Ice-sheet flow conditions deduced from mechanical tests of ice coreAnnals of Glaciology, Vol. 29, p. 179-183, 1999
A. Miyamoto, H. Narita, T. Hondoh
Institute of Low Temperature Science, Hokkaido University, Sapporo, Hokkaido 060-0819, Japan.
Kitami Institute of Technology, Kitami, Hokkaido 090-8507, Japan.
Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan.
National Institute of Polar Research, Itabashi-ku, Tokyo 173-8515, Japan.
D. Dahl-Jensen, N.S. Gundestrup, H.B. Clausen
Departement of Geophysics, The Niels Bohr Institute of Astronomy, Physics and Geophysics, University of Copenhagen.
Laboratoire de Glaciologie er Géophysique de l'Environnement du CNRS, BP 96, 38402 Saint-Martin-d'Hères Cedex, France.
Uniaxial compression tests were performed on samples of the Greenland Ice Core Project (GRIP) deep ice core, both in the field and later in a cold-room laboratory, in order to understand the ice-flow behavior of large ice sheets. Experiments were conducted under conditions of constant strain rate (type A) and constant load (type B). Fifty-four uniaxial-compression test specimens from 1327-2922 m were selected. Each test specimen (25 mm x 25 mm x 90 mm) was prepared with its uniaxial stress axis inclined 45o from the core axis in order to examine the flow behavior of strong single-maximum ice-core samples with basal planes parallel to the horizontal plane of the ice sheet. The ice-flow enhancement factors show a gradual increase with depth down to approximately 2000 m. These results can be interpreted in terms of an increase in the fourth-order Schmid factor. Below 2000 m depth, the flow-enhancement factor increases to about 20-30 with a relatively high variability. When the Schmid factor was >0.46, the enhancement factor obtained was higher than expected from the c-axis concentrations measured. The higher values of flow-enhancement factor were obtained from specimens with a cloudy band structure. It was revealed that cloudy bands affect ice-deformation processes, but the details remain unclear.