Subglacial Channels, Climate Warming, and Increasing Frequency of Alpine Glacier Snout Collapse

Alpine glacier retreat has increased markedly since the late 1980s and is commonly linked to the effects of rising temperature on the surface melt. Less considered are processes associated with glacier snout-marginal surface collapse. A survey of 22 retreating Swiss glaciers suggests that collapse events have increased in frequency since the early 2000s, driven by ice thinning and reductions in glacier-longitudinal ice flux. Detailed measurement of a collapse event at one glacier showed 0.02 m/day vertical surface deformation above a meandering main subglacial channel. However, with low rates of longitudinal flux (<1.3 m/year), this was insufficient to close the channel in the snout marginal zone. We hypothesize that an open channel maintains contact between subglacial ice and the atmosphere, allowing greater incursion of warm air up-glacier, thus enhancing melt from below. The associated meandering of subglacial channels at glacier snouts leads to surface collapse and removal of ice via fluvial processes.