Mapping potential release areas and runout path of rockfalls and rock avalanches in the French Alps

International audienceHigh mountain environments of the European Alps have been increasingly affected by rockfalls (V > 100 m3) over the past decades, in conjunction with the atmospheric warming and the resulting permafrost degradation. These processes, and their potential cascading effects, constitute a threat for population and infrastructure, especially in the frequented massifs such as those of the French Alps.The aim of this study is to characterize the distribution and propagation of rockfalls in order to map the potential release and deposit areas in the French Alps. To do so, we used a rockfalls database (>1000 events) that occurred in the Mont Blanc massif during the period 2007-2020. From this dataset, we analyze the topography and permafrost conditions the most prone to trigger a rockfall, considering the altitude, orientation, slope and MARST (Mean Annual Rock Surface Temperature) mapped with a statistical model. The topographic profile of rockfalls for which we know the precise deposit location is deeply analyzed to characterize the runout path according to the volume of the events. These results are then used to map potential release and deposit areas with a multicriteria approach in a GIS. These maps, combined with infrastructure or mountaineering routes, could be used to point out “hot spots” where more detailed analysis would be required to estimate the possible risks.This work aims to provide a baseline for future researches and for decision makers in short- and long-term planning to anticipate rockfall hazards at present and in the near future