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Direct shear tests of materials from a cold glacier: implications for landform development

Sean J. Fitzsimons1 Kevin J. McManus2, Paul Sirota1 and Regi D. Lorrain3

1 Department of Geography, University of Otago, Dunedin, New Zealand
2 Department of Civil Engineering, University of Canterbury, Christchurch, New Zealand
3 Département des Sciences de la Terre et de l'Environnement, Université Libre de Bruxelles, Brussels, Belgium

 

Abstract

The mechanical properties of materials at the ice-bed interface exert a major control on glacier behaviour and define the nature and rate of subglacial erosion. This paper presents new data on the strength and behaviour of basal ice and substrate of the Suess Glacier, south Victoria Land, Antarctica which is a small alpine dry-based glacier that has a basal temperature of -17°C. A tunnel excavated in the glacier revealed a substrate composed of frozen sand and gravel and a basal zone that was 3.8-m-thick. From bottom to top, the basal zone was composed of 1.8 m of stratified, complexly deformed layers of ice and debris-laden ice that was overlain by a 0.9-m-thick layer of frozen sediment and a 0.8-m-thick layer of discoloured ice that lies immediately beneath clean glacier ice. Direct shear tests were performed in the field on 36 samples using a strain rate of 0.85 mm/h and on replicate samples in a laboratory at strain rates of 0.08 and 0.01 mm/h. The experiments performed in the field show that the average peak shear strength of substrate samples was 2.53 MPa, which is almost twice as strong as the average value for basal ice (1.28 MPa), and the glacier ice samples (1.39 MPa). The laboratory experiments show that the behaviour and peak strength of samples sheared at the higher strain rates are considerably greater than the peak and residual strengths measured during the lower strain rate tests. The direct shear tests suggest that the glacier substrate is unlikely to deform at the current temperature.

 

Reference

Fitzsimons, S.J., McManus, K.J., Sirota, P. and Lorrain, R.D. 2001. Direct shear tests of material from a cold glacier: implications for landform development. Quaternary International 86, 129-137. [PDF 400 kb] doi:10.1016/S1040-6182(01)00055-6

 

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