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.

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.

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 14^th 2023 event, characterized by a high river discharge, and the debris flow of December 13^th 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.

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.

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.

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.

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.

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.

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.

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.

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 (La_N/Yb_N, 7.61-14.35), nearly flat HREE (Gd_N/Yb_N, 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 Gd_N/Yb_N) 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.

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.

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.

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.

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.

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.