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

Abstract

Abstract. 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, a 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 a 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 terrain 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 terms of both practical concerns and fundamental science.

Movements, failure and climatic control of the Veslemannen rockslide, Western Norway

“…In 2016, two rock-wall temperature loggers were installed in the back scarp of Mannen in a northerly and easterly direction. Mean annual rock-wall temperatures are + 1.2°C in the northern slope and + 2.5°C in the easterly directed part of the scarp (Magnin et al 2019). In view of the recent warming since 2000, rock-wall temperatures close or below the freezing point in recent past are probable.…”

“…This seasonal sensitivity pattern coincided with seasonal warming of the ground, implying that the thermal regime had an important influence on the slope dynamics. Indeed, Veslemannen was located in a zone of sporadic mountain permafrost (Magnin et al 2019) and deep seasonal frost.…”

Evolution of events before and after the 17 June 2017 rock avalanche at Karrat Fjord, West Greenland – a multidisciplinary approach to detecting and locating unstable rock slopes in a remote Arctic area

“…Semiautomatic methods have been developed to detect landslides based on either satellite optical or SAR data (e.g. Martha et al, 2010;Friedl and Hölbling, 2015), and the detection capability of such methods may be improved by combining the different data sources as indicated by the results of our study.…”

Snow-avalanche boulder fans in Jotunheimen, southern Norway: Schmidt-hammer exposure-age dating, geomorphometrics, dynamics and evolution

“…in the region (Ødegård et al 1992;Isaksen et al 2002;Farbrot et al 2011;Lilleøren et al 2012). In the Galdhøpiggen massif, however, the lower limit of permafrost in south-facing rockwalls is predicted to lie between 1500 and 1700 m a.s.l., which is several hundred metres higher than in rockwalls facing north (Hipp et al 2014;Magnin et al 2019). Thus, the depositional fans and their source areas currently lie wholly within the permafrost zone, a conclusion strengthened by available local and regional meteorological data.…”