Investigating the slope failures at the Lou rock glacier front, French Alps

• Published in: Permafrost and Periglacial Processes
• Main Authors: Marcer, Marco, Nielsen, Steffen, Ribeyre, Charles, Kummert, Mario, Duvillard, P.A, Schoeneich, Philippe, Bodin, Xavier, Génuite, Kim
• Other Authors: Environnements, Dynamiques et Territoires de la Montagne (EDYTEM), Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Pacte, Laboratoire de sciences sociales (PACTE), Centre National de la Recherche Scientifique (CNRS)-Université Grenoble Alpes (UGA)-Sciences Po Grenoble - Institut d'études politiques de Grenoble (IEPG ), Université Grenoble Alpes (UGA), Université Grenoble Alpes - Institut d'urbanisme et de géographie alpine (IUGA IUGA)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2020
• Subjects: Rock glacier; slope failure; natural hazard; destabilization; [SDU.STU.GM]Sciences of the Universe [physics]/Earth Sciences/Geomorphology; [SHS.GEO]Humanities and Social Sciences/Geography; permafrost; Permafrost and Periglacial Processes
• Online Access: https://hal.archives-ouvertes.fr/hal-02414643; https://hal.archives-ouvertes.fr/hal-02414643/document; https://hal.archives-ouvertes.fr/hal-02414643/file/A3_PPP_revision_2.pdf; https://doi.org/10.1002/ppp.2035

International audience On August 14 th 2015 a large debris flow initiated by the occurrence of two slope failures at the front of the Lou rock glacier flooded part of the town of Lanslevillard, France. The present study aims to understand the meteorological and geomorphological context that led to these failures. Investigations were conducted by combining meteorological data, surface movements, and geophysical transects. The analysis indicates that the Lou rock glacier is directly connected to an active torrential channel and has a natural predisposition to frontal failure due to the steepness of its front. The slope failures were triggered after a heat wave followed by a three-week period of almost continuous rainfall. Water flowing on top of the permafrost table was observed in the two head scarps, suggesting that regressive erosion consecutive to this concentrated subsurface water flow triggered the failures. For one of the slides, traces of previous failures were observable on historical aerial imagery dating back to the 1950's, while the second slide corresponded to a novel event and developed on the frontal slope of a fast-moving and destabilized rock glacier lobe. We also discuss the increase in local predisposition to failure related to the remarkable morphological modifications such as frontal advance and development of surface cracks associated with the lobe destabilization.