Frictional weakening in the highly mobile 2025 Blatten rock and ice avalanche in Switzerland Check for updates
Abstract
Cascading slope failures are increasing as glaciers retreat and slopes adjust to a warming climate, yet reconstructing their full dynamics from precursor to deposition remains challenging. Here we show that the 28 May 2025 Blatten rock-ice avalanche, which mobilized about 9.3 million cubic metres, can be reconstructed from seismic, geomorphological, and geotechnical evidence and numerical modeling. The observations reveal the timing, source, volume, and friction of over two weeks of accelerating rockfalls and minor glacier collapses before the main failure, followed by four stages of avalanche motion. Only with drastically reduced friction can both depth-averaged and threedimensional models reproduce the center-of-mass force history and the deposit distribution. These friction values reflect effective frictional weakening. Geotechnical observations suggest that transient excess pore pressures possibly contributed to this weakening, but are insufficient to rule out additional mechanisms such as ice frictional reduction, segregation, and fragmentation. This work provides a reproducible and robust framework for analyzing catastrophic avalanches under a changing climate.Cascading mass movements in high mountains are a rapidly growing hazard in a warming climate 1-4 . Cryosphere degradation (glacier retreat, permafrost thaw) and the intensification of hydrometeorological triggers (extreme rainfall, rapid snowmelt) are increasing the frequency and magnitude of these events, creating compounded risks for downstream communities 2,5-8 . From Alaska to the Himalayas, the European Alps, and the Andes, mountains are subject to a new regime of complex, cascading disasters, demanding a renewed focus on the physical processes governing slope failure and runout 8-11 .
Progress in understanding such events has advanced on two parallel but often disconnected fronts: pre-failure monitoring for early warning 12-15 and post-event modelling for process understanding and hazard assessment 16,17 . However, quantitative estimates of how the released volume of small precursory events evolves before large mass failure remain elusive. In the meanwhile, numerical models are usually validated only through back-analysis of final deposits 18-20 . This reliance on end-state geometries may fail to capture the dynamics and evolving frictional regimes at play 21 . Seismic observations offer the unique potential to bridge this observational gap. They provide continuous, real-time records of slope activity and capture the forces that moving masses exert on the Earth's surface 22-27 . Comparing these forces with those simulated by granular mass-movement models constrains key event properties such as volume, friction coefficient, and basal conditions 21,28 . For instance, glacier ice within or underneath the moving mass substantially reduces basal friction to enhance mobility 16,21,29 . Different seismic approaches are sensitive to different parts of the failure process. Low-frequency seismic signals are typically applicable only to large
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BibTeX
@article{kang2026frictional,
title = {{Frictional weakening in the highly mobile 2025 Blatten rock and ice avalanche in Switzerland Check for updates}},
author = {Jiahui Kang and Antoine Lucas and Anne Mangeney and Johan Gaume and Kate Allstadt and Clément Hibert and Liam Toney and Hervé Vicari and Michael Dietze and Mylène Jacquemart and Marc Peruzzetto and Lars Blatny and Michael L Kyburz and Joachim Rimpot and Daniel Farinotti and Fabian Walter},
journal = {Communications Earth \& Environment},
year = {2026},
month = sep,
doi = {10.1038/s43247-026-03983-1},
url = {https://hal.science/hal-05740557v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Frictional weakening in the highly mobile 2025 Blatten rock and ice avalanche in Switzerland Check for updates
AU - Jiahui Kang
AU - Antoine Lucas
AU - Anne Mangeney
AU - Johan Gaume
AU - Kate Allstadt
AU - Clément Hibert
AU - Liam Toney
AU - Hervé Vicari
AU - Michael Dietze
AU - Mylène Jacquemart
AU - Marc Peruzzetto
AU - Lars Blatny
AU - Michael L Kyburz
AU - Joachim Rimpot
AU - Daniel Farinotti
AU - Fabian Walter
PY - 2026
DA - 2026/09/07
JO - Communications Earth & Environment
DO - 10.1038/s43247-026-03983-1
UR - https://hal.science/hal-05740557v1
AB - Cascading slope failures are increasing as glaciers retreat and slopes adjust to a warming climate, yet reconstructing their full dynamics from precursor to deposition remains challenging. Here we show that the 28 May 2025 Blatten rock-ice avalanche, which mobilized about 9.3 million cubic metres, can be reconstructed from seismic, geomorphological, and geotechnical evidence and numerical modeling. The observations reveal the timing, source, volume, and friction of over two weeks of accelerating rockfalls and minor glacier collapses before the main failure, followed by four stages of avalanche motion. Only with drastically reduced friction can both depth-averaged and threedimensional models reproduce the center-of-mass force history and the deposit distribution. These friction values reflect effective frictional weakening. Geotechnical observations suggest that transient excess pore pressures possibly contributed to this weakening, but are insufficient to rule out additional mechanisms such as ice frictional reduction, segregation, and fragmentation. This work provides a reproducible and robust framework for analyzing catastrophic avalanches under a changing climate.Cascading mass movements in high mountains are a rapidly growing hazard in a warming climate 1-4 . Cryosphere degradation (glacier retreat, permafrost thaw) and the intensification of hydrometeorological triggers (extreme rainfall, rapid snowmelt) are increasing the frequency and magnitude of these events, creating compounded risks for downstream communities 2,5-8 . From Alaska to the Himalayas, the European Alps, and the Andes, mountains are subject to a new regime of complex, cascading disasters, demanding a renewed focus on the physical processes governing slope failure and runout 8-11 . Progress in understanding such events has advanced on two parallel but often disconnected fronts: pre-failure monitoring for early warning 12-15 and post-event modelling for process understanding and hazard assessment 16,17 . However, quantitative estimates of how the released volume of small precursory events evolves before large mass failure remain elusive. In the meanwhile, numerical models are usually validated only through back-analysis of final deposits 18-20 . This reliance on end-state geometries may fail to capture the dynamics and evolving frictional regimes at play 21 . Seismic observations offer the unique potential to bridge this observational gap. They provide continuous, real-time records of slope activity and capture the forces that moving masses exert on the Earth's surface 22-27 . Comparing these forces with those simulated by granular mass-movement models constrains key event properties such as volume, friction coefficient, and basal conditions 21,28 . For instance, glacier ice within or underneath the moving mass substantially reduces basal friction to enhance mobility 16,21,29 . Different seismic approaches are sensitive to different parts of the failure process. Low-frequency seismic signals are typically applicable only to large
SN - 2662-4435
ER -