Permafrost in monitored unstable rock slopes in Norway – New insights from rock wall temperature monitoring, geophysical surveying and numerical modelling

Abstract. The warming and subsequent degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. The unstable and monitored slopes of Mannen (More and Romsdal, southern Norway) and Gamanjunni-3 (Troms and Finnmark, northern Norway) were classified as high-risk sites by the Norwegian Geological Survey (NGU). Failure initiation has been suggested to be linked to permafrost degradation, but the detailed permafrost distribution at the sites is unknown. Rockwall (RW) temperature loggers at both sites have measured the thermal regime since 2015, showing mean rock surface temperatures between +2.5 °C and −1.6 °C depending on site and aspect. Between 2016 and 2019 we conducted 2D and 3D electrical resistivity tomography (ERT) surveys on the plateau and directly within the rock wall back scarp of the unstable slopes at both sites. In combination with geophysical laboratory analysis of rock wall samples from both sites, the ERT soundings indicate wide-spread permafrost areas, especially at Gamanjunni-3. Finally, we conducted 2D thermal modelling to evaluate the potential thermal regime. Rockwall temperatures, together with ERT measurements and modelling of the ground thermal regime strongly indicate, at least locally, the presence of permafrost. Displacement rates show a seasonality, with higher velocities during spring and early summer than the rest of the year, possibly related to snow melting.