From ice-filled fractures to pressurised water flow in permafrost bedrock: seasonal changes in rockwall hydrology

Alpine permafrost is warming globally and has been extensively studied through electrical resistivity monitoring and borehole temperature measurements. However, permafrost degradation is often primarily attributed to rising air temperatures and related conductive heat fluxes in the ground, while the crucial role of water flow on the thermal and mechanical regime of rockwalls is frequently oversimplified or overlooked. To address this research gap and improve the knowledgeof how bedrock permafrost will respond to climate change, year-round observations of hydrothermal processes are essential, despite the challenges posed by such extreme environments.

Here, we present results from daily repeated electrical resistivity tomography (ERT) and piezometric pressure measurements conducted in 2024 in the permafrost-affected north flank of the Kitzsteinhorn (Hohe Tauern range, Austria). Ground temperature time series from four deep boreholes indicate a maximum permafrost active layer thickness of 4.3 m, with evidence of non-conductive heat fluxes reflected in abrupt temperature anomalies and long-term regime changes between 2016-2019 and 2020-2024. A distinct reduction in electrical resistivity values at the end of May coincides with the onset of snowmelt recorded at a nearby weather station. Persistently low electrical resistivity values (<4 kΩm) throughout the summer suggest water-saturated conditions in the active layer. This hypothesis is additionally supported by piezometric measurements, which show water heads of up to 11.8 m, suggesting pressurised water injection into a widespread fracture network. In mid-September, rising electrical resistivity values in the upper layers coincide with the onset of the freezing season, with partial freezing of cleft water. Furthermore, we compared temperature-resistivity relations derived from laboratory experiments on rock samples from the study site with field observations.

Our study shows that high-frequency electrical resistivity monitoring can effectively detect seasonal periods of enhanced water flow, playing a critical role in the warming process of bedrock permafrost and increasing hydrostatic pressure on rock faces – both key factors contributing to slope instability and failure.