GM6.1 | Erosion, Weathering, and Sediment Transport in Mountain Landscapes
Erosion, Weathering, and Sediment Transport in Mountain Landscapes
Convener: Erica ErlangerECSECS | Co-conveners: Jesse ZondervanECSECS, Apolline MariottiECSECS, Romano ClementucciECSECS
Orals
| Mon, 15 Apr, 14:00–15:45 (CEST), 16:15–18:00 (CEST)
 
Room G1
Posters on site
| Attendance Mon, 15 Apr, 10:45–12:30 (CEST) | Display Mon, 15 Apr, 08:30–12:30
 
Hall X3
Orals |
Mon, 14:00
Mon, 10:45
Mountain belts are characterized by the fastest rates of physical erosion and chemical weathering around the world, making them one of the best places to observe sediment production (e.g. erosion, weathering) and transport processes. In these settings, varied processes such as rockfall, debris flow, hillslope failure, glacial and periglacial erosion, fluvial erosion, transport and deposition, and chemical weathering operate, often simultaneously, over a wide range of temporal and spatial scales.

As a result, tracking the interactions between denudation, climatic forcing, tectonic activity, vegetation and land use is complex. However, these feedbacks affect both long- and short-term natural surface processes, landscape development, and human interactions with the environment. Many of these processes also pose serious threats to the biosphere, mountain settlements and infrastructure. Therefore, understanding and quantifying rates of erosion, weathering, and deposition within mountain landscapes is a challenging, but crucial research topic in Earth surface processes.

We welcome contributions that (1) investigate the processes of production, mobilisation, transport, and deposition of sediment in mountain landscapes, (2) explore feedbacks between erosion and weathering due to natural and anthropogenic forcings, and (3) consider how these processes contribute to natural hazards specific to mountain landscapes. We invite presentations that employ observational, analytical or modeling approaches in mountain environments across a variety of temporal and spatial scales. We particularly encourage early career scientists to apply for this session.

Orals: Mon, 15 Apr | Room G1

Chairpersons: Apolline Mariotti, Romano Clementucci
14:00–14:05
14:05–14:25
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EGU24-14191
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solicited
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On-site presentation
Alexander L. Handwerger and Jeffrey S. Munroe

Rock glaciers occur in high numbers in alpine landscapes around the world. These mixtures of ice and rock move downslope at rates from mm/yr to m/yr and can remain active for decades to millennial timescales. Here, we use airborne and satellite interferometric synthetic aperture radar (InSAR) to track the motion of more than 300 rock glaciers in Colorado and Utah, USA. We present a first-of-its-kind inventory of rock glaciers measured with the NASA/JPL Uninhabited Aerial Vehicle Synthetic Aperture Radar (UAVSAR) for our field site in Colorado. UAVSAR provides high resolution (0.6 x 1.6 m pixel spacing) measurements of surface motion along multiple viewing geometries, which allows us to accurately delineate rock glacier boundaries and invert for true 3D surface motion (as opposed to the typical 1D line-of-sight InSAR measurement). We collected UAVSAR data two months apart (July and September) on 8 different flight paths during the summer of 2023. We found that the rock glaciers are moving at rates up to 50 cm/yr during the summer period. We also apply volume conservation techniques to infer the subsurface geometry of multiple rock glaciers and better constrain rock glacier sediment flux. To gain a broader perspective of rock glacier motion over longer time periods (i.e., yearly to near-decadal), we also processed and analyzed satellite InSAR data from the ESA Sentinel-1 A/B satellites between 2015-2024 in Colorado and Utah. The satellite data showed that rock glaciers display seasonal and annual velocity changes, which we infer are driven by liquid water availability (i.e., snowmelt and rainfall). Our findings illustrate that rock glaciers exhibit complex kinematic patterns and geometries. Our new UAVSAR measurements provide key information for constraining rock glacier volume and sediment flux, particularly when combined with field- (e.g., GPS) and lab-measurements (10Be surface-exposure dating).

How to cite: Handwerger, A. L. and Munroe, J. S.: New Constraints on Rock Glacier Geometry and Kinematics in the Western USA from Airborne- and Satellite-based Synthetic Aperture Radar, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14191, https://doi.org/10.5194/egusphere-egu24-14191, 2024.

14:25–14:35
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EGU24-15367
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On-site presentation
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Daniel Draebing, Till Mayer, Benjamin Jacobs, Steven Binnie, Miriam Dühnforth, and Samuel McColl

Periglacial and paraglacial processes drive rockwall erosion in alpine environments. The frequency and magnitude of periglacial and paraglacial erosion will vary in space and time due to topo-climatic effects and climatic changes. We reconstructed glacier retreat since the Last Glacial Maximum (LGM), modelled permafrost distribution and frost cracking activity using measured and reconstructed rock surface temperatures, quantified recent rockwall erosion using terrestrial lasercanning and paleo rockwall erosion by applying geophysical investigations on rockfall deposits. We conducted all measurements on north-facing rockwalls along an elevational gradient ranging from 2500 to 3200 m and adjacent talus slopes in the Hungerli Valley, Swiss Alps. In this study, we analyse periglacial and paraglacial control on rockwall erosion (i) across space along an elevational gradient, (ii) through time in the Holocene and (iii) compare our results to compiled rockwall erosion rates of the European Alps.

(i) Glacier reconstruction revealed that rockwalls became ice-free since LGM with recent glacier retreat affecting the cirque area between 2900 and 3200 m. Permafrost is present in rockwalls ranging from 2800 to 3200 m with elevation-dependent decreasing rock temperatures. Frost cracking magnitude increases with elevation until 3000 m followed by a slight decrease in magnitude at 3150 m. Recent erosion rates averaged 0.02 – 0.08 mm a-1 but were much higher (1.42 to 2.04 mm a-1) at elevation bands between 2900 to 3100 m where the magnitude of paraglacial and periglacial processes is highest. Therefore, recent rockwall erosion patterns follow elevation-dependent climate trajectories (Draebing et al., 2022).

(ii) We found that rockwalls which have been free of glacier ice since ~10 ka experienced erosion rates two orders of magnitude higher (1.2 -1.4 mm a-1 averaged over the Holocene) than the averaged recent erosion rates. Our modelling suggests this relates to periods of higher intensities of frost cracking and cycles of permafrost aggradation and degradation in the Holocene, relative to today (Draebing et al., 2024).

(iii) Compiled erosion rates of the European Alps show an elevation-dependent increase of recent erosion rates (Draebing et al., 2022) and Holocene -averaged rates that exceed recent erosion rates (Draebing et al., 2024). In summary, periglacial and paraglacial processes control spatial and temporal variation of rockwall erosion in alpine environments. Topo-climatic effects resulted in the  elevation dependency of periglacial and paraglacial processes while climatic changes during the Holocene resulted in elevational shifts. Consequently, ongoing climate change will move periglacial and paraglacial rockwall erosion up to higher elevation.

 

Draebing, D., Mayer, T., Jacobs, B., and McColl, S. T.: Alpine rockwall erosion patterns follow elevation-dependent climate trajectories, Communications Earth & Environment, 3, 21, https://doi.org/10.1038/s43247-022-00348-2, 2022.

Draebing, D., Mayer, T., Jacobs, B., Binnie, S.A., Dühnforth, M. and McColl, S. T.: Holocene warming of alpine rockwalls decreased rockwall erosion rates, Earth and Planetary Science Letters, 626, 118496, https://doi.org/10.1016/j.epsl.2023.118496, 2024.

How to cite: Draebing, D., Mayer, T., Jacobs, B., Binnie, S., Dühnforth, M., and McColl, S.: Periglacial and paraglacial processes control rockwall erosion across spatial and temporal scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15367, https://doi.org/10.5194/egusphere-egu24-15367, 2024.

14:35–14:45
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EGU24-19166
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ECS
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Virtual presentation
Li Fei, Tiggi Choanji, Marc-Henri Derron, Michel Jaboyedoff, and Chunwei Sun

Retreat of rock cliffs due to rockfall is a common geological phenomenon in various environments. Both the rockfall events and the subsequent retreat pose potential risks to the infrastructure located both above and below the cliff. Extensive research on rock wall retreat has been conducted in both high alpine and coastal environments, addressing single rock wall instability, as well as linear and catchment-scale rock cliff dynamics under climate change. However, investigations into rock wall retreat in sub-alpine regions have primarily relied on inventories at the linear or regional scale. More attention is still required to understand the retreat of individual rock cliffs in sub-alpine environments. In this study, we focus on a subalpine molasse (sandstone-marls) cliff located at La Cornalle, Vaud, Switzerland, as the case study.
Using monthly Structure-from-Motion (SfM) photogrammetry surveys, meteorological data from a weather station and the Swiss Meteorological Office, and rock temperature obtained from thermal couples installed in the subsurface of the rock from December 2019 to September 2023, we established the rockfall inventory, calculated the retreat rate for the cliff, and analyzed the spatial and temporal features of the retreat with the support of the correlation between meteorological parameters and rockfall data. We found that 4051 rockfalls were documented during the nearly four-year survey, resulting in an average retreat rate of 19.6 mm/year. Specifically, for the marl layers, the retreat rate is about 21.1 mm/year, and for the sandstone layers, it is about 23.7 mm/year. Regarding the newly formed and flat vertical cliff face resulting from a rock collapse between December 17, 2021, and January 11, 2022, the retreat rates vary significantly between the marl and sandstone layers. The retreat rate for the marl layer from the new face is measured at 45.5 mm/year, while for the sandstone layer, it is 22.5 mm/year. This discrepancy is reasonable due to the inherent weakness of marl compared to sandstone. Additionally, no sandstone overhang existed when the face was newly created. As time progresses, the retreat of the marl layer weakens the support for the overlying sandstone, leading to subsequent rockfalls from the sandstone layer. Rainfall played a crucial role in the retreat evolution, while freezing-thaw cycles did not show a clear impact on the occurrence of rockfalls. However, snow melting could be a triggering factor for rockfalls detected during the winter. Interestingly, extreme hot weather during the last two summers did not immediately trigger many rockfalls. 
Our study introduces a comprehensive rockfall inventory from the sub-alpine Molasse cliff and investigates potential contributing factors to rockfall events. Additionally, we propose a model to elucidate the historical evolution of rock cliff retreat.

How to cite: Fei, L., Choanji, T., Derron, M.-H., Jaboyedoff, M., and Sun, C.: Analysis of the spatio-temporal characteristics of retreat caused by rockfall on a cliff with interbedded soft and hard rock layers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19166, https://doi.org/10.5194/egusphere-egu24-19166, 2024.

14:45–14:55
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EGU24-11667
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ECS
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On-site presentation
Amalia Gutierrez, Michel Jaboyedoff, Marc-Henri Derron, Christian Gerber, Nicolas Gendre, and Gabriela Werren

The Diablerets Massif, in the Swiss Prealps, acts as a topographical barrier for northward and westward winds, contributing to the weather conditions and numerous hazards present in the area (avalanches, floods, landslides, etc.). Two main catchments emerge from this massif. The Dar River catchment originates at the Sex Rouge Glacier, comes down through a glacial circus, a series of cascades, and makes a sharp left turn before bordering the massif with a southwest direction. It joins the Grande Eau River catchment, which stems from the aggregation of torrents in the Creux du Champ, a steep-walled, complex-glacial circus followed by a U-shaped valley. After the confluence of both rivers, the Grande Eau crosses the village of Les Diablerets, a major tourist destination in the area.

The erosion and sedimentation dynamics in both catchments are similar, with an increasing production of available sediment in the upper part of the catchments in recent years, due to glacial melt and permafrost degradation. As well as a gradual unearthing of the bedrock in the Dar river due to the erosion of moraine deposits after the first cascade, and increased sedimentation after the second cascade. In the Grande Eau, the enlargement of erosion areas in the top part of the circus has caused numerous debris flow events along the tributaries. These large volumes of transported sediments produce a very dynamic environment, with lateral erosion and a series of small landslides on both sides of the river. The sediment excess is managed through extraction, carried out by the municipality, before the main river crosses the town, but remains a major problem for the inhabitants.

Large flooding events such as the June 2005 event are relatively rare, but small debris flows caused by very localized storm cells have become increasingly common throughout the valley, as well as high discharge events. Expected changes in climate, as depicted by the official Swiss climate change hydrological scenarios (HydroCH2018), include wetter regimes in winter and spring, and drier summers. This is already visible through recent events, such as the November 14th 2023 event, characterized by a high river discharge, and the debris flow of December 13th 2023, near Aigremont.

The dynamics in both catchments were studied using historical aerial images, topographical data, LiDAR scans, wildlife cameras and meteorological data. Changes in the morphology of the riverbed, caused by major natural events in the last 50 years, have been established. Available sediment and erosion rates, as well as erosion and accumulation zones, have been determined for the Dar catchment and will be calculated for the upper part of the Grande Eau catchment. The aforementioned events as well as other particularities in the daily and seasonal dynamics of both catchments related to their source areas have also been analyzed, using the time-lapses for the wildlife cameras and precipitation data. Using the identified source zones for debris flow hazard and the river dynamics we expect to model potential large events in these catchments, comparing single and multi-phase event scenarios, including damming and outburst.

How to cite: Gutierrez, A., Jaboyedoff, M., Derron, M.-H., Gerber, C., Gendre, N., and Werren, G.: Debris flows and river dynamics – a case study of two Alpine catchments in western Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11667, https://doi.org/10.5194/egusphere-egu24-11667, 2024.

14:55–15:05
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EGU24-14856
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ECS
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On-site presentation
Aude Lurin, Odin Marc, Patrick Meunier, and Sebastien Carretier
Landscapes are shaped by the interaction of diverse erosion processes, such as hillslope processes, fluvial erosion, debris-flow erosion. The efficiency of each of these processes depends differently on slope, on over- and underground water flow, on bedrock material properties and sediment grain size. Therefore, the competition of erosion processes structures landscapes into different domains where one process dominates over the others. These domains are characterized by a specific topographic signature, such as the slope-area power-law which characterizes fluvial domains or the convex profile of diffusive hilltops. In mountain landscapes high-resolution topographic data has only recently allowed researchers to study the topography of headwater catchments, where debris flows occur. Therefore, the topographic signature of debris-flow channels as well as their relationships with the hillslope and fluvial domain are still very partially understood.

Applying the CO²CHAIN method of Lurin et al (2023) on high-resolution topography, we studied the debris-flow domain in various mountain catchments in France and the United States, where debris-flow evidence has been found. First, combining the CO²CHAIN and DrEICH methods to detect channel heads and the fluvial upstream limit, respectively, we studied the extent of the debris-flow domain and its dependence to basin characteristics. Our results suggests that the debris-flow domain extends further both upstream and downstream when erosion rate increases, which is consistent with an analytical prediction of the channelization area building upon recent modeling work (McGuire et al., 2023). This also allowed us to constrain the morphology of convergent hillslopes upstream of debris-flow channels.

Then, a closer analysis of slope throughout the debris-flow channel network allowed us to study what constrains slope gradient within these channels. Overall, we found that the average gradient of the debris-flow domain increases with catchment-wide erosion rate, consistent with previous studies. Focusing on downstream gradient evolution, we found that gradient decreases sharply at channel confluences, while its dependence with drainage area in between confluence is much weaker. This suggests that the number of debris-flow sources upstream, and thus the frequency of debris flows is a key control of channel incision in the debris-flow domain, rather than sediment supply or flood discharge.

These results give us insight into the processes shaping the bedrock channels and could allow us to test new models for debris-flow erosion.

References:
Lurin, A., et al., (2023). A Robust Channel Head Extraction Method Based on High-Resolution Topographic Convergence, Suitable for Both Slowly and Fastly Eroding Landscapes.  https://doi.org/10.1029/2022JF006999
McGuire, L. A. et al. (2023). Steady-state forms of channel profiles shaped by debris flow and fluvial processes.  https://doi.org/10.5194/esurf-11-1117-2023

How to cite: Lurin, A., Marc, O., Meunier, P., and Carretier, S.: How debris flows shape mountain catchments? Insights from high-resolution topography., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14856, https://doi.org/10.5194/egusphere-egu24-14856, 2024.

15:05–15:15
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EGU24-8219
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ECS
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On-site presentation
Duna Roda-Boluda, Taylor Schildgen, Maarten Lupker, Aaron Bufe, Anne Sofie Søndergaard, Negar Haghipour, Jeff Prancevic, Stefanie Tofelde, Hella Wittmann, and Niels Hovius

Landslides are a major erosional mechanism in mountain landscapes, play a crucial role in source-to-sink systems by delivering coarse sediment, and constitute a major geohazard. However, quantifying long-term (>102 yrs) landslide sediment fluxes is challenging, because remote sensing offers high-resolution constraints only over the last few years or decades, and landslide scars and deposits are often obliterated in <102 yrs.

In the Southern Alps and the Fiordland of New Zealand, current estimates of long-term landslide frequency and erosion rates have previously been derived from mapping landslides over several decades and extrapolating frequency-magnitude relationships to ≥103 yr timescales. However, three main issues may limit the utility of these estimates. First, they were derived using linear landslide area-volume relationships, while recent findings suggest that landslide volumes scale non-linearly with landslide area. Second, they are based on landslide frequencies over the 1940-80s (Southern Alps) and 1960s-2007 (Fiordland). An updated inventory for the Southern Alps extending until 2014 shows that landslide frequency over those particular decades may have been anomalously high. Third, these decadal observations of landslide frequency are limited to the current inter-seismic period and, hence, remain insensitive to variability of landslide frequencies across a full seismic cycle.

Here, we address the first two issues by including the most recent landslide observations in the frequency-magnitude relationships and by implementing a new field-calibrated power law area-volume scaling relationship. We address the third issue by extrapolating landslide erosion rates to full seismic cycles using published estimates of seismic and post-seismic versus inter-seismic lake sedimentation rates, and known earthquake recurrence intervals. To estimate landslide recurrence intervals over thousand-year timescales, we avoid the limitations of using recent remote sensing data, and instead propose two new approaches that utilize timescale-appropriate cosmogenic radionuclide measurements.  First, using 17 new in situ 10Be concentrations from recent landslide deposits, we show how these concentrations, combined with drone photogrammetry of landslide scars, can be used to estimate the exposure age of the hillslope before the landslide occurred and, hence, provide information about millennial landslide recurrence intervals. Second, we present preliminary data on paired in situ 14C-10Be concentrations from 9 landslides and 20 catchments, and show how 14C/10Be ratios increase with landslide depth and can be used to track catchment-wide landslide activity. Finally, we examine whether the three updated landslide erosion rate estimates (inter-seismic, full seismic cycle, and 10Be exposure-age-based) are consistent with recently published 10Be catchment-averaged denudation rates, and with longer-term estimates of denudation in the Southern Alps and Fiordland.

 

 

 

How to cite: Roda-Boluda, D., Schildgen, T., Lupker, M., Bufe, A., Søndergaard, A. S., Haghipour, N., Prancevic, J., Tofelde, S., Wittmann, H., and Hovius, N.: Quantifying landslide erosion rates over millennial timescales in the Southern Alps and Fiordland, New Zealand, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8219, https://doi.org/10.5194/egusphere-egu24-8219, 2024.

15:15–15:25
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EGU24-16069
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ECS
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On-site presentation
Marion Fournereau, Laure Guerit, Philippe Steer, Jean-Jacques Kermarrec, Paul Leroy, and Dimitri Lague

River erosion, via abrasion and plucking, plays a crucial role in the dynamics of continental landscapes. Indeed, fluvial erosion is thought to give the pace to hillslope erosion and to lead to the rapid export of produced sediments. Erosion rates and mechanisms are influenced by several factors. Among them, fractures in bedrock rivers are assumed to exert a strong control over erosion and thus, on landscape evolution. However, there is to date no systematic study of the impact of fracture geometry and density on bedrock river erosion.  

In this study, we investigate the impact of fracturing on erosion modes and rates of bedrock rivers using an experimental approach. The setup is an erosion mill designed to simulate the erosion of a fractured bedrock in a river. Fractured substrates are built with 3D-printed plastic (PVA) artificial fracture networks placed in concrete disks (diameter of 17 cm). To simulate erosion in a river, water and gravels covering two-thirds of the disk surface are added on the top of the disk.  Water and gravels are entrained by a motor-driven propeller, inducing erosion of the disk by abrasion and plucking.  We use a set of 4 cameras to monitor the disk’s topography every 2 minutes by Structure from Motion photogrammetry, allowing us to record erosion dynamics at high resolution. The impact of fracture geometry and density is explored through 36 experiments with varied fracture spacings, dips, and azimuths.   

Our results reveal that fracture network density influences erosion processes and the distribution of plucking and abrasion occurrence. Abrasions dominates in experiments with a a low fracture density, while experiments with a high fracture density facilitate the occurrence of plucking episodes. 

Fracture dip can also influence erosion processes at the scale of one disk, by generating an asymmetric network with respect to the flow direction. This tends to favour plucking on one side and abrasion on the other side of the disk. In addition, we sometimes observe spatial and temporal clustering of plucking episodes aligned with the flow direction. Finally, at the scale of the whole disk, the experimental results indicate that abrasion leads to a constant average erosion rate through time, whereas plucking induces significant spatial and temporal variations. These findings emphasize the effect of fracturing on erosion rates and modes and highlight the importance of incorporating this parameter into riverbed erosion models.  

How to cite: Fournereau, M., Guerit, L., Steer, P., Kermarrec, J.-J., Leroy, P., and Lague, D.: Impact of Bedrock Fracturing on River Erosion: An Experimental Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16069, https://doi.org/10.5194/egusphere-egu24-16069, 2024.

15:25–15:35
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EGU24-11907
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On-site presentation
Marcel Hürlimann, Clàudia Abancó, Roger Ruiz Carulla, Nieves Lantada, Aritz Urruela, Alex Sendrós, Joan Martínez, José Moya, and Vicente Medina

Water reservoirs play a crucial role in providing important services, but they are facing increasing vulnerability due to the impacts of climate change. Changes in precipitation patterns are affecting the quantity and quality of water in the reservoirs. Sedimentation, which is one of the main impacts, reduces the reservoir's water storage capacity. Water reservoirs act as man-made sediment traps, with the amount of sediments trapped being directly proportional to the size of the water body. Most of the sediments produced in the watershed are accumulated at the bottom of the reservoir, leading to a decrease in water storage capacity. In the context of the SED4BUD project, we are analyzing the sediment stored in the Baells reservoir located in the Catalan Pre-Pyrenees region of Spain. The reservoir, which has a capacity of 109.4 hm3, was constructed in the 1960s.

We have conducted a survey of the uppermost 20% area of the reservoir, which is approximately 0.62 km2 in size, that has emerged during the 2023 drought. The purpose of the survey is to measure the amount of material that has accumulated since the last bathymetry conducted in 2001. Additionally, we aim to classify sediment fractions into coarse and fine categories to calibrate a sediment transport model. To achieve this, we have employed four observational techniques: UAV photogrammetry, boreholes, stratigraphic description, and electric resistivity tomography (ERT).

According to the UAV photogrammetry analysis, it has been observed that sediment accumulation of up to four meters is present in the surrounding areas of the active river channel. The ERT profiles reveal that the majority of the material in the top four meters of soil is fine, with sandy layers present in some areas. In the deeper layers, coarse material can be observed, and the basement is estimated to be between 15 and 20 meters deep.

The analysis of the boreholes and stratigraphic description aligns with the findings from the geophysics and the UAV in terms of sediment accumulation and granulometry. However, it was not possible to apply these techniques in the active channel area due to inaccessibility. This area, where the highest sediment accumulations were detected by the UAV, remains unexplored due to limited accessibility.

Boreholes and stratigraphic descriptions are precise but punctual measures, while UAV and ERT offer the spatial component. UAV is useful for surface measurements, and tomography provides precision in depth.

How to cite: Hürlimann, M., Abancó, C., Ruiz Carulla, R., Lantada, N., Urruela, A., Sendrós, A., Martínez, J., Moya, J., and Medina, V.: Assessment of sediment accumulation in la Baells water reservoir (Catalan Pre-Pyrenees, Spain), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11907, https://doi.org/10.5194/egusphere-egu24-11907, 2024.

15:35–15:45
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EGU24-4079
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ECS
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On-site presentation
Dongfeng Li, Ting Zhang, Irina Overeem, Albert Kettner, Jaia Syvitski, Bodo Bookhagen, Jinren Ni, and Desmond Walling

High Mountain Asia, encompassing the Tibetan Plateau and the surrounding high Asian mountains, has been experiencing a warmer and wetter climate since the 1950s. The amplified climate change has resulted in rapid glacier retreat and permafrost degradation that further cause mountain landscape instability associated with frequent cascading hazards including (rock-ice) avalanches, landslides, debris flows, and outburst floods from glacial- and landslide-dammed lakes. Moreover, the mountain erodible landscapes are expanding and greater amounts of sediment are mobilized in both glacierized and permafrost basins. The river sediment loads in High Mountain Asia have been increasing at a rate of 13% per decade since the 1950s and will likely double by 2050 under an extreme climate change scenario. The climate change-driven mountain landscape instability, increases in river sediment loads and changes in seasonal sediment-transport regimes affect water quality, carbon cycle, floods, infrastructure, and livelihoods. Such findings have implications for other high mountain areas and polar regions and we call for a global assessment of the warming and wetting-driven erosion and sediment transport.

How to cite: Li, D., Zhang, T., Overeem, I., Kettner, A., Syvitski, J., Bookhagen, B., Ni, J., and Walling, D.: Warming and wetting-driven increases in landscape instability and river sediment loads in High Mountain Asia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4079, https://doi.org/10.5194/egusphere-egu24-4079, 2024.

Coffee break
Chairpersons: Romano Clementucci, Apolline Mariotti
16:15–16:35
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EGU24-11945
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ECS
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solicited
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On-site presentation
Aaron Bufe, Jeremy Rugenstein, and Niels Hovius

Silicate weathering sequesters CO2 from the atmosphere and stabilizes Earth’s climate over geologic timescales. In turn, weathering of accessory carbonate and sulfide minerals is a geologically relevant CO2 source. Rock-uplift and -erosion is the primary mechanism by which fresh minerals are exposed to weathering at Earth’s surface. Therefore, the global inorganic carbon cycle is sensitive to mountain uplift and erosion. However, quantifying this sensitivity is complex, because existing data do not consider weathering of all relevant mineral phases, and because co-variation of multiple environmental factors obscures the role of erosion. Here, we analyze the sensitivity of silicate, carbonate, and sulfide weathering fluxes to erosion in four datasets of solute chemistry from small mountain streams that span well-defined erosion-rate gradients in relatively uniform metasedimentary lithologies and with limited or well-constrained variations in runoff. Across all datasets and 2-3 orders of magnitude of erosion rate, we find that silicate weathering fluxes are almost insensitive to erosion at rates >10-2 mm yr-1. In contrast, weathering fluxes from sulfide and carbonate minerals increase sub-linearly with erosion, contradicting expectations from soil data and theory. By fitting a weathering model to these data, we show that the contrasting sensitivities of silicate, carbonate, and sulfide weathering produce a distinct CO2-drawdown maximum at moderate erosion rates of ~0.1 mm/y. Below this maximum, mineral supply limits silicate weathering. Above the maximum, silicate weathering fluxes plateau and CO2 emissions from coupled sulfide oxidation and carbonate weathering increasingly dominate the carbon budget. Thus, for metasedimentary lithologies, uplift of landscapes to moderate relief and erosion rates can substantially bolster Earth’s CO2 sink whereas further uplift may decrease, rather than increase CO2 sequestration rates.

How to cite: Bufe, A., Rugenstein, J., and Hovius, N.: Non-linear sensitivity of mineral weathering to erosion implies an optimum of CO2 drawdown at moderate erosion rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11945, https://doi.org/10.5194/egusphere-egu24-11945, 2024.

16:35–16:45
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EGU24-5118
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On-site presentation
Marco Donnini, Ivan Marchesini, Augusto Benigni, Marco Dionigi, David Michele Cappelletti, Roberta Selvaggi, and Corrado Cencetti

Rivers' sediments can be classified as dissolved (ions transported in solution), suspended (small particles like clay and silt transported by the fluid's flow) and bedload (largest particles like sand, gravels and pebbles transported along the river bed). 

It is well known by the literature that chemical weathering of carbonate and silicate minerals consumes atmospheric CO2, enriching the dissolved load. In the “short-term” (<1 My) both carbonate and silicate weathering consume atmospheric CO2, while in the “long-term” only silicate weathering contributes to CO2 consumption. Assuming that the only reactions that occur in the river basins are the dissolution of silicates and carbonates by chemical weathering, knowing the dissolved load, as well as runoff and lithology, it is possible to calculate the atmospheric CO2 consumed by chemical weathering. 

Several authors highlighted that it is not clear the role in consuming atmospheric CO2 of mixed-carbonate or non-purely silicate lithologies such as sandstone and claystone, as well as sedimentary rocks like calcarenites, marls, and interlayered sandstone and limestone, where carbonate is not dominant. Moreover, the interactions that hydrological and geomorphological processes, such as variation in water runoff and erosion, may have with chemical weathering processes remain controversial and poorly understood.

In this paper we measured both the dissolved and the suspended load in the Niccone stream, a right tributary of Tiber basin (Central Apennines, Italy) mainly composed of siliciclastic sedimentary rocks, at different streamflow conditions. The dissolved load was estimated measuring alkalinity and electrical conductivity in stream waters, while the suspended load was measured by using the DH-59 sediment sampler.

The results of the fieldwork allowed us to investigate the relationship between electrical conductivity and water alkalinity, as well as the behavior of dissolved and suspended load with water discharge during flooding events. Moreover, starting from the knowledge of river water alkalinity, we estimated the amount of atmospheric CO2 consumed by chemical weathering and its variation with runoff. The comparison with literature data allowed us to suppose the presence of non-negligible carbonate components in the Niccone watershed, where lithology is mainly composed of siliciclastic rocks. 

The experimental activities carried out within the Niccone watershed represent a first step in understanding the extent to which atmospheric CO2 consumption processes by chemical weathering are influenced by meteo-climatic events and subsequent erosional phenomena. Moreover, the work confirms that lithologies usually considered without carbonate content like sandstones and claystones, could have a non-negligible carbonate component. This suggests that the estimates of atmospheric CO2 consumed by chemical weathering shown in the literature, should be slightly corrected, both in the “long-” and in the “short-term”.

How to cite: Donnini, M., Marchesini, I., Benigni, A., Dionigi, M., Cappelletti, D. M., Selvaggi, R., and Cencetti, C.: First experiences of correlation between erosion and chemical weathering at basin scale. The case study of Niccone stream (Central Apennines, Italy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5118, https://doi.org/10.5194/egusphere-egu24-5118, 2024.

16:45–16:55
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EGU24-951
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On-site presentation
H. M. Zakir Hossain, Anas Al Hossain, Md. Aminul Islam, Zhifei Liu, Mingyang Yu, and Ce Zheng

Geochemical analyses of major oxides, trace, and rare-earth elements (REE) were examined on the ~70 m core sediments collected from the southeast coast of Bangladesh to determine sediment provenance, maturity, and chemical weathering conditions. The sediment samples contained high SiO2 (62-91 wt.%) and low Al2O3 (~5-17 wt.%) contents and showed a marked negative correlation (r = -0.99) with strong linear trends, indicating that SiO2 was mainly controlled by the quartz content rather than aluminosilicates. Substantial depletion of major labile elements (Na2O, CaO, K2O, Ba, and Sr) compared to the upper continental crust (UCC) indicates the destruction of feldspar during chemical weathering in the source area. The chondrite-normalized REE patterns show LREE enrichment (LaN/YbN, 7.61-14.35), nearly flat HREE (GdN/YbN, 1.33-2.25), and marked Eu anomalies (Eu/Eu*, ~0.58-1.40), suggesting an influx of sediments from felsic provenance. Numerous provenance discrimination diagrams and elemental ratios (Th/Sc, La/Sc, Zr/Sc, Cr/Th, Th/Co, Eu/Eu*, and GdN/YbN) show that the core sediments were derived from felsic source rocks mostly granodiorites, rhyolites, and granites. The REE patterns and parameters are very similar throughout the sequence studied, indicating that the overall source composition in the basin remained unchanged. The Index of Compositional Variability (ICV) values of the sediments varied from 0.79 to 1.83, which indicates immature to moderate compositional maturity. The Chemical Index of Alteration (CIA, ~67 to 81), Chemical Index of Weathering (CIW, ~69 to 91), and Plagioclase Index of Alteration (PIA, ~71 to 92) parameters suggest moderate to high chemical weathering intensity in the source area, which was favored and accelerated by the warm and humid climatic conditions. The elemental ratios (V/Cr, Ni/Co, Cu/Zn, and V/V+Ni) suggested oxic to sub-oxic depositional environment for the accumulation of sediments in the studied Bengal coast. However, the variation of weathering patterns and proxies in the core sediments could be influenced by the strength of South Asian monsoon circulation over the Himalaya-Tibetan Plateau.

How to cite: Hossain, H. M. Z., Hossain, A. A., Islam, Md. A., Liu, Z., Yu, M., and Zheng, C.: Geochemistry of core sediments from the southeast coast of Bangladesh: Implications for provenance and chemical weathering intensity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-951, https://doi.org/10.5194/egusphere-egu24-951, 2024.

16:55–17:05
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EGU24-17114
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ECS
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On-site presentation
Martin Nauton-Fourteu, Gordon Bromley, Shane Tyrrell, Stephan Jorry, Samuel Toucanne, Apolline Mariotti, Pierre-Henri Blard, and Julien Charreau

Beginning by erosion at the source, through transport and intermediate storage, and to final deposition, sediment experiences various processes modifying its mineralogical composition. Among these processes, chemical weathering is governed by climatic conditions, with a cold and arid climate hindering dissolution or replacement of specific silicate mineral phases compared to a hot and humid setting. It is thus theoretically possible to utilise chemical weathering conditions reconstructed from the sedimentary record as a proxy to past climatic conditions. However, chemical weathering intensity, as determined from the final product of a sedimentary cycle, is strongly dependent on the duration of past exposure to weathering conditions, with shorter residence times in the sedimentary transport system resulting in lower chemical weathering intensities.

To address these issues, this study interrogates both a modern river catchment (Var River, southeast France) and its offshore sedimentary equivalent (the Var turbidite system), spanning the Upper Pleistocene to Holocene. In the area, five main river tributaries drain various lithologies of the Southern French Alps carrying sediments from a mountainous landscape to the turbiditic system. This sediment delivery has been mainly controlled over the past ca. 70 kyrs by millennial-scale Dansgaard-Oeschger oscillations, with more frequent turbidite activity during the Last Glacial Maximum (LGM). Additionally, previous work on the area highlighted higher denudation rates during the LGM compared to pre- and post-LGM times.

This project uses multiple proxies to reconstruct chemical weathering from both active river sandbars in the Var River catchment and from sediments collected in the adjacent turbiditic system. Bulk rock geochemistry data are used to calculate chemical weathering indices such as the traditional Chemical Index of Alteration and more recent alpha indices. Additionally, heavy minerals apatite and tourmaline are employed in the apatite-tourmaline index, a potential indicator of variations in past chemical weathering conditions. This dataset is compared to previously acquired neodymium isotope provenance data and palaeo-denudation rates (10Be). Whilst assessing the robustness of various chemical weathering techniques, this study also intends to shed light on the LGM impact on sediment delivery and chemical weathering in a mountainous landscape.

How to cite: Nauton-Fourteu, M., Bromley, G., Tyrrell, S., Jorry, S., Toucanne, S., Mariotti, A., Blard, P.-H., and Charreau, J.: A multi-proxy approach to assess chemical weathering in the Southern French Alps since Marine Isotopic Stage 4, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17114, https://doi.org/10.5194/egusphere-egu24-17114, 2024.

17:05–17:15
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EGU24-20646
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ECS
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On-site presentation
Chen Chen, Eric Gayer, Jérôme Gaillardet, Pascale Louvat, and Louis Derry

Silicate weathering plays an important role in sequestering CO2 over geological time scales. Physical erosion is an important process of mineral surface production, significantly promoting efficient chemical weathering. Landslides, in particular, contribute to physical erosion by generating debris avalanches, thereby accelerating the chemical weathering rate. On the one hand, this enhanced silicate weathering contributes to CO2 drawdown. On the other hand, the oxidation of sulfide minerals exposed by landslides produces H2SO4. H2SO4 weathers carbonate minerals and releases CO2 to the atmosphere, a faster weathering process than silicate dissolution. It is a consensus that landslide erosion favors chemical weathering, however, it still remains unclear to what extent it impacts chemical weathering fluxes, and resultant CO2 consumption rate or emission rate.

Réunion Island, characterized by volcanic basalt composition, is a well-known hotspot of physical and chemical erosion (Louvat and Allègre, 1997) with particularly intense bedrock landslides and river incision (Garcin et al., 2005; Rault et al., 2022). It is a very high standing volcanic island with erosion rates exceeding most active mountain ranges due to the strong interaction between volcanic rocks and climate (Gayer et al., 2019). These characteristics of Réunion Island make it an excellent natural lab to study the relationships between erosion and weathering. In this study, we use stream water chemistry and discharge time series to calculate the decennial chemical weathering rates of the main catchments across Réunion Island. Our analysis unveils a substantial contribution not only from basalt dissolution in the stable area but also from hydrothermal activity and landslides to the chemical weathering flux, which results in high CO2 consumption rates. Notably, streams impacted by thermal springs and landslides show different relationships between runoff and chemical weathering rates. In addition, extreme precipitation events promote landslide weathering, instead of high average rainfall. We were able to quantify the effect of landslides on chemical weathering. For the Salazie basin, we find that the landslides contribute to chemical weathering rates up to 62 t/km²/a, accounting for 73% of the chemical weathering in the basin although landslides only affect about 1/5 of its total surface area. This corresponds to an annual CO2 consumption rate of 2.9 × 106 mol/km²/a, approximately 4 times higher than the CO2 consumption attributed to basalt weathering in landslide-free nearby areas, establishing landslide-enhanced-weathering as a significant carbon sink. Our study illuminates some of the mechanisms coupling physical and chemical weathering processes at the Earth’s surface and the impact on the climate.

How to cite: Chen, C., Gayer, E., Gaillardet, J., Louvat, P., and Derry, L.: Enhanced CO2 consumption rate from silicate weathering by landslide erosion in the volcanic island, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20646, https://doi.org/10.5194/egusphere-egu24-20646, 2024.

17:15–17:25
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EGU24-12585
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On-site presentation
Caroline Le Bouteiller, Coline Ariagno, Peter van der Beek, Sebastien Klotz, Gregory Tucker, and Benjamin Campforts

Badlands are particularly sensitive components of the critical zone where weathering, erosion and transport processes can be observed on human time-scales. Within the Draix-Bléone Critical Zone Observatory (CZO), SE France, water and sediment (both bedload and suspended load) fluxes and climatic drivers have been recorded since more than 35 years, making it an ideal natural laboratory to develop a landscape-evolution model (LEM) for badland evolution calibrated with field data. Based on these records and existing knowledge on the sediment dynamics of these marly catchments, the aim of this study is to develop a LEM that is able to reproduce the observed intra-annual sediment-flux variability, in particular the transition from transport-limited to supply-limited conditions that occurs during summer. Our model predicts soil thickness and sediment export at monthly timescales, thereby providing potential links between “classical” LEM that run at long time scales and event-scale models, and simulating the physical processes driving the sediment dynamics in these catchments at their relevant timescale. We use the annual hysteresis cycle between rainfall and sediment export recorded in the Draix catchments as a quantitative indicator of the adequacy of the model. First, we model the supply-limited regime observed in the second half of the year in the badlands, illustrated by an clockwise loop in the annual hysteresis pattern, using depth-dependent hillslope regolith production and erosion laws. Next, we express the impact of rainfall intensity, identified as the main trigger of sediment motion both on hillslopes and in the drainage network, in order to reproduce the observed non-linear relation between sediment export and rainfall during the first part of the year (illustrated by an initial anti-clockwise loop in the hysteresis cycle). Parameter calibration is performed using average annual sediment export and soil depth in specific compartments of the catchment. The model successfully reproduce the hysteresis pattern but further work is needed on the calibration to obtain consistent magnitudes of sediment export. This new landscape evolution model appears to be a relevant tool to model observed annual morphology changes in badlands and to predict badland evolution in a context of climate change. 

 

How to cite: Le Bouteiller, C., Ariagno, C., van der Beek, P., Klotz, S., Tucker, G., and Campforts, B.: Modeling seasonal sediment dynamics and landscape evolution in a marly badland catchment, Draix-Bléone Critical Zone Observatory, SE France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12585, https://doi.org/10.5194/egusphere-egu24-12585, 2024.

17:25–17:35
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EGU24-14997
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ECS
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On-site presentation
Coline Hopquin, Éric Gayer, Laurent Michon, Delphine Smittarello, and Antoine Lucas

Landslides are efficient erosion processes that release large volumes of sediments in rivers, posing threats to nearby population when remobilised during large flood events. Thus, understanding the dynamics and controls of landslides and quantifying the volumes involved in subsequent sediment transfer are crucial for resilient development in mountainous settings.

In this study, we use the very high standing island of Réunion (Indian Ocean) as a natural laboratory to investigate the interaction between landslides, sediment transfer and climatic forcing. This volcanic island, characterised by mountainous landscapes resulting from intense river incision and frequent landslides, shows physical erosion and chemical weathering rates exceeding most of active mountain belts (Gayer et al, 2019). 

Here, we focus on studying the Grand Éboulis landslide short-term (i.e bi-monthly) and mid-term (i.e multi-decennial) dynamics using SAR imagery and photogrammetry. First, we computed cumulative displacement maps and time series using the AMSTer software and Sentinel-1 StripMap images acquired every 12 days between 2017 and 2021. These time series reveal velocity fluctuations, including acceleration and/or deceleration episodes, correlated with extreme climatic events such as intense precipitation and drought episodes. Furthermore, from 2017 to 2021, Grand Éboulis exhibited a characteristic slow-moving landslide behaviour with a consistent eastward movement of up to 14 cm/year, coupled with continuous subsidence of up to 9 cm/year. 

The mid-term dynamics of Grand Éboulis, spanning from 1950 to 2011, was investigated using a series of nine Digital Surface Models (DSM). Each DSM was derived from historical aerial photographs obtained by the French National Institute of Geographic and Forest Information (IGN) and processed through the photogrammetric workflow of Lucas and Gayer (2022). Preliminary findings indicate numerous catastrophic failures in or near the steepest slopes of the landslide that experience the highest velocity gradients. The sediment volumes involved in such events range from a few tens of thousands to millions of cubic meters, predominantly released into the nearby river and transported away from the landslide.

Our results suggest that the Grand Éboulis landslide is in an active mobilisation phase with a continuous slow displacement primarily influenced by extreme climatic events and with catastrophic failures that release large volumes of sediments in the nearby river.

How to cite: Hopquin, C., Gayer, É., Michon, L., Smittarello, D., and Lucas, A.: Dynamics and controls of a tropical slow moving landslide measured by remote sensing: the study case of Grand Éboulis, Réunion Island. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14997, https://doi.org/10.5194/egusphere-egu24-14997, 2024.

17:35–17:45
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EGU24-12787
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On-site presentation
Marek Ewertowski and Aleksandra Tomczyk

As climatic changes impact environmental conditions worldwide, the intensity and spatial distribution of geomorphic processes will be seriously modified in the foreseeable future. Mountain areas are particularly vulnerable to climate change as the general temperature and precipitation alteration trends are being amplified due to local variations in elevation and aspect. Many mountain areas are also under increasing human pressure, which is related to food production, settlement, mining, and other direct earth-moving activities. As a response to such external drives, the increase in frequency and magnitude of geomorphic processes has been observed in many mountain areas around the world, including tropical mountains of South America. This study aims to better understand the development of gullies in tropical mountains. The main objectives are: (1) To document the spatial distribution of gullies within three selected areas in Cordillera Vilcanota, Andes, Peru, and (2) To investigate the relationship between the distribution of geohazard sites and landscape topographic properties.

The study area is located in Cordillera Vilcanota in the Andes of Peru. Our research focuses on three areas (ranging from 25 to 80 km2) located along valley corridors in which several villages, roads and agricultural infrastructures are located. A relatively dense population (considering the remote mountain location) means that gully erosion constitutes serious problems for human life and infrastructure. The distribution of gullies was mapped based on high-resolution satellite data (resolution better than 1.0 m). We used satellite images from 2002, 2014, and 2020 captured by Ikonos, WorldView and Pleiades. The remote mapping was subsequently verified during the fieldworks in 2017, 2018, and 2019.

We mapped almost four thousand individual gullies and gully complexes. Their length varied from 10 to 2000 m; however, most were small (mean length 103 m, median length 60 m). Most of the gullies were located close to the roads and in the valleys' middle parts, between 4000 and 5000 m a.s.l. Gully erosion, settlements and infrastructures, and cultivated land in the studied mountain areas represent a coupled mechanism. Gully erosion transforms the landscape, impacting human activity by (1) directly damaging properties and infrastructure, (2) forcing the population to change and adapt to new landscape characteristics, and (3) limiting land available for cultivation. However, human activities are not only threatened by gully erosion but also belong to one of the principal factors enhancing the erosion and mass movements, e.g. by the construction of undercut roads, changes in drainage systems (blocking surface water flow), and changes in land cover (removal of native vegetation) promoting rapid gully erosion. To further consider the impact of gully erosion, more research is needed to evaluate the impact on land production and promote solutions which can limit negative consequences.

The research was funded by the Polish National Science Centre, Poland (Project number 2015/19/D/ST10/00251)

How to cite: Ewertowski, M. and Tomczyk, A.: Gully distribution at the local scale in high-mountain, tropical environment: a case study of Cordillera Villcanota, Andes, Peru, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12787, https://doi.org/10.5194/egusphere-egu24-12787, 2024.

17:45–18:00

Posters on site: Mon, 15 Apr, 10:45–12:30 | Hall X3

Display time: Mon, 15 Apr 08:30–Mon, 15 Apr 12:30
Chairpersons: Apolline Mariotti, Romano Clementucci
X3.1
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EGU24-4124
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ECS
Fang-Yu Li, Meng-Long Hsieh, Chun-Ran Wu, and Yi-Hao Chen

Fluvial bedrock incision, which creates topographic relief and influences hillslope stability, has been considered the key process linking denudation and tectonic uplift in non-glaciated mountains. However, taking the Taiwan orogen as an example, this study argues that landslides can dominate over river incision in governing the erosion of active mountains. The Taiwan orogen, reaching 3000 – 4000 m in elevation, is prone to landsliding triggered by heavy rains or large earthquakes. It is shown in the orogen that landslides could drive catchment expansion and bedrock-river avulsion. Also, by determining the yield/caliber of bedload sediment, landslides have controlled river incision/deposition processes and, thus, the morphology of bedrock rivers (width, gradient, sinuosity, and shape of longitudinal profiles). The significant spatial/temporal diversities in landslide sequences, with various magnitudes/frequencies, then account for: (1) the occurrence of tributaries that are atypically wider or gentler than trunk rivers; (2) the wide ranges of bedrock incision rates (ranging from zero to several centimeters per year) over different time spans; (3) the contrasts in terrace sequences (and thus river evolutionary histories) among catchments; (4) the differential bedrock incision along rivers, leading to the creation of knickpoints (including waterfalls). All the observations above challenge the applicability of stream power law (assuming the drive of river incision by hydraulic power) in modelling bedrock river incision in the Taiwan orogen. We further find that the activities of landslides around the major drainage divides > 3000 m in elevation have been much lower than the activities of landslides in the mid-elevation regions (perhaps due to the lower seismicity in the high mountains). Given this and the commonness of low-relief surfaces stranded on the major drainage divides, it is unlikely that erosion of the orogen has offset the tectonic uplift. We believe that the elevation of the orogen has been increasing and it is the glacial erosion that can balance the tectonic uplift in the future.   

 

 Landslide; Fluvial bedrock incision; stream power law; low-relief surface; Taiwan orogen

How to cite: Li, F.-Y., Hsieh, M.-L., Wu, C.-R., and Chen, Y.-H.: Beyond stream power: the dominance of landsliding on the active Taiwan orogen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4124, https://doi.org/10.5194/egusphere-egu24-4124, 2024.

X3.2
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EGU24-7340
Chun-Ran Wu, Fang-Yu Li, Meng-Long Hsieh, and Kuan-Cheng Peng

Tectonic uplift drives erosion which limits the height of a mountain. Many scholars regard the main part of the Central Range in the Taiwan orogen, now 3000 – 4000 m in elevation, as a paradigm that erosion dominated by river/hillslope processes for millions of years can offset active tectonics by which the mountain range has obtained the topographic steady state. Our observations, however, challenge this belief: (1) the glacier/periglacial remains (cirques/U-shaped valleys with talus slopes) > 3300 m in elevation are well preserved (even showing dissolution grooves where they are made up of limestones) since the deglaciation (starting ~8 ka ago); (2) there are commonly barely eroded low-relief surfaces, capped by bamboo grass and characterized by low-gradient channels/depressions, stranding on the major drainage divide > 3000 m in elevation; (3) rivers originating from > 3000 m-high mountains commonly show prominent knickpoints (including > 100 m-high waterfalls) where flowing downward to elevations < 1000 m; (4) modern landslides and alluvial terraces (evidence of paleo-landslides) sourcing from the > 3000 m-high mountains are far less than those in the mid-elevation regions which typically originated from the sides of hillslopes. The combination of these data points out the relatively slow erosion in the > 3000 m-high mountain areas, although they are undergoing the rapidest tectonic uplift (based on GPS and leveling surveys). We attribute this apparent hillslope stability to the rarity of large earthquakes in the high mountains (as the major seismogenic faults are all distributed around the orogen). It is noted that incised low-relief surfaces similar to those exhibited in the high mountains are widely distributed in the lower parts of the orogen down to hilly regions. This configuration suggests that the low-relief landforms now preserved in the high mountains were originally created in the low-elevation regions when both river incision and tectonic rates were low; they were then uplifted (while dissected and eroded) to their present elevations, apparently associated with the acceleration of river incision and tectonic uplift (perhaps starting as late as 0.5 Ma). We consider that when the low-relief surfaces were raised to > 3000 m in elevation, they facilitated snow accumulation and thus, glaciation (i.e., all the glacier landforms preserved are inherited from the preexisting low-relief surfaces). In sum, we propose the elevation of the Central Range has been increasing with the acceleration of tectonic uplift since < 1 Ma ago, and it is the glacial erosion that could balance the tectonic uplift in the future.

 

(Keywords: River incision; landslides: glacial erosion; topographic steady state; the Taiwan orogen)

How to cite: Wu, C.-R., Li, F.-Y., Hsieh, M.-L., and Peng, K.-C.: Was the active Taiwan orogen one million years ago as high as today?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7340, https://doi.org/10.5194/egusphere-egu24-7340, 2024.

X3.3
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EGU24-42
Hung-Chun Chao

    Radiogenic Sr isotope (87Sr/86Sr) is a robust tool for provenance identification in hydrology, affected mainly by chemical weathering, lithological background and climatic changes while stable Sr isotope (δ88Sr) may provide complementary information about weathering, adsorption, or carbonate precipitation. In this study, river water samples from the mainstream and the major tributary located at Gang-Kou River catchment were collected seasonally for two years. Major ions, trace elements, and Sr isotopes were measured. The results show that the major anions are bicarbonate (2.35 to 5.24 mM), chloride (0.413 to 1.11 mM), and sulfate (0.187 to 0.817 mM). The major cations are sodium (0.567 to 1.41 mM), calcium (0.720 to 1.66 mM), and magnesium (0.508 to 0.922 mM). The Sr isotopes of river water in the mainstream decrease from upper steam to down steam (from 0.71287 to 0.71174) and are higher than the major tributary. In reverse, the Sr isotopes of major tributary increase from upper steam to down steam (from 0.71066 to 0.71136). The major tributary shows lower Sr isotopes during wet season while the mainstream shows no seasonal variations. The major tributary also shows slightly higher δ88Sr than the mainstream without seasonal variation. The result of major elements with Sr isotopes indicates silicate weathering dominates the river water chemistry while the major tributary shows slightly higher portion of carbonate weathering. Besides that, river water chemistry shows higher carbonate weathering contribution in wet season than dry season. To summary, Sr isotopes are more sensitive to the source variations in water chemistry than the chemical compositions. The results of dissolved phase in Gang-Kou River catchment indicate possible implication to the province identification of the sediments at the estuary.

How to cite: Chao, H.-C.: Chemical composition and triple Sr isotopes of Gang-Kou River, Southern Taiwan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-42, https://doi.org/10.5194/egusphere-egu24-42, 2024.

X3.4
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EGU24-8368
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ECS
Yifan Du and Peter Clift

Silicate weathering is recognized as being critical in removing greenhouse CO2 gas from the atmosphere, which offsets the CO2 supplied by mantle degassing during magmatism. In doing so chemical weathering keeps the Earth’s climate in a relative steady state condition. However, where the most important CO2 sink is remains enigmatic. In this work, we analysed deep-sea clastic sediments recovered by International Ocean Discovery Program Site U1485 from the northern coast of Papua New Guinea to understand the evolution of weathering in New Guinea in the last 0.3 Ma. Major element compositions indicate increased chemical weathering. This is consistent with increasing proportions of kaolinite, indicative of enhanced tropical weathering. Sr and Nd isotopes, together with key trace elements indicate increasing erosion from magmatic arc and ophiolite sources. Isotope mixing calculations indicate that most of the sediment is derived from the colliding magmatic arc. Comparison of sediment with onshore bedrock compositions implies that the source terrains have been especially reactive and efficient at removing CO2 from the atmosphere, especially compared to Himalayan bedrocks. Weathering in eastern New Guinea now accounts for ~16% of global CO2 consumption. We argue that this island has played an important role in driving global cooling.

How to cite: Du, Y. and Clift, P.: Chemical Weathering of Mafic Sources in Neogene New Guinea as a Control on Global Climate, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8368, https://doi.org/10.5194/egusphere-egu24-8368, 2024.

X3.5
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EGU24-12576
Joachim Götz, Alexander Melchert, Heidi Bernsteiner, Sarah Bauch, Michael Dietze, and Margherita Stumvoll-Schmaltz

Alpine sediment transport from rockslopes to rivers occurs along cascades and by Earth surface processes of varying frequency and magnitude. Modulated by ongoing climate change, they pose hazards as well as matter fluxes that impact the hydrological, ecological and economic system. Typical source-to-sink sediment routing in non-glaciated alpine headwater systems include mechanical weathering, rockfall, debris flows or avalanches, and fluvial transport.

Characterized by a highly active sediment cascade, the Wimbach Valley in the Berchtesgaden National Park (A = 36 km²; δz = 2086 m) is the largest "Alpine Gries Landscape" in Europe and a textbook test site to study transient sediment dynamics in transport limited systems. Frequent rockfall from the strongly fractured, dolomitic rock faces supply huge amounts of sediments transported via debris flows and avalanches through numerous steep gullies towards the valley bottom. Fluvial transport only occurs when short-term surface runoff is triggered by heavy rainfall of variable thresholds, lending their non-linearity from the state of the water table within the sediment body. Runoff occurs on very limited spatial and temporal scales but is highly effective and controls this last link to the conveyor belt-like sediment routing system. This setting results in a massive valley fill that is frequently reshaped by different processes and led to a unique scenery with a complex pattern of so-called “Schuttströme” between vegetated areas of multiple successional stages after disturbance.

Since the frequency and magnitude of precipitation and sediment transport events will increase with climate change, constraints on sediment transport will become disproportionally important: Several groynes and a dam delimiting the sediment body towards the valley outlet are already filled with sediments, which, if reaching the Wimbach Gorge, might affect tourism, infrastructure, and drinking water supply.

We thus currently establish a comprehensive monitoring system to decode the entire sediment cascade based on cutting edge technologies covering all relevant processes with a high spatial and temporal resolution: Mechanical weathering, sediment production, rockfall, debris flow and avalanche dynamics as well as fluvial transport will be assessed using a multi-sensor approach, including rock temperature/humidity sensors, rockfall nets, annual airborne and event-based terrestrial Lidar data, SfM point cloud modelling based on historical aerial imagery and repeated UAV flights, stereo-webcams at neuralgic points, and a dense passive seismic network. The latter enables to detect, locate, track, and quantify major geomorphic processes and allow access to timing, magnitude, trajectory and coupling patterns amongst these processes, representative for many other mountainous landscapes subject to environmental change. The analyses of trigger mechanisms and variable thresholds will be based on dense climate data available to the project.

Preliminary remote sensing analyses of multi-temporal orthophotos and aerial imagery using manual and deep learning mapping approaches as well as Lidar based difference modelling are recently in progress. Here we present the entire monitoring system, which is currently under implementation, as well as first mapping and modelling results showing drastic amounts of sediment transport in almost the entire catchment and an increase in geomorphological activity since 2003.

How to cite: Götz, J., Melchert, A., Bernsteiner, H., Bauch, S., Dietze, M., and Stumvoll-Schmaltz, M.: The Wimbach Observatory – Alpine sediment dynamics in transport-limited systems (Wimbach Valley, Berchtesgaden National Park), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12576, https://doi.org/10.5194/egusphere-egu24-12576, 2024.

X3.6
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EGU24-11222
Rocio Jaimes-Gutierrez, Emmanuelle Puceat, David J. Wilson, Thierry Adatte, Marine Prieur, Claire Musajo, Philip Pogge von Strandmann, Jean Braun, and Sebastien Castelltort

Global warming and the associated hydrological cycle variations are known to disrupt the weathering regime over geological timescales. Enhanced weathering and erosion, which constitute denudation, are important feedback mechanisms for regulating Earth’s temperature over multi-million-year timescales. Weathering can draw down CO2 from the atmosphere, while enhanced physical transport can accelerate organic carbon sedimentation and sequestration. This study aims to uncover changes to the denudation regime accompanying a massive climatic disturbance in deep time, the Paleocene-Eocene Thermal Maximum (PETM). The global warming of 5-8 °C due to the PETM has been documented to have increased the magnitude and intensity of precipitation events in the Spanish Pyrenees. But how did weathering respond to such a climatic and hydrological disturbance?

We investigated the lithium (Li), hafnium (Hf), and neodymium (Nd) isotopic composition of the <2 mm clay size-fraction in three sections in the Spanish Pyrenees, from source to sink: the Esplugafreda, Campo, and Zumaia localities. The Li isotope record at Esplugafreda in the fluvial domain shows a positive δ7Li excursion during the onset and body of the event and a negative excursion during the PETM recovery, with no variation in the ΔεHf, i.e., εHf corrected for provenance changes with the εNd record. The Campo coastal section shows a negative δ7Li excursion during the body of the event. In the Zumaia deep marine section, the body of the event was characterized by a positive δ7Li excursion, coeval with a negative excursion in ΔεHf.

These results suggest a relative decrease in weathering (W) to denudation (D = W+E, where E is erosion) during the PETM. The terrestrial section (Esplugafreda) indicates a local decrease in clay formation relative to erosion (E). The coastal section (Campo), which integrates a larger catchment area, seems to record an absolute increase in weathering. Finally, the “sink” deep-marine section (Zumaia) appears to indicate a relative decrease in regional weathering to denudation (W/D), consistent with the positive Li isotope and negative ΔεHf excursions. The source-to-sink approach suggests that weathering in the Pyrenees increased during the PETM but that physical erosion increased even more, hence controlling the denudation regime in the region. These changes imply a trend towards a kinetically-limited weathering regime in the region, with local variations in weathering efficiency.

How to cite: Jaimes-Gutierrez, R., Puceat, E., Wilson, D. J., Adatte, T., Prieur, M., Musajo, C., Pogge von Strandmann, P., Braun, J., and Castelltort, S.: Source-to-sink weathering response to the Paleocene-Eocene Thermal Maximum (PETM) in the Southern Pyrenees, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11222, https://doi.org/10.5194/egusphere-egu24-11222, 2024.

X3.7
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EGU24-13586
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ECS
Henry Crawford, Mitch D'Arcy, Andreas Ruby, Taylor Schildgen, and Ana Laura Martínez López

Alluvial fans comprise abandoned sedimentary surfaces undergoing physical and chemical weathering. While weathering pathways and kinetics have been described over seconds to decades, few field-based studies have quantified these processes in alluvial deposits over geologic timespans. We examine 14 alluvial-fan surfaces flanking the Sierra del Aconquija, southern Central Andes, which have ages between 3 and 320 ka as determined by cosmogenic nuclide exposure dating. These fans present an opportunity to study the evolution of alluvial sediments across late-Quaternary timescales; including silicate weathering pathways, products, rates, and sensitivity to known past climate changes. We use space- and ground-based hyperspectral reflectance measurements to characterize surface mineralogy, and we test whether in-situ weathering records signals of landform age and regional climatic history. We collect fan-surface reflectance using both a handheld spectroradiometer and the PRISMA hyperspectral satellite sensor. In both datasets, bridging several orders of magnitude in spatial scale, we detect spectral features indicative of changing quantities of primary minerals, clays, and iron oxides. These patterns suggest a gradual increase in absolute weathering with surface age, but at progressively slower rates over time. Superimposed on the long-term weathering kinetics, secondary minerals are generated in amounts and at rates that correlate systematically with ~23 kyr precessional cycles and millennial-scale climate perturbations.  We interpret that these alluvial fans are sensitive archives of past weathering, which was more pronounced during episodes of wetter and warmer climate. Furthermore, the surface signals are corroborated by the downward accumulation of iron oxide, as shown in soil profiles from four alluvial fan units which were spectrally scanned from the surface to below the weathering front. Our findings highlight the geomorphological applications of hyperspectral data for (i) quantifying weathering processes over 1-100 kyr timescales; (ii) developing novel chronometers for alluvial sediments; and (iii) recovering new palaeoclimate signals from terrestrial sedimentary archives.

How to cite: Crawford, H., D'Arcy, M., Ruby, A., Schildgen, T., and Martínez López, A. L.: In-situ Weathering of Alluvial Sediments in the Southern Central Andes Recorded by Ground- and Space-Based Hyperspectral Reflectance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13586, https://doi.org/10.5194/egusphere-egu24-13586, 2024.

X3.8
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EGU24-13843
Mitch D'Arcy, Martin Lang, Taylor F. Schildgen, Henry T. Crawford, and Sam Brooke

There is growing recognition that multispectral satellite imagery can be used to characterise the weathering state of material exposed at the Earth’s surface. However, it remains unclear if and how satellite-derived weathering indices can be linked, in a universal way, to the fundamental controls on weathering (e.g., surface age and composition, temperature, moisture availability). Here, we use Landsat-8 Operational Land Imager (OLI) multispectral imagery to characterise the reflectance of 75 dated moraines, distributed throughout the Central Andes between 7 and 27 °S. As imaged from space, these moraines represent ageing surfaces composed of sediment that is undergoing physical and chemical weathering. The moraines present an ideal opportunity to explore the controls on weathering over 103-105 year timescales, because they span major gradients in age (1-112 kyr), temperature (2-9 °C), precipitation (100-1000 mm/yr), and also lithological composition.

From contrast-enhanced Landsat-8 imagery, we derive a simple band ratio that has been demonstrated to act as a weathering index, scaling with the extent of chemical weathering and the presence of secondary minerals. At every location, we observe a non-linear increase in the weathering index with moraine age. Older moraines exhibit a systematic shift in brightness from visible wavelengths to the short-wave infrared, driven by mineralogical changes during weathering. We also detect subtler variations in the rates and magnitudes of changes in the weathering index that relate to lithological composition. Moraines with mineralogically-diverse compositions (e.g., intrusives and volcanics) display faster and larger increases in the weathering index compared to moraines with mineralogically-simple lithologies (e.g., quartzite and carbonates). Next, we derive the rates of change of the weathering index as a function of moraine age, and compare with past climate. Precipitation emerges as a key control on the weathering index, with faster weathering coinciding with wetter conditions in both time and space. The weathering index increases faster during known episodes of wet climate in the past, registering both 23 kyr precessional cycles and abrupt, 1 kyr Heinrich events. The weathering index also exhibits significantly larger increases in the northern Central Andes, where the climate is much wetter, compared to the southern Central Andes where the climate is drier. Temperature exerts an inverse control on the weathering index, which we speculate reflects the role frost-shattering plays in facilitating chemical weathering.

This work demonstrates that freely-available Landsat-8 imagery can be used to reconstruct the weathering of sedimentary landforms across time and space. Furthermore, our results hint at the presence of fundamental relationships between weathering state, as detected by multispectral sensors, and primary variables such as time, substrate composition, and climate.

How to cite: D'Arcy, M., Lang, M., Schildgen, T. F., Crawford, H. T., and Brooke, S.: Using multispectral imagery to characterise weathering: A case study of moraines in the Central Andes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13843, https://doi.org/10.5194/egusphere-egu24-13843, 2024.

X3.9
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EGU24-20855
Deciphering Andean glaciovolcanic processes through geomorphic analysis: the Toro Chico valley, Chile's south (37ºS)
(withdrawn)
Alfonso Fernandez, Mariajose Herrera, Edilia Jaque, and Ianire Galilea
X3.10
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EGU24-14355
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ECS
Arihito Kondo, Yuki Matsushi, and Hiroyuki Matsuzaki

                 Soils on hillslopes in humid temperate regions move slowly downward with varying fluxes depending on depth. The soil creep contributes to enhance soil depth in head hollows and develop soil layer structures in a long time scale, which regulate short-term subsurface hydrological processes and hence slope instability by rainwater infiltration. This study attempted to model long-term soil creep processes, based both on terrestrial Be-10 concentrations in bedrock and depth profiles of meteoric Be-10 abundance in soil columns on a hillslope. The soil creep model developed here composes of two velocity profiles corresponding to viscous transport by plastic deformation of soil mass and discrete particle-flow transport due to the external disturbance from the soil surface. By coupling these distinct transport laws, the depth profile of soil creep rates was modeled as a combined formula of two exponential functions. Soil production function determined by terrestrial Be-10 and spatial distribution of soil depths combined with topographic curvature provided the rate and mass-budget constraints for the model, while meteoric Be-10 inventory in the soil columns served a clue to fix model parameters for the subsurface soil creep pattern. The model fitting to the meteoric Be-10 profiles output the soil residence time, which was then examined by C-14 dating for the charcoals obtained from the soil column.

             Model validation was conducted at a hillslope underlain by granodiorite in northern Abukuma Mountains, Japan. The target hillslope exhibits a convex ridge top with a planar midsection that becomes slightly concave toward downslope. A thick soil layer (>1 m) covers the entire hillslope, which characteristically composed of two layers: upper soft and lower stiff parts divided around 40–60 cm in depth. Bedrocks were sampled at bottoms of several soil pits excavated on hill-noses for terrestrial Be-10 measurement. Soil samples for meteoric Be-10 analysis were collected sequentially from ground surface to ~2 m depth in 10 cm interval at four pits located along a transect from the ridge to hollow. Charcoal grains imbedded in the soil layer were also collected for C-14 dating. The datasets of meteoric Be-10 profiles were well explained by fitting the two-layered soil creep model under the terrestrial Be-10 derived soil production rates and depth-dependent soil residence time evidenced by the charcoal ages.

How to cite: Kondo, A., Matsushi, Y., and Matsuzaki, H.: Modelling soil creep dynamics based on meteoric and terrestrial Be-10 coupling: validation on a hillslope profile in northern Abukuma Mountain, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14355, https://doi.org/10.5194/egusphere-egu24-14355, 2024.

X3.11
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EGU24-16621
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ECS
Amalie Skålevåg, Oliver Korup, and Axel Bronstert

In cold mountain environments, freeze-thaw processes significantly influence sediment dynamics. With the rapid warming of high mountain areas observed in recent decades, such freeze-thaw processes are likely to be affected. Thus examining the relationship between fluvial sediment transport and catchment freeze-thaw, may inform our predictions of the future sediment transport regime in mountain landscapes. Freeze-thaw has the potential to both increase and decrease suspended sediment concentrations in rivers. Freeze-thaw-driven erosion increases the sediment supply and thus can elevate the suspended sediment load. However, as the key hydrological processes driving sediment transport are thermally regulated, temperatures at the freeze-thaw boundary will generally result in lower transport capacity and less catchment area contributing sediment to the streams. Here, we aim to examine this diverging effect of freeze-thaw at the daily scale in a high alpine catchment. We use Bayesian analysis to quantify the modulating effect of catchment freeze-thaw state and cycles on sediment transport in an alpine catchment. We use daily 1-km rasters of maximum and minimum temperature to determine the catchment area affected by daily freeze-thaw cycles and the frozen catchment area to determine freeze-thaw influenced days. With daily suspended sediment and streamflow data, we then analyse the sediment-discharge relationship on days with and without freeze-thaw influence.

How to cite: Skålevåg, A., Korup, O., and Bronstert, A.: Quantifying the effect of freeze-thaw on daily sediment transport in an alpine catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16621, https://doi.org/10.5194/egusphere-egu24-16621, 2024.

X3.12
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EGU24-17766
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ECS
Yassine Boukhari, Caroline Le Bouteiller, Antoine Lucas, Stéphane Jacquemoud, Sébastien Klotz, and Mathilde Griffaton

With rates locally exceeding one centimeter of denudation per year [1,2], i.e., more than 100 t/ha/year, the Durance basin in the French Alps is one of the world’s most heavily eroding areas [3]. A combination of favorable conditions explains this phenomenon, including a very steep topography, sparse vegetation and a particular susceptibility of the Jurassic black marls, also called Terres Noires, to seasonal climatic forcing [4]. The Draix-Bléone observatory uses hydro-sedimentary stations to instrument several of these small, non-anthropized catchments, where hydrological responses to seasonal storms are rapid and intense [5]. The work presented combines the use of LiDAR time series from airborne, UAV and ground measurements, with sediment flux chronicles recorded at the outlet of the Laval catchment, a small steep watershed (0.86 m2), to address questions of upstream/downstream transport modalities. An assessment of the potential of remote sensing methods for attributing the contributions of each critical zone compartment (channel, gullies, landslides, etc.) to the erosive dynamics of this basin and its connectivity is carried out.

References :

[1] N. Mathys, S. Brochot, M.  Meunier and D. Richard (2003). Erosion quantification in the small marly experimental catchments of Draix (Alpes de Haute Provence, France). Calibration of the ETC rainfall-runoff-erosion model. CATENA. 50(2–4):527–548. DOI : 10.1016/S0341-8162(02)00122-4.

[2] A. Carriere, C. Le Bouteiller, G. E. Tucker, S. Klotz, and M. Naaim (2020). Impact of vegetation on erosion: Insights from the calibration and test of a landscape evolution model in alpine badland catchments. Earth Surf. Process. Landf., 45(5):1085–1099. DOI : 10.1002/esp.4741.

[3] D. E. Walling (1998). Measuring sediment yield from river basins. in Soil Erosion Research Methods (R. Lal, Ed.). Soil and Water Conservation Society, Iowa, USA, pp 39–73.

[4] L. Descroix and N. Mathys (2003). Processes, spatio-temporal factors and measurements of current erosion in the French Southern Alps: A review. Earth Surf. Process. Landf. 28( 9): 993–1011. DOI : 10.1002/esp.514.

[5] Draix-Bleone Observatory. (2015). Observatoire hydrosédimentaire de montagne Draix-Bléone [Data set]. Irstea. DOI : 10.17180/obs.draix

How to cite: Boukhari, Y., Le Bouteiller, C., Lucas, A., Jacquemoud, S., Klotz, S., and Griffaton, M.: LiDAR assessment of sediment transport in a small, highly erosive alpine catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17766, https://doi.org/10.5194/egusphere-egu24-17766, 2024.

X3.13
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EGU24-10899
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ECS
Sofia Garipova, David Mair, Sophia Demmel, Ludovico Agostini, Naki Akçar, Peter Molnar, and Fritz Schlunegger

We aim at exploring the sedimentary source-to-sink pathways in the Alpine Rhine, Switzerland through integrating hydrological modeling, connectivity mapping, and field observations. We hypothesize that either rainfall-driven overland flow erosion or landsliding (Battista et al., 2020) are the main mechanisms contributing to the generation of sediment and controlling the source-to-sink transport of sediment in the basin. We test this hypothesis through mapping such sediment sources in the field and on lidar DEMs, and we conduct conceptual models to characterize the sensitivity of these sources to temporally and spatially varying rainfall rates (Demmel et al, 2024). We complement this analysis with a coupled hydrology-erosion model, through which we predict how the water and suspended sediment waves propagate downstream from the source through the channel network (Agostini et al, 2024). We then test these model-based predictions on rainfall-dependent source-to-sink sedimentary pathways with field data. We start with the 370 km²-large Glogn river catchment, which is a tributary of the Alpine Rhine. In the headwater reaches, the Glogn catchment is made up of a dense network of channels that are perched on the hillslopes, whereas farther downstream, the basin hosts several deep-seated landslides that potentially supply large volume of sediment to the channel network (Cruz Nuñes et al, 2015). We proceed upon collecting data about the size of clasts and their petrographic composition to characterize the source signal for the bedload of the Glogn River, and we trace these signals from upstream to downstream. We complement this dataset with a petrographic characterization of the suspension load including the bulk geochemical and mineralogical composition of sand and the measurements of concentrations of cosmogenic 10Be and 26Al in riverine quartz minerals. We then apply a principal component analysis to this dataset to identify the material signals of the different sediment sources, and we estimate the relative contribution of material from tributary basins through mixing modelling. We postulate that in the upstream, less dissected part of the basin, overland flow erosion constitutes the major mechanism of the sediment production, whereas in the downstream area where the Glogn has deeply dissected into the substratum, mass failure processes such as landsliding is the most important mechanism contributing to the production of sediment.  

References:

Agostini, L., Demmel, S., Garipova, S., Sinclair, S., Schlunegger, F., Molnar, P. (2024) Suspended sediment transport in river network models: testing signal propagation and modelling approaches. EGU24. 

Battista, G., Schlunegger, F., Burlando, P., Molnar, P. (2020) Modelling localized sources of sediment in mountain catchments for provenance studies. Earth Surf. Process. Landforms, 45, 3475– 3487. 

Cruz Nuñes, F., Delunel, R., Schlunegger, F., Akçar, N., Kubik, P.W. (2015) Bedrock bedding, landsliding and erosional budgets in the Central European Alps. Terra Nova, 1-10. 

Demmel, S., Agostini, L., Garipova, S., Leonarduzzi, E., Schlunegger, F., Molnar, P. (2024) Climatic triggering of landslide sediment supply. EGU24. 

How to cite: Garipova, S., Mair, D., Demmel, S., Agostini, L., Akçar, N., Molnar, P., and Schlunegger, F.: Source-to-Sink Sediment Tracing in the Glogn River Catchment , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10899, https://doi.org/10.5194/egusphere-egu24-10899, 2024.

X3.14
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EGU24-18484
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ECS
Philipp Gewalt and Michael Krautblatter

Debris flows are amongst the most dangerous geomorphic processes world-wide. In alpine environments, settlements and infrastructure are commonly located on debris flow fans. An over-proportional increase in debris flow activity has been shown to occur in response to climate warming under transport-limited conditions. Enhanced debris flow activity might not only affect transport volumes on existing fans. It could trigger a phase shift from regular debris flow activity to mega-activity leading to the generation of outsized fans. However, sediment fan formation during phases of exceptionally high debris flow activity remains largely unexplored: While more than 65 outsized sediment fans have been identified throughout the European Alps, only for three of them detailed sub-surface information exists. Although outsized-fan activity may provide invaluable information on the “things to come” in the next decades, the potential of outsized fans as analogues for future debris flow activity is so far unknown. To enhance our understanding of the magnitude, style, and landform-building potential of future debris flow activity, this research project investigates the following research question: What can current and past mega-activity on alpine debris flow fans teach us about future debris flow activity? We will investigate the spatio-temporal patterns of debris flow activity on a small, a medium, and an outsized alpine debris flow fan over decadal, centennial, and millennial timescales. On the small spatio-temporal scales, we will use geomorphic mapping, aerial photography, dendrochronologic dating, and digital elevation model differencing to investigate links between decadal climate change and debris flow activity. On the larger scales, we will combine several methods of near surface geophysics to derive the subsurface architecture of the sediment fans and thus gain insights into their formation history. We will use this information to calibrate a landscape evolution model of outsized fan formation to test the plausibility of the inferred formation history and ensure transferability of the results. This research project systematically deciphers the magnitude and outsized fan building potential of massively changing debris flow activity in the past to anticipate phase shifts in the foreseeable future.

Key Words: Debris flow, polygenetic sediment fan architecture, climate change, outsized fan, geophysical tomography

How to cite: Gewalt, P. and Krautblatter, M.: A conceptual approach for deciphering mega-activity of debris flow fans and polygenetic fans for climate change anticipation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18484, https://doi.org/10.5194/egusphere-egu24-18484, 2024.