Permafrost distribution in steep rock slopes in Norway: measurements, statistical modelling and implications for geomorphological processes

• Published in: Earth Surface Dynamics
• Main Authors: Magnin, Florence, Etzelmüller, Bernd, Westermann, Sebastian, Isaksen, Ketil, Hilger, Paula, Hermanns, Reginald
• Other Authors: Environnements, Dynamiques et Territoires de Montagne (EDYTEM), Université Savoie Mont Blanc (USMB Université de Savoie Université de Chambéry )-Centre National de la Recherche Scientifique (CNRS), Department of Geosciences Oslo, Faculty of Mathematics and Natural Sciences Oslo, University of Oslo (UiO)-University of Oslo (UiO)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2019
• Subjects: [SDE.ES]Environmental Sciences/Environment and Society; [SDE]Environmental Sciences; [SDE.MCG]Environmental Sciences/Global Changes; Norway; Ice; Northern Norway; permafrost; polar night; midnight sun
• Online Access: https://hal.science/hal-02440626; https://hal.science/hal-02440626/document; https://hal.science/hal-02440626/file/Magnin_et_al_ESURF_Figures_revised.pdf; https://doi.org/10.5194/esurf-7-1019-2019

International audience Permafrost in steep rock slopes has been increasingly studied since the early 2000s in conjunction with a growing number of rock slope failures, which likely resulted from permafrost degradation. In Norway, rock slope destabilization is a widespread phenomenon and a major source of risk for the population and infrastructure. However, the lack of precise knowledge of the permafrost distribution in steep slopes hinders the assessment of its role in these destabilizations. This study proposes the first nationwide permafrost probability map for the steep slopes of Norway (CryoWall map). It is based on a multiple linear regression model fitted with multi-annual rock surface temperature (RST) measurements, collected at 25 rock slope sites, spread across a latitudinal transect (59-69°N) over mainland Norway. The CryoWall map suggests that discontinuous permafrost widely occurs above 1300-1400 and 1600-1700 m a.s.l. in the north and south rock faces of southern Norway (59°N), respectively. This lower altitudinal limit decreases in northern Norway (70°N) by about 500±50 m, with more pronounced decrease for south faces, as a result of the insolation patterns largely driven by midnight sun in summer and polar night in winter. Similarly, the mean annual RST differences between north and south faces of similar elevation range around 1.5°C in northern Norway and 3.5°C in southern Norway. The CryoWall map is evaluated against direct ice observations in steep slopes and discussed in the context of former permafrost studies in various types of terrains in Norway. We show that permafrost can occur at much lower elevations in steep rock slopes than in other terrains, especially in north faces. We demonstrate that the CryoWall map is a valuable basis for further investigations related to permafrost in steep slopes in both practical concerns and fundamental science.