Ongoing climate warming is shifting glacier equilibrium lines and freezing zones upslope, exposing vast areas of formerly ice-bound sedimentary material to potential mobilization by extreme floods or mass flows. Their high-altitude position, combined with gravitational potential energy on steep mountain slopes, makes them especially susceptible to cascading hazards in the future.
This session invites contributions that investigate, across spatial and temporal scales:
• catastrophic sediment mobilization and cascading hazard chains
• processes and hazards linked to deposition and runout
• concepts of compounding and cascading dynamics
• connectivity between hillslopes and river networks
• feedbacks between stabilizing and destabilizing slope processes
We welcome presentations employing observational, conceptual, methodological, or modeling approaches, individually or in combination, across diverse mountain environments. Early-career scientists are particularly encouraged to contribute.
Landslide sediment in small mountain rivers (SMRs), particularly in East Asia, is a major source of the sediment exported from land to ocean. These landslides are usually triggered by earthquakes or rainstorms, at different locations on the hillslope: earthquake-induced landslides tend to occur in hillslope crest regions, whilst rainstorm-induced landslides tend to occur at the hillslope base. These characteristic landslide locations affect the timescales over which the sediment is transported to and through the river network. Previous studies found that landslides closer to the river network will have a shorter sediment residence time, whilst earthquake-driven landslides in hillslope crest regions have a longer residence time. Our earlier work has shown that earthquakes have a legacy impact on the location of the subsequent rainstorm-induced landslides, potentially increasing the sediment residence time of these events, compared to rainstorm-driven landslides that are not shaped by previous earthquakes . However, the effects of these legacy earthquake impacts on controlling sediment export from SMRs during successive rainstorm-triggered landslide events are not well understood, yet are likely to be important in countries such as Taiwan that are exposed to the combined effects of earthquakes and tropical rainstorms. In this study, we used the MassWastingRouter (MWR) model to simulate landslide sediment transport from the landslide source location to the river outlet in the Nei-Mao-Pu catchment, Choshui River, Taiwan, for the 2013 Nan-Tou earthquake and three subsequent rainstorm events, each with a reduced legacy impact of the Nan-Tou earthquake: Typhoon Soulik (2013), an extreme rainfall event (2015), and Typhoons Lekima and Bailiu (2019). We simulated landslide movement on hillslopes using the MassWastingRunout(MWRu) submodel, and then simulated the sediment transport from hillslopes to the river network using the MassWastingEroder(MWE) submodel. Next, the NetworkSedimentTransporter (from Landlab) was used to simulate fluvial sediment transport process to characterize the spatial and temporal dynamics of sediment transport from landslide locations to the river outlet. We then applied a functional connectivity-based analysis to explore time and space scales over which landslide-derived sediment from landslide source locations is connected to downstream locations within the river network. This approach enables us to better understand how sediment from different landslide locations contributes to overall sediment residence time within the system. The results demonstrate how the interaction between earthquakes and subsequent rainstorms ultimately controls sediment transport, providing crucial knowledge of sediment transport regimes and sediment source management in SMRs.
How to cite: Lin, Y.-T., Turnbull-Lloyd, L., Wainwright, J., Keck, J., and Istanbulluoglu, E.: Investigating the interplay between landslide location, drivers, and the earthquake legacy impact on sediment flux in a small mountainous river in Taiwan, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-349, https://doi.org/10.5194/egusphere-egu26-349, 2026.
Yukon Territory is experiencing impacts of climate change, marked by elevated annual air temperatures, changes in precipitation patterns and increased wildfire activity. These shifts can lead to permafrost degradation, impacting highways and community infrastructure. This study characterizes the timing and morphology of post-wildfire permafrost landslides and documents a cascading hazard. It identifies relationships between permafrost characteristics, geology, weather conditions and ground disturbance. This work contributes to the growing body of research on how climate change is impacting communities and infrastructure in permafrost regions.
In 2017, a wildfire burned across a slope, underlain by permafrost, parallel to the Dempster Highway in northeastern Yukon. Within days, multiple active layer detachments (ALDs) occured caused by degradation of the insulating organic surface layer resulting in rapid permafrost thaw. Over forty ALDs occurred on the slope over the summers of 2017 and 2018, likely influenced by rainfall events and periods of above average air temperatures. Initiation angles for ALDs varied according to surficial geology. Areas with shale-rich colluvium had initiation angles as low as 10° while in sandstone dominated colluvium, initiation angles were greater than 25°. By 2019, portions of the slope appeared to stabilize as no new ALDs occurred; however, six retrogressive thaw flows (RTFs) initiated in ALD landslide scars. RTFs only occurred on topographic benches where ice-rich stratigraphy had been exposed by complete removal of the insulating surface organic layer by the ALD. The headwalls of the active RTFs consist of metre-scale ice wedges, as well as loess and organic-rich colluvium units. OSL ages indicate sediments accumulated over the last ~100,000 years. The surficial units were sampled and measured for volumetric and gravimetric ice-content. The ice content generally increased with depth.
RTFs have deposited significant amounts of sediment on the floodplain at the base of the slope near the highway, and four of the RTFs were still active during site investigations in the summer of 2023. The increased sedimentation in the valley bottom has led to stream blockages and flooding, degrading permafrost beyond the perimeter of the original burn. This research indicates complex cascading hazards can occur in permafrost areas due to anthropogenic global warming. At this site we document a forest fire, that triggers abundant ALDs, some of which then evolve into RTFs, which generate abundant sediments, blocking drainages and causing flooding which will likely trigger more permafrost degradation. This research indicates that wildfire on permafrost slopes can initiate a cascading hazard that can be further influenced by local precipitation and warm summer temperatures.
How to cite: Clarke, H., Ward, B., Cronmiller, D., Groeneveld, K., and Lamothe, M.: Post-wildfire permafrost landslides and cascading hazards, Dempster Highway,Yukon, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16304, https://doi.org/10.5194/egusphere-egu26-16304, 2026.
The eastern flank of Monte Rosa (4,634 m a.s.l.), the second-highest peak in the Alps, is among the largest and most extensively glacierized Alpine mountain faces and has been described as a “Himalayan-type” slope. Since the early 21st century, it has been intensively monitored by several institutional teams and academic research groups, primarily due to the exceptional surge event that affected the Belvedere Glacier, the main collector of glacier ice flowing down from Monte Rosa.
Over recent decades, this slope has undergone rapid deglaciation in response to climate change. Ice loss has been accompanied by the onset and intensification of geomorphological instability phenomena spanning the full spectrum typical of glacial and periglacial environments. Rock faces are increasingly prone to toppling, falls and rock avalanches; talus and debris cones are the site of erosion phenomena and feed debris flows; moraines undergo degradation, incision, and collapse. Key drivers include degradation of permafrost, increasingly intense precipitation at high altitude and rising 0°C isotherm. Of particular interest is the high magnitude that characterizes these events, especially if we consider that they occur with an unprecedented frequency.
Mass and energy transfers from high elevations trigger cascading effects across different geomorphological environments (glacial, periglacial) and they ultimately impact the anthropogenic system. Recent geomorphological investigations (CNR-IRPI, University of Turin) and monitoring activities (ARPA-Piemonte) focus on process identification, high-resolution mapping, and quantitative assessment. Two complementary multi-temporal approaches were adopted: (1) field-based and remote-sensing geomorphological mapping, and (2) 3D topographic modelling via photogrammetry. These methods produced detailed geomorphological maps at 1:5,000 scale (years 2010, 2012, 2015, 2018, 2021, 2023, 2024 and 2025) and original 3D photogrammetric models (50 cm resolution: years 2023, 2024 and 2025), which were compared with pre-existing metric-resolution DEMs (2011, 2017).
Data analysis and interpretation for the headwaters of Anzasca Valley (total area: 30 km²) indicate, from 2011 to the present, a total reduction of approximately 1.1 km² in glacierized area and an ice-volume loss of ~56 million m³. The multi-temporal (4D) geomorphological analysis enabled the identification of individual instability processes and the recognition of significant event sequences involving glaciers, rock walls, moraines, and fluvial channels.
These results provide a baseline for assessing where and how geomorphic dynamics intersect with human activities in an area of high value for scientific, mountaineering and tourism interests, recently designated as a geosite of international significance in the latest inventory compiled according to the Piemonte Regional Law 23/2023.
How to cite: Giardino, M., Alberto, W., Chiarle, M., Lanteri, L., Schiavon, G. S., and Mortara, G.: From ice loss to cascading mass movements: 4D geomorphological analysis of Monte Rosa’s eastern flank (NW-Alps, Italy), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17166, https://doi.org/10.5194/egusphere-egu26-17166, 2026.
In late May 2025, a series of large rock failures from Kleines Nesthorn in the Swiss Lötschental (Lötschen valley) fell directly onto the Birchgletscher (Birch Glacier), loading the latter with around 4 million m3 of rock. On May 28, following several days of acceleration, Birchgletscher collapsed in its entirety, claiming one life and causing the near-total destruction of the historic village of Blatten (which at this point was completely evacuated). Totaling more than 9 million m3 of rock and glacier ice (with a ratio of about 3:1), the rock-ice avalanche dammed the river Lonza and led to the formation of a lake that damaged additional parts of the village.
To reconstruct and understand the physical processes that controlled this remarkable hazard cascade, we used aerial topographic surveys, radar and time-lapse images, direct field observations, eyewitness accounts, meteorological data, and numerical modeling. From these data we 1) determined the precise chronology of the event, including the failure and deposition volumes and geomorphologic event traces; 2) reconstructed the pre-event (1946-2023) history of Kleines Nesthorn and Birchgletscher, including the substantial mass loss of the latter and its recent surge-type acceleration; 3) analyzed the kinematics of the rock instability on Kleines Nesthorn and the resulting rock failures that loaded the glacier; 4) used the 3-D finite element model Elmer/Ice to reconstruct the effect of the rock loading on the force balance of Birchgletscher and its relevance for the observed acceleration and collapse; and 5) processed data from several long-term weather stations, satellite data and climate models to evaluate the relevance of human-caused climate change on Birchgletscher, snow-cover, permafrost and the entire process chain. Our results highlight the complexity of the Nesthorn-Birchgletscher hazard cascade and provide valuable insights for the assessment and management of glacier-related hazards in high mountains.
How to cite: Jacquemart, M., Brondex, J., Knuth, F., Weber, S., Kenner, R., Aaron, J., Gischig, V., de Silva, R., Spielmann, R., Schneider, M., Schumacher, D. L., Welty, E., Gagliardini, O., Gaume, J., Gilbert, A., Huggel, C., Reist, F., Seneviratne, S. I., Senn, I., and Farinotti, D.: Reconstructing the 2025 Nesthorn-Birchgletscher hazard cascade, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19777, https://doi.org/10.5194/egusphere-egu26-19777, 2026.
High-magnitude mass flows originating in mountain terrain are often interpreted through their near-source geomorphic signatures—scarps, deposits, and valley-floor reworking. Yet some of the most widespread and immediate enviornmental impacts are transmitted far downstream by suspended sediment plumes, which can move rapidly through river corridors and interact with dams, barrages, and canal networks that regulate flow and sediment transport. Because plume fronts can outpace field response and because engineered infrastructure complicates sediment routing, the long-range behaviour and impact footprint of suspended-sediment pulses remain poorly constrained.
We examine the long-range transmission of suspended -sediment plumes triggered by the ~27 Mm³ Chamoli rock–ice avalanche–debris-flow cascade in the Garhwal Himalaya (Uttarakhand, India) in February 2021. The event caused >200 fatalities, major hydropower damage, and extensive valley-floor sedimentation, before highly turbid floodwaters propagated into the Ganga river system and the densely populated Ganga Canal network, where it severely disrupted water treatment serving millions in the greater Delhi region. Using high spatiotemporal resolution Earth observation, we reconstruct plume-front evolution from mountain headwaters into the Ganga main stem and canal pathways. The suspended sediment front is observed to propagate over 1000 km downstream in the main river and over 600 km within the canal network, extending far beyond the initial runout zone. We quantify hydro-sedimentary changes along the flood path, revealing a progressive downstream dilution of the plume. By linking plume dynamics to population distribution, we estimate that tens of millions of people across were potentially exposed to elevated water turbidity conditions. We use hydrodynamic modelling to explore how flow regulation, impoundment, and infrastructure condition modulate plume behaviour, showing rapid initial propagation rates (about 160 km per day) followed by pronounced downstream deceleration (<10 km per day) associated with regulated reaches and storage effects.
Our results demonstrate how high-resolution Earth observation can reveal the often overlooked, long-range footprint of mountain mass-flow sediment pulses which can extend many hundreds of kilometres from source, providing new insights relevant for downstream risk assessment and water resources management in regions where cascading hazards are expected to become more frequent.
How to cite: Chen, Q., Westoby, M., and Dunning, S.: The downstream story of a mountain disaster: how hydraulic infrastructure shapes sediment plume propagation , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15383, https://doi.org/10.5194/egusphere-egu26-15383, 2026.
Glacial lake outburst floods (GLOFs) are high-magnitude events that occur when the dam of a glacial lake fails, releasing huge volumes of water and entrained debris. The increasing frequency of GLOFs, driven by the ongoing effects of climate change, raises concerns about the long-term stability of high-mountain regions in Nepal and across the Himalayas. While the immediate impacts of catastrophic GLOFs are often devastating, the secondary hazards they trigger are frequently overlooked. These secondary hazards, including landslides, geomorphic instability, and stream channel destabilization, pose significant challenges to local communities. Although GLOF events typically last only minutes to hours, the geohazard cascades they initiate may affect communities for years or even decades. A recent GLOF event that caused extensive damage to infrastructure and farmland in Thame, a small mountain village in Nepal's Khumbu Himal region, demonstrated this chain of cascading hazards. Following the catastrophic outburst of two glacial lakes on August 16, 2024, the village now faces increased landslide risk due to significant stream-channel incision below the settlement. The geologic layers beneath the town are susceptible to slow-moving, deep-seated rotational landslides, particularly when lateral support is reduced by stream incision. As a result, the fluvial terrace on which the village is built is becoming increasingly likely to fail from landsliding. Field investigations in fall 2024 collected drone imagery and ground-based photographs of the flood deposits and affected downstream areas. These data were used to develop high-resolution photogrammetric topographic models, enabling reconstruction of the flood dynamics and the evolution of similar past events. Analysis of sediment deposits further reveals how GLOFs interact with ongoing geomorphic processes, contributing to landscape transformation over time. By integrating field observations with photogrammetric modeling, this study highlights the cascading nature of hazards following GLOFs and their role in shaping mountain landscapes.
How to cite: Manatschal, L., Wegmann, K. W., Bhandari, B., and Owen, L. A.: Glacial Lake Outburst Floods and Their Long-Term Impacts on Himalayan Landscapes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15420, https://doi.org/10.5194/egusphere-egu26-15420, 2026.
On 27–28 September 2024, the Kathmandu Valley experienced unprecedented rainfall, exceeding the previous record for 24-hour cumulative precipitation in Kathmandu and surrounding regions. This extreme event triggered severe flooding, resulting in loss of life and the burial of buildings, roads, and other infrastructure beneath thick sediment deposits. The flood also damaged hydrological gauging stations, preventing the recording of peak flood levels during the event. Despite this limitation, the flood left distinct geomorphic and sedimentary evidence along the floodplain, including high-water marks on building walls and indicators of sediment thickness. These field observations were used to reconstruct flood heights and sediment deposition, enabling the preparation of a field-based flood inundation map. We compare the reconstructed inundation extent with numerical model outputs, including (i) a 1-in-100-year return-period flood scenario and (ii) a hydrological model simulation driven by rainfall recorded during the 2024 event. The results show that flood inundation during the 2024 event was significantly greater than predicted by both model scenarios. The residual flood height inferred from field evidence is attributed to compounding effects, particularly increased sediment supply associated with anthropogenic activities, notably mining waste. In addition, we document pronounced backwater effects at river confluences and along river reaches confined within gorge sections, which further exacerbated flood severity by enhancing sedimentation and reducing the river’s conveyance capacity. We conclude that the combined effects of backwater conditions and high sediment accumulation significantly amplified flood inundation. Our findings highlight that, in many high-mountain settings where sediment supply and extreme rainfall are increasing, these processes, particularly at tributary junctions, should be explicitly considered in future flood models.
How to cite: Pokhrel, P., Sinclair, H., Thapa, S., and Creed, M.: Extreme Rainfall, Anthropogenic Sediment Supply, and Backwater Ponding: Compounding impacts on Flood Hazard in the Kathmandu Valley, Nepal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21969, https://doi.org/10.5194/egusphere-egu26-21969, 2026.
Keywords: Integrated model; Sediment dynamics; Sediment connectivity; Scenario analysis; Extreme events; HOTSED.
This study presents the preliminary results from the adaptation and implementation of the HOTSED framework (La Licata et al., 2025) in two high-altitude catchments in the Eastern Alps. The HOTSED model assesses the spatial distribution of sediment source hotspots and highlights the sediment transfer pathways driven by water runoff. Here, we adapted HOTSED to analyze how sediment sources and sediment patterns vary seasonally and between daily extreme rainfall events. We analyzed four seasonal scenarios as well as four daily scenarios including extreme events with different return periods (i.e. daily, 10-year, 30-year, and 50-year events). A polygon-based geomorphological map was used to spatially distribute sediment sources and sinks across the catchments. The potential contribution of each geomorphological unit as a sediment source was evaluated through a qualitative scoring system based on database attributes, complemented by numerical semi-quantitative indices of variables like slope, permafrost distribution, and a proxy of frost-cracking-induced slope instability. A geomorphometric connectivity index was used to calculate structural sediment connectivity. For each scenario, the potential for sediment transport was assessed using a sediment transport index calibrated to rainfall intensity, excluding snowfall-driven contributions using a 0°C ground surface temperature threshold to mask snow-covered areas. Finally, all components were integrated using a raster-based approach yielding the HOTSED model. Results show pronounced seasonal variability in hotspot distribution across the two catchments, where the strongest contrasts between winter and summer-autumn are driven by differences in rainfall-snowfall spatial patterns and intensity. Extreme rainfall scenarios led to significant increases in hotspot distribution and extent, with the most pronounced variance occurring between the standard and 10-year event scenarios. This suggests that more frequent extremes, expected to become even less rare under climate change, may have a greater overall impact than rarer high-intensity events. In addition, the model highlights sequences of connected landforms, classified with different degrees of hazard potential, which may represent the most interesting locations for the occurrence of cascading events. These findings offer critical insights for sediment-related risk management in Alpine catchments under ongoing climatic changes.
Acknowledgement
We express our gratitude to Anuschka Buter for providing the geomorphological map dataset used in this study.
References
La Licata, M., Bosino, A., Sadeghi S.H., De Amicis, M., Mandarino, A., Terret, A. & Maerker, M. (2025). HOTSED: A new integrated model for assessing potential hotspots of sediment sources and related sediment dynamics at watershed scale. Int. Soil Water Conserv. Res., 13(1), 80-101. DOI: 10.1016/j.iswcr.2024.06.002.
How to cite: Savi, S., Maerker, M., Cavalli, M., Pandey, A., Seppi, R., and La Licata, M.: From sediment source hotspots to toposequence-based cascade systems: Modelling potential hazard response under seasonal and extreme rainfall scenarios in Alpine catchments., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10761, https://doi.org/10.5194/egusphere-egu26-10761, 2026.
High mountain environments often experience hazards that do not occur in isolation but as interconnected processes. A typical setting may involve a steep rock face, sometimes topped by glacier ice, where failures can trigger rock-ice or mixed avalanches depending on seasonal conditions. When such events occur above a glacial lake, as is common in many regions, the impact can initiate secondary processes such as glacial lake outburst floods, with significant downstream consequences.
Numerical models are valuable tools for estimating the runout of individual processes; however, simulating entire hazard cascades involving multiple material types remains challenging—particularly for forward modeling. In this study, we explore methods for modeling cascading processes, either through integrated physical models or suites of specialized models, and assess which approaches are most suitable at different spatial scales (local, basin, regional, national).
At least two GLOFs in the recent five years in Nepal were caused by a cascade of a mass flow impacting the lake and causing dam failure or overtopping, followed by a downstream flood with significant impacts. Permafrost thaw induced slope instability as well as excessive snow melt in source areas contributed to the initial release and a variety of subsequent erosional processes further downstream exacerbated impacts. Previous modelling has been largely focused on the flood from the lake exit, not considering the multiple aspects contributing to the complexity of the cascade.
Our analysis focuses on the Thame area in the Everest region of Nepal, where a rock-ice avalanche impacted Thyanbo Lake in August 2024, triggering a glacial lake outburst flood that caused severe damage downstream. This is done in light of producing risk maps for the wider Dudh Kosi Basin, where a number of upstream processes can potentially exacerbate impacts for communities much lower than the periglacial terrain. We discuss the advantages and limitations of various modeling strategies, the challenges of representing full process chains, and potential ways to combine approaches to improve physical realism and predictive capability.
How to cite: Munch, J., Steiner, J., Huggel, C., Basniat, A., Pandey, V. P., Adhikari, B. R., Aaron, J., Mergili, M., and Allen, S. K.: Modeling Cascading Hazards in High Mountain Environments: Challenges and Approaches from the Thame Case Study, Nepal, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17163, https://doi.org/10.5194/egusphere-egu26-17163, 2026.
Mountain catchments host tightly coupled erosion, transport, deposition, and feedback processes that often interact during multi-hazard events. Yet, these interactions are rarely analysed through sediment connectivity, despite it acting as a key vector linking hillslopes, channels, and downstream processes across space and time. This limits our ability to understand how event-driven sediment transfer governs hazard propagation in mountain landscapes.
We present SCIMA (Sediment Connectivity Indexed Multi-hazard Assessment), a process-based framework that embeds functional sediment connectivity into multi-hazard analysis. SCIMA dissects an event into process-level segments according to its spatio-temporal evolution and quantifies each segment’s contribution to sediment mobilisation, transfer, and deposition. Connectivity is expressed as a sediment connectivity weight (SCW) derived via a fuzzy-logic scheme that integrates heterogeneous information typical of mountain settings, including qualitative process interpretation (event reports and expert judgement) and quantitative geomorphic indicators (Melton ruggedness number and drainage density). This design is deliberately data-agnostic and modular, enabling transferability and extension with additional indicators where available.
We apply SCIMA to eight Alpine multi-hazard events in Austria and Switzerland involving combinations of mass movements, debris flows, channel erosion, and flooding. Results show that connectivity is highly variable within events and peaks during phases of intense sediment mobilisation and channel erosion, particularly where steep topography and direct process–process interactions dominate. Connectivity declines during depositional phases and in out-of-catchment segments, marking effective termination of the sediment cascade. Mitigation structures emerge as dynamic elements that can switch from buffering to amplifying connectivity when overtopped or failing. Overall, SCIMA demonstrates that sediment connectivity is an event-driven, dynamic property controlling erosion–transport feedbacks and multi-hazard evolution in mountain landscapes.
How to cite: Kabir, I., Gems, B., Rutzinger, M., and Keiler, M.: Can sediment connectivity improve our understanding of multi-hazard events? A process-based perspective with SCIMA , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19589, https://doi.org/10.5194/egusphere-egu26-19589, 2026.
The July 2025 Matai'an (MTA) landslide, which created a large dam lake in the high mountains of eastern Taiwan, is one of the largest landslides in the 21st century and constitutes an impactful cascading land-surface hazard following regional earthquakes and intense precipitation from typhoons. The September 2025 dam breach caused fatalities and infrastructure damage, and the large volume of remaining landslide deposits poses long-term threats to downstream communities. The MTA event prompts investigation into whether such catastrophic events are coincidental or represent recurring phenomena in this rapidly uplifting, humid mountain range.
In this study, we integrate multi-temporal satellite imagery, historical and modern aerial photography, and high-resolution DEM topographic analysis to understand the MTA failure mechanism and regional landslide history. At the initiation zone, field and remote sensing observations reveal an extensive earthflow-type landslide complex, primarily composed of weathered and fluidized pelitic schist fragments with limited boulder-sized blocks. These materials originated near a marble-schist bedrock contact, where fracture zones act as groundwater conduits and promote weathering of pelitic schist into clay-rich, liquefiable material. Time-series analysis reveals strong seasonal variations and a decadal trend of increasing surface water retention (NDWI) and vegetation stress prior to failure, creating ideal conditions for producing weathered fine-grained materials that progressively reached saturation.
To accumulate approximately 300 million m³ of failable materials on over-steepened hillslopes in this rapidly uplifting terrain, we observe evidence for variations in channel-hillslope coupling that enable weathered materials to accumulate in abundance prior to the 2025 failure. Analysis of normalized channel steepness identifies a prominent knickpoint at the tributary junction where the dam lake formed. This knickpoint acts as a local base level, creating gentler upstream gradients that limit sediment connectivity and delivery. This configuration, combined with accelerated bedrock weathering, causes debris production to outpace river incision in the uplands of the catchment. Consequently, thick packages of weathered colluvium accumulate on hillslopes until mechanical thresholds are breached by earthquake ground shaking and typhoon triggers.
Our DEM-based inventory of historical landslides in MTA and nearby catchments reveals the signature and remnants of similarly sized ancient landslide complexes not yet evacuated by rivers. We identify several belts of comparable earthflow deposits preserved along equivalent lithological contacts in eastern Taiwan's Central Range, demonstrating that MTA-type events may be characteristic in this setting. Satellite and aerial imagery mapping since the 1940s provides evidence of repeated large landslide activity and decadal-scale rapid regeneration of slide-prone weathered materials. These findings reveal an extremely hazardous landscape where rapid bedrock weathering, coupled with transient river adjustments, generates large, periodic catastrophic landslides.
How to cite: Yen, J.-Y., Lai, L. S.-H., Roering, J., Lin, L.-H., Wang, P.-L., and Lien, W.-Y.: Geologic and geomorphic controls on the 2025 Matai’an landslide and downstream impacts, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8931, https://doi.org/10.5194/egusphere-egu26-8931, 2026.
GNSS Interferometric Reflectometry (GNSS-IR) exploits the multipath interference between direct GNSS signals and ground-reflected signals received by a geodetic antenna. Variations in the reflected signal phase and amplitude, observed in the Signal-to-Noise Ratio (SNR) data, encode changes in near-surface properties, most critically soil moisture. For landslides, soil moisture is a first-order control on effective stress reduction, shear strength loss, and pore-water pressure buildup. Thus, GNSS-IR provides a physically meaningful proxy for hydrologic preconditioning before slope failure. GNSS-IR was set to detect the hydrologic state around the station, and InSAR was used to obtain regional deformation. GNSS wet-delay data served as in situ rainfall measurements. All these data were combined to observe rapid wetting, sustained saturation, and deformation. This architecture significantly reduced false alarms compared with rainfall-only systems. Several dual-phase GNSS tracking stations have been installed in the mountainous regions of Taiwan to determine the precise location and detect slope stability. This approach collected historical data to train the machine learning model at each station, and the model parameters could predict rapid wetting before reaching the critical point. The preliminary results show an improvement of 20% compared to the traditional empirical method and could issue an early warning of as much as 5-10 minutes with a 20 Hz GNSS receiver.
How to cite: Yu, T.-T.: Applying GNSS-IR Technique with High-Rate Receiver to Reinforce the Accuracy of Landslide Early Waring in Tawain, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6275, https://doi.org/10.5194/egusphere-egu26-6275, 2026.
A landslide in July, 2023 mobilized loosely indurated clastic sediments at 3780 m elevation on the steep glacial headwall near Island Lake in the Uinta Mountains (Utah). Sediment mobilized by the failure was conveyed ~10 km downvalley by streams, turning a chain of connected lakes a striking orange color. This coloration persisted until the lakes froze at the end of October, and was still visible in satellite imagery when the lake ice cover melted the following June. The longevity of this effect testifies to the involvement of particularly fine-grained material that remained suspended in the water. Previous work at a similar elevation 7 km to the east documented the presence of orange-colored soils rich in clay-sized (<2 µm) material shown by XRD to be smectite. Grab samples (n=32) of sediment collected from the landslide area in August, 2024 were assessed for color (by spectrophotometry) and mineralogy (by XRD), and compared with selected samples (n=14) from a previously collected sediment core spanning the Holocene from a lake impacted by the landslide. This analysis revealed that the grab samples with the most orange colors contained the largest component of smectite. In contrast, none of the lake sediment samples displayed such high orange values, and all of the lake sediment samples were dominated by illite, with no detectable smectite in the XRD patterns. These results support the interpretation that the orange color in the lakes was produced by smectite mobilized by the landslide, and that the 2023 slope failure was unusual in the context of the Holocene.
Analysis of local meteorological data (1-hr resolution) revealed that the 2023 melt season (April 1st-July 31st) was anomalously cold relative to melt seasons in the previous decade (2013-22). By July 31st, 2023, 21,125 thawing degree-hours had accumulated over the melt season representing a 17% decrease from the 2013-2022 average. In addition, 2023 was characterized by an above average snowpack, with nearby SNOTEL stations recording >155% of the median April 1st snow water equivalent (SWE). Snow covered area was quantified using a machine learning approach in Landsat-8 and Sentinel-2 imagery, which revealed that snow persisted on the landscape substantially later in the 2023 melt season compared to the preceding decade. Particularly notably, during week 9 of the melt season (May 27-June 3) in 2023 the landscape was ~89% snow covered compared to the 2013-2022 average of only ~52%. Ultimate snowpack ablation occurred more rapidly in 2023, with a 27% greater daily average melt rate compared to the long term median from peak SWE to zero. This combination of persistent and greater snow cover, with delayed and accelerated snowmelt, likely triggered the July 2023 landslide.
How to cite: Weissman, L., Reynolds, L., and Munroe, J.: The 2023 Island Lake Landslide in the Uinta Mountains, Utah as an Example of an Emerging Climate Hazard in Mountain Regions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13769, https://doi.org/10.5194/egusphere-egu26-13769, 2026.
Landslides are increasingly recognized as dynamic agents that directly shape the Earth's surface, yet their role as fundamental drivers of geomorphic, climatic, and geochemical feedback remains poorly quantified. Current landscape evolution models largely treat landslides as episodic disturbances, neglecting their systemic influence on drainage reorganization, sediment cascades, and geochemical cycles. This proposal bridges these gaps by presenting an integrated framework that positions landslides as a central driver in landscape evolution.
Our project will pursue four interconnected objectives: (i) Quantify how landslides exclusively drive drainage divide migration and fluvial adjustments; (ii) Develop and validate a Thermal Stress Landslide Susceptibility Index (TSLSI) to model climate-sensitive slope preconditioning; (iii) Track the geomorphic impact of landslide-sourced sediment pulses using remote sensing and numerical modeling; and (iv) Assessment of CO₂ drawdown potential via chemical weathering within landslide scars, integrating this feedback into landscape evolution models. We will employ an interdisciplinary methodology, synthesizing high-resolution remote sensing, geochemical fingerprinting, field monitoring, and advanced numerical modeling. Study areas include the tectonically active Himalayas and the Alps.
The anticipated results have the potential to transform our understanding of landslide geomorphology. We expect to provide the first systematic link between landslide patterns and divide migration, deliver the TSLSI as a predictive tool for slope stability under climatic forcing, unravel the controls on sediment pulse generation and evacuation, and, critically, quantify a previously unrecognized carbon sink mechanism via landslide-enhanced weathering.
How to cite: Das, S. and Scaringi, G.: Landslides as systemic drivers of landscape evolution: bridging geomorphic, climatic, and geochemical feedback, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14162, https://doi.org/10.5194/egusphere-egu26-14162, 2026.
As the temperature rises due to climate change, the moisture-holding capacity of the atmosphere increases, which contributes to more frequent and intense extreme precipitation events. In recent years, there has been a significant increase in flooding caused by extreme multi-day precipitation, and this trend is projected to continue in the future. The Brahmaputra river basin has a greater risk of flooding compared to other regions in India. These major floods usually occur during the summer monsoon season, which can be attributed to their higher vulnerability, probability of hazard, and exposure as transboundary river basins, thus becoming a major concern. Therefore, it is crucial to characterize and rank precipitation extremes to comprehend the risk and impact and examine the underlying drivers that contribute to their occurrence and intensification. In this study, we ranked extreme precipitation events of different durations (1 to 7 days) on the basis of intensity and spatial extent during the Indian summer monsoon (ISM) season over the Brahmaputra basin using a high-resolution daily precipitation dataset for 71 years period (1951 - 2021). Further, we attempt to evaluate the association between moisture transport and these extreme precipitation events by quantifying moisture transport during identified top-ranked extreme precipitation events. Our analysis indicates strong moisture transport persisting over the extreme precipitation occurrence regions during the identified top-ranked extreme precipitation events. Quantifying the connection between extreme precipitation to moisture transport might help in the early prediction of extreme precipitation events and lower the associated risks.
How to cite: Gupta, H., Singh Raghuvanshi, A., and Agarwal, A.: Ranking extreme precipitation events of different duration over the Brahmaputra river basin during the Indian Summer Monsoon and their association with moisture transport , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16955, https://doi.org/10.5194/egusphere-egu26-16955, 2026.
In 2013, a cloudburst event devastated the town of Kedarnath in the Indian Himalaya. This widespread, extremely intense burst of rainfall triggered thousands of landslides and debris flows in several hours. Simultaneous rapid snow melt, an abundance of landslide debris and heavy rainfall led to the catastrophic breach of the Chorabari Tal lake, sending a sediment-laden flood wave through the town and propagating down valley, killing over 5000 people and causing around US$1 billion in damage. The catastrophic damage at Kedarnath means documentation and reconstructions of the event have focused largely along the Mandakini River. Furthermore, the spatial extent and intensity of cloudburst events is often difficult to ascertain due to events being highly localised and difficult to capture using satellite datasets or rainfall gauges. However, the effect of the cloudburst extended much further across the entire Alaknanda catchment, with several sediment-rich flow events also triggered in the neighbouring valley of Badrinath. Since sediment-rich flows typically occur individually, this event presents a unique opportunity to consider controls on the magnitude and characteristics of sediment-rich flows triggered under similar tectonic and climatic conditions.
Here, we present a manually mapped inventory of debris flows and sediment-rich floods for the high elevation regions of the Alaknanda catchment. By manually mapping debris flows and sediment-rich flood deposits using high-resolution imagery, we can document the geomorphic signature of the 2013 Kedarnath disaster in both Kedarnath and Badrinath. We use this inventory to determine controls on the magnitude and occurrence of sediment-rich flows within the Indian Himalaya, exploring the importance of topography, channel characteristics and sediment supply. We will simulate mapped flows using the model LaharFlow to evaluate controls on the size and triggering conditions of the flows. We will supplement our modelling analysis with metrics such as debris flow densities to better constrain the intensity of the cloudburst event across the full Alaknanda basin. This research will identify first-order controls on the magnitude and frequency of sediment-rich hazards triggered during the same cloudburst event. As cloudbursts are likely to increase in frequency and/or intensity with climate change, this research is time-critical.
How to cite: Howe, N., Clubb, F., and Harvey, E.: Reconstructing the magnitude and characteristics of the 2013 Kedarnath disaster using its geomorphic signature, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10711, https://doi.org/10.5194/egusphere-egu26-10711, 2026.
Glacial and paraglacial floods are among the most destructive natural hazards in high-mountain regions. These events result from cascades of processes, which rapidly transfer large amounts of water, sediment and energy across entire catchments. Their initiation typically occurs in remote, poorly instrumented areas, while impacts propagate far downstream, strongly limiting process-based understanding at the regional scale. Here, we present preliminary results from an ongoing analysis of glacial and paraglacial hazards in the Bhote Koshi catchment (Nepal), one of the best instrumented glacierized basins at the regional scale, with continuous seismic monitoring since 2016. This study is conducted within the framework of the French PEPR IRIMA program (project IRIMONT), which aims to improve the assessment and mitigation of natural hazards in mountain regions through integrated and interdisciplinary approaches.
First, we focus on the July 2016 glacial lake outburst flood (GLOF). Seismic records of this event provide a unique opportunity to investigate its mechanics from initiation to far-field propagation. Preliminary analyses reveal distinct seismic signatures associated with different phases of the flood, characterized by systematic variations in amplitude, frequency content and phase coherence as a function of time and distance. These signatures indicate an exceptional capacity of the GLOF to mobilize large boulders, leading to seismic energy levels and inferred sediment transport that far exceed those observed during seasonal hydrological events. In parallel, we investigate the temporal evolution of slope instabilities in the Bhote Koshi catchment following the 2015 Gorkha earthquake. We apply unsupervised machine learning approaches to cluster seismic signals, identify recurrent signal families, and establish a baseline of background hydrological and geomorphic activity at the catchment scale. The seismic observations reveal sustained post-seismic landslide activity, with evolving signal characteristics reflecting the progressive relaxation of hillslopes modulated by hydrometeorological forcing.
Overall, these preliminary results demonstrate the potential of environmental seismology, combined with data-driven approaches, to bridge the gap between local process understanding and regional-scale hazard assessment.
How to cite: Nanni, U., Cook, K., and Andermann, C.: Characterizing glacial and paraglacial flood processes across scales using environmental seismology, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20983, https://doi.org/10.5194/egusphere-egu26-20983, 2026.
Identifying the trajectories followed by mass movements, especially when they evolve into debris flows, is essential for producing hazard maps and for understanding the sediment inputs to channels associated with these processes. Hydrosedimentological connectivity makes it possible to estimate the transfer potential of material mobilized in source areas toward targets of interest, such as the drainage network, while also indicating possible preferential pathways. Because the trajectories of sediments and mobilized material are conditioned by topography and surface runoff, structural and functional elements of connectivity can serve as a proxy to interpret the dynamics and routes of mass movements. This study evaluates connectivity along the scars of mass movements, both connected and not connected to the channel network, triggered by an extreme precipitation event in the municipality of Angra dos Reis (Rio de Janeiro State), Brazil, in 2023. To this end, we analyze: (i) structural connectivity, represented by the Index of Connectivity (IC), and (ii) structural and functional connectivity, represented by the Index of Hydrosedimentological Connectivity (IHC). Differences between connected and disconnected scars were examined using statistical tests, including assessments of normality and between-group comparisons using Student’s t-test and the Mann–Whitney U test, applied to scar-level statistical metrics (mean, median, standard deviation, maximum, range, and variance), according to the data distribution. Effect magnitudes were quantified using Cohen’s d and r (rank-biserial). The results indicate that both indices were able to capture mass-movement trajectories, highlighting preferential sediment-transfer pathways. IC and IHC values show a significant difference between connected and disconnected scars. The approximately normal distribution observed for the IHC scar statistics (mean, median, and standard deviation) suggests control by multiple compensatory processes, whereas the non-normality of these statistics for IC, contrasted with the normality of maximum IC values, may indicate a stronger influence of local controls. In addition, IHC values for the scars show consistently high effect sizes for central metrics (mean, median, and variance), whereas IC values for the scars tend to show more pronounced effects in extreme values and in the overall connectivity range. Taken together, these results reinforce the potential of IC and IHC as useful indices to evaluate the trajectories of mass movements triggered by intense rainfall and their associated sediment delivery to the drainage network, as well as to support hazard-mapping analyses.
How to cite: Zanandrea, F., Michel, G. P., Bastos Marques Lopes, C., Nonato Vieira Cereto, A., Coutinho Loureiro Mansur, R., and Teixeira Silva, D.: Connectivity-based assessment of trajectories and channel linkage of rainfall-triggered mass movements, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15895, https://doi.org/10.5194/egusphere-egu26-15895, 2026.
Natural hazards such as landslides and floods can disrupt alpine transportation corridors far beyond the directly affected sites, cutting off critical access routes, delaying emergency response, and amplifying cascading socio-economic impacts. However, hazard susceptibility mapping and transportation resilience analysis are still often conducted as separate exercises. This study therefore proposes a GIS-based framework combining hazard susceptibility mapping with network resilience analysis. Landslide and flood susceptibility maps for Zell am See and Saalfelden (Pinzgau, Salzburg) were generated using a patch-based 2D convolutional neural network (CNN) with 15×15-pixel contextual inputs, after logistic regression screening to remove redundant factors. Node importance was evaluated via a principal component analysis (PCA)-derived composite of betweenness, straightness, and degree, followed by role-based classification and staged hazard simulations. The CNN achieved high accuracy (AUC = 0.89 for landslides and 0.90 for floods), with hazard zones strongly matching historical events. Simulation results show that removing just 10% of high-risk nodes can reduce average straightness by over 30% in Zell am See, while Saalfelden’s network degrades more gradually. The framework identifies hazard-exposed Fragile Hubs as priority targets for monitoring or reinforcement and highlights the resilience advantage of Robust Cores. This approach offers a transferable tool for multi-hazard transport resilience planning in alpine regions.
How to cite: Tang, Z. and Hölbling, D.: GIS-Based Assessment of Transportation Network Resilience under Hazard Scenarios, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4967, https://doi.org/10.5194/egusphere-egu26-4967, 2026.
The accurate assessment and early warning of avalanche disasters are crucial for disaster prevention and mitigation in mountainous areas during winter and spring. This study systematically developed a meteorological risk assessment framework for avalanches in the Tianshan region of Xinjiang, integrating historical avalanche cases with meteorological data and research literature. The framework comprises four key components: topographic factors (disaster-prone environments), pre-avalanche snow conditions, meteorological conditions prior to the event, and weather conditions during the avalanche period. It includes seven evaluation factors: pre-avalanche snow depth, altitude, slope gradient, prior temperature data, prior cumulative snowfall, and daily snowfall amount, new snow accumulation depth on the day of the event. On this basis, the paper first normalizes each disaster factor by the method of graded value assignment, then calculates the hazard index of the environment and the hazard index of meteorological factor respectively by the method of equal weight sum, and then obtains the comprehensive meteorological hazard index of avalanche by the algorithm of multiplication, and finally obtains the quantitative grading of avalanche meteorological hazard index and the evaluation result of avalanche meteorological hazard index. The model is applied to calculate the spatial distribution of avalanche risk in the Tianshan area of Xinjiang in February 2024. The results show that the actual avalanche occurrence area is consistent with the high risk area calculated by the model. This study provides a preliminary quantitative method and technical support for future avalanche risk assessment and early warning. In the future, it will further integrate the disaster-prone environment and underlying surface elements, optimize the normalized grading threshold and factor weight distribution, and attempt to conduct multi-scenario experiments to enhance the model's comprehensive predictive capability and applicability.
How to cite: Zhao, H.: Research on Avalanche Meteorological Hazard Assessment Based on Multi-source Data and Multi-factor, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3288, https://doi.org/10.5194/egusphere-egu26-3288, 2026.
