Permafrost changes in rock walls and the retreat of alpine glaciers: a thermal modelling approach

The shrinkage of Grosser Aletschgletscher changed the thermal and mechanical boundary conditions in its marginal rock walls. The temperature at the glacier bed is at the pressure melting point while the exposed rock surface (above the glacier) is subject to atmospheric conditions. At our study site, a north‐facing rock wall at Konkordiaplatz, the surface temperatures have cooled below the freezing point during glacier retreat. Sensitivity studies on the thermal evolution and the permafrost dynamics in the bedrock involve heat transfer models with changing glacier surface and rock surface temperatures. They indicate that even small amounts of moisture limit the permafrost dynamics to the surface decametres at secular time scale. The calculations further indicate that, in the investigated rock wall, permafrost is penetrating as a consequence of the glacier retreat. The delay of the response of the permafrost base is in the order of millennia. Freezing and thawing of rock moisture leads to frost damage. The model results predict areas of frost shattering in the surface decametres and in the region of the permafrost base. The frost action is also favoured by unloading during glacier recession