The 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.