GM3.1

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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 (c_v= 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.

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.

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.

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.

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.

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.

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.

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). δ¹³C_org­­_­ 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.

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 (CPOM_Bed, >1mm). Even so, we lack studies documenting the source of CPOM_Bed in river networks, the fate of CPOM_Bed during long distance fluvial transport, and the flux of CPOM_Bed 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 CPOM_Bed, we extracted leaf wax n-alkanes and measured stable hydrogen and carbon isotopes ratios (d²H_wax, d¹³C_wax). 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. d²H_wax ranges between 120 – 160 ‰ for all sampling sites and indicates a source elevation between 500 – 3500 m a.s.l. We suggest that downstream CPOM_Bed 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 CPOM_Bed 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.