Ice-Sheet Flow Properties Derived from Bore-Hole Shear Measurements Combined With Ice-Core Studies
Open Access
- 1 January 1979
- journal article
- Published by International Glaciological Society in Journal of Glaciology
- Vol. 24 (90), 117-130
- https://doi.org/10.3189/s0022143000014684
Abstract
A 345 m deep bore hole in ice about 385 m thick, near the edge of Law Dome, Antarctica, was drilled in 1974 about 3 km up-stream from the site of a previous bore hole, nearly reaching the bed, obtained in 1969. The core from this new bore hole has been studied comprehensively, particularly with regard to the ice-crystal orientation fabrics. Samples of the ice core were subjected to simple shear at temperatures and deviatoric stresses which match the in situ conditions of the ice sheet.Similar studies of randomly-oriented laboratory-made polycrystalline ice were undertaken. Long-term tests, lasting for up to two years, were required to determine minimum strain-rates. The flow law for the anisotropic ice was thus determined as a function of that for the isotropic ice together with a measure of c-axis fabric strength perpendicular to the shear plane.Core studies indicate that the upper part of the ice sheet has a polycrystalline structure appropriate to the surface longitudinal stress. Deeper in the core a strong concentration of near-vertical c-axes develops. Ice having very large crystals with multiple maxima fabrics was found in the lower quarter of the ice thickness.Shear measurements in the bore hole indicate the existence of high strain-rates in the zone of vertical c-axes, and of lower shear-rates below that level. The low values of shear-rates in the basal region cannot be explained in terms of crystallographic changes alone, and therefore it is inferred that the shear stress decreases in this layer–a result which also provides a possible explanation for the development of the observed basal crystal structure.Keywords
This publication has 17 references indexed in Scilit:
- International studies of ice sheet and bedrockPhilosophical Transactions of the Royal Society of London. B, Biological Sciences, 1977
- Resurvey of the “byrd” station, Antarctica, drill holeJournal of Glaciology, 1976
- Measured and Computed Temperature Distributions in the Law Dome Ice Cap, AntarcticaJournal of Glaciology, 1976
- Advances in geophysical exploration of ice sheets and glaciersJournal of Glaciology, 1975
- Structure and Flow in the Margin of the Barnes Ice Cap, Baffin Island, N.W.T., CanadaJournal of Glaciology, 1973
- Seismic-wave velocities in anisotropic ice: A comparison of measured and calculated values in and around the deep drill hole at Byrd Station, AntarcticaJournal of Geophysical Research, 1972
- The friction and creep of polycrystalline iceProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1971
- Sliding motion of glaciers: Theory and observationReviews of Geophysics, 1970
- Creep of Ice under Low StressJournal of Glaciology, 1969
- The creep of polycrystalline iceProceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1955