TY - JOUR
T1 - Predisposing, triggering and runout processes at a permafrost-affected rock avalanche site in the French Alps (Étache, June 2020)
AU - Cathala, Maëva
AU - Bock, Josué
AU - Magnin, Florence
AU - Ravanel, Ludovic
AU - Ben Asher, Matan
AU - Astrade, Laurent
AU - Bodin, Xavier
AU - Chambon, Guillaume
AU - Deline, Philip
AU - Faug, Thierry
AU - Genuite, Kim
AU - Jaillet, Stéphane
AU - Josnin, Jean Yves
AU - Revil, André
AU - Richard, Jessy
N1 - Publisher Copyright:
© 2024 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.
PY - 2024/8
Y1 - 2024/8
N2 - Although numerous recent studies have explored the relationship between permafrost degradation and rock slope failure, there is still a need for in-depth investigations to develop relevant hazard assessment approaches. We investigate the predisposing, triggering and propagation processes of a rock avalanche (c. 225,000 m3) that occurred in Vallon d'Étache (France) on 18 June 2020, whose scar was coated by ice and water. Weather records and energy balance models show that the rock avalanche occurred right after the warmest spring and winter since at least 1985, but also right after the spring with the highest water supply anomaly (snowmelt and rainfall). Measured ground surface temperature and geoelectrical surveys reveal that relatively ice-rich permafrost could exist in the NW face (release area) while it is inexistent below the SE face, contradicting certain permafrost maps. Heat transfer simulations suggest that the rock avalanche occurred during a transition from cold to warm permafrost conditions at failure depth (30 m), with a temperature increase of up to 0.6°C per decade since 2012 (when considering potential snow cover effect), and current temperature ranging between −3 and −1°C, depending on the applied model forcing. This warming certainly contributed to predispose slope to failure. In addition, the shift towards warm permafrost and water infiltration potentially enhancing permafrost degradation along fractures through heat advection or favouring the development of high hydrostatic pressures may have played as triggering factors. Finally, propagation simulations show that the rock avalanche involved several phases with different rheological properties due to the incorporation of snow and material segregation within the deposit. These new insights at various scales highlight the complexity of the triggering and propagation processes of rock slope failure occurring in high mountains, a significant part of which can be linked to snow effects on ground temperature, water supply and rheological properties.
AB - Although numerous recent studies have explored the relationship between permafrost degradation and rock slope failure, there is still a need for in-depth investigations to develop relevant hazard assessment approaches. We investigate the predisposing, triggering and propagation processes of a rock avalanche (c. 225,000 m3) that occurred in Vallon d'Étache (France) on 18 June 2020, whose scar was coated by ice and water. Weather records and energy balance models show that the rock avalanche occurred right after the warmest spring and winter since at least 1985, but also right after the spring with the highest water supply anomaly (snowmelt and rainfall). Measured ground surface temperature and geoelectrical surveys reveal that relatively ice-rich permafrost could exist in the NW face (release area) while it is inexistent below the SE face, contradicting certain permafrost maps. Heat transfer simulations suggest that the rock avalanche occurred during a transition from cold to warm permafrost conditions at failure depth (30 m), with a temperature increase of up to 0.6°C per decade since 2012 (when considering potential snow cover effect), and current temperature ranging between −3 and −1°C, depending on the applied model forcing. This warming certainly contributed to predispose slope to failure. In addition, the shift towards warm permafrost and water infiltration potentially enhancing permafrost degradation along fractures through heat advection or favouring the development of high hydrostatic pressures may have played as triggering factors. Finally, propagation simulations show that the rock avalanche involved several phases with different rheological properties due to the incorporation of snow and material segregation within the deposit. These new insights at various scales highlight the complexity of the triggering and propagation processes of rock slope failure occurring in high mountains, a significant part of which can be linked to snow effects on ground temperature, water supply and rheological properties.
KW - electrical resistivity tomography
KW - ground surface temperature monitoring
KW - periglacial geomorphology
KW - permafrost modelling
KW - propagation modelling
KW - rock avalanche
UR - http://www.scopus.com/inward/record.url?scp=85193284968&partnerID=8YFLogxK
U2 - 10.1002/esp.5881
DO - 10.1002/esp.5881
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AN - SCOPUS:85193284968
SN - 0197-9337
VL - 49
SP - 3221
EP - 3247
JO - Earth Surface Processes and Landforms
JF - Earth Surface Processes and Landforms
IS - 10
ER -