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Water Flows in Rockwall Permafrost: a Numerical Approach Coupling Hydrological and Thermal Processes
  • Florence Magnin,
  • Jean-Yves Josnin
Florence Magnin
CNRS - Université Savoie Mont Blanc

Corresponding Author:florence.magnin@univ-smb.fr

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Jean-Yves Josnin
Université Savoie Mont Blanc
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Rockwall permafrost is extremely sensitive to climate change and its degradation is supposedly responsible for the recent increase in periglacial rock slope failures. Investigations of rockwall permafrost dynamics and mechanics have so far neglected possible hydrogeological processes acting in bedrock fractures. In this study, we propose the first numerical approach to couple thermal and hydrological processes in alpine rockwall permafrost and show that the latter have major effects on permafrost (thermal) dynamics and mechanics when the fractures and/or rock matrix are saturated. Water flows into fractures favor deep-reaching of the permafrost body by driving cold water top-down. Ice-filled fractures delay permafrost thawing in a first stage due to latent heat consumption but then accelerate it when the ice starts to melt. Thus, frozen fractures may subsist in thawed bedrock while thawing corridors may form in frozen bedrock. As a result, tmperature gradients are exacerbated. When connected fractures thaw, bottom-up permafrost degradation can occur through upwards propagation of thawing wedges delineated by these fractures. High hydraulic head values are associated to perched water table over or within the impermeable permafrost body, and correspond to hydrostatic pressures that can reach critical valus in trms of rockwall stability. These results bear strong implications to understand permafrost response to climate signals, periglacial geomorphology and hazards assessment as well as alpine hydrothermal processes.