GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 2, 1090, doi:10.1029/2002GL016160, 2003
Diurnal variations in vertical strain observed in a temperate valley glacier
Institute of Low Temperature Science, Hokkaido University,
Sapporo, Japan
British Antarctic Survey,
Cambridge, United Kingdom
Abstract
[1] During a period of diurnal fluctuations in glacial flow speed, vertical strain was measured with sub-daily temporal resolution on Unteraargletscher, Switzerland. Mean vertical strain in boreholes up to 300-m deep in 400-m-thick ice was found to fluctuate diurnally. Vertical strain rates were tensile in the daytime and compressive at night, with a magnitude of up to 10-3 day-1. Horizontal surface strain was observed to fluctuate in a manner consistent with the vertical deformation. Diurnal surface flow speed variations correlated well with basal water pressure suggesting a basal control on temporal flow variations. Nevertheless, the strain rate measurements indicated that changes in surface flow speed are affected by internal ice deformation and not a direct measure of local basal motion. Basal conditions in the surrounding neighborhood and their temporal variations take an important role in short-term glacial flow fluctuations.
Received 22 August 2002; revised 3 October 2002; accepted 25 November 2002; published 30 January 2003.
Index Terms: 1827 Hydrology: Glaciology (1863); 1863 Hydrology: Snow and ice (1827); 0915 Exploration Geophysics: Downhole methods.
Citation: , Diurnal variations in vertical strain observed in a temperate valley glacier, Geophys. Res. Lett., 30(2), 1090, doi:10.1029/2002GL016160, 2003.