Glacier Sliding at Subfreezing Temperatures

Abstract

Nye’s theory of glacier sliding, when modified to incorporate Gilpin’s model of the liquid layer adjacent to foreign solids in ice, predicts non-zero sliding speeds at subfreezing temperatures. Although the predicted speeds are too small to affect glacier motion or even to be observed readily, the total distance of sliding of large glaciers should be adequate to produce bedrock striations. Dissolved solutes in the liquid layer increase the sliding speeds slightly. At temperatures below about – 1° C, 90% of the drag comes from the part of the bed-roughness spectrum at wavelengths between 0.2 and 20 mm regardless of solute concentration. If no more basal ice melts than refreezes (as in a cold glacier), the average liquid-layer thickness and, concomitantly, the sliding speed for given drag and roughness are governed by the ambient temperature. With net melting (as in a temperate glacier), on the other hand, they are governed by the rate of escape of the excess water and no conflict arises between the thickness requirement for run-off water flow and that for regelation water flow. Thus, the proper distinction is not between temperate and cold, but between net melting and no net melting. The theory applies to both cases.