Permafrost in monitored unstable rock slopes in Norway – new insights from temperature and surface velocity measurements, geophysical surveying, and ground temperature modelling

[摘要] The warming and subsequent degradation of mountain permafrost within alpineareas represent an important process influencing the stability of steep slopes androck faces. The unstable and monitored slopes of Mannen (Møre and Romsdalcounty, southern Norway) and Gámanjunni-3 (Troms and Finnmark county,northern Norway) were classified as high-risk sites by the NorwegianGeological Survey (NGU). Failure initiation has been suggested to be linkedto permafrost degradation, but the detailed permafrost distribution at thesites is unknown. Rock wall (RW) temperature loggers at both sites havemeasured the thermal regime since 2015, showing mean rock surfacetemperatures between 2.5 and −1.6   ∘ C depending onsite and topographic aspect. Between 2016 and 2019 we conducted 2D and 3Delectrical resistivity tomography (ERT) surveys on the plateau and directlywithin the rock wall back scarp of the unstable slopes at both sites. Incombination with geophysical laboratory analysis of rock wall samples fromboth sites, the ERT soundings indicate widespread permafrost areas,especially at Gámanjunni-3. Finally, we conducted 2D thermal modellingto evaluate the potential thermal regime, along with an analysis ofavailable displacement rate measurements based on Global NavigationSatellite System (GNSS) and ground- and satellite-based interferometricsynthetic aperture radar (InSAR) methods. Surface air and groundtemperatures have increased significantly since ca. 1900 by 1and 1.5  ∘ C, and the highest temperatures have been measured and modelledsince 2000 at both study sites. We observed a seasonality of displacement,with increasing velocities during late winter and early spring and the highestvelocities in June, probably related to water pressure variations duringsnowmelt. The displacement rates of Gámanjunni-3 rockslide co-vary withsubsurface resistivity and modelled ground temperature. Increaseddisplacement rates seem to be associated with sub-zero ground temperaturesand higher ground resistivity. This might be related to the presence ofground ice in fractures and pores close to the melting point, facilitatingincreased deformation. The study demonstrates and discusses the possibleinfluence of permafrost, at least locally, on the dynamics of large rockslope instabilities.

[学科分类] 土壤学