Multiparameter monitoring of crevasses on an Alpine glacier to understand formation and evolution of snow bridges

On glaciers, the snow bridges that form above crevasses have hardly been considered by researchers up to now, despite their importance for high mountain activities (skiing, mountaineering) and the risks that their possible failure poses to practitioners. In order to improve our understanding of the formation and evolution of these fragile snow structures, we monitored during two years a succession of three crevasses located at 3450 m a.s.l. in the Mont-Blanc massif (France) using a set of sensors including an automatic camera, air temperature sensors, a wind vane-anemometer, and an extensometer. Geophysical profiles (ground penetrating RaDAR) were also carried out to clarify the glacial context. Despite particularly extreme monitoring conditions, at the level of a bump formed by the bedrock under an ice thickness of c. 25 m, we have shown that a wind event parallel to the crevasse favours its filling by snow while a strong wind making a significant angle with the crevasse under largely negative temperatures can rapidly create a snow bridge by cornice accretion that grows by extending leeward. High temperatures are responsible for most of the natural failures of SBs. These elements are already used for risk mitigation.