HYDROLOGICAL PROCESSES AND THERMAL DYNAMICS IN HIGH MOUNTAIN PERMAFROST-AFFECTED ROCK WALLS

The increased rockfall activity in high Alpine ranges observed during the last two decades is commonly attributed to permafrost degradation associated with atmospheric warming. Although the connection between mountain permafrost thawing and rockfall initiation is intuitive and supported by field and lab observations, the physical processes behind it are still poorly understood. In this study, we focus on the role of hydrologic and thermo-mechanical processes acting in fractures of steep alpine bedrock permafrost. We combine field measurements (subsurface and borehole temperatures, permanent electrical resistivity tomography) from a high elevation Alpine site in the Mont Blanc massif (the Aiguille du Midi, 3842 m a.s.l.) with numerical models of heat and mass transport in fractured rocks. Our novel model approach combines a surface energy balance model designed for permafrost research with a coupled thermal and hydrologic model simulating groundwater flow and heat transport in porous media. Previous simulations of surface energy balance showed that the timing and depth of permafrost thawing is highly sensitive to snow cover dynamics (Florence Magnin et al., 2017), while coupled thermal and hydrological simulations of fractured rock showed profound effect of water in cracks on rock wall permafrost degradation(Magnin & Josnin, 2021). The key challenges of the model scheme are related to the quantification of snow meltwater available for infiltration and of groundwater flow patterns at different time scales. Progress on these issues will help us decipher the governing processes in the degradation of high mountain permafrost and its link with rockfall occurrence.

Magnin, F, & Josnin, J.-Y. (2021). Water flows in rockwall permafrost: a numerical approach coupling hydrological and thermal processes. Journal of Geophysical Research: Earth Surface.

Magnin, F, Westermann, S., Pogliotti, P., Ravanel, L., Deline, P., & Malet, E. (2017). Snow control on active layer thickness in steep alpine rock walls (Aiguille du Midi, 3842 m a.s.l., Mont Blanc massif). Catena, 149, 648–662.