Hazardous Glacier Instabilities: Ice Avalanches, Sudden Large-Volume Detachments of Low-Angle Mountain Glaciers, and Glacier Surges

Abstract

Ice avalanches, sudden large-volume detachments of low-angle mountain glaciers, and glacier surges are glacier instabilities that can pose a significant hazard to mountain communities and infrastructure. Together, these three processes form a continuum of hazards where the volume of mobilized ice is inversely proportional to the surface slope of the glacier it originated from: Ice avalanches involve 103–106 m3 of ice breaking off from glaciers on slopes steeper than 25°. They can reach velocities of around 100 km h− 1, but are limited to short runout distances. Glacier detachments are abrupt releases of tongues of valley glaciers that are typically 10°–20° steep. The mobilization of 106–108 m3 of ice results in highly mobile and destructive mass flows that often involve significant amounts of lithic material from below and adjacent to the glacier. Glacier surges manifest as rapid increases of ice flow velocities and rapid tongue advances that can involve the entire glacier. In contrast to ice avalanches and detachments, where the hazard stems directly from the released ice masses, the rapid advance of glacier tongues during the surging process can dam rivers and lead to the formation of ice-dammed lakes that are prone to rapid drainage. Outburst floods from such lakes can impact communities tens to hundreds of kilometers downstream. Due to increasing pressure on mountain regions through infrastructure development, recreation, and the presence of humans in increasingly remote places, understanding these ice hazards and finding effective mitigation strategies has gained importance. Here we summarize the current state of knowledge of these processes, highlight the most common monitoring and early warning practices, and discuss the expected impacts of climate change on glacier hazards.