| Summary: | This thesis explores the morphology, dynamics and causes of landslides and debris flows in mountainous regions of northern Iceland. The primary objectives are to define the initiation and evolution of Icelandic landslides and debris flows, and to understand the link between ground-ice thaw and rapid mass movements. Slopes are predicted to react more intensely to global warming, so improving our knowledge of rapid mass movements in cold environments, which are even more sensitive to climate change, is crucial, as they could pose at risk local population in Iceland and other mountainous periglacial areas. I first perform a detailed study of debris flows in north-western Iceland, distinguishing through quantitative geomorphological methods the different mechanisms of debris-flow initiation and the associated geomorphic features. The approach of this study is easily applicable to similar settings, and its results could help in anticipating new potentially destructive events. Secondly, I describe and quantify the morphometric characteristics of two landslides in northern Iceland, whose source materials comprised ground ice-cemented deposits. This study reveals different dynamic landslide processes and the crucial role of thawing ground ice in landslide emplacement. I then analyse meteorological and seismic data near these two landslides. I define and distinguish precipitation, seismic activity and permafrost degradation as the preparatory and triggering factors for the failures. Finally, through a geomorphic approach I analyse molards, conical mounds of debris that I found in both landslides deposits. I show conclusive evidence that molards form from thawing of blocks of ice-rich sediments that degrade into cones of debris. I demonstrate that molards are the 'fingerprint" of permafrost degradation, and their different morphology and distribution can reveal different types of landslide processes in periglacial terrains. This thesis widens our knowledge of the conditions and processes controlling rapid mass movements in cold environments, which is crucial in the perspective of hazard assessment, and opens up new avenues for the study of potentially hazardous geomorphic responses of cold landscapes to changing climate conditions.
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