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.
Highlights
Permafrost affecting steep bedrock slopes has been increasingly studied since the early 2000s in conjunction with both the high frequency of rock fall activity during hot summers (e.g. Gruber et al, 2004a; Fischer et al, 2006; Allen et al, 2009; Ravanel et al, 2017) and the occurrence of highmagnitude rock–ice avalanches (e.g. Haeberli et al, 2004; Sosio et al, 2008; Huggel et al, 2012; Deline et al, 2015)
The lowest mean annual RST (MARST) registered over the measurement period (Table 4) is found at Juv_S (−4.9 ◦C), the second highest measurement point, in 2012–2013, while the highest MARST (3.5 ◦C) is registered at Fla_S in 2017–2018, which is the most sun-exposed sensor installed at the lowest latitude
These simulations estimated a lower limit of permafrost (0 ◦C isotherm) at about 650 m, which is the top of the rock slope failure and the lower limit of discontinuous permafrost suggested by the CryoWall map (Fig. 12b)
Summary
Permafrost affecting steep bedrock slopes has been increasingly studied since the early 2000s in conjunction with both the high frequency of rock fall activity during hot summers (e.g. Gruber et al, 2004a; Fischer et al, 2006; Allen et al, 2009; Ravanel et al, 2017) and the occurrence of highmagnitude rock–ice avalanches (e.g. Haeberli et al, 2004; Sosio et al, 2008; Huggel et al, 2012; Deline et al, 2015). Gruber et al, 2004a; Fischer et al, 2006; Allen et al, 2009; Ravanel et al, 2017) and the occurrence of highmagnitude rock–ice avalanches (e.g. Haeberli et al, 2004; Sosio et al, 2008; Huggel et al, 2012; Deline et al, 2015) These increasing rock slope failures bear both fundamental and societal concerns. They are essential events of periglacial and paraglacial mass-wasting processes (McColl, 2012) and of sediment transport (Korup, 2009). Magnin et al.: Permafrost distribution in steep rock slopes in Norway ondary effects, such as displacement waves and catastrophic flooding through debris flows (e.g. Huggel et al, 2005; Romstad et al, 2009; Hermanns et al, 2013)
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