Hydrothermally influenced rock slope kinematics: The role of water on Wisse Schijen

Long-term ground temperature records from high-alpine environments document a persistent warming trend and a progressive thickening of the active layer of permafrost across the European Alps. This thermal evolution directly affects the internal hydrological regime of rock slopes. In frozen rock masses with ice-filled fractures, hydraulic permeability is markedly reduced relative to unfrozen conditions. Permafrost warming and thawing thus promote water infiltration, perched water, and elevated water pressures once ice melt occurs. Surface water input infiltrates through fracture systems or heterogeneous ground layers within the active layer, causing local concentrations of convective heat transport that can initiate the development of preferential thaw pathways in the underlying permafrost.

Such hydrothermal interactions are expected to exert a first-order control on the stability and kinematics of failure-prone rock slopes. However, the role of water in governing thermo-mechanical coupling and deformation in mountain permafrost remains poorly understood. Evidence for the presence, distribution, and temporal variability of water in permafrost rock slopes is scarce, with only a few studies documenting temporal changes in water content using piezometric measurements. In-situ observations and laboratory experiments remain limited, providing only partial information on the role of water in frozen ground. Consequently, non-conductive heat fluxes, phase-change processes, and their implications for rock slope deformation are still insufficiently quantified, primarily due to their strongly nonlinear nature and the challenges associated with direct measurement.

To address the role of water in permafrost rock slope dynamics, we investigate the Wisse Schijen study site (Valais, Switzerland), a deep-seated permafrost rock slope instability with an estimated volume exceeding 1 million m³, located on an approximately 40° steep, east-facing slope between 3010 and 3140 m a.s.l. We apply a multi-method analysis that integrates spatially and temporally resolved geological, thermal, kinematic, and seismic data and relates these observations to atmospheric and hydrological forcing. The combined dataset reveals a clear kinematic response of the rock slope to hydrothermal forcing, manifested by seasonally variable deformation patterns that coincide with periods of enhanced water availability and elevated subsurface temperatures. Our results indicate that water-driven thaw processes and associated hydrogeological changes likely reduce effective stresses and alter the geotechnical properties of the rock mass, thereby modulating deformation rates and kinematic behavior. These observations highlight the critical role of hydrothermal processes in controlling the mechanical response of permafrost rock slopes and emphasize the importance of explicitly accounting for hydrothermal coupling in assessments of high-alpine slope stability under ongoing climate warming.