Sediment entrainment by a soft-bedded glacier: a model based on regelation into the bed


  • Neal R. Iverson

    Corresponding author
    1. Department of Geological and Atmospheric Sciences, Iowa State University, Ames, IA 50011, USA
    • Department of Geological and Atmospheric Sciences, Iowa State University, 253 Science Hall I, Anes, Iowa 50011-3212, USA
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Experimental results indicate that wet-based, soft-bedded glaciers may penetrate their substrates by regelation (melting and refreezing) and thereby entrain sediment. In principle, there should be a steady depth of penetration at which the downward regelation speed, driven by the interfacial effective pressure, equals the basal melt rate. Herein, the magnitude and distribution of penetration are estimated for the case of a glacier resting on a deformable bed with channelized basal drainage. The distance between channels and the distribution of effective pressure across the bed are calculated, and special attention is paid to the interdependence of the basal melt rate and effective pressure. A major uncertainty is whether fine-grained tills may impede or prevent regelation as a result of high surface tension at the ice/water interface.

Predicted penetration depths range from millimetres to a few decimetres, and thus, dirty basal ice layers of such thicknesses might be expected. Predicted distances between channels agree well with those indicated by borehole measurements at Ice Stream B, West Antarctica. Effective pressures, and hence penetration depths, increase toward channels. Therefore, the edges of interfluves, bounded by anastomosing subglacial channels, should be eroded preferentially. This motivates the testable hypothesis that such erosion contributes to the formation of streamlined landforms, such as drumlins. Copyright © 2000 John Wiley & Sons, Ltd.