A FIRST ROCKFALL SUSCEPTIBILITY ASSESSMENT IN THE M ONT BLANC MASSIF BASED ON ROCKFALL INVENTORIES

In the last two decades, many rockfalls and rock avalanches occurred in high mountain areas throughout the world. We term rockfall the sudden collapse of a rock mass from a steep rockwall, with a volume exceeding 100 m. Among geomorphological phenomena affecting mountain regions, rockfalls and rock avalanches are the most unexpected ones because of their high speed, the large volume of rock involved, and the risks they generate: destabilization of infrastructures, danger for population and buildings along the path of the rockfalls, and in the valleys through cascading effects. Frequency of rockfalls rises in the Alps mainly due to the permafrost degradation controlled by the global warming, while vulnerability is increasing both at high elevation and at the bottom of the valleys. Our study presents a method for assessing the rockfall susceptibility in the Mont Blanc massif, based on the characterisation of rockfalls through the analysis of two types of inventories. Results are convincing and show that it is possible to assess rockfall hazard in high mountain.