Abstract

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