Abstract
As consequence of ongoing climate change, permafrost degradation is thought to be increasingly affecting slope stability in periglacial environments. This is of growing concern in Iceland, where in the last decade, permafrost degradation has been identified among the triggering factors of landslides. The role of ground ice in conditioning the morphology and dynamics of landslides involving loose deposits is poorly understood. We show the geomorphological impact of the Móafellshyrna and Árnesfjall landslides that recently occurred in ice-cemented talus deposits in northern Iceland. Using field and aerial remote-sensing measurements of the morphological and morphometric characteristics of the landslides, we assess the influence of thawing ground ice on their propagation style and dynamics. The two mass movements are complex and are similar to rock- and debris-ice avalanches, changing trajectory and exhibiting evidence of transitioning their style of motion from a dry granular mass to a debris flow-like movement via multiple pulses. We infer that the thawing of ground ice together with the entrainment of saturated material provided the extra fluid causing this change in dynamics. The hazardous consequences of permafrost degradation will increasingly affect mountain regions in the future, and ground-ice thaw in steep terrain is a particularly hazardous phenomenon, as it may induce unexpected long-runout failures and can cause slope instability to continue even after the landslide event. Our study expands our knowledge of how landslides develop in unstable ice-cemented deposits and will aid assessment and mitigation of the hazard that they pose in Iceland and other mountainous periglacial areas.
Highlights
Introduction and state of the artRapid mass movements are one of the most obvious reactions to climate change of mountain slopes affected by permafrost (e.g. Fischer et al 2006; Allen et al 2011; Huggel et al 2012; Haeberli et al 2017; Patton et al 2019)
Few examples of rapid mass movements involving loose deposits, such as debris flows and debris slides, in ground-ice cemented terrains are reported in the literature (Huscroft et al 2004; Brideau et al 2009; Lyle et al 2014; Sæmundsson et al 2018), and little is known about how their dynamics are conditioned by thawing ground ice
This study contributes to the understanding of a complex type of landslide, as we show how ground ice has an impact on landslide morphology and dynamics and should be included when evaluating the potential hazard posed by rapid mass movements in periglacial areas
Summary
Introduction and state of the artRapid mass movements are one of the most obvious reactions to climate change of mountain slopes affected by permafrost (e.g. Fischer et al 2006; Allen et al 2011; Huggel et al 2012; Haeberli et al 2017; Patton et al 2019). Direct observation during or immediately after the occurrence of rapid mass movements involving frozen debris, such as talus or moraine deposits, is rare This is because, once mobilised, frozen material thaws rapidly; this type of landslide commonly occurs in remote glacial and periglacial areas, so they are either not observed or reported a long time after their occurrence when direct evidence of the presence of ice has gone. These sparse observations help to understand the effect of ice on the mobility of the landslide. Ground ice is thought to have provided cohesion to blocks of surficial material that were “mobilized by high pore water pressure in the surrounding saturated sediments”, and ground ice degradation is inferred to have caused the failure (Brideau et al 2009)
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