Observations of a reversal in vertical and horizontal strain-rate regime during a motion event on Unteraargletscher, Bernese Alps, Switzerland

During a motion event on Unteraargletscher, Bernese Alps, Switzerland, in spring 1996, surface velocities were measured up to eight times a day at four different locations along the central flowline using global positioning system equipment. In addition, accumulated vertical strains over the uppermost 50 and 100 m were measured at a location where the total ice thickness is 260 m. The motion event was accompanied by high horizontal and vertical strain rates as compared to annual mean values. A reversal in strain regime was observed, with horizontal strain rates changing to extension while vertical strain rates became compressive. This strain-rate reversal coincided, within the temporal resolution of the data, with a maximum in vertical ice displacement at the surface. Within a day, variations in vertical strain from 0.04 a(-1) to -0.06 a(-1) were observed over the uppermost 100 m. Vertical stretching is estimated to have contributed to at least 20% of the anomalous vertical ice movement at the surface. There were significant differences between measured longitudinal strain, averaged over a distance corresponding to a few ice thicknesses, and measured vertical strain. In spring 1997 a similar, but more detailed, set of measurements was collected at the same measuring site, and vertical strain rates were found to vary non-uniformly with depth, with the largest values closest to the surface.

Details

Publication status:
Published
Author(s):
Authors: Gudmundsson, G. Hilmar

On this site: Hilmar Gudmundsson
Date:
1 January, 2002
Journal/Source:
Journal of Glaciology / 48
Page(s):
566-574
Digital Object Identifier (DOI):
https://doi.org/10.3189/172756502781831043