Basal perturbations under ice streams: form drag and surface expression

Classical sliding theories consider ice sliding over obstacles which are much shorter than the thickness of overlying ice. Here we present a theory which considers "form drag" generated under ice streams by large obstacles such as subglacial bedforms, which may have lengths comparable to ice thickness. We also investigate how perturbations at the surface of an ice stream can be generated by such bedforms, and develop a mathematical framework for separating the effects of such local (kilometre-scale) variations in ice flow from the bulk flow of the ice stream.