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GM3.1

Landscape evolution, erosion processes, and sediment dynamics from source to sink

The production, transport, and deposition of sediment and the evolution of hillslopes and river networks govern the fluxes and distribution of solid mass on the surface of the Earth. The frequency, magnitude, and physical and chemical properties of these fluxes are initially controlled by external forcing (climate and tectonics) before being modulated by the complex interplay of surface processes. Understanding the interplay of these processes and how they are affected by external forcing is vital to understanding how sediment fluxes and topography have changed through time.

A growing body of studies continues to develop a process-based understanding of the coupling between climate, tectonics, and the evolution of catchments and the production and transport of solids within them. However, many challenges remain including; (1) fully quantifying the rates and patterns of erosion, sediment transport, and landscape evolution, (2) assessing the importance of large and infrequent events in controlling erosion and sediment transport, (3) bridging the gap between short- and long-term or small- and large-scale records of erosion, deposition, and landscape evolution, and (4) determining the impact of lithology on these records.

In this session we welcome field-based, experimental, and modelling studies, that (1) constrain mechanisms, rates, and scales of erosion, transport, and deposition processes, (2) analyse the influence of internal and external forcing on these processes or resulting landscape evolution, and/or (3) investigate the propagation of geochemical or physical signals across the earth surface (such as changes in river network morphology, sedimentary fluxes, grain size distributions, or cosmogenic nuclide concentrations).Contributions across all temporal and spatial scales are welcome.

Convener: Oliver FrancisECSECS | Co-conveners: Kimberly HuppertECSECS, Aaron BufeECSECS, Fiona ClubbECSECS, Jingtao Lai, Amanda WildECSECS, Jörg Robl, Erin Harvey, Boris GailletonECSECS
Presentations
| Mon, 23 May, 08:30–11:37 (CEST), 13:20–14:44 (CEST)
 
Room G2

Mon, 23 May, 08:30–10:00

Chairpersons: Kimberly Huppert, Jingtao Lai, Amanda Wild

08:30–08:37
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EGU22-11870
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ECS
Selçuk Aksay et al.

Development of erosive landscapes leading to Quaternary badland formation (i.e. recognised with highly erodible, poorly consolidated, clay-size sediments and deep gully systems) is commonly associated with various controls such climate change and Anthropocene influence. However, structural control (e.g. in tectonically active areas) plays an essential role in erosional and morphological evolution of badland landscapes as well.

There is a paucity of combining thorough field mapping (e.g. structural mapping) and morphometric analysis (e.g. normalised SL-index calculations) to study the interaction between structural control and Quaternary erosion-sedimentation dynamics in badland landscapes. This multidisciplinary approach, applied in a badland landscape in an extensional tectonic regime in western Turkey, may provide a good understanding to study the influence of structural control on badland development.

Field data analysis supported with the quantitative assessment of longitudinal gully profiles in this study demonstrates that the fault geometry and rock structure play an essential role in net erosion-sedimentation cycles and development of deepened gully networks, influenced by the local adjustments of an asymmetric mini horst-graben system with extension-related faulting. Overall, the development of badlands in our study area is likely to be conditioned by the rock structure and controlled by Quaternary fault activity and its geometry. Further work with age control might provide further insights in understanding the development of this badland topography in future work.

How to cite: Aksay, S., Schoorl, J., Veldkamp, A., Demir, T., Aytaç, S., and Maddy, D.: The influence of structural control in erosion-sedimentation dynamics and morphology of a badland topography , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11870, https://doi.org/10.5194/egusphere-egu22-11870, 2022.

08:37–08:44
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EGU22-1724
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ECS
Anne Voigtländer et al.

Landscapes – simulated or natural – exhibit various textures. Some appear gentle and smooth, while others show off sharp edges, steep descents or roughness. Erosion controls the sculpting of landscapes. Bedrock and material are eroded where weakened or unconfined. Analogous models have us speculate that stress controls might impact landscape evolution across scales. A first order control behind this is the landscape’s internal stress state or strength. The internal stress state or strength is a result of the geometry, material properties, gravity and geodynamic stresses.  Depending on the mode, orientation and magnitude of internal stress can have a strengthening or toughening effect on the rock, which can retard erosion. We expect emergent effects from the tectonic/regional to the local/topographic stress field on erosion rates and landforms. We use experimentally constrained equations to explore the consequences of stress-strengthening on landscape evolution. Within a numerical landscape evolution modelling framework, Fastscape, we test these variations in erosion due to the stress field by modulating the erodibility factor K as a function of the simulated internal stress. We observe the local effects on erosion rates and compare where in a fluvial or diffusion driven landscapes the implemented stress control has a dominant effect.

How to cite: Voigtländer, A., Turowski, J. M., and Gailleton, B.: Stressed landscape evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1724, https://doi.org/10.5194/egusphere-egu22-1724, 2022.

08:44–08:51
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EGU22-9090
Vincent Godard and Gregory Tucker

Assessing rivers' and hillslopes' sensitivity to external forcing is paramount to understand landscape evolution, in particular as a response to Quaternary climate changes. River networks are usually considered to be the main conveyors of environmental signals, such as changes in precipitation, temperature, or baselevel. Yet because hillslopes provide the source of sediment for river networks, their response to environmental change  also  modulate landscape dynamics. In order to characterize such  behavior we analyse the response times of a transport-limited hillslope.
We use simple numerical models of denudation to study hillslope responses to oscillatory forcing and understand their filtering effects on  environmental signals. Modifications in the frequency of climate oscillation, such as the change that occurred at the Mid-Pleistocene Transition, can significantly modulate hillslope sediment-flux response. We infer a wide range of hillslope responses, ranging from negligible change over the full range of climate-forcing frequencies, to a significant filtering of long-period signals. 

How to cite: Godard, V. and Tucker, G.: Hillslope response to oscillating forcing, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9090, https://doi.org/10.5194/egusphere-egu22-9090, 2022.

08:51–08:58
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EGU22-1383
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ECS
Emma Lodes and Dirk Scherler

While lithological differences are well known to affect the morphology of landscapes, less is understood about how subtle differences in the composition of granitoid bedrock may affect weathering, erosion, and landscape evolution. Here, we investigate a landscape in the semi-arid Coastal Cordillera of Central Chile, whose bedrock is made up of two plutons of differing composition; a monzogranite and a diorite/gabbro. The landscape underlain by the diorite/gabbro appears to consist of taller hills and a lower drainage density compared to the landscape underlain by the monzogranite, which appears to be characterized by smaller hills and a higher drainage density. We hypothesize that the contrast in landscape morphology is related to differential weathering rates, due to the mineralogical compositions of the underlying bedrock. Most importantly, differences in feldspar composition can affect dissolution rates as potassium-rich feldspars are less weatherable than calcium- and sodium-rich feldspars. To test our hypothesis, we obtained the major oxide composition of the bedrock using X-Ray Fluorescence and measured in situ cosmogenic 10Be to obtain denudation rates of bedrock and soils. We also measured surficial sediment grain sizes, and conducted topographic analysis of the landscape using a 1-m resolution digital elevation model (DEM). Preliminary results suggest that the surface sediments of the monzogranite have – on average – a smaller grain size, and the chemical composition of the bedrock shows higher levels of SiO2 and K2O, and lower levels of Na2O and CaO, compared to the gabbro/diorite. DEM analysis supports our field impression and indicates significant differences in drainage density between the two plutons. In addition, 10Be results so far suggest similar erosion rates between the two plutons. We plan to further investigate the mineralogy using thin sections obtained from bedrock outcrops and obtain more field measurements.

How to cite: Lodes, E. and Scherler, D.: A tale of two plutons: Compositional control on weathering, erosion, and landscape morphology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1383, https://doi.org/10.5194/egusphere-egu22-1383, 2022.

08:58–09:05
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EGU22-2614
Coline Ariagno et al.

Sparsely vegetated, badlands are loci of intense erosion that is sufficiently rapid to have observable effects on human timescales and is partly controlled by climate. Characterizing and understanding the physical weathering processes in these areas are key to predict the temporal variability of regolith production and sediment flux, as well as their evolution under changing climate conditions.

Here, we study intra-annual changes of hillslopes properties and explore the relationship between production and transport of sediments in steep marly badland catchments of the Draix-Bléone Critical Zone Observatory (SE France), where decades-long monitoring records show rapid morphologic changes. Remote-sensing imagery has recorded the seasonal dynamics of these badlands, but characterization and quantification of physical weathering processes have been lacking up to now. We explore this gap by monitoring key regolith parameters including grain size distribution (GSD), surface resistance, and water content in the regolith layer (surface to ∼10 cm depth) at different locations, through repeated field surveys over a 2-year period. While water content appears to be directly controlled by the last previous rainfall event, GSD and resistance show a similar cyclic annual pattern, with a maximum at the end of summer and a minimum during winter. Principal component analysis (PCA) highlights the strong correlation between resistivity and GSD (characterized by D50). However, resistance is also partly controlled by water content. We therefore suggest that D50 provides the best proxy of regolith weathering in these marls; this is supported by vertical GSD profiles that show an exponential decrease of D50 toward the surface, resembling the theoretical profile of weathering intensity (e.g., Heimsath et al., Nature, 1997). The cyclic annual pattern in observed D50 suggests that loose and finaly fragmented regolith is mainly produced and accumulates during the winter season, whereas sediment transport is dominant during spring-autumn, reducing regolith thickness and inducing a coarsening of hillslope surface material. These observations thus support a model in which frost-cracking is the main process controlling sediment production in these catchments (Ariagno et al., ESurf, 2022). These results also corroborate the strong annual dynamics of these catchments, where hillslopes and gullies are drained during spring and early summer high-intensity precipitation events, inducing high sediment yields.

We use these quantitative observations to develop and calibrate a landscape-evolution model at (sub-) annual timescales. We aim to use this model to (1) reproduce sediment dynamics in badland catchments and (2) improve predictive models of sediment export from such catchments under a changing climate.

How to cite: Ariagno, C., Le Bouteiller, C., and van der Beek, P.: Seasonal dynamic of marls sediments illustrated by field records on hillslopes properties, Draix-Bléone CZO, SE France., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2614, https://doi.org/10.5194/egusphere-egu22-2614, 2022.

09:05–09:15
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EGU22-6311
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solicited
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Highlight
Laure Guerit et al.

Landscape evolution is intimately related to processes of erosion and rock fragmentation that transform the bedrock into granular material that can be transported by rivers. Among the involved processes, rock fracture seems to play a key role on the mechanisms and rates of erosion, and on the size of the produced sediments. Efforts have been focused on erosion along hillslopes, yet, as far as we know, there is no systematic study of the impact of fracture density and orientation on bedrock erosion within rivers and on the geometry of the produced grains. This is partly due to the characteristic timescales of the processes at stake (abrasion and plucking) that strongly limit direct field observations.

            To address this question, we develop an experimental setup designed to simulate the erosion of a fractured bedrock within a river. The setup is made up of an annular plexiglas cylinder, at the bottom of which is placed a fractured concrete disk. The fracture network is designed numerically and then printed in 3D in PolyVinyl Alcohol (PVA), a thermo-plastic that softens when in contact with water. Water and granite sediments are added on the top of the disk, and a motor-driven propeller circulates the water and the sediments so that erosion can proceed. A set of cameras is used to reconstruct the topography by Structure From Motion so that the erosion dynamics is recorded quantitatively and at high-frequency.

            The first set of experiments explore the role of fracture spacing and azimut. The preliminary results suggest that for a given lithology, the relationship between fracture density and sediment size controls the dominant mode of erosion (abrasion vs plucking). We also observe a clear relationship between the fracture spacing and the size of the concrete clasts produced by plucking. We are currently running additional experiments with different fracture orientation and we also explore the role of the granite sediment size. Based on these experimental results, our objective is to build and validate a conceptual model of erosion and landscape evolution that integrates the role of bedrock fracture within rivers.

How to cite: Guerit, L., Fournereau, M., Steer, P., Lague, D., and Astrié, C.: Fracture, erosion and grain size within rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6311, https://doi.org/10.5194/egusphere-egu22-6311, 2022.

09:15–09:22
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EGU22-10110
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ECS
Dnyanesh Borse and Basudev Biswal

River networks have been studied in geosciences and hydrology for many theoretical and practical purposes. Self-organization into self-similar tree-like network patterns is observed in many natural phenomena including river networks, blood vessels, vascular organization in plants, lightning etc. River networks self-organize into tree-like network patterns as a result of complex landscape evolution processes. All of these patterns follow certain statistical scaling laws. There have been attempts to explain river network evolution, but it is still unclear how networks self-organize into such patterns. These power-law scaling relationships mainly include Hack’s law, exceeding probability distribution for contributing area and upstream length. Although various models exist in the literature, many questions related to river-network evolution are yet to be answered. In particular, the existing models try little to explain the diversity of network characteristics. We propose a new modeling framework that explains drainage network evolution considering certain key physical processes associated with randomness. The model follows the growth of drainage networks in the headward direction based on probabilistic decisions. The model comprises two free parameters and is demonstrated using a planar matrix. The simulation results show the formation of tree-like drainage networks that exhibit power-law scaling relationships as observed in natural river networks. Furthermore, the model parameters provide flexibility to generate networks with different shapes and characteristics.

How to cite: Borse, D. and Biswal, B.: A probabilistic model to explain drainage network evolution and emerging scaling laws of river networks , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10110, https://doi.org/10.5194/egusphere-egu22-10110, 2022.

09:22–09:29
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EGU22-11615
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Highlight
Elco Luijendijk

The role of groundwater flow in landscape evolution and the evolution of stream networks has long been debated but is still uncertain. This contribution explores the role of groundwater in the evolution of stream networks using a new model code, GOEMod, that simulates coupled groundwater flow, overland flow and erosion. The model results show that groundwater flow exerts a strong control on drainage density in humid areas. Drainage density is inversely correlated with transmissivity. Stream networks evolve by a newly identified process named groundwater capture, whereby streams that receive more water and incise faster draw the watertable below adjacent streams, which causes these streams to fall dry. This process is more efficient in areas with high transmissivity due to a relatively flat watertable. This contribution also discusses sensitivity analyses that compare the importance of groundwater to other landscape evolution processes. In addition, a set of model experiments is discussed that explores the persistence of stream networks in response to changes in base level, groundwater recharge and other parameters. 

How to cite: Luijendijk, E.: Groundwater and transmissivity exert a strong effect on drainage density and landscape evolution, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11615, https://doi.org/10.5194/egusphere-egu22-11615, 2022.

Mon, 23 May, 10:20–11:50

Chairpersons: Aaron Bufe, Kimberly Huppert, Erin Harvey

10:20–10:27
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EGU22-4050
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ECS
Terry Cox and Christine Alewell

The prevention of the negative consequences induced by accelerated soil erosion depends on well thought out and economically viable mitigation policies that are founded on the accurate source apportionment of erosion hotspots. Typically, quantification of sediment source apportionment is difficult and requires the impractical and economically unfeasible solution of in-situ sampling at all possible erosion hotspots. An alternative and commonly applied technique is source and sediment fingerprinting with complimentary unmixing of the sediment fingerprint by mass balance equations, with a recent surge of Bayesian inference to incorporate uncertainty in sediment apportionment.

The compound-specific isotope analysis of fatty acids are commonly used for land-use specific fingerprints. However, fingerprinting using isotopic tracers has shown limitations in multiple catchments in which δ13C of fatty acids plot in a 1-dimensional mixing line, resulting in the contribution of the central source being mis-classified as source contribution from either source located at the mixing line endpoints. In this study, we used δ15N as an additional land-use specific tracer to expand the fatty acid linear mixing line into a more suitable N-dimensional mixing polygon. We use an initial “brute force method” with virtual mixtures to explore all combinations and permutations of tracers and their model performance.

Results show that increasing the number of fatty acid tracers had a detrimental effect on unmixing performance, suggesting that increasing the number of conservative tracers does not always produce an improved unmixing result as previously understood when using a Bayesian framework. 

Expanding on this, we hypothesised that if the relative source-source values are constant between different length fatty acids, the mixing space will also be constant, resulting in the application of additional δ13C of fatty acid tracers being comparable to applying repetitions of an identical tracer making additional fatty acid tracers potentially redundant. The performance of the unmixing models using δ13C fatty acid tracers can then be understood to depend on the model’s capacity to handle redundant tracers. The effect of tracer redundancy was quantified by adding identical duplicate tracers (repetitions of the same tracer, δ13C FA C26) or different fatty acid tracers (δ13C FA C24, C28, C30) to the δ15N and δ13C FA C26 tracer set in a three, four and five tracer set and unmixed using the Bayesian framework MixSIAR.

Increasing the number of identical tracers in a tracer set decreased model performance resulting from the propagation of the source-based uncertainty outweighing any discrimination power gained. The latter contradicts the previous idea that MixSIAR handles non-informative tracers. The addition of fatty acids (C24, C28, C30) to C26 showed a lower but proportional decrease in model performance compared to additional identical tracers. This suggests that using multiple tracers which have the same relative mixing space are practically equivalent to applying identical tracer multiple times. We conclude that when using a Bayesian framework for unmixing models, it is beneficial to remove redundant tracers which display the same relative mixing space to improve model performance.

How to cite: Cox, T. and Alewell, C.: Defining and evaluating the effect of redundant isotopic tracers in Bayesian unmixing models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4050, https://doi.org/10.5194/egusphere-egu22-4050, 2022.

10:27–10:34
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EGU22-4404
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ECS
Fruzsina Gresina et al.

The granulometric (particle size and shape) data of sediments provide insights into the processes of grain formation, transport, deposition, and post-depositional alteration mechanisms. Therefore, granulometric proxies are widely used in paleogeographical research.

A statistically robust, objective, and representative description of the particle size and shape characteristic of a sample can only be achieved with a large number (n>104-5) of observed mineral grains. Automated image analysis techniques meet the above requirements. Not only the size distributions of the scanned particle populations are determined, but also the distributions of different shape (e.g., circularity, convexity, solidity) and other shape-dependent size parameters (e.g., circular equivalent diameter, length, width, circumference, area) of each grain.

The presented granulometric analyses were based on sediments from the Carpathian Basin (Central Europe): filling material from Pleistocene periglacial sand wedges (Kemeneshát, Mogyoród gravel pit –Danubian Plain), recent wind-blown sand (Nyírség, Danube-Tisza Midland Ridge), fluvial sand from floodplain and transport media (Lower-Tisza Plain and Dráva Plain). The grains were analysed primarily for their circularity, solidity, and convexity properties. Our aim was to identify fingerprints related to the environment and the transport processes (e.g., type, time).

According to our granulometric results, the Kemeneshát and the Mogyoród site sand wedges can be distinguished. Most samples from Kemeneshát contained fresh, less rounded grains while the other source contained mature, rounded grains. Although, it was also possible to differentiate between the Kemeneshát samples based on the grain shape parameters. Granulometric differences can be detected between the fluvial and eolian sand samples, especially in the case of roundness parameters. Using granulometric proxies, it can be concluded that the filling material of the wedges in the Mogyoród gravel pit is mainly eolian. Therefore, the origin of Kemeneshát samples cannot be clearly identified due to the less mature nature of the grains. Examination of more samples is required to reveal granulometric fingerprints that characterise certain sedimentary environments.

The application of granulometric proxies on relict and recent sand materials can be used to reconstruct the paleoenvironmental conditions. The method can be a new tool for investigating the origin of different sediments and can extend the interpretation of granulometric data.
Support of the National Research, Development and Innovation Office (Hungary) under contract NKFIH FK138692 is gratefully acknowledged.

How to cite: Gresina, F., Farkas, B., Fábián, S. Á., Szalai, Z., and Varga, G.: The applicability of automated static image analysis to identify sedimentary environments, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4404, https://doi.org/10.5194/egusphere-egu22-4404, 2022.

10:34–10:41
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EGU22-2807
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ECS
Colin Chanteloube et al.
Over the last two decades, source-to-sink studies have provided a wealth of information on fluvial-dominated landscapes and their response to tectonic, climatic and biologic forcings. This approach is now expanding for a variety of morpho-sedimentary systems in glacial, submarine and aeolian environments, not only on Earth but also on other planetary bodies. However, works dedicated to aeolian-dominated landscapes often remain qualitative or limited to a single component of the sediment budget such as erosion or accumulation, dust or sand. Hence, the potential of source-to-sink methods is still to be exploited to bring new quantitative information on aeolian sediment-routing systems and associated landforms. The Lut Desert in Iran is nested in an endorheic basin which provides an appropriate context to develop such an aeolian source-to-sink approach. Thanks to remote sensing data and new cosmogenic dating, together with higher resolution wind data and a modern understanding of dune dynamics, we analyze the aeolian transport properties from closed depressions and mega-yardangs upwind to dune fields downwind over decades to millions of years. These erosional and depositional Quaternary landforms cover areas that geographically coincide perfectly with the present-day geometry of the aeolian sediment-routing system. Sandflows derived from modern wind data are sufficient to explain the exchange of mass from the aeolian depressions to the dune fields, providing a coherent scenario for the long-term spatial organization and temporal evolution of these features. In addition, bedform alignments predicted from the wind data are in agreement with the observed dune orientations, which suggests a stability of wind regimes and transport properties over the intermediate time scales from centuries to millennia associated with dune growth and migration. Estimates of the sand discharges associated with the developments of the erosional and depositional landforms show that only a fraction of the wind-blown sediments has accumulated in dune fields since the onset of aeolian erosion. As there is no evidence of sand evacuation through the mountain ranges surrounding the desert, the difference likely corresponds to the emission of dust into the atmosphere. Accordingly, the Lut Desert is not only an internal aeolian routing system for sand, it is also a major source of atmospheric dust leading to an overall loss of mass at the scale of the endorheic basin. Performed at the scale of a whole desert, this sediment budget reveals the full potential of source-to-sink methods to document how aeolian processes drive landscape dynamics and closely link the evolution of continental surfaces to atmospheric circulations.

 

How to cite: Chanteloube, C., Laurie, B., Derakhshani, R., Gadal, C., Braucher, R., Payet, V., Léanni, L., and Narteau, C.: Source-to-sink aeolian landscape dynamics in the Lut Desert (Iran), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2807, https://doi.org/10.5194/egusphere-egu22-2807, 2022.

10:41–10:48
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EGU22-2826
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Highlight
John Armitage et al.

The transport of sediment within a catchment is a complex interaction between the physics of granular transport and the intrinsic local conditions of the sedimentary basin. In trying to understand the causal relationship between climate and sediment transport within a process-based numerical model, the system needs to be simplified. At one extreme at geological timescales there are simple diffusion or advection-based models of transport with only a handful of parameters. At the other extreme complex land surface models for weather forecasting rely on a multitude of user defined parameters. In geomorphology we are faced with the challenge of scale – at what spatial and temporal scale are events important – combined with the uncertainty of various processes and the associated parameters. If we wish to forecast future sustainability for land use over the next 20 to 100 years (including soil loss), the problems of scale and unknown parameters becomes acute. To enter this problem, we have explored the potential of the process-based CAESAR-Lisflood (C++ version) model to simulate the observed erosion of a small sub-catchment within the upper Canche River watershed in the Haut-De-France region. The Pommeroye catchment is of a scale of 0.5 km2, it is composed of 14 cultivated fields and has had continuous monitoring of sediment yield for two years. We focus on using CAESAR-Lisflood as a platform to explore (1) what spatial and temporal scale and (2) what processes are required to match the observed relation between rainfall and sediment yield. We find that a relatively simple model with a 30 cm transport-limited top-soil layer above a detachment-limited layer can match the magnitude of sediment yield. In our set-up the model has only three unconstrained parameters that we tune to give a better fit to the observations: an infiltration parameter that controls peak run-off and the recession curve, a Manning’s roughness within the water routing algorithm, and the erodibility for the detachment-limited law. However, this reduced complexity model cannot capture the ephemeral nature of the landscape, where only certain rainfall events lead to significant sediment yield. A key uncertainty is infiltration and groundwater flow. The transition from precipitation to run-off is calculated by a local recession curve assuming storage at each model cell. However, within the study catchment groundwater pathways cannot be ignored, and it is only when the soil is saturated or when rainfall exceeds the infiltration rate that significant sediment transport occurs. We would therefore suggest that future efforts should be focused on understanding the relationship between the water flux at surface and in the sub-surface to understand how precipitation is translated into sediment flux.

How to cite: Armitage, J., Venisse, N., Franke, C., Alary, C., and Delaporte, M.: Modelling sediment yield in an elementary catchment: reducing the complexity to the key processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2826, https://doi.org/10.5194/egusphere-egu22-2826, 2022.

10:48–10:55
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EGU22-11880
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ECS
Fergus McNab et al.

Environmental conditions exert a primary influence on surface processes such as the production, transport and deposition of sediment. An implication of this behaviour is that sedimentary deposits may record information about past environmental change and its influence on landscape evolution. Extracting this information requires an understanding of the ways in which material is transported from upstream source regions to downstream sedimentary sinks. As such, many recent studies have explored responses of alluvial rivers, the principal agents of sediment transport, to variations in sediment and water supply. In general, these studies have focused on resulting variations in sediment delivery to downstream sinks. However, changing sediment and water supply also results in changes in slope along alluvial rivers, accommodated by aggradation and incision of the valley floor. Cycles of aggradation and incision appear to be recorded by fluvial landforms such as cut-and-fill terraces at many sites around the world. These records may therefore provide an important yet underutilised link between climatic change and resulting variation in sediment production upstream, and the stratigraphic record downstream.

Here, we investigate responses of alluvial rivers to environmental change, with particular focus on resulting variations in channel elevation that could be recorded as fluvial terraces. We employ a recently developed model describing the long-profile evolution of gravel-bed rivers that takes a non-linear diffusive form. This model is defined in terms of measurable properties of river valleys, so should be readily applicable to real settings. For the simple case in which properties such as water discharge and valley width do not vary downstream, we obtain approximate analytical solutions to the diffusive equation that describe resulting variations in the river long profile and bedload sediment discharge. When periodic variation in sediment or water supply is imposed, periodic aggradation and incision occurs that is damped and phase shifted with respect to the imposed variation. Depending on whether sediment or water supply is varied, variation bedload sediment discharge can be damped or amplified. The extent to which signals are modified depends on the distance down valley and the relationship between the forcing period and the valley’s intrinsic response time. Using numerical models, we also explore more complex cases in which water discharge is supplied along the valley, and describe a method for estimating the response time of gravel-bed river networks. Finally, we compare our predictions with observations from a selection of well-studied terrace sites. Our results highlight which kinds and timescales of past environmental change could be represented in fluvial terrace and stratigraphic records and will facilitate improved interpretation of those records.

How to cite: McNab, F., Schildgen, T., Turowski, J., and Wickert, A.: Responses of gravel-bed river networks to periodic environmental change, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11880, https://doi.org/10.5194/egusphere-egu22-11880, 2022.

10:55–11:02
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EGU22-2995
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ECS
Fiona Clubb et al.

Mountainous landscapes often contain sediment-filled valleys that control ecosystem diversity, flood hazard, and the distribution of human populations. Various mechanisms have been proposed to control the spatial distribution and width of valley floors, including climatic, tectonic and lithologic drivers. Attributing one of these drivers to observed valley floor widths has been hindered by a lack of reproducible, automated valley extraction methods that allow continuous measurements of valley floor width at regional scales. We have developed a new method for measuring valley floor width in mountain landscapes from digital elevation models (DEMs). This method first identifies valley floors based on thresholds of slope and elevation compared to the modern channel and uses these valley floors to extract valley centrelines. It then measures valley floor width orthogonal to the centreline at each pixel along the channel. The result is a continuous measurement of valley floor width at every pixel along the valley, allowing us to constrain how valley floor width changes downstream.

We demonstrate the ability of our method to accurately extract valley floor widths by comparing with independent Quaternary fluvial deposit maps from sites in the UK and the USA. We find that our method extracts similar downstream patterns of valley floor width to the independent datasets in each site. The method works best in confined valley settings and will not work in unconfined valleys where the valley walls are not easily distinguished from the valley floor. We then test current models of lateral erosion by exploring the relationship between valley floor width and drainage area in the Appalachian Plateau, USA, selected because of its tectonic quiescence and relatively homogeneous lithology. We find that an exponent relating width and drainage area (cv= 0.3 ± 0.06) is remarkably similar across the region and across spatial scales, suggesting that valley floor width evolution is driven by a combination of both valley wall undercutting and wall erosion in the Appalachian Plateau. Finally, we suggest that, similar to common metrics used to explore vertical incision across mountain regions, continuous observations of valley width have the potential to act as a network-scale metric of lateral fluvial response to external forcing.

How to cite: Clubb, F., Weir, E., and Mudd, S.: Valley width as a metric to explore lateral erosion in mountain landscapes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2995, https://doi.org/10.5194/egusphere-egu22-2995, 2022.

11:02–11:09
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EGU22-10920
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ECS
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Highlight
Leif S. Anderson et al.

In mountainous environments, steep hillslopes tend to erode rapidly. These hillslopes, where present above glaciers, trundle rocks onto glacier surfaces below them. The loose rocks (debris) are subsequently transported along with glacial ice as it moves down valley. Debris can be so abundant that it produces continuous blankets across glaciers. Where debris cover is extensive it reduces ice melt and lowers the surface slope of glaciers. This feeds back to reduce basal sliding, thus impacting bedrock erosion. The erosion of bedrock produces loose sediment that is transported down valley along with the ice and by subglacial water flow.

Here, using a coupled numerical model, we tie three realms of sediment transport (supraglacial, englacial, and subglacial) with feedbacks between ice dynamics and surface melt. The model runs in 2D (x, z) using the shallow-ice approximation and a simple formulation for melt under debris. Our simulations use glaciological parameters meant to loosely represent glaciers in the Khumbu region of Nepal. We present numerical experiments to reveal the first order effects of debris cover on erosion and landscape evolution.

How to cite: Anderson, L. S., Delaney, I., Scherler, D., and Herman, F.: The effects of (supra-, en-, and sub-glacial) sediment on mountain glaciers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10920, https://doi.org/10.5194/egusphere-egu22-10920, 2022.

11:09–11:16
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EGU22-1060
Kejing Liu and Dawei Liu

In the northern hemisphere, river subjects the right bank to the pressure generated by the Coriolis force, which will increase the erosion of the river on the right bank. On the other hand, the Coriolis force also causes the sediments in the water to move to the right bank, which will increase the sediment deposition on the right bank of the river. Therefore, for rivers with low sediment content, Coriolis force will increase the erosion of river water on the right bank; for rivers with high sediment content, Coriolis force will increase the sedimentation of sediment on the right bank. It is noted that the Lanzhou section of the Yellow River has siltation of sands and pebbles to the right (south) bank. It is believed that this is caused by the Coriolis force moving the sands and pebbles to the right bank.

How to cite: Liu, K. and Liu, D.: The influence of Coriolis force on sedimentation of the Yellow River, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1060, https://doi.org/10.5194/egusphere-egu22-1060, 2022.

11:16–11:23
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EGU22-11457
Laura Quick et al.

The gravel-sand transition is a distinct morphological boundary in continental foreland basins characterised by an abrupt downstream reduction in grainsize and lowering of channel gradients. Tectonic convergence between foreland basins and mountain fronts results in the progressive migration of the gravel-sand transition into the basin. As a result, the stratigraphy of the basin fill records a vertical coarsening with an abrupt transition from sandstones to conglomerates. Analysis of this stratigraphic boundary enables insight into the long-term stability of the gravel-sand transition, and records evidence of extreme flood events that were able to transport gravel far out into the basin. Floodwaters sourced from mountain ranges transport and re-suspend finer sediment commonly resulting in them becoming ‘hyperconcentrated’, further increasing the ability to mobilise coarse bedload; however, observations of sediment transport during such extreme flood events are limited. Here, we combine sedimentological analyses of Miocene deposits from the front of the Himalaya, with sediment entrainment calculations. We record the sedimentological transition between the Middle Siwalik sandstones and the Upper Siwalik conglomerates exposed across the Mohand anticline in North West India; this stratigraphic transition records the gravel to sand transition in the Miocene Gangetic Plains. Rather than this being an abrupt, single stratigraphic boundary, it shows a series of thick, coarse conglomeratic beds that punctuate the sandstones beneath the boundary. We focus on these beds as examples of major sediment transport events, and demonstrate the transport of cobble and gravel-rich bedload, facilitated by hyperconcentrated flow conditions, tens of kilometres beyond the gravel-sand transition. Such extreme flow conditions require intense monsoon precipitation, and enhanced suspended sediment concentrations, which in the modern system would represent a 1 in 500 to 1000 year flood event.

How to cite: Quick, L., Sinclair, H., Creed, M., Attal, M., Borthwick, A., and Sinha, R.: Hyperconcentrated floods required to transport coarse bedload over the Gangetic Plains , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11457, https://doi.org/10.5194/egusphere-egu22-11457, 2022.

11:23–11:30
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EGU22-7922
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ECS
Junjian Deng et al.

Fine sediment is a fundamental component of the river system. Fine sediment conditions support good ecological status in different environments since they can affect river habitat and also transport pollutants and nutrients. Moreover, fine sediments can lead to security issues for hydroelectric buildings in the river channel, i.e. sedimentation in reservoirs, turbine erosion, etc. In alpine rivers, a large amount of fine sediments travels over the gravel-bed system as suspension and interacts with the gravel matrix (deposition, infiltration, resuspension). Recent studies highlight that fine sediment stocks in the river bed can be a significant source of suspended load at the event scale, and can have a non-negligible effect on sediment budget estimation. However, there exists no proper estimation of fine sediment stocks in gravel-bed rivers, especially for the sand fraction. One can also question the spatial and temporal variability of these stocks, which makes the estimation of such source of fine sediments challenging.

In this study, we intend to quantify fine sediment stocks in an Alpine river system (Arc-Isère in the French Alps) characterized by the presence of alternate bars. We estimate the potentially resuspended fine stocks from the gravel bar matrix for different discharges by coupling field measurements, GIS spatial analysis, and 1D modelling. Fine sediment stocks in the gravel bars are firstly measured using a field protocol optimized from the one proposed by Misset et al. (2021). The evaluation of the total stocks of fine sediments is made by combining these local measurements to GIS spatial analysis based on LiDAR data. Then, in order to predict the resuspended fine stocks, a 1D numerical hydraulic model is used to calculate bed shear stresses on the bar surface and evaluate the thickness of the potential remobilized coarse sediments. Having the volume of sediments remobilized, one can evaluate the potentially re-suspended fine stocks for different discharges. The measured fine stocks show a significant amount of sand present in the river bed, which was rarely if not measured in most studies. The silt-clay part of the calculated re-suspended stocks is found equivalent to around 30% of annual Suspended Sediment Matter (SSM) flux for a 15-year return period flood event, which appears consistent since such a large event may yield up to 50% of the annual SSM flux. However, the silt-clay stocks represent around 20% of the total fine stocks only, 80% corresponding to sand. Therefore, a large amount of sand could be re-suspended from the gravel bar matrix and should not be neglected when estimating the downstream sediment budget.

How to cite: Deng, J., Piednoir, T., Pénard, L., and Camenen, B.: Estimation of Fine Sediment Stocks in Embanked Alpine Rivers, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7922, https://doi.org/10.5194/egusphere-egu22-7922, 2022.

11:30–11:37
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EGU22-8709
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ECS
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Highlight
Emma Graf et al.

Large earthquakes can contribute to mountain growth by building topography, but also contribute to mass removal from mountain ranges through widespread mass wasting. On a shorter timescale, large earthquakes also have the potential to significantly alter fluvial sediment dynamics if a significant volume of the sediment generated reaches the fluvial network. For example, up to 18 m of channel bed aggradation were observed following the 1999 Chi-Chi (Taiwan) earthquake. In this contribution, we focus on the Melamchi River in central Nepal. This catchment experienced widespread landsliding associated with the 2015 Gorkha (Nepal) earthquake, and was struck by a devastating high concentration flow in June 2021, resulting in up to 15 m of channel aggradation. Using a time series of high-resolution satellite imagery, we have mapped exposed gravel along the river from 2012-2021 to identify zones of channel aggradation and document changes over time. We show that the increase in exposed gravel following the 2015 earthquake is negligible compared to the signal associated with the 2021 event. We consider whether the scale of the high concentration flow event was amplified by the Gorkha earthquake preconditioning the landscape for large-scale sediment evacuation, which raises the question of whether an event such as the Melamchi disaster could occur in other Gorkha-affected catchments. 

How to cite: Graf, E., Sinclair, H., and Attal, M.: Lag time in evacuation of coarse sediment generated by large earthquakes: a case study of the Melamchi River (central Nepal), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8709, https://doi.org/10.5194/egusphere-egu22-8709, 2022.

Mon, 23 May, 13:20–14:50

Chairpersons: Fiona Clubb, Boris Gailleton

13:20–13:27
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EGU22-3135
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ECS
Camila Arróspide et al.

The Atacama rocky coast in Northern Chile is a tectonically active region that displays a particular morphological assemblage along its extension. There is a major morphostructural element named the Great Coastal Cliff (GCC) that runs parallel to the coastline for almost 1000 km in hyper-arid conditions. This cliff reaches heights between 800 and 2000 m a.s.l. and its continuity is only interrupted by a few, great fluvial valleys that drain from the High Andes and by several, small creeks of the Coastal Cordillera. At the mouth of these creeks and valleys, it is possible to recognize sequences of staircased marine terraces formed and preserved by the interplay between the tectonic uplift, sea-level changes, and marine erosion action. The Pan de Azúcar National Park (~26°) is a segment of the Atacama rocky coast which exhibit a morphological segmentation along strike into three domains that shows how the GCC is limited by areas characterized by marine terraces: one domain with a high, steep scarp (>500 m) that sits on top a single shore platform, and two domains with a further inland, degraded cliff (heights <300 m) and a sequence of dated marine terraces (<400 kyr). A numerical model was used to study the morphological evolution of this segment. Results unravel that a particular tectonic history should have taken place to develop all domains. This history begins with a slow subsidence event (0.04 mm/yr) between 1 Myr and 400 kyr ago, followed to the present by several uplift events with different rates (0.25-0.35 mm/yr). These last allow the terrace emersion. Particularly, a faster uplift event after 100 kyr should have taken place to preserve the lowest terrace recorded in the study area at 7-20 m. With this tectonic history, models suggest marine erosion rates of at least > 1.5 m2/yr (1.5 m3 for one meter of coast length) to develop the morphology of the GCC without stair-cased terraces. Instead, much lower erosion rates of 0.25-0.5 m2/yr or less are necessary to reproduce a shorter cliff with different terraces, i.e. low erosion rates to preserve terraces. This erosion variability is likely due to alongshore gradients in erosion efficiency by sediments-fed beaches that act as natural barriers against incoming waves, dissipating their energy. These sediments are provided by creeks with large catchment areas that discharge into the Pacific Ocean.

How to cite: Arróspide, C., Aguilar, G., Martinod, J., Rodríguez, M. P., and Regard, V.: Unraveling the landscape evolution of the Atacama Desert coast of Northern Chile through numerical models: the Pan de Azúcar National Park study case (~26°S). , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3135, https://doi.org/10.5194/egusphere-egu22-3135, 2022.

13:27–13:34
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EGU22-11675
Romano Clementucci et al.

Topographic relief results from the complex interactions between tectonics and erosional surface processes. The efficiency of surface processes is a function of topographic slopes, bedrock erodibility and climatic conditions. Ancient orogens offers a favourable setting to isolate the contribution of lithology, as tectonically driven surface uplift is typically negligible and channel steepness is directly controlled by bedrock erodibility. The Anti-Atlas in NW Africa is a late Paleozoic orogen that contains a well-preserved, uplifted, relict landscape that has been slowly eroding since the late Cretaceous. Here, we combine geomorphic analysis with 10Be-derived denudation rates, to quantify the impact of bedrock erodibility and get insight into the surface evolution of the Anti-Atlas and the adjacent Siroua Massif. Specifically, we show that basin-wide denudation rates from the relict landscape range from 5 to 20 m/Myr, in agreement with the average long-term rates estimated from eroded volumes of Miocene volcanics and available thermochronometric data. This suggests that the regional relict topography has attained an erosional steady state and has been slowly decaying over geological time. Our results are comparable with data from other tectonically quiescent settings and demonstrate a positive linear correlation between denudation rates and normalized channel steepness indices. This allows constraining a narrow range of bedrock erodibility values for different rock-types (quartzite, granitic and sedimentary rocks), that are comparable with estimates from different stable settings. Finally, our compilation from tectonically inactive regions indicates that channel steepness, denudation rates and bedrock erodibility do not change significantly across different climatic zones and precipitation regimes highlighting the critical role of lithology in controlling the topographic relief.

How to cite: Clementucci, R., Ballato, P., Siame, L., Faccenna, C., Yaaqoub, A., Essaifi, A., Leanni, L., and Guillou, V.: Lithological control on erosional dynamics in a tectonically inactive mountain belt (Anti-Atlas, Morocco), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11675, https://doi.org/10.5194/egusphere-egu22-11675, 2022.

13:34–13:41
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EGU22-9737
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ECS
Bastian Ringleb and Markus Fuchs

When modeling landscape evolution a uniform set of defining parameters is used to describe a heterogeneous landscape. This poses a particular challenge when reconstructing the fluvial history of the Weismain river basin (~125 km2). Located in the Northern Franconian Jura, Germany, the evolution of the landscape is closely related to its underlying bedrock. The Weismain river and its tributaries are deeply incised into a limestone plateau forming small, well-defined valleys that are opening up to wider floodplains in the lower parts of the catchment, where sandstone is dominant. The karstic nature of the catchment complicates a model calibration for the whole basin and therefore the reconstruction of its evolution.

In this study, we focus on two sub-catchments of the Weismain River where either lime- or sandstone are prominent. We are using the landscape evolution model CAESAR-Lisflood to model the sediment outputs of those tributaries and compare them to high-resolution, OSL-dated fluvial archives derived from extensive fieldwork. The numerical modeling approach should give insight into geomorphic processes, connectivity inside the system, and the possible impact from sub-surface irregularities in the area.

 

 

How to cite: Ringleb, B. and Fuchs, M.: Landscape Evolution of a mesoscale catchment in the Northern Franconian Jura, Germany: Impacts of Geology when using Landscape Evolution Models., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9737, https://doi.org/10.5194/egusphere-egu22-9737, 2022.

13:41–13:48
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EGU22-9176
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ECS
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Highlight
Camille Litty et al.

Erosion is a key parameter involved in the evolution of the Earth’s surface, and regulates the coupling between climatic and tectonic processes. The quantification of erosion at different spatial and temporal scales is a major challenge in earth sciences to better understand the nature and importance of these interactions. In addition, erosion processes are associated with significant natural hazards like landslides and debris flow. These relatively low-frequency but high-intensity events seem to play an important role in erosion budgets and in the long-term landscape evolution. It has been shown that rare and catastrophic erosion events can even dominate the long-term erosion rates. The aim of this study is to understand the respective role of long-term/continuous erosion dynamics versus extreme and rare events on long-term landscape evolution.

We focused on the ideal case of the western Peruvian Andes between Lima and Pisco (12°S and 13°S), where the hyper arid environment allows unequaled preservation of Pleistocene alluvial archives. This area presents several alluvial deposits including at least three mega-alluvial fans resulting from the upstream erosion of the western Andes and located at the outlet of the Rio Rimac in Lima, Rio Omas and Rio Cañete. These alluvial mega-deposits are mainly made up of rounded pebbles with a sandy matrix intercalated by sand lenses and levels of debris-flow deposits. To obtain the paleo-erosion rates from these deposits, we used in-situ produced cosmogenic 10Be concentrations in quartz and feldspar in deposits previously dated by Optically-Stimulated Luminescence (OSL) with ages ranging from 10 to 90 ka.

Our results show that the measured paleo-erosion rates differ depending on the type of deposits. In the fine grain debris-flow deposits, the paleo-erosion rates are of the same order of magnitude as the erosion rates measured in the current rivers, ranging from 10 to 100 mm/ka. But, paleo-erosion rates measured in conglomeratic deposits are ranging from 200 to 600 mm/ka and are therefore higher than erosion rates measured in both modern river sands and any debris-flow deposits. This shows that in order to precisely understand the governing erosional processes for a given context, it is necessary to constrain both the erosion rates responding to continuous and non-exceptional forcing (recorded in conglomerate deposits), and erosion rates related to extreme events recorded by low-frequency and high-intensity debris-flow deposits.

How to cite: Litty, C., Audin, L., Robert, X., Gribenski, N., Carcaillet, J., Valla, P. G., and Zerathe, S.: Role of long-term/continuous erosion events versus extreme and rare events on long-term landscape evolution , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9176, https://doi.org/10.5194/egusphere-egu22-9176, 2022.

13:48–13:55
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EGU22-6167
F. Xavier Castelltort et al.

The Lleida-Monzón Plain, with an area of 7.700 km2, is the largest transfer and storage zone in the central-eastern South Pyrenees source area outlet. It drains four main South-Pyrenean rivers: the Cinca River, the Noguera Ribagorçana River, and the Segre River joined to the Noguera Pallaresa River. The source area covers about 13.600 km2 forming part of the Pre-Pyrenees and the Pyrenees.

In the Lleida-Monzón Plain, we differentiate three groups of staircase terraces: upper, middle, and lower terraces. The upper flight of terraces outcrops near and above the Cinca and the Segre Rivers confluence. It is a flight of at least four terraces located between 230 and 285 m above the current channel. The middle terraces also form a flight of at least three terraces outcropping between 120 and 190 m above the current channel. Finally, the flight of the six lower terraces lies between 5 and 90 m above the current channel.

The uppermost terrace, 285 m above the riverbed, is an eroded remnant of Pyrenean polygenetic, sub-rounded, and boulder-rich unsorted clasts. Laterally, at the headwaters of two small tributary valleys of the Cinca River, three other terraces (260, 250, and 230 m) of sorted polygenetic gravels are found.

The three middle terraces are the most extensive in the Lleida area. They are elongated, several meters thick, gravel sheet bodies near 40 km long. They are made up of sub-rounded polygenetic and boulder-rich unsorted Pyrenean clasts. Usually, terraces are built up a one-storey layer; occasionally, they are two-storey deposits.

The lower flight of terraces located in the fluvial valleys incised into the middle accumulations. Deposits are up to ten meters thick, and they are poor in sedimentary structures, as much, horizontal, and tabular cross-stratification. Gravel accumulations are composed of sub-rounded polygenetic clasts from the Pyrenees, boulder-rich and unsorted.

Remnants and gravel sheets made up of Pyrenean boulder-rich unsorted clasts can be interpreted as glacial-lake catastrophic outburst flood deposits. When leaving the intramontane confined river courses, floods spread at the plain storage area and form gravel sheet deposits. Accumulations show scarce sedimentary structures, at most some imbrications, and they are characterized by a wide grain-size distribution with boulders in an ungraded and disorganized fabric. Floods can flow up into lateral tributaries where bedload and suspended load are sorted and deposited some kilometers upstream.

The upper flight of terraces correlates with a deposit (250 m above the current riverbed) with an ESR age of 1.276 ± 104 ka (Duval et al., 2015). The lower flight of terraces of the Segre River has been dated with TCN (10Be), showing exposure ages between 202 ka and 62 ka for the upper four terraces of the flight (Stange et al., 2013).

How to cite: Castelltort, F. X., Rodriguez, R., Balasch, J. C., Cires, J., Colombo, F., and Parés, J. M.: The plain of Lleida-Monzón: more than one million years of megaflooding in the eastern South-Pyrenees Drainage Basin. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6167, https://doi.org/10.5194/egusphere-egu22-6167, 2022.

13:55–14:02
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EGU22-11873
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ECS
Sandeep Panda et al.

The occurrence of catastrophic events i.e. floods has proven to play a key role in the rapid sediment delivery from the source area to depocenters and in understanding the focused erosion zones in highland areas. Tracking the provenance of these catastrophic flood sediments provides an insight into the linkage between climate-tectonic coupling and earth surface processes. In general, information on sediment sources has been derived through petrographic and mineralogical investigations on distinct grain-sized sediment or on a grain-by-grain basis, zircon U–Pb geochronology. However, information from fractionated sediment investigations has made it impossible to distinguish source areas using different methods. Sr-Nd isotopes on bulk sediment on the other hand, are still uncommon in tracing the sediment provenance. All three methods discuss the provenance based on the geology of the catchment area, cycles of erosion, mineral maturity. The petrographic and mineralogical investigations respond to short-term sedimentary processes, U-Pb zircon chronology responds to long-term sedimentary processes, however, Sr-Nd responds to both the processes. Therefore, it is crucial to critically examine all these methodologies in tracking the origin of sediment. This research gives an integrated mineralogical–geochemical database on sediments carried by the extreme events in the Tsangpo-Siang-Brahmaputra river system. We attempted to compare the above-mentioned fingerprint approaches and determine the optimal strategy by comparing them on the same samples to determine the relative relevance of various sources. The petrographic analysis was done using Gazzi-Dickinsion method and implied that most of the samples were eroded from Higher Himalaya with a minute amount sourced from Tibet Plateau. This was a bit mystifying as the floods were sourced by the bleaching of glacial dammed lakes from the Tibetan Plateau (Panda et al., 2020). In normal conditions, some studies using the zircon U–Pb geochronology have also suggested Higher Himalaya (Namche Barwa massif) as an erosional hotspot in North-Eastern Syntaxis but in case of extreme events, such study are yet to be done. While the Sr-Nd analysis was done and shows the dominancy of sediments derived from the Tibetan Plateau. Thus, the provenance fingerprinting using the two proxies gives dissimilar results. However, the robustness of Sr-Nd systematics allows us to suggest that the megafloods in the Siang River carried a large amount of sediments that were eroded from Tethyan sequences before entering into the George area, adding additional sediment from crystalline material of the higher Himalaya.

Keywords- Paleofloods, Provenance fingerprinting, sediment petrography, U–Pb zircon chronology, Sr-Nd isotopes.

How to cite: Panda, S., Kumar, A., Singhal, S., Srivastava, P., and Sagwal, S.: Evaluating the use of Petrography, zircon U–Pb ages and Sr–Nd isotopes in tracking provenance: A case study from Tsangpo-Siang-Brahmaputra Basin, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11873, https://doi.org/10.5194/egusphere-egu22-11873, 2022.

14:02–14:09
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EGU22-7357
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ECS
Stéphane Al Reda et al.

The North Pyrenean foreland basin evolved from underfilled to overfilled during the Eocene time in mirror of the development of the Pyrenean orogeny. The resulted Eocene syn-orogenic conglomerate series, known as “Poudingues de Palassou”, recorded the evolution of the mountain belt and the draining system. Three units are classically differentiated in the eastern part: the first and third units deposited during the late Ypresian – Lutetian and Priabonian times respectively, contain clasts from the Meso-Cenozoic regional sedimentary cover. A second unit deposited during the Bartonian corresponds to clasts of magmatic and metamorphic origin (including granites). The objective of this study is to identify the sources of the sediments and to reconstruct the drainage evolution during the Eocene. To this end, U/Pb zircon dating was carried out on granite clasts from Unit 2 and on the conglomerate matrix of the three units using laser ablation-ICP-MS. These analyses are coupled with sedimentary characterization of depositional environments, paleocurrent directions measured in the fluvial deposits and Raman analyses performed on black flysch clasts from the Unit 1/Unit 2 transition. The zircon U/Pb results show a dominance of Variscan ages (290-360 Ma) in the upper part of the Unit 1 and for the matrix of Unit 2 conglomerates. Granite clasts of Unit 2 show mostly ages between 324±2 and 335±1 Ma. For Unit 3, the age spectrum is broader, ranging from Variscan to Cadomian (290 – 600 Ma). Sedimentary analysis of units 1 and 2, show an increase of the amount of sediments and a greater alluvial system during the deposition of the unit 2. The Raman analyses on the black flysch show temperature peaks ranging from 495 to 587°C, comparable to those obtained in the eastern part of the North Pyrenean Zone (NPZ) on black flysch deposits. Interpretation of the results shows that the deposits of Unit 1 are mainly derived from the erosion of the Meso-Cenozoic cover of the NPZ in the Late Ypresian and Lutetian, ending with black flysch of the NPZ, followed by erosion of the Variscan massifs. For Unit 2, the deposition is accompanied by a change in the nature of the clasts and a widening of the depositional zone reflecting wider drainage area including the Axial Zone (AZ). For Unit 3, the broad spectrum of ages obtained, as well as the nature of the clasts, suggest a fairly large catchment area drained from the AZ and significant recycling from the actively deformed foreland sedimentary cover during Priabonian. This research work was financed and carried out as part of the BRGM-TOTAL source-to-sink program.

How to cite: Al Reda, S., Barbarand, J., Lasseur, E., Briais, J., Prieur, M., Gautheron, C., Loget, N., and Lahfid, A.: Evolution of the syn-orogenic sediment routing system in the North Pyrenean foreland basin - France, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7357, https://doi.org/10.5194/egusphere-egu22-7357, 2022.

14:09–14:16
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EGU22-12498
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ECS
Mathias Vinnepand et al.

Loess-Palaeosol-Sequences (LPS) are the most widespread aeolian sedimentary deposits providing climatic- and environmental records across continents. As dust sinks, they may archive information on dust source dynamics, if targeted source signals survived processes operating during production, transport, and syn- and post-depositional alteration of particles and sediments. Yet, our knowledge about such dynamics through palaeoenvironmental changes during the Upper Pleistocene remains vague. This limits our understanding of thresholds that may have (de-) activated dust sources causing major environmental changes in prevalent areas. We thus combine results of isotope- (87/86Sr, 143/144Nd) and major element (Si/Al) provenance proxies that react differently to pre-, syn- and post depositional alteration processes, with granulometry (U-ratio) and the anisotropy of magnetic susceptibility (AMS). Granulometry is recognised as an indicator for wind strengths and the primary magnetic fabric of loess deposits has been successfully used to reconstruct surface near wind directions. We apply our approach on the RP1 profile of the Schwalbenberg LPS that covers the late OIS 3 and the OIS 2 in centennial-scale resolution. The site is embedded in the Middle Rhine Valley (Germany) dividing the Rhenish Massif in its western and eastern part. Consequently, the Schwalbenberg seems appropriate to trace provenance shifts as it is linked to a distal dust source via the Rhine and as it is surrounded by potential local dust sources of the Rhenish Massif. Our results indicate shifts in source areas NNE-SSW off the site, contemporary with increasing frost dynamics and aridification. Both factors seem to enhance dust inputs from the Rhine system up to a threshold where the Rhenish Massif gets activated as a dominant source. Geochemical fingerprinting and AMS at the Schwalbenberg RP1 LPS reveal insights into dust source dynamics that allow for estimating their emission potential during Upper Pleistocene palaeoenvironmental changes.  

How to cite: Vinnepand, M., Fischer, P., Craig, C.-A., Hambach, U., Zeeden, C., Thornton, B., Tütken, T., Jöris, O., Prud'homme, C., Schulte, P., Moine, O., Fitzsimmons, K., Lehmkuhl, F., Schirmer, W., and Vött, A.: Upper Pleistocene dust dynamics reconstructed by isotope fingerprinting and the magnetic fabric of Loess-Palaeosol-Sequences , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12498, https://doi.org/10.5194/egusphere-egu22-12498, 2022.

14:16–14:23
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EGU22-4535
Hella Wittmann et al.

Knowledge of the flux of material eroded and transported from mountains to oceans is a key factor across the Earth Sciences, for constraining global carbon cycling, interpreting the sediment record properly, and environmental management. The analysis of cosmogenic nuclides in sediment of large rivers has been shown to derive mean denudation rates of the sediment-producing areas, averaging out the local variations commonly found in small rivers. When analyzed in Earth largest rivers, cosmogenic nuclides provide the possibility to constrain global mean denudation rates that integrate over millennial time scales and to compare those longer-term fluxes to those from decadal-scale river monitoring. Using this approach, we measured in situ cosmogenic 26Al and 10Be in sand of >50 large rivers over a range of climatic and tectonic regimes covering 32% of the Earth’s terrestrial surface.

In 35% of the analyzed rivers, we find 26Al/10Be ratios to be significantly lower than these nuclides´ surface-production-rate ratio of 6.75 in quartz, indicating radioactive decay over periods exceeding 0.5 Myr. We invoke a combination of slow erosion, shielding in the source area, and sediment storage and burial during long-distance transport to explain these low ratios. In the other 65% of studied rivers we find 26Al/10Be ratios to be within uncertainty of their surface production-rate ratio, indicating cosmogenic steady state. For these rivers, we obtain a global source area denudation rate of 141 t/km2/yr (54 mm/kyr of rock-equivalent) that translates to a flux of 3.07 +/- 0.56 Gt/yr. By assuming that this sub-dataset is representative of the global land surface, we upscale this value to the total surface area for exorheic basins, thereby obtaining a global denudation flux of 15.2 +/- 2.8 Gt/yr that integrates over the past 11 kyr. This value is slightly lower than published values from cosmogenic nuclides from small river basins (23 (+53/-16)) Gt/yr) upscaled using a global slope model, and also lower than modern sediment and dissolved loads exported to the oceans (24.0 Gt/yr). Our new approach confirms an estimate of global dissolved and solid matter transfer that converges to an encouragingly narrow range of within 35% of previous estimates. The use of paired nuclides in large rivers hence provides estimates of the buffering timescales of sediment transport. The Myr-scale duration of this buffering derived for rivers with low Al/Be ratios has important implications for interpreting the sediment record obtained from these mostly dry and slowly eroding river basins. Evidently in these basins, the eroding mountain source is not directly linked to downstream sediment archives, resulting in poor connectivity within the sediment routing system.

How to cite: Wittmann, H., Oelze, M., Gaillardet, J., Garzanti, E., and von Blanckenburg, F.: Cosmogenic nuclides in the Earth’s largest rivers – lessons for deriving global denudation and buffering timescales of sediment transport, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4535, https://doi.org/10.5194/egusphere-egu22-4535, 2022.

14:23–14:30
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EGU22-1844
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ECS
Amy I. Hsieh et al.

Collision between the Philippine Sea Plate and the Eurasian Plate in the late Miocene-early Pliocene resulted in the uplift of Taiwan, and lithospheric flexure to the west formed the adjacent Western Foreland Basin (WFB). Petrographic studies of late Miocene to Recent sediment and sedimentary strata in the WFB indicate that Taiwan was the main sediment source to the WFB in the early- to mid-Pleistocene, and prior to this, sediments were assumed to be derived primarily from the Eurasian continent. However, uplift of Taiwan began significantly earlier, and sediment derived from the island should reflect the onset and acceleration of uplift and subsequent erosion.

To resolve the timing of changes in sediment sources in the WFB, we present clay mineralogy, carbon and nitrogen geochemistry, and magnetic susceptibility data from the late Miocene to late Pliocene Kueichulin Fm that outcrops along the Da’an River in western Taiwan. This formation is composed of the lower Kuantaoshan Member, the middle Shihliufen Shale, and the upper Yutengping Sandstone. Clay mineralogy shows an upward increase in illite and illite crystallinity, and a decrease in chlorite and kaolinite starting at the base of the Shihliufen Shale, and this suggests that rapid erosion of Taiwan became a major sediment source to the WFB between the late Miocene and early Pliocene (Shihliufen Shale). δ13Corg­­­ and C/N ratios preserve the dominance of Taiwan-derived sediment in the early Pliocene where there is a marked change from dominantly marine- to dominantly terrestrially sourced carbon at the transition from the Shihliufen Shale to the overlying Yutengping Sandstone. Finally, a rapid decrease (>50%) in magnetic susceptibility across the Shihliufen/Yutengping boundary indicates a significant dilution of magnetic minerals deposited in the WFB by the high flux of non-magnetic minerals delivered from the Taiwan orogenic belt. Together, these datasets record a major shift in sediment source to the WFB during the late Miocene to early Pliocene, and that Taiwan became the dominant source of sediment supply to the WFB by the early Pliocene, approximately two million years earlier than previously thought.

How to cite: Hsieh, A. I., Dashtgard, S. E., Wang, P.-L., Horng, C.-S., Su, C.-C., Lin, A. T., Vaucher, R., and Löwemark, L.: Multi-proxy evidence for the denudation of Taiwan at the start of the Pliocene, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1844, https://doi.org/10.5194/egusphere-egu22-1844, 2022.

14:30–14:37
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EGU22-13393
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ECS
Sophia Dosch et al.

The long-term burial flux of organic carbon is typically constrained based on the flux of suspended sediment; however, organic carbon can travel in the bedload of rivers as coarse particulate organic matter (CPOMBed, >1mm). Even so, we lack studies documenting the source of CPOMBed in river networks, the fate of CPOMBed during long distance fluvial transport, and the flux of CPOMBed to ocean basins. Collectively, this lack of knowledge limits our ability to constrain the global carbon budget.  Here, we present a first survey to investigate the sources of bedload CPOM transported over a 1000 km long stretch of the Rio Bermejo, Argentina, which has no tributary inputs. We sampled river bed material from six locations along the Rio Bermejo and its headwaters. To trace the source of the CPOMBed, we extracted leaf wax n-alkanes and measured stable hydrogen and carbon isotopes ratios (d2Hwax, d13Cwax). We compared bedload samples with samples from suspended sediment, soil and leaf litter from the floodplain, from the Rio Bermejo mainstem and the headwater catchment. The n-alkane carbon preference (CPI) index shows no difference between upstream and downstream sampling locations and remains relatively higher compared to the suspended sediment CPI. d2Hwax ranges between 120 – 160 ‰ for all sampling sites and indicates a source elevation between 500 – 3500 m a.s.l. We suggest that downstream CPOMBed is derived mostly from distal headwater sources of relatively fresh organic debris and largely preserved during long distance fluvial transit. Our initial results imply that headwater erosion of terrestrial plant debris contributes substantial amounts of bedload CPOM, which can be efficiently transported through lowland rivers for hundreds of kilometres. Our results are the first of their kind and pave the way for future work measuring the flux of CPOMBed to ocean basins. Together, this work will allow us to quantify a currently unincorporated term in carbon budgets and improve our estimates of source to sink carbon cycling.

How to cite: Dosch, S., Hovius, N., Repasch, M., Turowski, J., Scheingross, J., and Sachse, D.: Sourcing and Long-Range Bedload Transport of Fluvial Particulate Organic Matter: Rio Bermejo, Argentina, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13393, https://doi.org/10.5194/egusphere-egu22-13393, 2022.

14:37–14:44
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EGU22-5023
Silvana Martin et al.

The Gavon basin hosts one of the major landslide deposits of the Eastern Italian Dolomites (Falcade, Belluno). This deposit is due to different phases of erosion carried out by the Gavon, which is a sinistral tributary of the Cordevole River, and it consists of a thick erodible sequence of Upper Permian Bellerophon Formation and Lower Triassic Werfen Formation (divided into Tesero, Mazzin, Andraz, Siusi, Gastropod Oolite, Campil, Val Badia, Cencenighe, San Lucano Members) that have been tectonically duplicated by thrust activity and uplifted by two superposed folding and diapiric deformations, rising the sequence to an elevation of 2499 meters a.s.l. at the Forca Rossa pass.

The Gavon basin is 5.98 km long and is characterized by a mean slope greater than 18%. The Lower Triassic sequence was eroded producing a 7.86 km2 basin in pre-glacial time. The basin was filled up by early landslide deposits before the last glaciation, which onset date back to about 30 thousand years before present, and during historic time.

The catchment is now subjected to high erosion due to the frequent rainfall/snowfall events. The solid transport has always been high (up to 34400 m3/y) and, for this reason, some dams were built 80 years ago. Three more check dams were built in 2005 to further decrease the erosion.

A reconstruction of the events in the postglacial time is carried out based on (a) the volume of the deposits and (b) the missing volume in the detachment area. A volume of 173 to 216 million cubic meters has been eroded by a series of events (or a unique large event) that ended approximately 4000 years ago (Fenti, 2018).

To complete this analysis, we numerically modelled the detachment and runout of a block of rock located in the top portion of the basin, where some tension cracks are now evident, and assuming that an intense rain event could mobilize it. The analysis has been processed using LiDAR data with QGis software, while the simulations are performed with GeoFlow-SPH.

How to cite: Martin, S., Gabrieli, F., Da Ros, M., Rossato, S., Brezzi, L., Rigo, M., and Monegato, G.: The Gavon basin: a model of post-glacial debris-flow, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5023, https://doi.org/10.5194/egusphere-egu22-5023, 2022.