| Summary: | International audience The number of rockfalls actually seems to rise in the Alps, while vulnerabilities are increasing in high altitude and in valleys. Due to a lack of systematic observations, frequency and magnitude of rockfalls, as well as their triggering factors remain poorly understood. We here analyse different inventories of rockfalls acquired in the whole Mont Blanc massif by three innovative methods in order to emphasize the role of permafrost. Permafrost degradation appears to be the most likely triggering factor. In particular, almost all of the recorded rockfalls occurred in a context of permafrost, a very good correlation exists between climate (temperatures) and rockfalls, the other temperature-dependent factors may only explain a little part of the rockfalls, and topographic factors are highlighting the importance of permafrost in rockfall trigger. Within the context of global warming scenarios for the twenty-first century, these results raise the question of risk assessment and management in high mountain regions.
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