Rock avalanches onto glaciers (chapter 9)

International audienceThe chapter looks mainly at massive rock slope failures that generate high-speed, long-runout rock avalanches onto glaciers in high mountains, from subpolar through tropical latitudes. Drastic modifications of mountain landscapes and destructive impacts occur, and initiate other, longer-term hazards. Worst-case calamities are where mass flows continue into inhabited areas below the glaciers. Travel over glaciers can change landslide dynamics and amplify the speed and length of runout. Conversely, landslide material deposited onto ice modifies glacier behavior, protecting ice from ablation, usually causing advances and hugely increasing glacier sediment delivery. Hitherto, recognition of the risks associated with these processes has been compromised by observational difficulties and theoretical disagreements, lack of evidence in many re-gions and widespread misclassification of rock avalanche deposits as moraines. The latter has also compromised glacial sequences and risk scenarios. We emphasize the need for improved understanding of processes and diagnostics, as prelude to risk assessments, including the roles of earthquakes and climate change. 9.1 INTRODUCTION Landslide processes that affect glaciers range from small rockfalls and snow avalanches to massive rock slope failures and deep-seated gravitational creep 1 . The more frequent, smaller events may have a significant role as they affect virtually all mountain glaciers seasonally every year. This is reflected in the debris-covered ablation zones common in high mountain glaciers, and substantial delivery of coarse, angular debris to glacier margins. However, though infrequent, large volume and long-runout events can have powerful influences on glacier 1 Photos by authors unless otherwise state