| Summary: | This is the published version. Patterns of strain rate and slope on the ice streams are unusual. They cannot be accounted for in the usual way as due to standing waves in ice flow over a basal obstruction to flow (such as a sticky spot) . The features are studied using the force-budget technique. The conventional flow law is used, together with measurements of surface strain rate and shape of the glacier, to compute basal drag. The results for Ice Stream C are as expected, in that the drag varies from site to site but is directed inland, restraining the flow. The calculated drag at the base of Ice Stream B, on the other hand, is in places such that it acts to propel the glacier forward. This result is untenable. Either the conventional flow law is not applicable to Ice Stream B or there are large spatial variations in ice stiffness, perhaps associated with foliation, or both.
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