On the Origin and Transport of Englacial Debris in Svalbard Glaciers

Very considerable amounts of englacial debris derived from the glacier bed are contained in the polar glaciers of Svalbard. It is suggested that this debris is largely incorporated by basal freezing on the down-glacier flanks of bedrock obstructions, although other freezing mechanisms and thrusting may be important. The basal freezing hypothesis predicts that vertical and lateral variations in englacial debris content should reflect the variation in subglacial rocks over which the glacier passes; this prediction is tested against an actual englacial debris sequence. The mode of transport of debris, including its stone orientation fabrics, is described, and also the way in which it reacts in zones of intense compression. A generalization is suggested: that polar glaciers tend to contain much larger amounts of basally derived debris than temperate glaciers. This supports the view that the englacial incorporation of debris is controlled by the temperature regime of the glacier, and could be of considerable importance in the interpretation of the regimes of ancient glaciers from their deposits.