- Journal Article
Annual aerial photographs of Balmhorngletscher, available since 1973, have furnished data on large ice avalanches originating in one particular location. The avalanches characteristically occur during an active phase of fast sliding. The analysis of a photogrammetric 1:2000 bedrock map, of longitudinal ice surface profiles from photographs taken at various times, and of velocity measurements by theodolite has shown that the fast sliding and the release of the avalanches in an area of about 250 by 100 m is quite independent of ice thickness. It is suggested that besides the slope of the bed, rock roughness, and topographical features, the particular structure of the rock surface in the fashion of tiles on a roof is a factor which influences the processes of fast sliding and avalanche formation. It is suggested that meltwater gains access to cavities at the rock steps, from where it is dragged along on the ice-rock interface, getting slowly worked into the basal ice layer. Many weeks after the beginning of the melt season the evolving acceleration becomes apparent, characteristically at the beginning of September. Once the surface meltwater gains direct access to the bed through fresh crevasses, the glacier accelerates progressively as water enters cracks, faults, and microfissures. Water pressure effects may become important as cavities grow. While the gradual development of the active phase permits to forecast the growing avalanche risk, the prediction of the event in time is a long way off, if practical at all. Show more
Journal / seriesJournal of Geophysical Research: Solid Earth
Pages / Article No.
PublisherAmerican Geophysical Union
Organisational unit09599 - Farinotti, Daniel / Farinotti, Daniel
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