We investigate the Gisla perched talus slope (Trollaskagi peninsula, northern Iceland), from which a landslide (more specifically a debris avalanche) occurred in October 2020. Although this talus slope is located outside of the permafrost climatic boundaries, geomorphological evidence (i.e., molards in the landslide deposits) suggest that degradation of azonal permafrost could be among the destabilising factors of the landslide. The thermal dynamics of talus slopes is currently poorly understood, as air convection ( the 'chimney effect') can play a role in the persistence of permafrost at the base of talus slopes. We use the software FEFLOW to run physical-based simulations of heat transfer within a cross- of the Gisla talus slope, from -20,000 years to present. We explore the sensitivity of our model to document the initial porosity/ ice content of the talus slope (0.3, 0.5 and 0.8), and the thermal conductivity (TC) of the rock phase (0.75, 1.1 and 1.75 W.m(-1).K-1). Analysis of air temperature data show that the region has been undergoing a general temperature increase for the last similar to 40 years, supporting the possibility that permafrost degradation is among the destabilising factors of the landslide. Our temperature measurements show that a chimney effect indeed occurs at the Gisla talus slope. Although our modelling approach does not simulate air convection itself, permafrost persists at the base of the talus slope in all model scenarios. Increasing the initial porosity/ice content and decreasing the TC of the rock phase enhances persistence of permafrost in the Gisla talus slope. Our approach is unconventional as we initially know that ground ice was present in the Gisla talus slope at the time of the landslide; it attests that the permafrost dynamics in the talus slope is best represented by our most ice-conservative scenario - i.e., with a TC of 0.75 W.m(-1).K-1.

Air and near-surface ground temperatures were measured using dataloggers over 14 years (2006-2020) in 10 locations at 2262 to 2471 m.a.s.l. in a glacial cirque of the Cantabrian Mountains. These sites exhibit relevant differences in terms of substrate, solar radiation, orientation, and geomorphology. Basal temperature of snow (BTS) measurements and electrical resistivity tomography of the talus slope were also performed. The mean annual near-surface ground temperatures ranged from 5.1 degrees C on the sunny slope to 0.2 degrees C in the rock glacier furrow, while the mean annual air temperature was 2.5 degrees C. Snow cover was inferred from near-surface ground temperature (GST) data, estimating between 130 and 275 days per year and 0.5 to 7.1 m snow thickness. Temperature and BTS data show that the lowest part of the talus slope and the rock glacier furrow are the coldest places in this cirque, coinciding with a more persistent and thickest snow cover. The highest temperatures coincide with less snow cover, fine-grained soils, and higher solar radiation. Snow cover has a primary role in controlling GST, as the delayed appearance in autumn or delayed disappearance in spring have a cooling effect, but no correlation with mean annual near-surface ground temperatures exists. Heavy rain-over-snow events have an important influence on the GST. In the talus slope, air circulation during the snow-covered period produces a cooling effect in the lower part, especially during the summer. Significant inter-annual GST differences were observed that exhibited BTS limitations. A slight positive temperature trend was detected but without statistically significance and less prominent than nearby reference official meteorological stations, so topoclimatic conditions reduced the more global positive temperature trend. Probable existence of permafrost in the rock glacier furrow and the lowest part of the talus slope is claimed; however, future work is necessary to confirm this aspect.