Diurnal variations in vertical strain observed in a temperate valley glacier

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An edited version of this paper was published by AGU.Copyright 2003, American Geophysical Union, Geophysical Research Letters, 30-2During a period of diurnal fluctuations in glacial flows speed, vertical strain wasmeasured with sub-daily temporal resolution on Unteraargletscher, Switzerland. Mean verticalstrain in boreholes up to 300-m deep out of 400-m-thick ice was found to fluctuate diurnally.Vertical strain rates were extensile in the daytime and compressive at night, with a magnitude ofup to 10-3 day-1. Horizontal surface strain was observed to fluctuate in a manner consistent withthe vertical deformation. Diurnal surface flow speed variations correlated well with basal waterpressures suggesting a basal control on temporal flow variations. Nevertheless, the strain ratemeasurements indicated that changes in surface flow speed is affected by internal icedeformation and not a direct measure of local basal motion. Basal conditions in the surroundingneighborhood and their temporal variations take important role in short-term glacial flowfluctuations.
2003-01-30