Abstract:
Debris-rich ice is a commonly observed basal ice facies found at the base of many temperate and polar glaciers and at the base of cores through major ice sheets. The effects of the presence of debris on the mechanical behaviour of ice was investigated and then the implication of those effects for the overall dynamics of ice masses was examined at the Taylor Glacier, Taylor Valley, Antarctica over ... three field seasons. 51 uniaxial compression tests, 30 shear strength tests, 120 point load tests and 31 Brazilian tensile strength tests were carried out on debris-laden ice samples, and 140 point load tests were carried out on clean ice samples. Debris laden and clean ice were sampled (blocks and cores) and analysed for characteristics and crystallography. Relative rates of deformation were determined by measuring over time the relative positions of a grid of metal pegs installed. The mechanical strength of debris-laden and clean ice in uncontrolled field conditions and in temperature controlled laboratory conditions (cold room laboratories at -5, -15 and -25°C) was measured to determine the effect of temperature on strength on both types of ice. Temperature data was collected from ice away from the glacier margin by placing a line of temperature sensors in a 10m long bore-hole and recording it to investigate the variation in the ice thermal regime away from the ice margin. Ice samples were obtained in situ for unconfined compressive strength testing and laboratory tests for triaxial and constant stress tests. The importance of deformation of the basal ice layer (with different characteristics) in the overall motion of the Taylor Glacier, was also assessed. A detailed map of stress fields and surface velocity over the lower part of the glacier was completed using GPS and GPR. The surface topography was obtained by GPS surveying comprising sampling along a series of approximately evenly spaced profiles. The bed topography was obtained by GPR. Surface velocities were obtained by establishing a network of about 70 surface markers extending approximately 5km up the glacier and repeatedly resurveying every 2-4 days. The role of sublimation in moisture loss from debris-laden ice at the margins of the glacier was determined by installing a climate station on the alluvial fan where the stream at the north side of the glacier runs into Lake Bonney and installing three small lysimeters on the debris-laden ice at the margin of the glacier to enable the moisture balance of a sample of surficial material to be evaluated. Basal ice was sampled for comparative testing in order to differentiate behaviours of different facies. The types and characteristics of basal ice facies found in the basal layer of the Taylor Glacier were determined by sampling and examining the physical, chemical and isotopic characteristics of the ice. To explore the hypothesis that clear basal ice forms by metamorphism of clean glacier ice, analysis and comparison of the included-gas compositions of clear basal ice facies and overlying glacier ice was carried out on collected samples. An array of markers was placed in a marginal ice cliff and was re-surveyed at regular intervals to determine if debris-laden ice deforms more rapidly in situ than overlying clean glacier ice.
Lawson W J, 1996, The relative strengths of clean and debris-laden ice: evidence from Taylor Glacier, Antarctica, Annals of Glaciology, Vol 23, pp 270-276.
Lawson, W. Elliott, C. Strain-rate effects on the strength of debris-laden glacier ice. New Zealand journal of geology and geophysics 46(3): 323-330, 2003.
Hubbard, A., Lawson W., Anderson B., Hindmarsh R., Hubbard, ... B. 2004 Evidence for extensive subglacial ponding across the tongue of Taylor Glacier, Antarctica. Annals of Glaciology 39, 79-84
Hindmarsh, R.C., Anderson, B.M., Arthern, R.J.. Kluiving, S.J., Lawson, W.J., Le Meur, E, and Van der Wateren, D. 2002 Measuring and modelling the Holocene Retreat of the Antarctica Ice Sheet. Eos Transactions AGU 83(19, Spring Meeting Supplement Abstract U42-05 2002
Hubbard, A., Lawson, W., Anderson, B., Hubbard, B. and Blatter, H. 2003 Evidence for temperate subglacial conditions in the terminus region of Taylor Glacier, Antarctica. 8th International Symposium on Antarctic Glaciology, Milan, Italy: August 2003
