosimetry.

This study shows that it is informative to have an exhaustive, detailed, and direct comparison between dating methods on a single depth profile to discuss the geomorphic processes and allow a more detailed understanding of the long-term rates of the Changhua Fault.

How to cite: Rizza, M., Lebrun, B., Siame, L., and Guillou, V.: How to reconcile OSL and TCN data: the potential of high-resolution sampling on the Choushui Tableland (West Central Taiwan), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4595, https://doi.org/10.5194/egusphere-egu2020-4595, 2020.

EGU2020-10720 | Displays | GM2.5

Interpreting erosion frequency and magnitude from luminescence profiles in boulders

Nathan Brown and Seulgi Moon

Exposed bedrock is ubiquitous on terrestrial and planetary landscapes, yet little is known
about the rate of bedrock erosion at a granular scale on timescales longer than the
instrumental record. As recently suggested, using the bleaching depth of luminescence
signals as a measure of bedrock erosion may fit these scales. Yet this approach assumes
constant erosion through time, a condition likely violated by the stochastic nature of erosional
events. Here we simulate bleaching in response to power-law distributions of removal
lengths and hiatus durations. We compare simulation results with previously measured
luminescence profiles from boulder surfaces to illustrate that prolonged hiatuses are unlikely
and that typical erosion scales are sub-granular with occasional loss at mm scales,
consistent with ideas about microflaws governing bedrock detachment. For a wide range of
erosion rates, measurements are integrated over many removal events, producing
reasonably accurate estimates despite the stochastic nature of the simulated process. We
hypothesize that the greater or equal erosion rates atop large boulders compared to rates at
ground level suggest that subcritical cracking may be more influential than aeolian abrasion
for boulder degradation in the Eastern Pamirs, China.

How to cite: Brown, N. and Moon, S.: Interpreting erosion frequency and magnitude from luminescence profiles in boulders, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10720, https://doi.org/10.5194/egusphere-egu2020-10720, 2020.

EGU2020-18537 | Displays | GM2.5

OSL rock surface exposure dating as a novel approach for reconstructing transport histories of coastal boulders over decadal to centennial timescales

Dominik Brill, Simon Matthias May, Nadia Mhammdi, Georgina King, Christoph Burow, Dennis Wolf, Anja Zander, and Helmut Brückner

Wave transported boulders represent important records of storm and tsunami impact over geological timescales. Their use for hazard assessment requires chronological information that in many cases cannot be achieved by established dating approaches such as radiocarbon and U-Th dating. To fill this gap, we investigated the potential of optically stimulated luminescence rock surface exposure dating for estimating transport ages of coastal boulders. The approach was applied to wave-emplaced calcarenite clasts at the Rabat coast, Morocco. Calibration of the OSL surface exposure model was based on samples with rock surfaces exposed for ~2 years, and OSL exposure ages were evaluated against age control deduced from satellite images. The dating precision is very limited for all boulders due to the local source rock lithology, which contains low amounts of quartz and feldspar and was formed after MIS 5 (OSL signals are not in field saturation). Nevertheless, we propose a robust relative chronology for boulders that are not affected by significant post-depositional erosion and that share surface angle of inclination with the calibration samples. The relative chronology indicates that most boulders were moved by storm waves; these storms lifted boulders with masses of up to ~40 t; indicating that the role of storms for the formation of boulder deposits along the Rabat coast is much more significant than assumed previously. While OSL rock surface exposure dating cannot provide reliable absolute exposure ages for the coastal boulders from Rabat, the approach has great potential for boulder deposits composed of rocks with larger amounts of quartz or feldspar, older formation histories and lower susceptibility for erosion.

How to cite: Brill, D., May, S. M., Mhammdi, N., King, G., Burow, C., Wolf, D., Zander, A., and Brückner, H.: OSL rock surface exposure dating as a novel approach for reconstructing transport histories of coastal boulders over decadal to centennial timescales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18537, https://doi.org/10.5194/egusphere-egu2020-18537, 2020.

EGU2020-19195 | Displays | GM2.5

Direct dating of lithic surface artefacts using luminescence and application potential in geomorphology

Michael Meyer, Luke Gliganic, and Jan-Hendrik May

Lithic surface artefacts are anthropogenically formed stone materials (stone tools and spall generated during knapping) resting atop or being semi-embedded into the uppermost sediment layer of a stratigraphic sequence on a given landform. Such surface artefacts lack a secure stratigraphic context are encountered worldwide and often comprise a significant proportion of the archaeological record. Yet, direct absolute dating techniques for constraining the age of lithic surface scatters are currently not available.

 

Promising recent work has shown the potential of using the optically stimulated luminescence (OSL) signal from rocks to date the emplacement of gravel pavements and blocks in both, archaeological and geological contexts (e.g. Sohbati et al., 2015; Jenkins et al., 2018). We build on this work and introduce a novel way of directly dating lithic surface artefacts using OSL-rock surface burial dating. We use this approach to date a surface lithic artefact scatter site, in southern Tibet. By calculating spatially resolved OSL burial ages for slices at 1 mm increments into each artefact’s buried surface we (i) infer the timing of artefact discard by humans at the site, (ii) demonstrate that most artefacts are not in-situ but were transported downslope and/or flipped and (iii) for some samples constrain the timing and number of cycles of artefact burial and re-exhumation.

 

This is the first time that the OSL signal is used to date sunlight exposure of artefacts. The method is not limited to archaeological contexts but can be applied to other surface clasts that yield a reasonable OSL signal too. OSL rock surface burial dating of surface clasts and artefacts thus holds great potential to (i) constrain manufacture and artefact discard by humans and (ii) detect and reconstruct post-depositional disturbances and transport pathways. We discuss the application potential of this approach in archaeology and geomorphology. 

 

References:

Jenkins, G.T.H., Duller, G.A.T., Roberts, H.M., Chiverrell, R.C., Glasser, N.F., 2018. A new approach for luminescence dating glaciofluvial deposits – High precision optical dating of cobbles. Quaternary Science Reviews 192, 263-273.

Sohbati, R., Murray, A.S., Porat, N., Jain, M., Avner, U., 2015. Age of a prehistoric Rodedian cult site constrained by sediment and rock surface luminescence dating techniques. Quaternary Geochronology 30, 90–99.

How to cite: Meyer, M., Gliganic, L., and May, J.-H.: Direct dating of lithic surface artefacts using luminescence and application potential in geomorphology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19195, https://doi.org/10.5194/egusphere-egu2020-19195, 2020.

EGU2020-8960 | Displays | GM2.5

How many grains do we need for tracer thermochronology?

Andrea Madella, Christoph Glotzbach, and Todd A. Ehlers

Detrital tracer thermochronology exploits the relationship between bedrock cooling age and elevation, whereby detrital cooling age distributions can inform the pattern of erosion in the upstream area. Typically bedrock ages exhibit a positive relation with elevation, since the exhumation path from the closure isotherm to the surface is longer. Therefore, spatially uniform erosion should yield a detrital cooling age distribution that mirrors the catchment’s hypsometric curve, corrected for mineral fertility. Applying thermochronometers is time consuming and expensive, hence measured detrital age populations have a limited sample size (rarely exceeding 100 grains) and only provide an approximation of the natural continuous detrital age distribution. With such limited sample sizes, discerning between two detrital age distributions resulting from different erosional patterns may be statistically impossible at a high confidence level.

Here, we investigate the impact of sample size on the detrital cooling age distributions and the resulting uncertainty in addressing the erosional pattern of the upstream area. To do so, we forward model a continuous detrital age distribution as a function given parameters, such as catchment hypsometry, mineral fertility, exhumation rate, analytical uncertainty and erosion scenario. A random subsample of the entire detrital population is drawn for each possible sample size, from which an approximate cumulative distribution function (CDF) is calculated. Then we compute the divergence of the approximate CDF from the reference continuous CDF as well as from the continuous CDF obtained for a different erosion scenario. The confidence level at which an approximate CDF can be tied to a specific erosion scenario is iteratively estimated for each sample size. We carry out the outlined approach for a synthetic catchment with elevations ranging between 0.5-2.2 km, where bedrock cooling ages increase by 30 My/km and prescribing a 10% standard deviation for single grain ages.

We find that, if the location of the erosion maximum coincides with the peak of the hypsometric curve, 100 grains do not suffice to resolve a local tenfold increase in erosion at the 95% confidence level. In this worst case scenario 240 grains would be required. However, for the same case, 70 grains are enough at the 68% confidence level. This study provides a method to consistently quantify the uncertainty of detrital tracer thermochronology as a function of sample size, case-specific variables and the initial scientific question.

How to cite: Madella, A., Glotzbach, C., and Ehlers, T. A.: How many grains do we need for tracer thermochronology?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8960, https://doi.org/10.5194/egusphere-egu2020-8960, 2020.

EGU2020-9577 | Displays | GM2.5

EnvironMICADAS C-14 AMS Gas ion source performance and its applications at HEKAL Laboratory, Debrecen, Hungary

Mihály Molnár, Róbert Janovics, István Major, Katalin Hubay, Botond Buró, Tamás Varga, Titanilla Kertész, Virág Gergely, Mihaly Veres, and A.J. Timothy Jull

A coupled accelerator mass spectrometer - gas interface system successfully has been operating at the Hertelendi Laboratory of Environmental Studies, Debrecen, Hungary since 2013. Over the last 6 years more than 500 gas targets were measured below 100 µg carbon content for carbon isotopic composition. The system was tested with blanks, OxII, IAEA-C1, IAEA-C2 and IAEA-C7 standards. The performance of our instrumentation shows good agreement with other published gas-interface system data and also shows a quite good agreement with the nominal value of international standard samples.  There is a measurable but quite small memory effect after modern samples, but this does not significantly affect the final results. Typical ion currents at the low energy side were between 10-15 µA with a 5% CO2 in He mixing ratio. The relative errors average ±6% for samples greater than or equal to 10 µgC sample with mean count rates of 300 counts per microgram C for OxII. The blank is comparable with other systems, which is 0.0050 ± 0.0018 F14C or 34000-47000 yr BP, which allows for the routine measurement of both of small environmental and archeological samples.

The research was supported by the European Union and the State of Hungary, co-financed by the European Regional Development Fund in the project of GINOP-2.3.2-15-2016- 00009 “ICER”. This work was carried out in the frame of the János Bolyai Research Scholarship (Mihály Molnár) of the Hungarian Academy of Sciences

How to cite: Molnár, M., Janovics, R., Major, I., Hubay, K., Buró, B., Varga, T., Kertész, T., Gergely, V., Veres, M., and Jull, A. J. T.: EnvironMICADAS C-14 AMS Gas ion source performance and its applications at HEKAL Laboratory, Debrecen, Hungary, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9577, https://doi.org/10.5194/egusphere-egu2020-9577, 2020.

Interpretations of surface exposure ages derived from the accumulation of cosmogenic isotopes commonly are hampered by a lack of field documentation that is necessary to identify and constrain if any post-depositional surface modifications have occurred (e.g. surface erosion, burial) that will impact age interpretations. Previous authors have discussed these issues, but the community still has not fully adopted the practice of interpreting surface exposure ages in conjunction with detailed soil stratigraphic observations. We employ this “novel” approach by documenting a soil chronosequence from the Gould wash alluvial fan sequence near Cibola, AZ to demonstrate how soil stratigraphy can provide constraints for the relative stability of depositional surfaces and can influence interpretations of TCN ages.


The Cibola chronosequence represents a range of alluvial fan ages that extend well beyond those commonly observed in the desert southwestern US (typically <100 ka) and provides evidence for extended periods of surface stability. We identified seven different alluvial fan surfaces within the sequence, documented their soil morphological and chemical properties, and dated four of the fan surfaces with 36Cl depth profiles. Fan deposits largely consist of volcaniclastic alluvium derived from the local Trigo Peaks and distal Castle Dome mountain blocks and show both a reduction of bar-and-swale surface topography and an increasing expression of desert pavement with relative surface age. The soil profiles consist of Av-Bk-BCky-Cky-Ck vertical horizon sequences (~125-cm thick) in the youngest fan units to Avk-Btky-Bkym-Bky-BCky-Cky-C (~400-cm thick) in the oldest fan unit that reflect systematic changes in soil thickness, structure, rubification of B horizons, and relative accumulations of eolian derived silt, clay, and salts as a function of relative surface age.


Chlorine-36 depth profile analysis yielded variable fan ages that are largely controlled by the magnitude of allowable erosion. Model results for which input data were parameterized to optimize unconstrained erosion rates indicate surface exposure ages of 46 (2A), 114 (2B), 268 (3A), and 386 (4A) ka. These are associated with best-fit erosion rates of 0-6 mm/kyr that indicate 0-136 cm net erosion. By comparison, results for which erosion rates were constrained to ~1 mm/kyr based on soil stratigraphic observations yielded exposure ages of 41 (2A), 114 (2B), 209 (3A), and 287 (4A) ka, resulting in differences of 10-25% of the unconstrained ages. The systematic morphological trends observed in the soil profiles do not support inferences of net erosion exceeding 30 cm and therefore cannot support the results from unconstrained parameter optimization. Although statistical optimization schemes provide better model fits to the data as indicated by chi-shared minimization routines, current models cannot account for field observations or for inferred constraints on surface modifications based on cosmogenic isotope concentrations alone. That task is better suited for and required by the sampling protocol to achieve more reliable surface exposure dates.

How to cite: Sion, B., McDonald, E., and Bustarde, J.: Using Soil stratigraphic observations to constrain TCN depth profile ages of relict alluvial fan surfaces in the Sonoran Desert, USA, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10614, https://doi.org/10.5194/egusphere-egu2020-10614, 2020.

EGU2020-9427 | Displays | GM2.5

Temporal evolution of surface processes inferred from cosmogenic nuclides in a slow erosion setting, insights from the Sera do Cipo range, Brazil

Vincent Godard, André Salgado, Lionel Siame, Jules Fleury, and Team Aster

Understanding the degree of sensitivity of the Earth Surface to past climate changes is key to assess the strength of postulated links between weathering, denudation, rock uplift and climate. Numerous studies have investigated the response of surface processes to the evolution through time of temperature and precipitation, in various settings and over different time periods. In particular, an important question still actively debated concerns whether or not Late Cenozoic climate change had an effective impact on denudation rates. It is noteworthy that this Late Cenozoic climatic evolution is often described as a long-term cooling over several Ma. However, although it has been postulated to be an important control on this response, the impact of its orbitally-controlled high-frequency component has been less investigated.

Studies focusing on climate-denudation links have often been carried out in regions of high tectonic activity. Therefore, they encountered associated significant limitations, such as: (1) high denudation rates that reach the analytical limits of many measurement methods; (2) stochastic events introducing a high degree of variability in the denudation signal; and, (3) high rates of tectonic uplift that can limit the sensitivity to the low-frequency component of the climatic boundary condition. Less active tectonic settings with lower denudation rates may thus provide conditions allowing to focus specifically on the coupling between climate variations and surface processes. Additionally, approaches combining different cosmogenic nuclides have proven to be very effective to unravel changes in surface processes over several time scales.

We present a new cosmogenic nuclides dataset from the Sera do Cipo range in Minas Gerais, Brazil. The core of the range is made of resistant quarzite bedrock with a relief of 500 m with respect to the surrounding low lands, and reported denudation rates are <10 m/Ma. Streams sediments from small catchments near the summit divide, as well as clasts derived from massive quartz veins at hilltop locations, were sampled. Both 10Be and 26Al concentrations were measured in the collected samples, as in such slow denudation settings the ratio between the two nuclides is sensitive to changes in denudation rates through time. A high-resolution (1 m) Digital Elevation Models was also produced from tri-stereo Pléiades satellite images. This allows to compute high resolution metrics such as hilltop curvature at the sampling sites. Hilltop denudation rates display a strong positive correlation with curvature. 26Al/10Be values significantly departing from the theoretical steady state denudation ratio are interpreted at hilltop sites as reflecting the fluctuation of denudation through time. Concerning the catchments samples, the determined ratio can also be impacted by the sediment transport history along hillslopes. Combining cosmogenic nuclides and high-resolution topographic datasets, the measured concentrations were inverted to constrain the variation of denudation over the last 2 Ma. We observe a significant change in the denudation regime at 1 Ma, with different kind of responses between ridges and small catchments across the landscape.

How to cite: Godard, V., Salgado, A., Siame, L., Fleury, J., and Aster, T.: Temporal evolution of surface processes inferred from cosmogenic nuclides in a slow erosion setting, insights from the Sera do Cipo range, Brazil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9427, https://doi.org/10.5194/egusphere-egu2020-9427, 2020.

EGU2020-2316 | Displays | GM2.5

Along-stream variations in valley flank erosion rates measured using 10Be concentrations in colluvial deposits from Atacama canyons: implications for valley widening

Valeria Zavala, Sebastien Carretier, Vincent Regard, Stephane Bonnet, Rodrigo Riquelme, and Sandrine Choy

The downstream increase in valley width is an important feature of fluvial landscapes that may be evident to anyone: even if local exceptions exist, wide fluvial valleys in plains are distinctive of narrow upstream mountainous ones. Yet, the processes and rates governing along-stream valley widening over timescales characteristic of landscape development (>1-10 ka) are largely unknown. No suitable law exists in landscape evolution models, thus models imperfectly reproduce the landscape evolution at geological timescales, their rates of erosion and probably their response to tectonics and climate. Here, we study two 1 km-deep canyons in northern Chile with diachronous incision initiation, thus representing two time-stage evolutions of a similar geomorphic system characterized by valley widening following the upward migration of a major knickzone. We use 10Be cosmogenic isotope concentrations measured in colluvial deposits at the foot of hillslopes to quantify along-stream valley flank erosion rates. We observe that valley flank erosion rate increases quasi-linearly with valley-bed slope and decreases non-linearly with valley width. This relation suggests that lateral erosion increases with sediment flux due to higher channel mobility. In turn, valley width exerts a negative feedback on lateral valley flank erosion since channels in wide valleys have a lower probability of eroding the valley sides. This implies a major control of river divagation on valley flank erosion rate and valley widening. Our study provides the first data for understanding the long-term processes and rates governing valley widening in landscapes.

How to cite: Zavala, V., Carretier, S., Regard, V., Bonnet, S., Riquelme, R., and Choy, S.: Along-stream variations in valley flank erosion rates measured using 10Be concentrations in colluvial deposits from Atacama canyons: implications for valley widening, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2316, https://doi.org/10.5194/egusphere-egu2020-2316, 2020.

The eastern seaboard of Australia is characterized by a passive margin and a continental divide that separates the inland-draining rivers from those that drain to the Coral and Tasman seas. Seaward of this divide lies the Great Escarpment (GE) of Australia that separates a moderate relief coastal plain from a low relief, high elevation plateau. Quantifying the spatial variation of erosion rates from temperate New England (NE), NSW and tropical Bellenden Ker (BK), Queensland, two regions with distinctly different climates and escarpment embayment, could help constrain erosional controls that contribute to escarpment form. In this study, we compared forty detrital 10Be samples collected from sediments in the main trunk and tributaries of five major rivers: the Macleay, Bellinger, and Clarence in NE and the Russel-Mulgrave and North Johnstone in BK. We then traced the escarpment position in ARCGIS and calculated a sinuosity ratio to better compare the degree of embayment in each region. Across both datasets we found that for NE, which has deep gorges cutting into the plateau, the degree of embayment was twice that of BK, where the escarpment position is significantly less embayed and erosion rates significantly more variable (ratio of .18 vs .38). Erosion rates in low slope areas, such as on the plateau, were universally low with no other significant controlling factors. There was no correlation between erosion rates and catchment area, and that our data echo previous studies that find that once mean rainfall passes an approximate threshold (around 2000mm/yr) basin characteristics that are known to control erosion rates, such as slope and lithology, are subdued.

 In temperate NE, where rainfall ranges from approximately 800-1200mm/yr, there was a moderate linear correlation with mean catchment rainfall and erosion rates (R2 .50), which is likely due to a strong orographic effect due to the escarpment. Erosion rates from tributaries below the plateau were highly variable and ranged from 5m/Ma up to 60m/Ma and correlated strongly with mean catchment slope (R2 .86). In addition, there were moderate inverse linear correlations between erosion rate and the catchment total percent granite and sedimentary rock (R2 .53 and .63 respectively) and a moderate correlation between erosion rate and catchment total percent metamorphic rock (R2 .57). Similar to previous studies, these data suggest that in temperate climates with moderate amounts of annual rainfall, individual basin characteristics play a significant role in controlling basin wide erosion rates.

In contrast, data from tropical BK, where mean rainfall amounts are in excess of 2000mm/yr, erosion rates from tributaries below the plateau were significantly less variable than NE. Rates had a mean of 37m/Ma ± 9 (standard deviation 5m/Ma, N=10) and were not significantly correlated with mean catchment slope nor catchment lithology. The mean erosion rate of BK is similar to that of other studies in the region, though with slightly less variability, and possibly reinforces the hypothesis from other researchers that in tropical climates with significant mean rainfall, soil depth effectively armors hillslopes and prevents bedrock erosion from occurring.

How to cite: Glass, J., Codilean, A., Fülöp, R., Wilcken, K., Cohen, T., and Abbott, L.: Spatial variation of erosion rates and passive margin escarpment embayment from New England, NSW and Bellenden Ker, Queensland, Australia: an analysis using GIS and in-situ 10Be basin-wide cosmogenic nuclides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12751, https://doi.org/10.5194/egusphere-egu2020-12751, 2020.

EGU2020-8432 | Displays | GM2.5

Quantifying post-glacial erosion at the Gorner glacier, Switzerland, using OSL and 10Be surface exposure dating.

Joanne Elkadi, Benjamin Lehmann, Georgina King, Olivia Steinemann, Susan Ivy-Ochs, Marcus Christl, and Frédéric Herman

Quaternary erosion through glacial and post-glacial processes has left an imprint on Alpine topography. There are few methods capable of resolving these processes on Late glacial to Holocene timescales. The aim of this study is to contribute towards a more detailed understanding of post-glacial erosion across the Central and Western Alps by better constraining the post-glacial erosion history of the Gorner glacier in Zermatt, Switzerland. This is done using a new approach that combines Optically Stimulated Luminescence (OSL) and 10Be cosmogenic nuclide surface exposure dating to invert for post-glacial erosion rates (Lehmann et al., 2019). Both dating methods are influenced by surface erosion but operate on different spatial scales- OSL signals form within the first 1-5 mm of a rock surface (Sohbati et al., 2011) whereas the 10Be signal accumulates within approximately the first 3 m (Lal, 1991). Six bedrock samples, exposed progressively since the Last Glacial Maximum, were collected along a vertical transect spanning an elevation of 641 m. Preliminary results show inheritance in the bottom three samples suggesting multiple advances and retreat. Further results for the post-glacial erosion rates down the transect, and comparison to other glaciers in the Western Alps, will be presented.

References:

Lal, D., 1991. Cosmic ray labelling of erosion surfaces: in situ nuclide production rates and erosion models. Earth and Planetary Science Letters, 104, 424-439.

Lehmann, B et al., 2019. Evaluating post-glacial bedrock erosion and surface exposure duration by coupling in situ optically stimulated luminescence and 10Be dating. Earth Surface Dynamics, 7.

Sohbati, R. et al., 2011. Investigating the resetting of OSL signals in rock surfaces. Geochronometria, 38(3), 249-258.

How to cite: Elkadi, J., Lehmann, B., King, G., Steinemann, O., Ivy-Ochs, S., Christl, M., and Herman, F.: Quantifying post-glacial erosion at the Gorner glacier, Switzerland, using OSL and 10Be surface exposure dating. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8432, https://doi.org/10.5194/egusphere-egu2020-8432, 2020.

EGU2020-3737 | Displays | GM2.5

Illuminating the speed of sand – quantifying sediment transport using optically stimulated luminescence

Jürgen Mey, Wolfgang Schwanghart, Anna-Maartje de Boer, and Tony Reimann

Sediment burial dating using optically stimulated luminescence (OSL) is a well-established tool in geochronology. Yet, an important prerequisite for its successful application is that the OSL signal is sufficiently reset prior to deposition. However, subaqueous bleaching conditions are vastly understudied, for example the effect of turbidity and sediment mixing on luminescence bleaching rates is only poorly established. The possibility that slow bleaching rates may dominate in certain transport conditions led to the concept that OSL could be used to derive sediment transport histories. The feasibility of this concept is still to be demonstrated and experimental setups to be tested. Our contribution to this scientific challenge involves subaquatic bleaching experiments, in which we suspend saturated coastal sand of Miocene age in a circular flume and illuminate for discrete time intervals with natural light. We further record the in-situ energy flux density received by the suspended grains in the UV-NIR frequency range by using a broadband spectrometer with a submersible probe.

Our analysis includes pre-profiling of each sample following a polymineral multiple signal protocol (Reimann et al., 2015), in which we simultaneously measured the quartz dominated blue stimulated luminescence signal at 125°C (BSL-125) and the K-feldspar dominated post-infrared infrared stimulated luminescence signal at 155°C (pIRIR-155). Preliminary results from the flume experiments show that the bleaching rates are indeed slow, differ for both signals and that the pIRIR155 seem to bleach faster than the BSL125. Besides the good prospects of acquiring a new tool for quantifying sediment transport, these results might have potentially far-reaching implications regarding the preferred target mineral for OSL dating in fluvial settings.  

How to cite: Mey, J., Schwanghart, W., de Boer, A.-M., and Reimann, T.: Illuminating the speed of sand – quantifying sediment transport using optically stimulated luminescence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3737, https://doi.org/10.5194/egusphere-egu2020-3737, 2020.

EGU2020-19218 | Displays | GM2.5

Using the portable luminescence reader to assess the historical lateral mobility of river channels: preliminary promising results

Laurent Schmitt, Timothée Jautzy, Dominik Brill, and Gilles Rixhon

Timothée Jautzy1,2, Dominik Brill3, Laurent Schmitt1, Gilles Rixhon4

Obtaining robust chronological data on landforms and their related deposits together with constraining rates of earth surface processes have constantly represented a major challenge in Quaternary science. In the fluvial context, Optically Stimulated Luminescence (OSL) is particularly well-established but still faces several limitations. It notably requires expensive and time-consuming sample processing and measurement, frequently resulting in a poor spatial and stratigraphical distribution of sampling which may negatively impact the chronological information. To overcome this main limitation, a Portable OSL reader (POSL) has been recently developed (Sanderson & Murphy, 2010). It consists in directly capturing a luminescence signal (counts per seconds) on unprepared sediment samples. This technique is quick and affordable but, unlike conventional OSL, is not able to yield numerical age estimates.

This contribution explores POSL capacities to provide useful relative age information on alluvial sediments from the last centuries. We study and compare 42 samples collected from three alluvial profiles located in the floodplain of a gravelly-sandy mid-sized river: the Bruche (i.e. a sub-tributary of the Upper Rhine, France). POSL stimulations, including both blue and infra-red signals, are performed in combination with grain size analysis. We observe (i) an overall increase of signal intensity with increasing depth, (ii) a very good match between blue and IR signals and (iii) no systematic correlation between signal intensity and grain size. Whilst this last point must still be confirmed (i.e. signal intensity does not primarily depend on grain size), our preliminary results positively suggest that POSL is a promising tool to provide a relative chronology for very young alluvial sediments. Furthermore, it may also provide information on geomorphic processes. These results will be combined soon to numerical dating (OSL and 14C) and compared to outcomes of a planimetric analysis to thoroughly reconstruct the historical lateral mobility of the Bruche river.

How to cite: Schmitt, L., Jautzy, T., Brill, D., and Rixhon, G.: Using the portable luminescence reader to assess the historical lateral mobility of river channels: preliminary promising results, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19218, https://doi.org/10.5194/egusphere-egu2020-19218, 2020.

EGU2020-20236 | Displays | GM2.5

Exploring the application of IRSL rock surface exposure dating of archaeological stone structures in Val di Sole, Italy

Lucas Ageby, Diego E. Angelucci, Dominik Brill, Francesco Carrer, Helmut Brückner, and Nicole Klasen

Reconstructing exposure histories of rock surfaces with luminescence dating is a recently developed tool which has proven valuable to chronologically constrain archaeological rock structures (e.g. Sohbati et al., 2012). Here, we explore the possibility to use infrared stimulated luminescence (IRSL) exposure dating to constrain the period of usage of two dry stone enclosure complexes (MZ001S and MZ005S) in Val di Sole, Trentino, Italy. Archaeological investigations confirm that the enclosures were used to keep livestock and radiocarbon ages and archaeological finds from MZ005S restrain the oldest time of use to the Late Middle Ages or Early Modern Period (Carrer and Angelucci, 2018). One 19th-century potshard has been recovered from MZ001S and interviews with residents indicate that MZ001S may have been in use until the mid-20th century. Mica and quartz-rich gneiss rocks of both structures were sampled, together with calibration rock surfaces which had been exposed for one year. Cores were extracted from the rocks with a water-cooled bench drill and cut with a cooled precision saw. Whole rock slices (approx. 0.7 mm thin) were heated to 180 °C for 100 seconds and were subsequently measured with infrared diodes at 50 °C for 300 seconds to create IRSL-depth profiles. Exposure ages were calculated with the exposure dating model developed by Sohbati et al. (2011) for which we used de-trapping rates calculated from the exposed calibration surfaces. IRSL-with-depth profiles are presented from both natural and calibration surfaces. Preliminary ages severely underestimate expected exposure ages (decades of exposure, compared to expected centuries of exposure) and precision of the ages is low.  More investigations are necessary but possible reasons for this age discrepancy are denudation of the rock surface, heterogenic mineralogy with patches of opaque minerals which locally increase light attenuation, or the calibration samples do not represent good analogues for the rocks from the stone structures. The low precision of the ages appears to originate from variations in the IRSL-depth profiles between different cores cut from the same sample.

 

References

Carrer, F., Angelucci, D.E., 2018. Continuity and discontinuity in the history of upland pastoral landscapes: the case study of Val Molinac and Val Poré (Val di Sole, Trentino, Eastern Italian Alps). Landscape Research 43, 862–877. doi:10.1080/01426397.2017.1390078.

Sohbati, R., Murray, A., Jain, M., Buylaert, J.P., Thomsen, K., 2011. Investigating the resetting of OSL signals in rock surfaces. Geochronometria 38. doi:https://doi.org/10.2478/s13386-011-0029-2.

Sohbati, R., Murray, A. S., Chapot, M. S., Jain, M., and Pederson, J. 2012. Optically stimulated luminescence (OSL) as a chronometer for surface exposure dating J. Geophys. Res., 117, doi:10.1029/2012JB009383.

How to cite: Ageby, L., Angelucci, D. E., Brill, D., Carrer, F., Brückner, H., and Klasen, N.: Exploring the application of IRSL rock surface exposure dating of archaeological stone structures in Val di Sole, Italy , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20236, https://doi.org/10.5194/egusphere-egu2020-20236, 2020.

EGU2020-7982 | Displays | GM2.5

Testing direct dating of Alpine faults by luminescence and ESR

Sumiko Tsukamoto, David Tanner, Christian Brandes, and Christoph von Hagke

For a better understanding of the recent exhumation history of the Alps and the distribution of palaeo- and recent earthquakes within the orogen, it is important to elucidate the Quaternary activity of major faults. In this study, we test the applicability of luminescence and electron spin resonance (ESR) dating, which have ultralow closure temperatures, to directly date fault gouge of the Simplon Fault. A dark grey to black, fine-grained fault gouge was sampled near Visp, Switzerland, from an outcrop that exposes rocks that formed at ductile/brittle conditions. Quartz and feldspar grains were extracted from the sample; quartz grains were used for ESR dating, whereas feldspar grains were used for infrared stimulated luminescence (IRSL) dating.

The IRSL measurements reveal that the natural post-IR IRSL signal, stimulated at 225°C (pIRIR225) was in saturation. The pIRIR225 signal had an extremely low saturation dose, with a characteristic saturation dose (D0) of ~90 Gy. The natural IRSL signal at 50°C (IR50) is about 80 % of the laboratory saturation, so that this signal is presumably in the field saturation. The IR50 also showed a small D0 of ~250 Gy. Although these D0 values are unexpectedly small, the IRSL signals can be used to calculate the minimum age of the last seismic movement of the fault.

Both natural and laboratory-irradiated ESR spectra did not contain detectable Ti centre. Therefore, only the Al centre was used for ESR dating. The natural Al centre from the fault was not in saturation, with a preliminary equivalent dose value of ~1500 Gy. Since the last seismogenic movement most likely only partially reset the Al centre, the ESR age can be regarded as the maximum age of the last event.  We show that by combining luminescence and ESR dating, it is possible to narrow down the age range of the last seismic activity on the fault.

How to cite: Tsukamoto, S., Tanner, D., Brandes, C., and von Hagke, C.: Testing direct dating of Alpine faults by luminescence and ESR, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7982, https://doi.org/10.5194/egusphere-egu2020-7982, 2020.

Dating of loess deposits using optically stimulated luminescence (OSL) enable us to extract important information about the climate during the last ~150 ka. A good estimation of the dose rate during the past is essential for OSL and depends, among others, on the history of the moisture content in the proximity of the dated sample. While the current moisture content can be measured by heating/drying, the history of the moisture variations of a sample is generally unknown. Reference values reported on similar materials and climate conditions may provide a range for the expected moisture variations in the past, but these values are generally rough guesses and not depth- and time-specific.

Nuclear magnetic resonance (NMR) relaxometry targeting the hydrogens of the pore fluid can estimate the current moisture content of a sample without heating. Additionally, the NMR relaxation time distribution yields information of the expected moisture content for a given field potential (e.g. wilting point). This can help to estimate a sample-specific range of likely moisture variation in a quick (several min) and no-invasive way.

We discuss this new approach on a loess profile from Toshan (Iran) published previously by (Lauer et al., 2017) and (Vlaminck, 2018). The later pointed out inconsistencies in the obtained age model. The estimated sample specific moisture content for the wilting point (15 to 35 wt.%) provide the low boundary for the moisture content estimate, which is higher than previously assumed (5 wt.%). The new dose rate calculated for these sample specific moisture content values lead to clearly older and more consistent ages (less age inversions).

We suggest that NMR derived moisture content data is valuable for obtaining information on the moisture content of samples. Especially the minimum moisture can be derived reliably, giving more robust water content estimates for OSL dating.

 

 

References

Lauer, T., Vlaminck, S., Frechen, M., Rolf, C., Kehl, M., Sharifi, J., Lehndorff, E., Khormali, F., 2017. The Agh Band loess-palaeosol sequence – A terrestrial archive for climatic shifts during the last and penultimate glacial–interglacial cycles in a semiarid region in northern Iran. Quaternary International, Loess, soils and climate change in Iran and vicinity 429, 13–30. https://doi.org/10.1016/j.quaint.2016.01.062

Vlaminck, S., 2018. Northeastern Iranian loess and its palaeoclimatic implications (PhD Thesis). Universität zu Köln.

How to cite: Dlugosch, R., Zeeden, C., Lauer, T., and Tsukamoto, S.: Can moisture content estimates from nuclear magnetic resonance improve optically stimulated luminescence dating - first results on Loess samples from Toshan/Iran, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1493, https://doi.org/10.5194/egusphere-egu2020-1493, 2020.

EGU2020-5889 | Displays | GM2.5

Investigations on paramagnetic centres in quartz for provenance studies

Alida Timar-Gabor, Aditi Dave, and Kathryn Fitzsimmons

The sediment rooting concept [1] relies on the potential to track individual mineral grains from their source to their ultimate sinks. Quartz is the second most abundant mineral in the Earth's crust and occurs in a broad variety of rocks and sediments. It is resistant to weathering and does not form solid solutions, thus being considered a pure mineral. However, even the purest quartz crystal contains a vast number of point defects, which may be either intrinsic (e.g., O-vacancies and related defects or Si vacancies) or due to impurities, most often as combination of monovalent (H+, Li+, and Na+) and trivalent (Al3+, Fe3+, and B3+) cations. Some of these defects remain unchanged under ionising radiation bombardment by the omnipresent natural radioactivity, while others are being transformed, generally by charge trapping. Based on the dynamics of some of these radiation sensitive defects under irradiation, quartz can be used for dating by luminescence or by electron spin resonance.

Another less explored application of these defects is fingerprinting the sources of the sediments. For provenance applications to be successful, the signals used when looking at quartz from the sediment should match the corresponding signals of quartz from host rocks, thus they should remain unchanged during transport and/or weathering.

Here we are conducting an exploratory study on quartz from loess from Central Asia (Kazakhstan and Tajikistan). This specific study site was chosen as very recent studies based on geochemical fingerprinting, grain size modelling and present-day meteorological data suggest contribution from different source areas in this Westerlies dominated region [2,3]. Consequently, this area is an ideal test site to look for spatial and temporal variability in source change. We are investigating the signature of E’ (an unpaired electron at an oxygen vacancy site) and peroxy intrinsic defect centers (nonbonding oxygen) as well as the Al-hole ([AlO4]0, a hole trapped by substitutional trivalent aluminum at a silicon site) paramagnetic signals by electron spin resonance in loess samples, as well as in rock samples. We are also investigating the behaviour of these defects during laboratory experiments that aim at reproducing natural conditions during transport. While work is still in progress, we have observed a significant difference between the E’ and peroxy signals for Kazakh and Tajik samples, which is in tune with the current hypothesis regarding the dust sources in the area presented above.

References

How to cite: Timar-Gabor, A., Dave, A., and Fitzsimmons, K.: Investigations on paramagnetic centres in quartz for provenance studies, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5889, https://doi.org/10.5194/egusphere-egu2020-5889, 2020.

EGU2020-4505 | Displays | GM2.5

Contribution of magnetite (U-Th-Sm)/He thermometer to quantify the final exhumation of high-pressure ultramafic rocks : example of the Rocher Blanc ophiolite (western Alps)

Stéphane Schwartz, Cécile Gautheron, Richard A Ketcham, Fabrice Brunet, Arnaud Agranier, and Marianna Corre

This contribution investigates the use of the (U-Th-Sm)/He dating method to unravel the exhumation history of ultramafic ophiolite rocks. Magnetite-bearing rocks are widely distributed on the Earth's surface and are associated with a large range of geological and geodynamic settings. However, little is known of the crystallization and exhumation history of in case of oceanic accretion to orogenic zones, due to a lack of datable minerals. In the past few years, the (U-Th-Sm)/He method applied on magnetite or spinel appears to be very relevant and promising. However, the applicability of this method to access the thermal history has never been quantitatively investigated, limiting the age interpretation. To highlight the applicability and to access geological information using magnetite (U-Th-Sm)/He method (MgHe), we applied it on a well-known high-pressure low-temperature alpine ophiolite (Rocher Blanc ophiolite, Western Alps) where the P-T-t exhumation history is well constrained. A study of magnetite petrology, mineralogy and geochemistry has allowed us to characterize that magnetite crystallize at T>250°C. MgHe ages that range between apatite and zircon fission track (AFT and ZFT) ages of surrounding rocks in agreement with the known thermal sensitivity of those methods. MgHe data were co-inverted with AFT and ZFT data to determine the most robust thermal history associated with the ophiolite cooling. This first MgHe age inversion is consistent with experimental He diffusion data, opening the use of MgHe as a thermochronometer. This result allows us to refine the thermal history and to precise the geodynamical context associated to the final exhumation of this alpine ophiolite.

How to cite: Schwartz, S., Gautheron, C., Ketcham, R. A., Brunet, F., Agranier, A., and Corre, M.: Contribution of magnetite (U-Th-Sm)/He thermometer to quantify the final exhumation of high-pressure ultramafic rocks : example of the Rocher Blanc ophiolite (western Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4505, https://doi.org/10.5194/egusphere-egu2020-4505, 2020.

EGU2020-5228 | Displays | GM2.5

Uplift history of the Western Ecuadorian Andes: new constraints from low-temperature thermochronology

Audrey Margirier, Peter Reiners, Ismael Casado, Stuart Thomson, Alexandra Alvarado, and Manfred Strecker

The Cenozoic growth of the Ecuadorian Andes has been strongly influenced by the compressional reactivation of inherited crustal anisotropies, strike-slip faulting and uplift, and the erosional effects of a wet tropical climate superposed on the deforming orogen. Some authors have linked uplift in the Western Cordillera to the interaction between the South American Plate and the subduction of the oceanic Carnegie Ridge. However, recent studies have alternatively suggested that the tectonic evolution of a northward-escaping crustal sliver in western Ecuador along the Pallatanga strike-slip zone may equally well explain mountain building and topographic growth in this region. While the importance of the Pallatanga Fault has been recognized in the context of seismic hazards, its long-term impact on the development of topography and relief has not been explored in detail. To evaluate the possible roles of oceanic ridge subduction and/or strike-slip motion in prompting the growth of the Western Cordillera, we present new thermochronological data to constrain the deformational history of the Western Cordillera at different latitudes. We focus on two sites in the vicinity of the Pallatanga strike-slip fault (3°S and 1°30’S) and a location farther to the north (0°30’N). Our apatite and zircon (U-Th-Sm)/He dates range from 26.0 ± 0.4 Ma to 3.9 ± 0.1 Ma and from 23.7 ± 0.3 to 5.9 ± 0.1 Ma, respectively. The three sampled sites record a clear age-elevation relationship. The inverse modeling of apatite and zircon (U-Th-Sm)/He dates and upcoming apatite fission-track data is expected to provide new constraints on the recent uplift and exhumation history of the Western Ecuadorian Andes and thus furnish information on the paleo-geographical evolution of the northern Andes.

How to cite: Margirier, A., Reiners, P., Casado, I., Thomson, S., Alvarado, A., and Strecker, M.: Uplift history of the Western Ecuadorian Andes: new constraints from low-temperature thermochronology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5228, https://doi.org/10.5194/egusphere-egu2020-5228, 2020.

EGU2020-12624 | Displays | GM2.5

Spatial distribution of U-Pb ages across a basement uplift in the Northern Andes and its implications for the interpretation of the detrital record in adjacent basins.

Jose R. Sandoval, Nicolas Perez-Consuegra, Ricardo A. Gomez, Andres Mora, Mauricio Parra, Victor Valencia, Brian Horton, Ricardo Bueno, Andres Reyes, Alejandro Beltran, and Andres Cardenas

Foreland basins represent a unique record of the evolution of mountain building processes in the adjacent hinterland. In the southern Colombian Andes and the adjacent foreland basin (i.e. Caguán-Putumayo Basin) no detrital U-Pb and heavy mineral studies have been conducted. This is due to the fact that the geochronological characterization of the basement rocks is poor, complicating the interpretation of source areas for provenance analysis.  Here we present a complete provenance study using U-Pb and Heavy mineral data. In order to gain a better understanding of the spatial distribution of the different potential basement sources we planned a characterization of the different basement provinces west of the Caguan-Putumayo basin. Here we present results from samples of active sediments (N=21), basements (N=16) and sedimentary rocks (N=4) older than Cretaceous. This characterization allowed the identification of eight (8) different domains with different age ranges. (1) The southern part of the Central Cordillera with populations of 150 - 250 m.y., (2) Southern part of the eastern flank of the Eastern Cordillera with ages around 150 - 180 m.y., (3) south of the Garzón Massif with age ranges between 1000 - 1150 m.y, (4) north of the Garzón Massif where rocks of 1500 m.y. dominate, (5) Paleozoic sedimentary rocks above the basement to the north of the Garzón Massif and the Serrania de la Macarena with a distinct population of 1300 m.y, (6). The basement of the Serrania de la Macarena with ages between 1650-1800 m, (7). The Serranía de Lindosa with ages around 500 m.y and (8). Amazonian Craton with ages between 1500 - 2000 m.y. Additionally, the relationship between Epidotes and Garnets displays a special behavior in each area. The provinces related to the Garzon Massif have a high amount of Garnets and low amount of Epidotes. On the other hand, the behavior of the areas away from the Garzon Massif is different. Based on the U-Pb detrital signal and the Epidote/Garnet relationship, we suggest that the stratigraphic intervals where we observe ages between 1000 and 1150 m.y. for the first time and high Garnet contents reflect uplift peaks of the Garzon Massif.

How to cite: Sandoval, J. R., Perez-Consuegra, N., Gomez, R. A., Mora, A., Parra, M., Valencia, V., Horton, B., Bueno, R., Reyes, A., Beltran, A., and Cardenas, A.: Spatial distribution of U-Pb ages across a basement uplift in the Northern Andes and its implications for the interpretation of the detrital record in adjacent basins., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12624, https://doi.org/10.5194/egusphere-egu2020-12624, 2020.

GM2.6 – Advances in the observation of Earth surface processes: Environmental seismology and novel monitoring techniques

EGU2020-1673 | Displays | GM2.6 | Highlight

Distributed acoustic sensing for seismic monitoring in challenging environments

Zack Spica, Takeshi Akuhara, Gregory Beroza, Biondo Biondi, William Ellsworth, Ariel Lellouch, Eileen Martin, Kiwamu Nishida, François Pétrélis, Mathieu Perton, Masanao Shinohara, Tomoaki Yamada, and Siyuan Yuan

Our understanding of subsurface processes suffers from a profound observation bias: ground-motion sensors are rare, sparse, clustered on continents and not available where they are most needed. A new seismic recording technology called distributed acoustic sensing (DAS), can transform existing telecommunication fiber-optic cables into arrays of thousands of sensors, enabling meter-scale recording over tens of kilometers of linear fiber length. DAS works in high-pressure and high-temperature environments, enabling long-term recordings of seismic signals inside reservoirs, fault zones, near active volcanoes, in deep seas or in highly urbanized areas.

In this talk, we will introduce this laser-based technology and present three recent cases of study. The first experiment is in the city of Stanford, California, where DAS measurements are used to provide geotechnical information at a scale normally unattainable (i.e., for each building) with traditional geophone instrumentation. In the second study, we will show how downhole DAS passive recordings from the San Andreas Fault Observatory at Depth can be used for seismic velocity estimation. In the third research, we use DAS (in collaboration with Fujitec) to understand the ocean physics and infer seismic properties of the seafloor under a 100 km telecommunication cable.

How to cite: Spica, Z., Akuhara, T., Beroza, G., Biondi, B., Ellsworth, W., Lellouch, A., Martin, E., Nishida, K., Pétrélis, F., Perton, M., Shinohara, M., Yamada, T., and Yuan, S.: Distributed acoustic sensing for seismic monitoring in challenging environments , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1673, https://doi.org/10.5194/egusphere-egu2020-1673, 2020.

EGU2020-18086 | Displays | GM2.6

Listening the Womb of the Earth: iXblue sonars, transponder & rotational seismometers for extreme environment imaging & monitoring

Guillaume Jouve, Frédéric Guattari, Théo Laudat, Nathalie Olivier, Hubert Pelletier, Maurizio Ripepe, Heiner Igel, Joachim Wassermann, Felix Bernauer, Thomas Braun, Corentin Caudron, and Marc-André Gutscher

iXblue company develops technologies to listen and image the Earth dynamics. Among them, Echoes high-resolution sub-bottom profilers, Seapix 3D multibeam echosounder, Canopus transponder and blueSeis rotational seismometers are particularly useful for imaging and monitoring marine and continental volcanic activities. Here, we present recent implementations and acquisitions of those systems, demonstrate the great potential of these technologies to record present and past volcanic dynamics in Hawaii, Stromboli, Sicilia and Eifel region, and emphasize their benefits to better anticipate volcanic hazard.

The Hawaii island experienced a dramatic volcanic crisis during the summer of 2018. To demonstrate the potential of observing the complete ground motion in the near field of seismic sources, Geophysical Observatory (LMU, Munich, Germany), in cooperation with USGS Hawaiian Volcano Observatory (USA), installed a high sensitive rotational motion sensor (blueSeis-3A) near the erupting crater returning spectacular data for almost daily M5 seismic events due to the collapse of the caldera. BlueSeis-3A, based on fiber optical gyroscope technology, at very close distance from the Stromboli volcano in 2016 and 2018, was installed together with classical instrumentation (i.e., translational seismometer, infra sound and tilt meter) and recorded four weeks of permanent strombolian activity at Stromboli during these two experiments. The resulting six axis measurements reveal clear rotations around all three-coordinate axis. We are furthermore able to demonstrate how these six component measurements can help to improve solving the inversion problem on large and complex system like volcanoes.

Eight Canopus transponders are involved in an ERC project in underwater geodesy, the FOCUS project headed by IUEM laboratory (Brest, France). Together with a 6 km-long optical fiber deployed across the trench at the base of the Etna volcano, two groups of four Canopus will be installed on tripods each side of the trench at 1500-2000 m of water depth. This will help quantify the speed of the southeastern flank collapsing of Etna volcano into the Ionian Sea.

In collaboration with French, Belgian and German geoscience laboratories, Echoes 10 000 (10 kHz) sub-bottom profiler and Seapix 3D multibeam echosounder, both installed on the kiXkat cataraft and remotely controlled, were mobilized to produce images of the water column and sediments of a lake formed in a volcanic crater in Germany (Laacher See). By using Seapix to obtain backscatter profiles of elements in the water column, it was possible to clearly distinguish fish and gas bubbles, which demonstrates a potential for the development of an automatic gas detection module using the Seapix software. Meanwhile, the Echoes 10 000 provided high-resolution images of the architecture of the lake deposits and visualized in real time using Delph Software. More than 30 m of penetration with a theoretical 8 cm-resolution highlight paleoenvironmental and paleoclimatic reconstruction perspectives and 3D modeling of remobilized materials and tephra deposits from volcanic activity.

How to cite: Jouve, G., Guattari, F., Laudat, T., Olivier, N., Pelletier, H., Ripepe, M., Igel, H., Wassermann, J., Bernauer, F., Braun, T., Caudron, C., and Gutscher, M.-A.: Listening the Womb of the Earth: iXblue sonars, transponder & rotational seismometers for extreme environment imaging & monitoring, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18086, https://doi.org/10.5194/egusphere-egu2020-18086, 2020.

EGU2020-1519 | Displays | GM2.6

Matching seismic activity with potential sources using machine Learning

Gerrit Hein, Artemii Novoselov, Florian Fuchs, and Götz Bokelmann

Detecting seismic signals and identifying their origin is more and more used for understanding environmental activity. This usually depends on a good signal/noise ratio (S/N), especially for the more distant sources.

A test area for detection and identification is the urban setting of the University of Vienna, a challenging environment with more than 4000 strong-acceleration events per day. These repetitive noise events would normally classify the site as "too noisy" for any advanced earthquake research.

With the real-time open database from Wiener Linien it is possible to attribute many of the repetitive seismic signals (e.g. on a Raspberry Shake Citizen Science Station) to the surrounding trams and train lines. The detection challenge was initiated in a Citizen Science Hackathon, where public interest sparked this research. The available train schedule and more than one year of continuous seismic records is sufficient to train and test a machine learning classifier which finds most characteristic features in the signals of commuter trains and trams, such as the energy in each frequency band.

The labeled dataset can be used to train our detection algorithm to find similar signals and to help determine whether a certain signal is present or not. An additional second seismic Raspberry Shake sensor is installed in the vicinity, to further constrain the directionality of the trains.

Studying the vibrations of train signals and solving the classification task of these repetitive patterns first can help develop robust methods
for seismically loud environments, and might lead to the detection of lower magnitude events such as regional earthquakes or landslides. 

How to cite: Hein, G., Novoselov, A., Fuchs, F., and Bokelmann, G.: Matching seismic activity with potential sources using machine Learning , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1519, https://doi.org/10.5194/egusphere-egu2020-1519, 2020.

EGU2020-13054 | Displays | GM2.6

Deriving sediment transport information from debris-flow impact force signals

Hui Tang, Yan Yan, and Kaiheng Hu

Runoff-generated debris flow has hazardous implications for downstream communities and infrastructure in alpine landscapes. Our understanding of fluid mechanisms of debris flows is very limited, in part, by a lack of direct observations and measurements. Seismic ground motion-based observations provide new constraints on debris flow physics, but it is still not widely applied due to the missing of validated inversion models for interpreting the impact force which generates seismic ground motion. Here we propose a physical model for the high-frequency spectral distribution of impact force signal generated by debris flows. Then we present a new inversion model based on the physical model for the impact force signal and apply this to the devastating debris flows in Dongchuang, China, on 25 August 2004. The amplitude and frequency characteristics of the impact force data can enable the estimation of grain size, sediment concentration, and sediment flux. Results suggest that in-situ data from three sensors could have provided a reconstruction of sediment flux profile in the vertical direction. Meanwhile, an inversion model designed for debris flows impact force would potentially provide hydrodynamics information as well.

How to cite: Tang, H., Yan, Y., and Hu, K.: Deriving sediment transport information from debris-flow impact force signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13054, https://doi.org/10.5194/egusphere-egu2020-13054, 2020.

EGU2020-10080 | Displays | GM2.6

Extraction of River Planforms from Synthetic Aperture Radar Imagery using Superpixel Classification

Odysseas Pappas, Byron Adams, Nantheera Anantrasirichai, and Alin Achim

Algorithms for the detection and extraction of river planforms from remotely sensed images are of great interest to numerous applications including land planning, water resource monitoring, and flood prediction. Synthetic Aperture Radar (SAR) is a very promising modality for river monitoring and analysis as it can provide high resolution imagery regardless of weather conditions and the day/night cycle.

In this work we present an algorithm for the detection and segmentation of rivers in SAR images, with emphasis on accurate riverbank extraction. The algorithm utilises a novel superpixel segmentation algorithm that segments the image into perceptually uniform clusters of pixels based on a modelling of the SAR data with the Generalised Gamma Distribution.

The generated superpixels adhere to the edges of objects in the image (such as riverbanks) with great accuracy. Superpixels are then characterised according to several features that describe their statistical and textural properties which allows for the discrimination between river- and land-cover superpixels. The river-forming superpixels are then grouped together using unsupervised agglomerative clustering to produce river planform masks.

We demonstrate our proposed method on high resolution SAR images from the SENTINEL-1 and ICEYE platforms. Future work will focus on incorporating more complex heuristics for the identification of false positives and to circumvent apparent river discontinuities (e.g. bridges), as well as on the release of a toolbox providing open access to the geosciences community.

How to cite: Pappas, O., Adams, B., Anantrasirichai, N., and Achim, A.: Extraction of River Planforms from Synthetic Aperture Radar Imagery using Superpixel Classification, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10080, https://doi.org/10.5194/egusphere-egu2020-10080, 2020.

EGU2020-20833 | Displays | GM2.6 | Highlight

Tracking surface and subterranean water flow using continuous seismic tremor

Haleh Karbala Ali, Chris Bean, David Craig, Ka Lok Li, Gareth O’Brien, Caoimhe Hickey, and Billy O'Keeffe

Water is a critical resource that can range from being either available in short supply or excess, causing floods. In many locations the majority of this supply is underground. In some geological terrains such as karst these underground systems transport water primarily through crack or conduit flow. Determining the subsurface locations of the dominant flowing structures and their flow rates in such karst systems is a significant challenge. The details of these complex flow networks can, for example, have a first-order control on water supply, surface floods and the locations of seasonal lakes. Current geophysical methods focus on active geophysical imaging of karst structures but usually fail in determining if such structures are flowing. In this work, we take a different approach locating flowing conduits in Irish karst via a multi-method analysis of ground vibrations from temporary deployments of passive seismic sensors. We start by testing the methodology on surface rivers.

Hydrological processes including turbulent water flow and sediment transport create ground vibrations that can be detected on seismic stations. In the initial test, we deployed two small aperture arrays of 4 and 6 three-component (3C) short-period seismometers and a short linear array beside a river with a typical flow rate of 25 m3/second. We see clear spectral peaks associated with water flow at frequencies of 10 to 40 Hz. We locate the sources for these frequency bands using both conventional beamforming array analysis and an Amplitude Source Location Method (ASLM). Before ASLM, we constrain the velocity based on array analysis. Both methodologies perform well in determining the known locations of rapid flow in the river. We then move to a test karst location where the subsurface pathways of large conduits are known through cave dives. We deploy 3C short period seismometers for a few hours. Again we see clear peaks in the seismic spectra which, using ASLM and Frequency-Dependent Polarization Analysis (FDPA), located close to the known conduits. In the station close to a known conduit, we see sustained very high-frequency signals which are in agreement with numerical simulation of crack dominated flow for secondary short narrow cracks. This work is the prelude to a larger seismic nodal deployment that will take place in the winter/spring of 2020 in the same location. Initial results from that experiment will also be presented.

How to cite: Karbala Ali, H., Bean, C., Craig, D., Li, K. L., O’Brien, G., Hickey, C., and O'Keeffe, B.: Tracking surface and subterranean water flow using continuous seismic tremor, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20833, https://doi.org/10.5194/egusphere-egu2020-20833, 2020.

EGU2020-7033 | Displays | GM2.6

Modelling the source of glacial earthquakes for a better understanding of the impact of iceberg capsize on glacier stability

Pauline Bonnet, Vladislav Yastrebov, Alban Leroyer, Patrick Queutey, Anne Mangeney, Olivier Castelneau, Eleonore Stutzmann, Jean-Paul Montagner, and Amandine Sergeant

One current concern in climate science is the estimations of the amount of ice loss by glaciers each year and the corresponding rate of sea level rise. Greenland ice sheet contribution is significant with about 30% to the global ice mass losses. Ice loss in Greenland is distributed approximately equally between loss in land by surface melting and loss at the front of marine-terminating glaciers that is modulated by dynamic processes. Dynamic mass loss includes both submarine melting and iceberg calving. The processes that control ablation at tidewater glacier termini, glacier retreat and calving are complex, setting the limits to the estimation of dynamic mass loss and the relation to glacier dynamics. It involves interactions between bedrock – glaciers – icebergs – ice-mélange – water – atmosphere. Moreover, the capsize of cubic kilometer scale icebergs close to a glacier front can destabilize the glacier, generate tsunami waves, and induce mixing of the water column which can impact both the local fauna and flora.

We aim to improve the understanding of iceberg capsize using a mechanical modeling of iceberg rotation against the glacier terminus, constrained by the generated seismic waves that are recorded at teleseismic distances. To achieve this objective, we develop a fluid-structure interaction model for the capsizing iceberg. Full scale fluid-structure interaction models enable accurate simulation of complex fluid flows in presence of rigid or deformable solids and in presence of free surfaces. However, such models are computationally very expensive. Therefore, our strategy is to construct a simple solid dynamics model involving contact and friction, whose simplified interaction with water is governed by parametrized forces and moments. We fine tune these parametrized effects on an iceberg capsizing in contact with a glacier with the help of reference direct numerical simulations of fluid-structure interactions involving full resolution of Navier-Stokes equations. We assess the sensitivity of the glacier dynamics to the glacier-bedrock friction law and the conditions for triggering a stick-slip motion of the glacier due to iceberg capsize. The seismogenic sources of the capsizing iceberg in contact with a glacier simulated with our model are then compared to the recorded seismic signals for well documented events.

How to cite: Bonnet, P., Yastrebov, V., Leroyer, A., Queutey, P., Mangeney, A., Castelneau, O., Stutzmann, E., Montagner, J.-P., and Sergeant, A.: Modelling the source of glacial earthquakes for a better understanding of the impact of iceberg capsize on glacier stability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7033, https://doi.org/10.5194/egusphere-egu2020-7033, 2020.

EGU2020-728 | Displays | GM2.6

What ground tilt tells us about debris flow parameters

Michaela Wenner, Fabian Walter, Kate Allstadt, Brian McArdell, and Andrew Lockhart

Large mass movements cause the surface of the earth to deform, depending on the spatial distribution and magnitude of the mass movement and the response of the ground. In volcanology, tilt measurements are used to study earth surface displacement during volcanic processes such as dyke intrusions and magma chamber collapses. Broadband and long period seismometers also record tilt signals at periods of tens to hundreds of seconds, with the horizontal components being most sensitive to tilt. To obtain tilt from seismic recordings the signal from true ground motion and from apparent ground motion due to tilt have to be seperated. Nevertheless, seismometers have shown similar sensitivities as tiltmeters and are, depending on the type of tiltmeter and study site, less cumbersome to install. In this study, we explore the capability of tilt measurements from surface tiltmeters and broadband seismic sensors to determine debris flow parameters like mass, density and flow velocity. We focus on seismic broadband data recorded within a few meters of the Illgraben torrent in Switzerland. Illgraben’s catchment is one of the most active mass wasting sites in the European Alps, producing several debris flows per year. Our seismic records show clear tilt signals from more than ten debris-flow events in 2018 and 2019, which we compare to data from large-scale laboratory experiments at the U.S. Geological Survey (USGS) debris-flow flume at which broadband seismometers and tiltmeters were installed for six 8-10 m3 experiments in 2016.

To explain our observations, we present a model for the loading response of a layered elastic half-space to a moving surface load. This model can be used to invert our observed tilt signals for the surface load, i.e., the mass, density and/or geometry of the debris flow. To verify our model, we use nearby force plate and flow height measurements at both study sites. We discuss to what extent and under which assumptions, compared to force plate installations, the relatively simple and inexpensive tilt measurements can be used to determine debris flow parameters, which to date require sophisticated equipment.

How to cite: Wenner, M., Walter, F., Allstadt, K., McArdell, B., and Lockhart, A.: What ground tilt tells us about debris flow parameters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-728, https://doi.org/10.5194/egusphere-egu2020-728, 2020.

Normalized Difference Water Index (NDWI) has been widely used to detect water bodies and enhance them in the satellite imagery. In order to determine water bodies in Landsat TM, Mid-Infrared and Green bands are used but this combination is often encountered with vegetation, soil and build-up land noises and the water bodies area was not calculated accurately and most of the time the results are higher than the actual area and was overestimated, NDWI does not remove soil and vegetation noises completely because of using the NIR band reflection, therefore, to eliminate these noises, Modified Normalized Difference Water Index (MNDWI) with different bands in Landsat TM such as Shortwave and Near-Infrared bands has been used and best image that shows water bodies more accurate has been provided. We need to test different band combination and also different NDWI and MNDWI indexes in the range of Red, Near-Infrared, Shortwave Infrared and Mid-Infrared to determine the best performing index. For this purpose, Gorganroud river basin was selected as study area, which is located in north-east of Iran and is one of the largest rivers in Iran and because of 2 dams located in the river basin and long distance of river, studying water bodies could be easier in comparing with other river basins of Iran. we compared NDWI and MNDWI indices and results shown that MNDWI index using Landsat TM bands Green and Mid-infrared has higher accuracy than NDWI and other calculated indices with different bands of Landsat TM. It can remove the vegetation, soil and build-up noises better than NDWI and water bodies can be shown clearly. The MNDWI is more suitable to extract water bodies and study the information of water regions with dominating the soil, vegetation and build-up land noises because of its advantage in reducing or even removing those noises over NDWI.

Key words: Normalized Difference Water Index (NDWI), Modified Normalized Difference Water Index (MNDWI), Landsat 5, water bodies, Gorganroud river basin

How to cite: eishoeei, E. and Miryaghoubzadeh, M.: Capability assessment of two water indexes in remote sensing data in order to water bodies classification (case study: Gorganroud River - North east of Iran), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1135, https://doi.org/10.5194/egusphere-egu2020-1135, 2020.

EGU2020-1950 | Displays | GM2.6

Environmentally hardened, high-altitude, high-latitude seismic stations on Mt. Erebus, Antarctica

Bruce Beaudoin, Kirsten Arnell, Paul Carpenter, Narendra Lingutla, John Meyers, Kevin Nikolaus, and Aurora Roth

The IRIS/PASSCAL Instrument Center is installing 5 seismic stations around the summit of Mt. Erebus, Antarctica. IRIS is funded by the National Science Foundation to install and maintain these stations long-term, a task undertaken by the Polar team at PASSCAL. The purpose of the network is to provide a baseline measurement of volcanic events and act as a fiducial array for future experiments. Each station’s instrument package comprises a data logger recording a broadband and strong-motion seismometer, and a separate data logger recording an infrasound sensor. Station state of health and near real-time data are transmitted via Iridium modems.

The Mt. Erebus network is installed between 2000 m and 3400 m elevation spaced around the volcano summit. This is a particularly harsh environment for operating autonomous seismic stations with extreme low temperatures and high winds. Station power systems need to have enough capacity to winter-over for roughly 6-months without recharge. Station enclosures need to provide sufficient insulation to keep the data logger within its temperature operating range.

To design these stations for long term, 365/24/7 operation, we leveraged proven station enclosure and power system designs developed over the last 12 years of PASSCAL engineering seismic systems for Antarctica. The Mt. Erebus station design is modular and standardized, separating the bulk of the power storage and electronics' enclosures, allowing for streamlined upgrades or additions without having to overhaul the entire station. Power for the system will rely on lead acid batteries and solar charging; forgoing higher efficiency primary lithium thionyl chloride batteries used elsewhere in Antarctica, to reduce long-term station costs.

Station health will be monitored at IRIS/PASSCAL and low sample rate (20 sps) broadband data will be captured in near-real time. Higher sample rate data are recorded locally and collected annually during the austral summer. All data will be available from the IRIS Data Management Center.

How to cite: Beaudoin, B., Arnell, K., Carpenter, P., Lingutla, N., Meyers, J., Nikolaus, K., and Roth, A.: Environmentally hardened, high-altitude, high-latitude seismic stations on Mt. Erebus, Antarctica, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1950, https://doi.org/10.5194/egusphere-egu2020-1950, 2020.

Southeastern Mongolia has limited access due to its extreme environments (long and harsh winter) and lack of infrastructure (e.g., road). Satellite remote sensing technique is one of the most effective methods to get geological information in areas where field survey is difficult. WorldView-3 (WV3), launched in August 2014, is high-spatial resolution commercial multispectral sensor developed by DigitalGlobe. WV3 measures reflected radiation in eight visible near infrared (VNIR) bands between 0.42 and 1.04 ㎛ and in eight short-wave infrared (SWIR) bands between 1.20 and 2.33, which have 1.24- and 7.5-m spatial resolution, respectively. In this study, WV3 VNIR and SWIR data were used to identify and map the various minerals in the Ikh Shankhai porphyry Cu deposit district, Mongolia.

The Ikh-Shankhai porphyry Cu deposit is located within Gurvansayhan island arc terrane in southeastern (SE) Gobi mineral belt, Mongolia. The Ikh-Shankhai district include the porphyry system containing Cu-Au with primary chalcopyrite, which is classified into disseminated type and stockwork quartz type. This district consists of Late Devonian-Early Carboniferous andesite, tuff and siltstone intruded by Carboniferous-Permian granite, granodiorite and granodiorite porphyry.

The WV 3 data were analyzed using mixture-tuned-matched filter (MTMF) which locates a known spectral signature in the presence of a mixed or unknown background. MTMF does not require knowledge of all of the spectral endmembers and is suited for used where materials with distinct spectral signatures occur within a single pixel. From the WV3 analysis result using mixture-tuned-matched filter (MTMF), we identified the location and abundance of alteration minerals. Advanced argillic minerals (alunite, kaolinite (or dickite), and pyrophyllite) were dominant in the lithocaps of the Budgat and Gashuun Khudag prospects; whereas, phyllic (illite) and propylitic (calcite and epidote) minerals were dominant in the areas surrounding the lithocaps. In addition, the distribution of ferric minerals (hematite and goethite) was mapped because of the oxidation of pyrite. Field work at the Ikh-Shankhai porphyry Cu district to evaluate the accuracy of the mineral mapping results was carried out in August, 2018. Reflectance spectra acquisition using a portable ASD TerraSpec Halo mineral identifier (the attached GPS covered a spectral range of 0.35 – 2.5 µm) was conducted in the altered outcrops of the Ikh-Shankhai porphyry Cu district. Mineral mapping results compared well with the field spectral measurements collected for the ground truth and demonstrated WV3 capability for identifying and mapping minerals associated with hydrothermal alteration. Evaluation of the WV3 mineral mapping results using ground truth data indicates, however, a difficulty in mapping spectrally similar minerals (e.g., kaolinite and dickite) due to spectral resolution limitation.

How to cite: Youngsun, S. and Kwang-Eun, K.: Mineral mapping at the Ikh Shankhai porphyry Cu deposits, Mongolia using WorldView-3 data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2359, https://doi.org/10.5194/egusphere-egu2020-2359, 2020.

EGU2020-2445 | Displays | GM2.6

Swiss Geophone Plate system: Quantification of the variability of signal response and of the signal propagation across plates using field-based impact experiments

Gilles Antoniazza, Tobias Nicollier, Carlos R. Wyss, Stefan Boss, and Dieter Rickenmann

Impact sensors are increasingly used to indirectly monitor bedload transport in streams. Among them, the Swiss geophone impact plate system has notably proved its efficiency to continuously record bed load transport rates. Nevertheless, this approach still requires a robust calibration of the sensors to transform the relative signal of the geophones into an absolute mass of sediment in transport. Typically, the calibration is performed through the sampling during natural bedload transport events of all the particles that impact the plates, in order to build up rating curves between the signal recorded by the geophone sensors and the characteristics of the sediment that impact them (e.g. mass, grain size).  To better understand the system behavior it is important to quantify to what extent the signal response is similar (i) between sensors of a same geophone measuring station and (ii) between different geophone measuring stations. Also (iii), the amount of signal that propagates from impacted plates towards non-impacted plates (or ‘neighbouring noise’) needs to be quantified to improve the understanding of the system.

In this study, we investigate the above three elements by performing an impact experiment on the Swiss geophone plate system, and systematically record the signals produced at different plates by defined impacts of similar magnitude, and how the signal (maximum amplitude) propagates through neighbouring non-impacted plates. Each Swiss Geophone Plate of four measuring stations in the Swiss Alps – Vallon de Nant (VD), Albula (GR), Naviscence (VS) and Riedbach (VS) – were hit alternatively with impacts of increasing magnitude, and the signal they produced was systematically recorded over all the sensors of a given measuring station. Results of the study allow (i) to quantify the neighbouring noise that propagates from impacted plates towards non-impacted plates; (ii) to evaluate the attenuation rate of the signal for an impact of a given magnitude and (iii) to evaluate the variability in the propagation of neighbouring noise between sensors at a given measuring station and between different measuring stations.

How to cite: Antoniazza, G., Nicollier, T., Wyss, C. R., Boss, S., and Rickenmann, D.: Swiss Geophone Plate system: Quantification of the variability of signal response and of the signal propagation across plates using field-based impact experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2445, https://doi.org/10.5194/egusphere-egu2020-2445, 2020.

EGU2020-3357 | Displays | GM2.6

Locating the rock hazard and understanding its physical process using seismic signals

Jui-Ming Chang, Wei-An Chao, and Hongey Chen

Rock hazard is a common geohazard event that occurs in the orogenic mountain belt and often causes the destruction of road and casualties. The steep topography, fractured bedrock and frequent earthquakes favor to happen. Those are usually fast and unpredictable, leading a lack of direct observation of physical process. Recent seismological studies highlighted the rock hazard induced seismic signals could improve understanding of its dynamics. This study focuses on the three provincial highways that cross the Taiwan Island from east to west. The regions along the highways have the complexity in tectonic structure and extreme climate-forced erosion, causing the hazard frequently occurred. In order to understanding seismic features and physical process of rock hazard, we conducted a series of seismic analyses using the seismic records collected form regional seismic network for ten events, which were reported by the government agency. Four of them have the video recordings, which would be helpful to understanding the relationships between physical process (falling, rolling, bouncing and fragmentation), movement type (fall, topple, slump, slide, avalanche or complex) and seismic features. We developed the hybrid method of determination of geohazard event location (GeoLoc) that combines the cross-correlation-based method and the amplitude-attenuation-based approach. We apply the GeoLoc scheme to locate the events recorded by the seismic station with epicentral distance ranging from 2 to 56 kilometers (km) and it helps to reduce the location error. The leading seismic signals of the mass detachment linked to the crack propagation or slope response can be observed, and we also found that the seismic feature caused by fragment of rock block exhibits the higher frequency than the seismic signals corresponding to impaction of rock particles. Our results highlight the possibility of the seismic technique for locating rock hazards distributed along highways in a regional scale and further understanding its physical process. The aforementioned results would be helpful to build the near-real-time monitoring system along the highways for hazard mitigation of events.

How to cite: Chang, J.-M., Chao, W.-A., and Chen, H.: Locating the rock hazard and understanding its physical process using seismic signals, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3357, https://doi.org/10.5194/egusphere-egu2020-3357, 2020.

EGU2020-6680 | Displays | GM2.6

Non-tectonic seismological events in Greenland - Cryo-generated events and landslides

Trine Dahl-Jensen, Tine B. Larsen, and Peter H. Voss

Following the large June 17 2017 landslide in Karrat Isfjord, Central West Greenland the necessity to differentiate between different kinds of seismological events has become relevant for hazard assessment. Greenland is the origin of a many different kinds of seismic signals.  In addition to the than a thousand small to moderate magnitude tectonic earthquakes, most of them ranging between ML 1.0 and 3.0 are located along the coasts of Greenland every year, many other non-tectonic events are located. This is largely possible thanks to the data collected and distributed by the Greenland Ice Sheet Monitoring Network (GLISN) federation and its members (glisn.info). The non-tectonic events include cryo-generated events, and signals from landslides as for example illustrated by the globally seen seismological signal from the Karrat 2017 landslide. It is possible to separate tectonic events from non-tectonic events, based on the characteristics of the seismological signal alone, but the signals from cryo-generated events and landslides have many similar features. In the Karrat Isfjord area, several large glaciers terminate in the sea where for example calving generate seismological events. With poor location resolution due to large station spacing in the remote areas of Greenland, the differences in the seismological signals are important to determine the cause of the events.

How to cite: Dahl-Jensen, T., Larsen, T. B., and Voss, P. H.: Non-tectonic seismological events in Greenland - Cryo-generated events and landslides, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6680, https://doi.org/10.5194/egusphere-egu2020-6680, 2020.

EGU2020-14290 | Displays | GM2.6

Set-up and performance evaluation of a seismic rock fall observatory in the Alps

Anne Schöpa, Niels Hovius, and Jens Turowski

Rock falls are important agents of erosion shaping the topography of bedrock slopes. Despite the considerable attention rock falls get when causing damage we still lack detailed information about the triggers, lag times, seasonal and elevation-dependent rock fall occurrence. This is due to the difficulty in observing rockfalls directly as the mobilisation of rock masses occurs rapidly, infrequently and distributed at a priori unknown locations. To identify seasonal and elevation-dependent rock fall activities and characteristics and their environmental drivers and triggers in an alpine setting, we have operated a monitoring network to detect and classify rock falls in the Reintal valley, German Alps, since 2014. The Reintal is an Alpine valley in the Wetterstein massif close to the Zugspitze, Germany’s highest mountain. The Reintal observatory produces nearly continuous datasets of seismic, meteorological and camera data. To our knowledge, these datasets are one of a few that permit a systematic study of rockfall patterns and their controls over a period of several years in an alpine setting.

In this contribution, we present the layout of the observatory and the instrumental network. Six seismometers record the motion of the ground; different types of seismic signals are shown and their sources discussed. This is done in combination with the meteorological data of the two weather stations in the valley and the images of the optical and infrared cameras of the observatory. We evaluate the performance, limitations and capabilities of the observatory. In addition, we discuss how we dealt with challenges such as power consumption of the instruments in the field, data storage and data loss. Our experience with the set-up and maintenance of the observatory can help guide the design and construction of other observatories in mountain environments.

How to cite: Schöpa, A., Hovius, N., and Turowski, J.: Set-up and performance evaluation of a seismic rock fall observatory in the Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14290, https://doi.org/10.5194/egusphere-egu2020-14290, 2020.

EGU2020-9528 | Displays | GM2.6

Geophysical insights on the internal dynamics of lahars from Lumbre channel, Volcán de Colima, Mexico

Braden Walsh, Velio Coviello, Lucia Capra, Jonathan Procter, and Victor Márquez-Ramirez

Here, we present data from lahars through the use of a 3-component broadband seismometer, accelerometer, and a video camera installed 3 m from the Lumbre channel on Volcán de Colima, Mexico to understand rheology differences within multiple events, which occurred in late 2016. We used a combination of peak frequency content, directionality, and video analysis to determine rheology changes amongst the multiple events. Our findings show that different peak frequency patterns in each seismic component correspond to differing rheologies and flow processes. For instance, in the vertical and flow parallel directions the transition from streamflow to lahar coincides with a narrow frequency distribution to wide. Conversely, the cross-channel frequency content is opposite with streamflow portraying a wide frequency distribution transitioning to a narrow distribution with the lahars. Furthermore, there is a drop in overall peak frequencies when transitioning from streamflow to lahar. The directionality ratios computed further yielded evidence for a rheologic change between streamflow and lahar. Directionality ratios >1 were calculated for each lahar, and <1 for streamflow. We go on to show that componential analyses yielded channelization or freedom of movement in the cross-channel, bedload transport in the flow parallel, and channel geology in the vertical direction are possibly the main drivers in the peak frequency output of debris flows.

How to cite: Walsh, B., Coviello, V., Capra, L., Procter, J., and Márquez-Ramirez, V.: Geophysical insights on the internal dynamics of lahars from Lumbre channel, Volcán de Colima, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9528, https://doi.org/10.5194/egusphere-egu2020-9528, 2020.

EGU2020-9734 | Displays | GM2.6

Classification of Seismic Events with Deep Learning Strategies: Insights from the Moosfluh Landslide

Nadir Dazzi, Andrea Manconi, Nikhil Prakash, and Valentin Bickel

Rockfalls affect steep slopes in several geographic regions. Different systems from remote to in-situ instruments are used for their detection and study. In this scenario, seismic signals produced by the detachment, bouncing, and rolling of rockfalls are being increasingly used for the detection and classification of such events. This is typically done by using different manual, semi-automatic and/or automatic signal processing strategies. In this work, we applied a new Deep Learning (DL) algorithm in order to test the performance on the automatic classification of seismic signals. We applied the method to seismic data acquired by a low-cost Raspberry Shake 1D seismometer (sampling rate 50Hz) in order to discriminate rockfall from not-rockfall events occurred at the Moosfluh active slope region in Wallis (CH). Here we present the methodology and show the results obtained on a continuous record of more than 2-years of seismic data. The performance accuracy of the DL approach reached values larger than 90%. Our results show that the application of DL strategies in this context can be very useful and save time on seismic data classification.

How to cite: Dazzi, N., Manconi, A., Prakash, N., and Bickel, V.: Classification of Seismic Events with Deep Learning Strategies: Insights from the Moosfluh Landslide, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9734, https://doi.org/10.5194/egusphere-egu2020-9734, 2020.

EGU2020-9797 | Displays | GM2.6

Testing seismic noise caused by highly concentrated sediment flows in laboratory experiments

Marco Piantini, Florent Gimbert, Alain Recking, and Hervé Bellot

Sediment transport processes and fluxes play a key role in fluvial geomorphology and hazard triggering. In particular, extreme floods characterized by highly concentrated flows set the pace of mountain landscape evolution, where the linkage between streams and sediment sources leads to strong solid inputs characterized by significant grain sorting processes. The main observation that river processes generate ground vibrations has led to the application of seismic methods for monitoring purposes, which provides an innovative system that overcomes traditional monitoring difficulties especially during floods. Mechanistic models have been proposed in the attempt to invert river flow properties such as sediment fluxes from seismic measurements. Although those models have recently been validated in the laboratory and in the field for low transport rates, it remains unknown whether they are applicable to extreme floods.

Here we carry a set of laboratory experiments in a steep (18% slope) channel in order to investigate the link between seismic noise and sediment transport under extreme flow conditions with highly concentrated sediment flows. The originality of this set-up is that instead of feeding the flume section directly as usually done, we feed with liquid and solid discharge a low slope storage zone connected to the upstream part of the steep channel. This allows us to produce sediment pulses of varying magnitude (up to the transport capacity) and granulometric composition, traveling downstream as a result of alternate phases of deposition and erosion occurring in the storage area. We measure flow stage, seismic noise, sediment flux and grain size distribution. We find that the previously proposed relationships between seismic power, sediment flux and grain diameter often do not hold in such sediment transport situations. We support that this is due to granular interactions occurring between grains of different sizes within the sediment mixture and leading to complex grain sorting processes. In particular, we observe that bigger grains do not directly impact the bed but rather roll over fines or smaller grains, such that observed seismic power is much lower than expected. These results constitute a starting point for the development of a new mechanistic model for seismic power generated by highly concentrated bedload sediment flows.

How to cite: Piantini, M., Gimbert, F., Recking, A., and Bellot, H.: Testing seismic noise caused by highly concentrated sediment flows in laboratory experiments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9797, https://doi.org/10.5194/egusphere-egu2020-9797, 2020.

EGU2020-12051 | Displays | GM2.6

A Versatile and Complete Technology Platform for Autonomous Ocean Bottom Seismometry

Andrew Moores, Bruce Townsend, Sylvain Pigeon, and Ted Somerville
Ocean Bottom Seismometry has more constraints than terrestrial seismometry due to the challenging environment, complex logistics and high costs associated with operating on the seafloor. However, the scientific objectives of a station are the same: to reliably record high-quality ground motion signals with sufficient fidelity to discern phenomena of interest that manifest above the baseline background earth noise at any given site. To better address the specific needs and challenges of ocean bottom seismology, Nanometrics in conjunction with Scripps Institute of Oceanography, is developing a comprehensive OBS solution that comprises versatile but compact instrument platforms, ultra-low power high-performance seismometers and datalogger, and an end-to-end workflow that spans the entire process from on-shore campaign design to shipboard operation, delivering ready-to-use complete datasets. Recent SWaP (Size, Weight and Power) breakthroughs in seismometer and datalogger technology realize more than 50% power reduction and 40% size/weight reduction for broadband and very broadband sensors, and high precision low-power digitizing technology, which together offer very low noise OBS stations with extremely low power consumption. This next-generation seismometer technology is based on proven intermediate and very broadband sensors that have been deployed widely by oceanographic institutes globally. Key benefits of the complete OBS ecosystem and end-to-end workflow include significantly extended deployment durations, the same seismic sensor performance options for OBS as on land,from geophones to the newest generation of ultra broadband seismometers, optimal operational cost resulting from greatly improved ease-of-use and low SWaP, and high outcome certainty due in part to integrated simple workflows designed specifically for the autonomous OBS use case. Ultra-fast harvesting of data produces a ready-to-use dataset including automatically generated StationXML response metadata and automatic time correction, and facilitates rapid recovery and redeployment of OBS stations.  

 

How to cite: Moores, A., Townsend, B., Pigeon, S., and Somerville, T.: A Versatile and Complete Technology Platform for Autonomous Ocean Bottom Seismometry , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12051, https://doi.org/10.5194/egusphere-egu2020-12051, 2020.

Heatwaves are extended periods of extremely hot weather and high temperature that have a major impact on human health, socioeconomics and natural systems. As predicted by climate models, ongoing global warming will potentially increase the incidence, intensity and duration of summertime heatwave events. Nevertheless, heat-related health impacts are largely preventable if populations, health and social care systems and public infrastructure are prepared. Therefore, this is plausible if heatwave events are studies for which heatwave real-time monitoring and assessment are central components. It is well recognized that land surface temperature retrieved by satellite sensors is an important variable associated with heatwaves and surface warming research. Land surface temperature retrieved by satellite sensors can be observed spatially and temporally, adequate for applications needing real-time and continuous measurements in quick response. In this study, Chinese Fengyun satellite data were used to monitor the land surface thermal environment during the heatwave event in Belt and Road communities. Split-window algorithm were applied to retrieve land surface temperature from thermal sensor. Spatial temporal distributions of Land surface high temperature are monitored in West Europe, India, and Australia as examples during their high temperature weather. The result shows that monitoring the real-time heatwave hazards in quick responds help provided information to the decision makers and get insight into the thermal environment characteristics over urban areas.

How to cite: Xu, R.: Land Surface High Temperature Monitoring in Belt and Road Communities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13486, https://doi.org/10.5194/egusphere-egu2020-13486, 2020.

EGU2020-18637 | Displays | GM2.6

Certimus, a seismic station optimized for rapid deployment in rugged terrain

Marie Balon, Sofia Filippi, Sally Mohr, Phil Hill, and Neil Watkiss

Operators of broadband seismic stations, particularly in hostile locations, are restricted in experiment design and deployment time-frames by the significant constraints of historical instrumentation. Manufacturers need to move away from the strict requirements on tilt tolerance and associated performance compromises, fixed frequency responses, unfriendly interfaces, slow data downloads and power-hungry systems in favour of simple, flexible and smart instruments that allow the operator to focus on the science at hand.

This transition is already happening with the evolution of seismic monitoring towards compact technologies: rapid-response deployments have, in recent years, become more and more feasible. However, installing low-noise, broadband instruments in remote areas has remained a challenge: low-noise force-balance broadband seismometers are typically heavy and delicate. They require significant infrastructure and logistics.

By developing the standalone, compact Certimus - with the same level of performance as traditional force-balance broadband seismometers - Güralp now offers researchers the opportunity to further push the boundaries of seismic monitoring and deploy stations in more and more challenging environments.

Unique sensor components allow Certimus to function up to 90 degrees tilt, removing the need for time-consuming centring, and allowing the station to be placed in small, hand-dug shallow holes. In 1s mode, the sensor will settle quickly and reliable data can be available in a matter of hours.  The frequency range is fully configurable in the long-period corner to allow this level of flexibility: 120s, 10s and 1s to 100Hz.

Certimus offers easy ways to check installation integrity – State-of-Health and live waveforms – before leaving the site: both with the surface and the burial variants, either via Bluetooth, LCD screen or Web Interface.

Since power consumption is a major limitation, Certimus comes with an ultra-low power mode (under 300mW) and a rugged battery module to gain up to six weeks of data before retrieval – or before a permanent power supply is arranged.

All files are recorded in industry standard miniSEED format making data download and management simplistic and universal. The metadata auxiliary channels record a vast range of state of health parameters to ensure optimal qualification of the seismic data with the environmental conditions of the seismic station.

All these advanced features are gathered in a compact, lightweight case that can be carried with all its accessories in a backpack to the most inaccessible areas. Quality seismic data is made available swiftly from anywhere, anytime.

How to cite: Balon, M., Filippi, S., Mohr, S., Hill, P., and Watkiss, N.: Certimus, a seismic station optimized for rapid deployment in rugged terrain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18637, https://doi.org/10.5194/egusphere-egu2020-18637, 2020.

GM3.4 – Biogeomorphology/Ecogeomorphology: conceptualising and quantifying processes, rates and feedbacks

EGU2020-3700 | Displays | GM3.4 | Highlight

Biogeomorphological research frontiers: from ant mounds to Mars

Heather Viles

Biogeomorphology is a vibrant area of scientific research which focuses on the two-way interrelationships between ecological and geomorphological processes across a wide range of temporal and spatial scales. Whilst ecological influences on geomorphology were often perceived in the past as a rather niche topic, most geomorphologists now  consider the ecological dimension as being crucial to the evolution and behaviour of geomorphological systems. However, there is still much to be done to explore the intersections between ecology and geomorphology. It is now timely to investigate what frontier research in biogeomorphology might look like over the coming years. This paper explores some characteristics of frontier research (addressing scientific controversies, focusing on hard-to-answer questions, employing atypical methods and concepts, being paradigm-challenging, and having a high risk of failure) in the context of tomorrow’s biogeomorphology. As examples, the paper addresses current progress in research on the geomorphological contributions of ants on Earth, and microbial biosignatures on Mars.

How to cite: Viles, H.: Biogeomorphological research frontiers: from ant mounds to Mars, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3700, https://doi.org/10.5194/egusphere-egu2020-3700, 2020.

Under natural conditions, the structure and development of river corridors is controlled by an interplay of hydrological, geomorphological and ecological processes. Over the past decade, the concept of biogeomorphology has become increasingly popular to describe and analyze the manifold feedback mechanisms within river systems leading to an increasing number of studies. However, the majority of this work focuses either on conceptual development or on investigations on the scales of single geomorphic units or study reaches. Only very few studies enlarge the spatial scale to entire river corridors or networks despite the fact that recent frameworks emphasize these scales to be relevant for river research and management. A recent trend in remote sensing of terrestrial ecosystem is the use of dense imagery time series to assess trends and disturbances of vegetation development. In this study, we transfer this idea to the analysis of biogeomorphological interactions within fluvial environments on large spatial scales. We take the Naryn River in Kyrgyzstan as an example for demonstrating our satellite time series approach to biogeomorphological analysis of river corridors. The Naryn is still in a natural state on an entire flow length of more than 600 km with full longitudinal and lateral connectivity. Along the central part of the catchment, the Naryn is a highly dynamic braided river system shaped by the annual summer floods of a glacial discharge regime. This makes this river ideal to study large scale biogeomorphological dynamics. In our study, we follow the well-established concept of biogeomorphological succession suggested by Dov Corenblit and his colleagues. We mapped the different succession phases in the field and used the results to derive spectral-temporal indices of the succession phases. These indices are on the one hand used for a supervised classification based on Sentinel-2 imagery. On the other hand, we use Sentinel-2 as well as the longer term Landsat imagery time series to analyze the data for statistical trends and changepoints and evaluate this regarding biogeomorphological succession and disturbance events. The results reveal that dense time series of optical satellite imagery are well suited data sources to derive indicators of biogeomorphological interactions on large spatial scales. Especially when using the recently available Sentinel-2 imagery, such indicators have the potential to analyze biogeomorphological dynamics of entire river corridors or networks in a spatially and temporally continuous way at a reasonable spatial resolution.

How to cite: Betz, F., Lauermann, M., Egger, G., and Cyffka, B.: Biogeomorphology from Space: Using optical satellite imagery time series for analyzing the dynamic interaction of vegetation and hydromorphology along the Naryn River, Kyrgyzstan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10291, https://doi.org/10.5194/egusphere-egu2020-10291, 2020.

EGU2020-3162 | Displays | GM3.4

Biological weathering by the Devonian trees

Lukasz Pawlik, Brian Buma, Pavel Samonil, Jiri Kvacek, Anna Galazka, Petr Kohout, and Ireneusz Malik

We applied the biogeomorphic ecosystem engineers concept to the Devonian Plant Hypotheses. By linking these two ideas we want to explore how recent discoveries on the role of trees in weathering processes could support the explanation of global environmental changes in the Devonian period. The occurrence of first land plants, vascular plants, trees, and complex forest ecosystems likely changed the nature and pace of many geomorphic and pedogenic processes. For instance, intensification of biological weathering driven by vascular plants might have influenced the global climate through consumption and accumulation of a large volume of atmospheric CO2. Innovation in the form and function of trees likely strongly influenced these processes, including soil stabilization via deep root systems. Mycorrhizal relationships further influenced weathering via chemical processes. While the lack of solid evidence in the fossil record still pose a problem, the progress in our understanding of soil-weathering processes induced by trees and root systems has expanded greatly in recent years, especially in terms of their biogeomorphic functions (e.g. tree uprooting, pedoturbations, biomechanical weathering, etc.), and can provide insights and testable hypotheses regarding the role of trees in the Late Devonian.

How to cite: Pawlik, L., Buma, B., Samonil, P., Kvacek, J., Galazka, A., Kohout, P., and Malik, I.: Biological weathering by the Devonian trees, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3162, https://doi.org/10.5194/egusphere-egu2020-3162, 2020.

EGU2020-6840 | Displays | GM3.4

Modelling of interactions between bioturbation and mud distribution reveals effects on large-scale estuarine morphology

Muriel Brückner, Christian Schwarz, and Maarten Kleinhans

Macrobenthic species that live within or on top of estuarine sediments can destabilize local mud deposits through their bioturbating activities. Resulting enhanced sediment availability will affect redistribution of fines and hence large-scale morphological change. To quantify this biological control on the morphological development of estuaries, we numerically model two contrasting bioturbating species present in NW-Europe by means of our novel literature-based eco-morphodynamic model. We find significant effects of both bioturbators on local mud accumulation and bed elevation change, leading to a large-scale reduction in deposited mud and gently sloped intertidal floodplains. In turn, the species-dependent reduction of mud content redefines their habitat and leads to constricted species abundances. Our results show that species-specific macrobenthic bioturbation determines large-scale morphological change through mud redistribution. This suggests that macrobenthic species have subtly changed estuarine morphology through space and time, depending on their distribution and composition.

How to cite: Brückner, M., Schwarz, C., and Kleinhans, M.: Modelling of interactions between bioturbation and mud distribution reveals effects on large-scale estuarine morphology, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6840, https://doi.org/10.5194/egusphere-egu2020-6840, 2020.

EGU2020-22185 | Displays | GM3.4

Hydrodynamic Stressing and the Response of Endangered Freshwater Pearl Mussels to Turbulent Flows

Edward Curley, Rhian Thomas, Colin Adams, Manousos Valyrakis, and Alastair Stephen

Whilst there is encouragement to be taken from the fact that Scotland remains a stronghold for M. margaritifera populations, a trend of continued population decline persists. Our understanding of the hydraulic characteristics associated with successful M. margaritifera proliferation in the wild is poor. Additionally, evidence to suggest how M. margaritifera respond to variation in the associated parameters, is limited. The primary motif of this research project is to address the knowledge gap. Initial experimental analysis sought to establish a non-invasive method of quantifying acute mussel stress; using behavioural response indicators, coupled with measures of physiological condition. Results from this work have provided a foundation for investigating mussels as biosensors to remotely track alterations in chemical, hydraulic, and geomorphological parameters. Further research has investigated the response of live mussels to alterations in flow depth, with consideration of riverbed geomorphology, in both a laboratory flume and regulated river. Current experimental work in a laboratory flume is utilising remote sensor technology to understand the impact of flow velocity on mussel behaviour; examining how flow velocity may impact habitat selection, and how a mussel’s behaviour may in turn affect the surrounding hydrodynamics. The results emanating from this research will be novel and will ultimately provide urgently needed empirical data to drive future conservation strategies implemented by government (SNH, SEPA) and utilized by the hydroelectric industry (SSE).

How to cite: Curley, E., Thomas, R., Adams, C., Valyrakis, M., and Stephen, A.: Hydrodynamic Stressing and the Response of Endangered Freshwater Pearl Mussels to Turbulent Flows , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22185, https://doi.org/10.5194/egusphere-egu2020-22185, 2020.

EGU2020-19155 | Displays | GM3.4

Seeing through the fluid dynamics of flexible vegetation and canopy turbulence

Robert C. Houseago, Liu Hong, James L. Best, Daniel R. Parsons, and Leonardo P. Chamorro

Submerged aquatic vegetation within river and coastal environments alters the local flow hydraulics, in turn influencing sediment dynamics and bed morphology. Vegetation canopies complicate bottom topography, with flexible elements often invoking complex spatial variability. Acquisition of quantitative, long time-scale data concerning the fluid dynamics associated with flexible aquatic canopies has remained limited due to the physical and visual obstruction presented by vegetation.

The experimental based research detailed here implements a novel Refractive Index Matching (RIM) technique, combined with Particle Image Velocimetry (PIV), to acquire flow field measurements within, and above, a dynamically scaled surrogate flexible seagrass canopy. RIM provides an undistorted optical view through the vegetation canopies, facilitating the investigation of coherent flow structures and canopy dynamics at five different Reynolds numbers. A flexible vegetation canopy of length 1.4m, width 0.45m, and height 0.12m, occupied the entire width of the 2.5m long RIM flume facility at the University of Illinois. The flume was operated in a free surface mode with a flow depth of 0.36m. Results from a counterpart rigid canopy also offer comparability and broader application of these findings to a range of flow-biota environments. Transparent rods formed the rigid canopy, while the flexible canopy elements comprised of four thin polymer blades extending from a short rigid stem. Vegetation elements were placed in a staggered arrangement to form canopies with a density of 566 stems m2.

The results provide insights into canopy-based turbulence processes, including mixing layer properties associated with the canopy and vortex penetration. Deflection of the canopy and its waving motion is quantified, and linked to distinct hydrodynamic differences between the rigid and flexible canopies. Spatiotemporal variability associated with deflection of the flexible canopy, combined with the plant morphology, is shown to promote the spatial heterogeneity in turbulence distribution. Elucidation of instantaneous turbulent flow structures at various time intervals also reveals the links between above-canopy and in-canopy flow processes. This research provides new insights into the hydraulic processes of complex vegetated beds, including quantification of coherent flow structure evoultion. Application of these findings will help advance our knowledge of associated sediment transport dynamics, which is essential for interpreting larger-scale morphodynamic response and its role in environmental management.

How to cite: Houseago, R. C., Hong, L., Best, J. L., Parsons, D. R., and Chamorro, L. P.: Seeing through the fluid dynamics of flexible vegetation and canopy turbulence, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19155, https://doi.org/10.5194/egusphere-egu2020-19155, 2020.

EGU2020-11453 | Displays | GM3.4 | Highlight

Influence of plant traits on biogeomorphic patterns of gravel bed rivers

Francesco Caponi, David F. Vetsch, and Annunziato Siviglia

Feedbacks between riparian vegetation and river morphodynamic processes are pivotal for predicting river morphology in the face of a changing climate and anthropogenic pressures. The effects of vegetation on flow and sediment transport, which ultimately contribute to shape distinct landform structures, depend on plant morphological traits that often reflect plant’s own strategy to cope with fluvial disturbances. Recent observations show that canopy biomechanics and root structure in Populus nigra seedlings tend to adapt depending on hydro-morphological conditions. However, quantitative understanding on how plasticity in plant traits influences river morphology is still limited.

Here, we propose a novel numerical model coupling river morphodynamics and vegetation dynamics that specifically accounts for above- and below-ground plant traits and their effects on morphodynamic processes.  We performed a series of numerical experiments simulating the co-evolution of alternate bars and vegetation under a sequence of flood events and qualitatively compared the results with satellite image observations in the Alpine Rhine river in Switzerland. In particular, we tested the influence of plant traits on the observed reach-scale biogeomorphic patterns by considering different vegetation configurations in which we varied the relative growth of above- and below-ground plant biomass.

Results show that vegetation cover extended over time at a rate that depends on vegetation traits, bar morphology, and the hydrological regime. On more stable bars, which experience little riverbed modification during floods, a clear signature of plant traits in plant survival to floods was observed after a long disturbance-free period, which enable plants to develop enough to interact with flow and sediment transport. As expected, plants that allocate more biomass below-ground were able to resist uprooting, while plants with taller canopies to avoid sediment burial. Along bars where riverbed scour was more pronounced during floods, vegetation was not able to develop as downstream bar migration caused extensive plant uprooting.

These results qualitatively agree with the observations in the Alpine Rhine river, where vegetation has been found to develop only on steady (more stable) bars and not on migrating bars. Our results suggest that the time required by vegetation to modify flow and sediment transport, i.e. biogeomorphic feedback window, can be associated with the time needed for plants to develop specific morphological traits. Moreover, they indicate that bar morphodynamics is able to mute or favor the emergence of plant trait-signature on biogeomorphic patterns.

This study provides a first quantitative-mechanistic understanding of the processes underlying feedbacks between vegetation and river morphodynamics highlighting the importance of plant traits, with potential implications for management purposes and river restoration projects.

How to cite: Caponi, F., Vetsch, D. F., and Siviglia, A.: Influence of plant traits on biogeomorphic patterns of gravel bed rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11453, https://doi.org/10.5194/egusphere-egu2020-11453, 2020.

How to balance ecosystem health and economic development is essential to study sustainability of urban ecosystems. Many methods for assessing urban sustainability have been developed, among which ecological footprint analysis (EFA) has been widely applied as a promising policy and planning tool. This paper proposed a modified EFA with the local ecological footprint being justified by adapting equivalence and yield factors in context of net primary productivity (NPP) from the Miami model. Biodiversity reserves were also incorporated using GIS technology and synthetic assessment of attributes to reflect various eco- logical functions. In addition, ecological footprint deficit (EFD), implying that the productive land cannot sustain current levels of consumption for a given population, was used to reveal the extent of ecological debt, while the ecological footprint variation index (EFVI) was proposed to describe the tradeoffs between real consumption and the carrying capacity of a specific region. A case study of urban areas in the middle stream of the Yangtze River Basin showed that the per capita EFD of the Wanjiang urban belt, central Poyang Lake urban agglomeration, suburban Poyang Lake urban agglomeration, Wuhan megalopolis, Jingmen–Jingzhou–Yichang urban agglomeration, central Changsha–Zhuzou–Xiangtan urban agglomeration, and suburban Changsha–Zhuzou–Xiangtan urban agglomeration increased by 64.83%, 178.05%, 214.82%, 59.08%, 71.68%, 100.62%, and 91.06% between 2000 and 2010, respectively. The local ecological footprint pressure index (EFPI) was classified into five levels. The Poyang lake urban agglomeration was found to be in a slight deficit, while all others were in a severe deficit in 2010. Calculations of EFVI also revealed that the booming urbanization occurred at great cost to the deteriorating ecosystems between 2000 and 2010. Accordingly, relevant influence factors were investigated using a forward stepwise regression method, which indicated that ecological deficit was positively correlated with GDP, population density, and emission of industrial waste, but negatively correlated with the tertiary industry.

How to cite: Wang, H.: Ecological footprint analysis for urban agglomeration sustainability in the middle stream of the Yangtze River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9097, https://doi.org/10.5194/egusphere-egu2020-9097, 2020.

EGU2020-11635 | Displays | GM3.4

Dynamics of riparian vegetation as impacted by sedimentation in reservoirs

Olga Segura Jimenez, Enrique Gonzalez Sosa, and Pascal Breil

Riparian vegetation along the rivers is one of the ways that allows restoration of surface water quality, stabilizing the banks, reducing erosion risks and offering habitat to flora and fauna. The modification of these ecosystems affects sediment transport and deposition in rivers. Sediments retained in a reservoir suggest an impact on the dynamics of the erosion processes and on the equilibrium of riparian ecosystems. If this tendency continues, it will not only affect the generation of electricity, but it will also impact ecosystems, either due to the excess of sediments or to lack of them. This paper analyzes the dynamics of the riparian ecosystems, upstream and downstream of “El Caracol”, a hydroelectric dam located in Guerrero, Mexico, based on Landsat TM and ETM + images corresponding to early spring (March-April) for the period of 1984-2010. The analysis was established by mapping the dynamics of the NDVI as an indicator of the areas affected by the migration of the vegetation and the erosion of the margins. The results show a decrease in NDVI in the study period. While degraded areas have a negative NDVI trend, there are areas within the same reservoir, where the index increases, indicating an increase in sediment deposition being an important factor in explaining vegetation migration.

How to cite: Segura Jimenez, O., Gonzalez Sosa, E., and Breil, P.: Dynamics of riparian vegetation as impacted by sedimentation in reservoirs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11635, https://doi.org/10.5194/egusphere-egu2020-11635, 2020.

EGU2020-2988 | Displays | GM3.4

Biogeomorphodynamic of fluvial-tidal levees and accommodation space infilling

Marcio Boechat Albernaz, Lonneke Roelofs, Harm Jan Pierik, and Maarten Kleinhans

Densely populated low-lying areas are under pressure of relative sea level rise and human impacts. Low-lying areas like most of The Netherlands were built with fluvial-marine sediment supply interacting with peat and vegetation. The morphology and sedimentological architecture of such areas is controlled by initial conditions (e.g. accommodation space), boundary conditions (fluvial-tidal discharges) and internal biogeomorphodynamic feedbacks. The relative importance of these controls varies per system and we need generic rules to better understand the past and future delta and alluvial plain evolution. Here we setup novel long-term idealized morphodynamic models including stratigraphy and vegetation to unravel the effect of initial and boundary conditions in building landscape and creating complex depositional environments. Larger accommodation space creates and preserves a bayhead delta while limited space resulted in ebb-delta growth. Fluvial-tidal discharge fluctuations promote larger levees and more crevasses, contributing to floodplain accretion. The presence of sparse vegetation (i.e. trees) also contributed to floodplain infilling and created wide levees and more crevasses. On the other hand, dense vegetated floodplain inhibits levee widening and the formation of crevasses leaving the floodplain rather starved. Our results agree with the dimensions and evolution from geological reconstructions of the Rhine Delta in The Netherlands. In general, discharge fluctuations by rivers and tides, sediment delivery and (sparse) vegetation are crucial to create more land. These findings are important for the reconstruction of past environments and sediment budget estimative as well to future management of low-lying areas where raising the land-level is a challenge.

How to cite: Boechat Albernaz, M., Roelofs, L., Pierik, H. J., and Kleinhans, M.: Biogeomorphodynamic of fluvial-tidal levees and accommodation space infilling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2988, https://doi.org/10.5194/egusphere-egu2020-2988, 2020.

EGU2020-20115 | Displays | GM3.4

Monitoring of groundwater, morphological and ecological development of the Perkpolder managed realignment following tidal restoration

Wietse van de Lageweg, Joao Salvador de Paiva, Jebbe van der Werf, Lodewijk de Vet, Perry de Louw, Tjeerd Bouma, Brenda Walles, Tom Ysebaert, and Anton van Berchum

Innovative, sustainable and cost-effective coastal protection solutions are required to adapt to environmental change and enhance ecosystem functioning. Managed realignment is an example of an ecosystem engineering coastal management approach motivated by concerns about biological conservation and sea-level rise. It involves relocating the line of defense landward, thereby mimicking what would normally happen with marine environments during a period of sea-level rise. The retreat allows new salt marshes to develop offering a range of ecosystem services. Despite the ongoing execution of managed realignment projects in, amongst others, the UK, Germany, the Netherlands, Belgium and Spain, it remains unclear whether management realignment is able to deliver on the expected socio-economic and environmental benefits.

Here we report on the short-term (0-4 years) development of physical and ecological processes of the Perkpolder managed realignment area in the Scheldt estuary, the Netherlands, following tidal restoration in 2015. The overarching goal of the Perkpolder project was to realize 75 hectares of low-dynamic tidal nature contributing to Natura2000 conservation goals for the Western Scheldt estuary as well as serving as a compensation measure for the extension of the navigation channel for the Antwerp harbor.

The Perkpolder managed realignment is considered a unique opportunity to monitor and study the biotic and abiotic changes in an area transforming from a freshwater agricultural area to a tidal saline natural area. An interdisciplinary monitoring framework was set up to record the abiotic and biotic developments of the Perkpolder realignment area, particularly focusing on morphological changes, colonization of the new tidal area by benthic macrofauna and vegetation, and its function as foraging area for water birds. Also the groundwater system is studied and its effect on the surrounding agricultural land.

A mitigation measure, called ‘SeepCat’, was installed on the border of the new tidal area and the agricultural land to protect the freshwater lens used by farmers for irrigation. The lens was expected to shrink by this local sea level rise. From the groundwater measurements, it was concluded that the SeepCat system was functioning well enough to compensate for the effects of the new tidal area.

Using a Delft3D numerical model simulation, it was shown that the design of the morphological template has a large impact on the rates of morphological change. Additionally, the sediment import, estimated from SPM concentration and discharge measurements, varied strongly in time, and sediment was also being exported for a number of tides. Controlled laboratory experiments show that seedlings of pioneer marsh plant species survive best in a well-drained soil without sediment dynamics. Yet, seedlings can tolerate some moderate sediment dynamics. From a benthic community perspective, the development of the managed realignment Perkpolder is encouraging. A biologically active intertidal area has formed within a short time frame. Within 3 years, the benthic macroinfaunal community shows a development towards a community found on natural tidal mudflats and is expected to reach a stable community in years rather than decades. The area is also frequently visited by birds, which forage during low tide and rest on the surrounding dikes during high tide.

How to cite: van de Lageweg, W., Salvador de Paiva, J., van der Werf, J., de Vet, L., de Louw, P., Bouma, T., Walles, B., Ysebaert, T., and van Berchum, A.: Monitoring of groundwater, morphological and ecological development of the Perkpolder managed realignment following tidal restoration, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20115, https://doi.org/10.5194/egusphere-egu2020-20115, 2020.

EGU2020-10765 | Displays | GM3.4

Biogeomorphic modeling: how to account for subgrid-scale interactions between hydrodynamics and vegetation patches

Olivier Gourgue, Jim van Belzen, Christian Schwarz, Tjeerd J. Bouma, Johan van de Koppel, and Stijn Temmerman

Interactions between water flow and patchy vegetation are governing the functioning of many ecosystems, such as river beds, floodplains, wetlands, salt marshes, mangroves and seagrass meadows. However, numerical models that simulate those interactions explicitly, including at the patch-scale (that is, at resolutions below a m²), together with their far-reaching geomorphological and ecological consequences at the landscape-scale (that is, for domain sizes of several km²), are still very computationally demanding. In this communication, we will present a novel efficient technique to incorporate biogeomorphic feedbacks across multiple spatial scales (from below a m2 to several km2) in biogeomorphic models. Our new methodology is based on the mathematical concept of convolution, allowing to spatially refine coarse-resolution (order of meters) hydrodynamic simulations of flow velocity fields around fine-resolution (order of dm) patchy vegetation patterns. We will demonstrate the power of our new method, by comparing our results with reference fine-resolution (order of cm) hydrodynamic model runs, which themselves are calibrated against flume measurements. We will show that our new model approach enables to refine a coarser-resolution hydrodynamic model, by resolving subgrid-scale fine-resolution flow velocity patterns within and around patchy vegetation distributions. With simple example cases, we will show evidence that our novel approach can substantially improve the representation of important processes in current biogeomorphic models, such as subgrid-scale effects on sediment transport and vegetation growth. Finally, we will demonstrate that our convolution method is an important step forward towards more computationally efficient multiscale biogeomorphic modeling, as compared with what is possible to date.

How to cite: Gourgue, O., van Belzen, J., Schwarz, C., Bouma, T. J., van de Koppel, J., and Temmerman, S.: Biogeomorphic modeling: how to account for subgrid-scale interactions between hydrodynamics and vegetation patches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10765, https://doi.org/10.5194/egusphere-egu2020-10765, 2020.

Braided rivers have complex and dynamic bed morphologies. In Alpine streams, they may be impacted upon by natural flow variability (e.g. snow and ice melt) that can lead to the lateral displacement of suitable habitat. To date, this process has been investigated in two-dimensional models due to the difficulty of applying fully three-dimensional computational fluid dynamics at the scale of river reaches. This is problematic because lateral and vertical variations in kinetic energy and vorticity and their change through time are crucial determinants of where good habitat is found and where it migrates to as river discharge changes. Here we attempt a reach-scale three-dimensional model of stream habitat using the open-source toolbox OpenFoam, with turbulence resolved by Delayed Detached Eddy Simulation (DDES), to model the flow structures in a braided reach of the Turtmanna, a tributary of the Rhône river, Switzerland. The results show that locations deemed suitable in a 2D solution are not when looked at in 3D, and vice versa. This result has important implications for the use of hydraulic habitat modelling for the design of environmental flows in human impacted Alpine streams.

How to cite: Ni, Y. and Lane, S. N.: Hydraulic modelling of brown trout habitat in a hydropower-impacted Alpine braided stream, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11231, https://doi.org/10.5194/egusphere-egu2020-11231, 2020.

EGU2020-17857 | Displays | GM3.4

Quantification of biogeomorphic interactions between small-scale sediment transport and primary succession in the Gepatschferner glacier foreland, Austria

Stefan Haselberger, Lisa Maria Ohler, Robert R. Junker, Jan-Christoph Otto, and Sabine Kraushaar

Landscape change is an interplay of abiotic and biotic processes with bi-directional and interwoven relationships. Glacier foreland areas can act as open-air laboratory to observe biogeomorphic interactions. Paraglacial adjustment establishes initial conditions for ecological succession and requires constant feedbacks between plants and landscapes. Frequency and magnitude of geomorphic processes and functional composition and abundance of plants govern these responses. Up to now, biogeomorphic studies have mainly focused on the qualitative description of the relationship between biotic and abiotic processes. However, in order to test biogeomorphic concepts, it is necessary to jointly quantify (i) geomorphic process rates as a function of vegetation and (ii) successional development as a function of geomorphic conditions.

The proglacial area of the Gepatschferner (Kaunertal) in the crystalline Central Eastern Alps presents a showcase environment to investigate these interactions as the retreating glacier and highly active slope processes provide the ground for different stages of ecological succession and promotes high rates of sediment reworking within the proglacial deposits.

In this particular study, we investigate small-scale biogeomorphic interactions at 30 test sites of 2*3m size. Experimental plots are established on slopes along an ecological succession gradient that reflect different stages of erosion-vegetation interaction. To cover the abiotic condition for the plot sites morphometric characteristics and edaphic variables were determined. In order to quantify abiotic process rates, we use mechanical measurements (i.e. erosion plots) to determine sediment yield and to measure the effect of vegetation on particle size distribution. Relative Dating, historical image analysis and knowledge of glacial retreat helped to estimate time since last perturbation. A detailed vegetation survey was carried out to capture biotic conditions at the sites. Species distribution and abundance at each site, as well as plant functional types provide information on successional stage and functional diversity.

This data set provides a vital opportunity to test conceptual models on biogeomorphic succession in glacier forelands and to evaluate the bi-directional influence of primary succession on small-scale sediment transport and vice versa.

How to cite: Haselberger, S., Ohler, L. M., Junker, R. R., Otto, J.-C., and Kraushaar, S.: Quantification of biogeomorphic interactions between small-scale sediment transport and primary succession in the Gepatschferner glacier foreland, Austria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17857, https://doi.org/10.5194/egusphere-egu2020-17857, 2020.

Tropical rivers are fundamental elements of global hydrosphere, hydrological cycle, Earth natural systems and social system. Tropical rivers are one of the main sources of supply and availability of drinking water, generating multiple direct and indirect contributions to ecosystems and society. Anthropic pressures on tropical river systems, such as canalization, construction of lateral dams, dams, floodplain occupation, among others, generate alterations in the morphology of the channel, change sediment dynamics, and disturb ecosystems and interrelationships between them and the hydrological regimes and geomorphological units. These anthropogenic transformations can generate unpredictable changes, not linear in the medium and long term, and can become irreversible. In this light, this PhD research in Geography, analyze the relationships between geomorphology, hydrology and vegetation that occur in the middle basins of four main rivers in Colombia: Meta, Sinu, Magdalena and Cauca, assessing the vulnerability of tropical river systems in Colombia taking into account the historical relationship of human beings and rivers generating guidelines for management and sustainability of water resources in Colombia, in a context of global change, based on scientific knowledge, which allows criteria for decision-making for its management, use and conservation.

How to cite: Pereira, M. and Vargas, G.: Sustainability of tropical river systems in Colombia, Integrating geomorphology, hydrology and vegetation analysis in the context of global change, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12576, https://doi.org/10.5194/egusphere-egu2020-12576, 2020.

Recent decades have seen worldwide glacier retreat that has resulted in a significant increase in the spatial extent of proglacial margins. Such margins, by switching from being ice-covered to light-exposed, are open to potential colonization by new organisms. However, ecological succession in glacial forefields may be slowed or even precluded by the highly unstable nature of these environments and habitability might be highly variable both in time and in space.

Discharge-related processes are likely to dominate forefields, in particular during the melt season. Discharge defines the shear forces acting upon the streambed, and ultimately bed and suspended loads and the rate of morphodynamic change through the floodplains. Evidence suggests that during the melt season glacial streams continuously rework their accommodation spaces by erosion and deposition processes, resulting in low rates of environmental stability. This means that benthic organisms, such as biofilms, inhabiting those streams may continuously be under pressure.

Biofilms are surface-attached communities composed of microorganisms, they are at the base of instream food webs, and they are involved in multiple ecosystem processes. Nevertheless, their surface-attached nature leads them to be easily removed from their lodging substrates by hydraulic disturbances. Because disturbance-dominated regimes exist during the melt season in glacial streams, it should be expected that biofilms might not be able to develop or persist during the melt season. A core idea in glacial stream ecology is that biomass, either of biofilms but also of macrozoobenthos, increases by moving away from the glacial snout, but also that it fluctuates during the year and reaches its highest mass during windows of opportunity (i.e., spring and fall). Even though this paradigm might hold, it does not fully capture the complexity of glacial floodplain morphodynamics, and the possibility that some stable zones exist even in summer. This explains why biofilms are able to develop in summer, and why well-developed biofilms can be found even close to the glacier snouts during the melt season.

In this paper, we present the first insights about the reasons why biofilms can develop in glacial floodplains during the melt season and, in particular, how important stable zones are for biofilm development. Through classical morphological and morphodynamic analysis, we seek to demonstrate that disturbances are not spatially homogenous, and geomorphic processes can shape the environment creating hot spot for biota. In this view, we argue that floodplain terraces, either permanent or temporary, play a crucial role in defining where biofilms – and consequently organisms that feed on them – settle, develop and grow.

How to cite: Roncoroni, M., Clémençon, M., and Lane, S.: A better appreciation of glacial floodplain morphodynamics reveals that disturbances are not spatially homogenous: implications for biofilm development, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5216, https://doi.org/10.5194/egusphere-egu2020-5216, 2020.

EGU2020-19077 | Displays | GM3.4

Effect of a surface biofilm on sediment transport implemented in a 1D numerical model

Elena Bastianon, Jonathan Malarkey, and Daniel Parsons

The transport of sediment shapes rivers and deltas, and has a huge impact on natural fluvial processes and human interaction within these environments. Conservation and hydraulic engineering applications in river basins crucially depend on understanding the processes of scour, transport and deposition of sediments. The sediment entrainment process in mathematical models are typically based on laboratory experiment using clean (abiotic) sediments. However, natural sediments are rich in biological communities, often forming visible biofilms which include sticky Extracellular Polymeric Substances (EPS). The presence of biological communities has been shown to significantly increase the critical shear stress of sediment entrainment compared with clean sediment, and these communities are recognized as ‘ecosystem engineers’ as they act as bio-stabilizers. Furthermore, biofilms provide stability, such that only the most energetic conditions can remove them in a sudden catastrophic way. In this study, a one-dimensional (1D) morphodynamic model for rivers is implemented to account for the development and growth of a surface biofilm subject to variable hydrodynamic disturbances (e.g. tidal forces) and with a biofilm-dependent erodibility. The 1D form of the shallow water equations are simplified with the aid of the quasi-steady approximation and the Exner equation expressing the conservation of bed material is used to compute the changes in channel bed elevation. The effect of geochemical drivers such as light, temperature and nutrients, which affect the presence or absence and growth of a biofilm, is accounted for in the model. Previous studies have shown that when sediments are covered by biofilms, entrainment occurs via biomat failure and the carpet-like detachment of biofilm-sediment composites. Different hydrodynamic conditions are tested to investigate their role in eroding the biofilm and detaching it from the sediment surface.

How to cite: Bastianon, E., Malarkey, J., and Parsons, D.: Effect of a surface biofilm on sediment transport implemented in a 1D numerical model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19077, https://doi.org/10.5194/egusphere-egu2020-19077, 2020.

Biogeochemical weathering of stable rock surfaces in warm and cold deserts is a notable biogeomorphological process, which contribute to mineralogical transformation of rock constituents and rock disaggregation. Endolithic microorganisms (mostly bacteria, fungi and lichens) play a major role in controlling the destabilization and rejunevation of rock surfaces; but occasionally, biofilms can stabilize rock surfaces. In most of the casis, endolithic communities precipitates byproducts (e.g. oxalates) contributing to enhance discotnituity and promoting exfoliation and disaggregation. On the contrary, rock varnish can develop as an external crust protecting the underliyng rock from erosion and dissolution. In this contribution, a number of case-studies of fossil and active examples of biogeochemical weathering from warm deserts of Africa and Arabian peninsula and from Antarctica are considered. The comaprison of evidence suggests a highly differentiate –  and occasioanlly surprisingly – array of effects of endolithic communities on rock surfaces.

How to cite: Zerboni, A.: Biogeomorphology at the micro-scale: biogeochemical weathering of rock surfaces in the cold and warm deserts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21269, https://doi.org/10.5194/egusphere-egu2020-21269, 2020.

EGU2020-5504 | Displays | GM3.4

Data-based machine learning unveils ecosystem metabolic regimes at the scale of entire stream networks

Pier Luigi Segatto, Tom J. Battin, and Enrico Bertuzzo

Inland waters are major contributors to the global carbon cycle. Nowadays, new sensor technology has changed the way we study ecosystem metabolism in streams. We are able to produce long-term time series of gross primary production (GPP) and ecosystem respiration (ER) to infer drivers of the stream ecosystem metabolic regime and its seasonal timing. Despite big data availability, most studies are limited to individual stream reaches and do not allow the appreciation of metabolic regimes at the scale of entire networks, which, however, would be fundamental to properly assess the relevance of metabolic fluxes within streams and rivers for carbon cycling at the regional and global scale. Machine learning (ML) has great potential in this direction. Firstly, ML could be used to extrapolate both in time and space heterogeneous forcings (e.g., streamwater temperature (T) and photosynthetic active radiation (PAR)) required to run a process-based model for reach-scale metabolism to the scale of an entire stream network. Secondly, the same procedure could be applied to reach-scale estimates of ecosystem metabolism to check whether available data contain enough information to explain the network scale variability. In this study, we used Random Forest to predict patterns of environmental forcings (T and PAR) and stream metabolism (GPP and ER) at the scale of an entire stream network. We used available high-frequency measurements of T and PAR, estimates of ecosystem metabolism and major proximal controls (e.g., incident light, discharge, stream-bed slope, drainage area, water level,  air temperature) from twelve reaches within the Ybbs River network (Austria) and explicitly trained our Random Forests by integrating distal factors, namely:  vegetation type, canopy cover, hydro-geomorphic properties, light,  precipitation, and other climatic variables. We designed two different training setups to assess spatial and temporal predicting model capabilities, respectively. This approach allowed us to reliably infer the target variables (T, PAR, GPP, and ER) on annual basis across a stream network, to filter the most important predictors, to assess the relative contribution of the metabolic fluxes from small to large streams, to estimate annual metabolic budgets at different spatial scales and to provide empirical evidence for long-standing theory predicting shifts of ecosystem metabolism along the stream continuum. Finally, we estimated autochthonous and allochthonous respiration for the entire stream network, which is crucial to integrate the role of ecosystem processes for the carbon cycle.

How to cite: Segatto, P. L., Battin, T. J., and Bertuzzo, E.: Data-based machine learning unveils ecosystem metabolic regimes at the scale of entire stream networks, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5504, https://doi.org/10.5194/egusphere-egu2020-5504, 2020.

EGU2020-13731 | Displays | GM3.4

Carbon sequestration in tropical meandering rivers

Luca Salerno, Francesca Bassani, and Carlo Camporeale

Lateral activity and morphological evolutions of fluvial corridors play an active role in the river carbon cycle that is not completely understood so far. Organic carbon (OC) is produced and conveyed by river dynamics, but a quantification of OC sequestration from river systems is still lacking.
By combining stochastic processes and deterministic modeling for the meandering evolution, we develop a minimalistic model to evaluate the amount of carbon moved by tropical meandering rivers through the reworking of riverbed and riparian vegetation. The model assess the eroded area (by river sinuosity) and couples it with satellite-based data of vegetation carbon density. We assess the carbon sequestration in riparian zone of six fluvial reaches of the Amazon basin, and test the results with satellite-based data of vegetated area lost in the same regions. The process of continuous rejuvenation of the riparian community, due to uprooting of trees by the stream followed by recolonization, allows the riparian zone to produce more OC compared to an equivalent riparian vegetated area not subjected to flood disturbances and lateral erosion. This study shows that river carbon sequestration is closely connected to the river activity and is negatively affected by the anthropogenic activities, such as damming and mining.

How to cite: Salerno, L., Bassani, F., and Camporeale, C.: Carbon sequestration in tropical meandering rivers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13731, https://doi.org/10.5194/egusphere-egu2020-13731, 2020.

Reservoirs efficiently trap the riverine sediment flux, and therefore rapidly accumulate sediment. Since the sediments contain organic carbon (OC), reservoirs globally store significant amounts of OC in their sediments. The source of the OC buried in reservoir sediments is currently not well-known, but has important implications for the accounting of reservoir C burial as a new anthropogenic C sink. On the other hand, sediment OC can be degraded to the greenhouse gas methane (CH4) in anoxic sediment layers, and at high sediment accumulation rates, CH4 reaches oversaturation and forms gas bubbles which efficiently transport CH4 to the atmosphere. Accordingly, CH4 ebullition (bubble emission) is the main pathway of the globally significant CH4 emission by reservoirs. Both sediment OC accumulation and CH4 production is spatially extremely heterogeneous in reservoirs, and we currently lack understanding of the drivers of this spatial variability. We therefore mapped the spatial variability of sediment OC accumulation and of gas bubble-rich, CH4-oversaturated sediments in a large (1300 km2) tropical reservoir in Brazil, using both seismic sub-bottom profiling and sediment coring. In addition, we performed analyses of the sediment stable isotopic signature (13C and 15N) and lipid biomarkers (alkanes, alkanols, and acids) in order to discern the origin of the buried OC. We found that the OC accumulation rate was strongly dependent on the sedimentation rate, which in turn varied with water depth, bottom slope and proximity to river inflows. The spatially-resolved mean OC burial rate was 44 g C m-2 yr-1, twice as high as the global average for natural lakes, but lower than the global average for reservoirs. Gas bubble-containing sediment was detected in 30% of the sub-bottom survey length and occurred along the whole reservoir, but was most abundant in areas of high primary productivity, high sediment accumulation rate, and < 25 m water column depth. Evidence from stable isotopes and lipid biomarkers indicates that a significant share of the OC accumulating in the reservoir sediment is of aquatic origin, and therefore is accountable as a new C sink that results from reservoir construction. These results indicate that the spatial variability of both the burial of OC from terrestrial and aquatic origin, and of gas bubble-rich sediments prone for CH4 ebullition can be understood from the reservoir characteristics.

How to cite: Sobek, S., Mendonça, R., Isidorova, A., and Grasset, C.: Mapping sediment carbon in a large tropical reservoir: burial of terrestrial and aquatic organic carbon, and occurrence of potential methane ebullition hot spots , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20241, https://doi.org/10.5194/egusphere-egu2020-20241, 2020.

EGU2020-17834 | Displays | GM3.4

Revealing hidden peat structures along the stream network of a boreal forest catchment

Thomas Grabs, José L.J Ledesma, Hjalmar Laudon, Jan Seibert, Stephan Köhler, Claudia Teutschbein, and Kevin Bishop

Peat stored in large wetlands plays an important role in the carbon cycle and strongly influences water quality of terrestrial surface water bodies. At the same time, peat is also stored in the direct vicinity of many boreal forest streams. From this strategic position, peat can receive and chemically reset hillslope water before it reaches the stream network. Yet, in contrast to large wetlands, only little spatial information is available on the lateral extent of near-stream peat and even less about its vertical variation. Here, we present field data on peat depth and lateral extent collected from approximately 200 transects (with 12 soil profiles taken per transect) distributed across the entire stream network of the Krycklan boreal catchment in Northern Sweden. This soil profile data revealed a considerable heterogeneity of peat and organic horizon thicknesses. By combining the field data with morphological and geological maps, we show how parent material, stream order and local topography influence near stream peat structures. Furthermore, we discuss potential consequences on surface water quality by linking the detailed peat data set to estimates of lateral, shallow groundwater inflows derived from hydrometric measurements and digital terrain analysis.

How to cite: Grabs, T., Ledesma, J. L. J., Laudon, H., Seibert, J., Köhler, S., Teutschbein, C., and Bishop, K.: Revealing hidden peat structures along the stream network of a boreal forest catchment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17834, https://doi.org/10.5194/egusphere-egu2020-17834, 2020.

Point discharges of pollution such as effluents, enriched in bioavailable nutrients, organic matter and multiple contaminants, are often considered as having both strong local and cumulative downstream effects on aquatic ecosystem quality. Since potential impacts of effluents involve many multiple stressor interactions it requires an integrated suite of in-situ and ex-situ techniques to evaluate the biotic and abiotic interplay of the ecosystem effects. This study aimed to evaluate impacts using sampling transects around discharges from wastewater treatment works (WWTW) to a range of watercourses. The hypothesis was that major effluent discharges would lead to local downstream enrichment in nutrient and microbial contaminants, altered microbial communities and impairment in P processing rates with downstream recovery distances related to cumulative upstream pollution.

Five river transects were evaluated on two dates comprising points 100m above then 100, 200, 500 m below stream-side WWTW. Stream water samples were collected (effluents where possible) and analysed for C, N, P forms, coliforms, pesticides and pharmaceuticals. Biofilms (grown on tiles between sampling dates) and recovered for analysis alongside bed sediments for stoichiometry, P enzyme activity, substrate induced respiration assays and chlorophyll (biofilms). Catchments were characterised using spatial data on landcover, stream network and cumulative pollution sources.

Patterns of pollution presence in the waters and cycling indicators in the bed and periphyton did not show clear patterns of high local and declining downstream impacts. Instead a surprising complexity of weak transect effects amongst a high background heterogeneity was seen. This likely results from a heterogeneous biophysical environment of the channel as well as the complexity of the catchment ‘diffuse’ pollution inputs. Hence, WWTW impacts on aquatic pollution presence and processing factors were unclear and masked by catchment system heterogeneity and complexity.   

How to cite: Stutter, M. and Richards, S.: Point effluent discharges have unclear direct impacts on local biogeochemical P cycling against high background complexity in catchment pollution processes and ecosystem responses , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5736, https://doi.org/10.5194/egusphere-egu2020-5736, 2020.

GM3.5 – Multi-scale Investigation of sediment transport processes in geophysical flows

EGU2020-7333 | Displays | GM3.5

Recognition and Occurrence of Different Sediment-Water Flows Triggered by High-Magnitude Hydrological Events in Mountain Catchments

Andrea Brenna, Nicola Surian, Marco Borga, Massimiliano Ghinassi, and Lorenzo Marchi

Sediment mobilization in small-medium size mountain catchments occurs by different flow types, categorized as debris-flows, hyperconcentrated-flows and water-flows, depending on the physical mechanisms governing flow rheology and particles interaction. During high-magnitude flow events, such transport mechanisms may take place concurrently in the same catchment at different sites of the channel network. One of the most important tasks in investigating dynamics of floods in these mountain catchments is to identify the transport mechanisms, since different flow types induce peculiar geomorphological hazards and dynamics. This work aims to improve criteria to recognize different flow types, with particular regard to hyperconcentrated-flows, and to analyze the transport mechanisms in mountain catchments in response to high-magnitude hydrological events.

Since direct monitoring of sediment mobilization during a flood is extremely difficult, a sound alternative is to consider the characteristics of the deposited material, which depend on the rheological proprieties of related flow. Through an extensive literature review, we identified the diagnostic criteria of the different flow types, grouping them in morphological and sedimentological evidences. A field-survey worksheet has been developed to ease the field-data collection and interpretation. The case-study selected for applying the survey procedure is the Tegnas catchment (Dolomites, Italy), a mountain basin draining an area of 51 km2 affected by the Vaia Storm in October 2018, which induced large floods in several catchments of the Eastern Italian Alps. The deposits field-survey has been conducted in 35 sub-reaches of the Tegnas river and its major tributaries. In addition, we carried out detailed grain-size analyses, measured the angle of clasts-imbrication and collected samples for estimating the vegetal organic matter content through Loss-of-ignition procedure.

Field criteria allowed us to classify each sub-reach according to the deposits left after the event. Most of the steep tributaries have been interested by debris-flows, but also hyperconcentrated-flows have been recognized. Along the main stem, water-flow was the dominant process, although debris-flows and hyperconcentrated-flows deposits are documented where channel slope was very high (i.e. from 9 to 21%).   Hyperconcentrated-flow deposits occur also in the lower sub-reaches (i.e. channel slope from 0.3 to 6%), either at the confluence with debris-flow fed tributaries of where severe bank erosion occurred. We statistically analyzed data about clast imbrication angle (δ) and content of vegetal organic matter (OMLOI) obtaining significant results for both parameters. δ measured in debris-flow (50°-65°) and hyperconcentrated-flow deposits (45°-60°) is considerably higher than in water-flow sediments (30°-40°). Debris-flow and hyperconcentrated-flow deposits have higher OMLOI (2.5-5.5%) than water-flow deposits (1.5-3%). 

The combination of field diagnostic-criteria and quantitative measure of additional parameters allows a reliable recognition of the flow types based on post-flood survey. Besides, this study allowed to point out that during high-magnitude floods the sediment mobilization in small-medium size catchments occurs through mechanisms that can be different from those expected for ordinary hydrological events using morphometric approaches. Solid material concentration or dilution (e.g. due to lacking of sediment sources or sediment disconnectivity) can explain the “unexpected” flow types during high magnitude events.

How to cite: Brenna, A., Surian, N., Borga, M., Ghinassi, M., and Marchi, L.: Recognition and Occurrence of Different Sediment-Water Flows Triggered by High-Magnitude Hydrological Events in Mountain Catchments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7333, https://doi.org/10.5194/egusphere-egu2020-7333, 2020.

EGU2020-2074 | Displays | GM3.5 | Highlight

A simple transport rate relation that unifies aeolian and fluvial nonsuspended sediment transport

Thomas Pähtz and Orencio Duran

Nonsuspended sediment transport driven by streams of liquid or air is an important driver of the morphodynamics of planetary landscapes, seascapes, and riverscapes. Laboratory and field measurements of the sediment transport rate as a function of the fluid shear stress have enabled us to predict such processes with reasonable accuracy on Earth. However, sediment transport is also ubiquitous in extraterrestrial environments, such as on Venus, Mars, Titan, and occurs possibly even on Pluto. This raises the question of whether we can extrapolate transport rate expressions validated with measurements on Earth to extraterrestrial environments. The answer is probably, yes, but only if the used expressions capture the essential physics. Here, using coupled DEM/RANS numerical sediment transport simulations, we show that nonsuspended sediment transport in a large range of aeolian and fluvial environments has a conceptually simple common physical underpinning that allows treating these different transport regimes in a universal manner. That is, a conceptually simple universal model captures simulated and measured transport thresholds and transport rates. In particular, when the transport layer thickness substantially exceeds the viscous sublayer thickness (true for many environments), this model yields a mathematically simple transport rate expression that agrees, simultaneously, with existing measurements in air and water.

How to cite: Pähtz, T. and Duran, O.: A simple transport rate relation that unifies aeolian and fluvial nonsuspended sediment transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2074, https://doi.org/10.5194/egusphere-egu2020-2074, 2020.

EGU2020-2218 | Displays | GM3.5 | Highlight

Have we misunderstood the Shields curve?

Orencio Duran Vinent and Thomas Pähtz

The Shields curve, which compiles measurements of fluvial sediment transport thresholds in terms of the nondimensionalized threshold fluid shear stress and shear Reynolds number, is a standard reference in geophysics and hydraulic and coastal engineering and commonly thought to describe the critical flow conditions that are required for flow-driven entrainment of bed sediment. However, recent findings from several independent research groups have challenged this belief on various grounds: (i) particle-bed impacts predominately trigger sediment entrainment [1]; (ii) such impact-triggered entrainment can sustain continuous transport even when flow-driven entrainment events are (almost) completely absent [2, 3, (4)]; and (iii) extrapolating measurements of the transport rate of such impact-sustained continuous transport to zero yields transport thresholds that still fall on the Shields curve [5]. The question that thus emerges from these findings is, if not flow-driven entrainment, then what is the physics behind the thresholds shown in the Shields curve? We will try to give an answer to this question based on our latest research.

 

[1] Vowinckel et al., Journal of Hydraulic Research, 2016, doi: 10.1080/00221686.2016.1140683

[2] Pähtz & Duran, Physical Review Fluids, 2017, doi: 10.1103/PhysRevFluids.2.074303

[3] Lee & Jerolmack, Earth Surface Dynamics, doi: 10.5194/esurf-6-1089-2018

[4] Heyman et al., Journal of Geophysical Research: Earth Surface, 2016, doi: 10.1002/2015JF003672

How to cite: Duran Vinent, O. and Pähtz, T.: Have we misunderstood the Shields curve?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2218, https://doi.org/10.5194/egusphere-egu2020-2218, 2020.