Ice-sheet flow conditions deduced from mechanical tests of ice core

Annals 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.
H. Shoji
Kitami Institute of Technology, Kitami, Hokkaido 090-8507, Japan.
K. Kawada
Faculty of Science, Toyama University, Gofuku 3190, Toyama 930-8555, Japan.
O. Watanabe
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.
P. Duval
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.