| Summary: | International audience Mountain environments are very sensitive to climate change, yet assessing the potential impacts of these changesis not easy because of the complexity and diversity of mountain systems. The Himalayan permafrost belt presentsthree main specificities: (1) it develops in a geodynamically active mountain, which means that the controllingfactors are not only temperature but also seismo-tectonic activity; (2) due to the steepness of the southern flankof the Greater Himalaya and potential large scale rock failures, permafrost evidence manifests itself best in theinner valleys and on the northern, arid side of the Himalayas (elevations >4000m); (3) the east-west strike ofthe mountain range creates large spatial discontinuity in the “cold” belt, mostly related to precipitation natureand availability. Only limited studies have been carried to date, and there is no permanent “field laboratory”, norcontinuous records but a few local studies. Based on preliminary observations in the Nepal Himalayas (mostlyin Mustang and Dolpo districts), and Indian Ladakh, we present the main features indicating the existence ofpermafrost (either continuous or discontinuous). Rock-glaciers are quite well represented, though their presencemay be interpreted as a combined result from both ground ice and large rock collapse. The precise altitudinalzonation of permafrost belt (specifying potential permafrost, probable permafrost, observed permafrost belts) stillrequires careful investigations in selected areas.Several questions arise when considering the evolution of permafrost in a context of climate change, with itsimpacts on the development of potential natural hazards that may affect the mountain population. Firstly, permafrostdegradation (ground ice melting) is a cause of mountain slope destabilization. When the steep catchmentsare developed in frost/water sensitive bedrock (shales and marls) and extend to high elevations (as observedin Mustang or Dolpo), it would supply more mass-wasting and debris-flow events ...
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