The December 2008 Crammont rock avalanche, Mont Blanc massif area, Italy

• Published in: Natural Hazards and Earth System Sciences
• Main Authors: Deline, Philip, Alberto, W., Broccolato, Massimo, Hunger, Oldrich, Noetzli, Jeannette, Ravanel, Ludovic, Tamburini, Andrea
• Other Authors: Environnements, Dynamiques et Territoires de Montagne (EDYTEM), Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Servizio Geologico della Regione Autonoma Valle d'Aosta, Administration Régionale de la vallée d'Aoste, Department of Earth and Ocean Sciences Vancouver (EOS), University of British Columbia (UBC), Glaciology, Geomorphodynamics & Geochronology
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2011
• Subjects: Mont Blanc; permafrost
• Online Access: https://hal.science/halsde-00653747; https://doi.org/10.5194/nhess-11-3307-2011

International audience We describe a 0.5 Mm3 rock avalanche that occurred in 2008 in the western Alps and discuss possible roles of controlling factors in the context of current climate change. The source is located between 2410 m and 2653 m a.s.l. on Mont Crammont and is controlled by a densely fractured rock structure. The main part of the collapsed rock mass deposited at the foot of the rock wall. A smaller part travelled much farther, reaching horizontal and vertical travel distances of 3050 m and 1560 m, respectively. The mobility of the rock mass was enhanced by channelization and snow. The rock-avalanche volume was calculated by comparison of pre- and post-event DTMs, and geomechanical characterization of the detachment zone was extracted from LiDAR point cloud processing. Back analysis of the rock-avalanche runout suggests a two stage event. There was no previous rock avalanche activity from the Mont Crammont ridge during the Holocene. The 2008 rock avalanche may have resulted from permafrost degradation in the steep rock wall, as suggested by seepage water in the scar after the collapse in spite of negative air temperatures, and modelling of rock temperatures that indicate warm permafrost (T > −2 °C).