De l'observation des écroulements aux solutions opérationnelles: près de deux décennies d'études sur les risques cryo-gravitaires dans le massif du Mont-Blanc

The increase in the frequency of rock collapses (V > 100 m³), first observed in the European Alps since the 2000s, has prompted studies on high altitude walls and wall permafrost. The Mont-Blanc massif (MMB) has gradually become a pilot study area thanks to the numerous data and knowledge acquired through various research projects. The statistical analysis of the distribution of collapses (> 1300 events recorded between 2007 and 2021) highlights their link with the distribution of permafrost as well as with the increase in air temperature. This analysis opens up promising prospects in terms of the development of forecasting tools to help high mountain practitioners and stakeholders in their risk mitigation strategies. However, understanding the mechanisms of rock wall destabilization is hampered by the diversity of thermo-hydro-mechanical processes potentially involved. To improve this understanding, current research in the MMB focuses on water infiltration and circulation processes in permafrost walls by combining advanced numerical modeling approaches with ad hoc field studies . Coupling thermal and hydrogeological models, and combining them with geoelectric methods could make it possible to assess the distribution and quantity of pore water or ice, crucial information for geotechnical applications. At the same time, the synthesis of data and knowledge acquired in integrated approaches to landscape changes and risks linked to the degradation of permafrost, the retreat of glaciers, the potential formation of lakes and the destabilization of rock faces, appears to be a basis essential for land use planning projects. Finally, the thermal and hydrological exchanges between the permafrost walls and the snow-glacial devices nestled there (ice aprons and hanging glaciers) are another research perspective to explore, with multidisciplinary implications.