| Summary: | The ground thermal regime substantially influences geomorphological processes operating in periglacial environments, although the connection may not be straightforward. Recent studies provide more evidence for enhanced rockfall activity and accelerating rockslides in terrain underlain by thawing permafrost. In contrast, there is an ongoing debate on the periglacial imprint for long-term landscape evolution. Furthermore, the concept of "frost cracking window", which refers to an optimal ground temperature range for frost weathering, was established over two decades ago to describe in a simple way the connection between frost weathering and ground temperature. Therefore, knowledge of the ground thermal regime is essential in the geomorphological context on both short- and long-term scales. This dissertation employs permafrost modelling, modelling of frost weathering, space-borne and ground-based remote sensing approaches as the main methods to investigate various concepts within cold-region geomorphology. Ground temperature is modelled using a one-dimensional heat flow model for Iceland and a two-dimensional heat flow model for rock walls in Norway. This modelling showed that Iceland’s shallow and warm permafrost and Norway’s rock wall permafrost are susceptible to the atmospheric warming that has been lasting since the 1980s. The number of cells with simulated permafrost in Iceland decreased by approximately 40 % between the 1980s and 2010–2016. The average warming of Norway’s rock walls has been 0.2 °C per decade at 20 m depth since the 1980s. Recent permafrost thawing in Norway and Iceland may have consequences for slope stability, rockslide and rock glacier dynamics, and lead to the disappearance of palsas. Sites with enhanced frost weathering were identified using the two-dimensional modelling of frost cracking performed for steep rock walls in Jotunheimen, southern Norway. Such sites are typically found between the rock wall and melting ice sheet or glaciers, as well as where the snow depth changes abruptly, ...
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