Sediment entrainment by a soft-bedded glacier: A model based on regelationinto the bed

Experimental results indicate that wet-based, soft-bedded glaciers may pene trate their substrates by regelation (melting and refreezing) and thereby e ntrain sediment. In principle, there should be a steady depth of penetratio n at which the downward regelation speed, driven by the interfacial effecti ve pressure, equals the basal melt rate. Herein, the magnitude and distribu tion of penetration are estimated for the case of a glacier resting on a de formable 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, an d thus, dirty basal ice layers of such thicknesses might be expected. Predi cted distances between channels agree well with those indicated by borehole measurements at Ice Stream B, West Antarctica. Effective pressures, and he nce penetration depths, increase toward channels. Therefore, the edges of i nterfluves, bounded by anastomosing subglacial channels, should be eroded p referentially. This motivates the testable hypothesis that such erosion con tributes to the formation of streamlined landforms, such as drumlins. Copyr ight (C) 2000 John Wiley & Sons, Ltd.