Relative importance of lateral and vertical shear on Rutford Ice Stream, Antarctica
Survey data from three transverse profiles across Rutford Ice Stream show that most of the shear deformation occurs in boundary layers about 10 km wide on both sides of the glacier. There is a central part, also about 10 km wide, where lateral shear-stress gradients are not significantly different from zero. This implies that friction from the side walls does not impede the flow in the middle of the glacier. Instead, a basal shear stress of around 40 kPa is required in order to provide the necessary restraint. Even then, only a small proportion of the forward movement will be caused by internal deformation of the ice and the remainder must arise from sliding or rapid deformation at or near the base of the glacier. Although the present analysis does not consider in detail the variation with depth in stresses and strain-rates, the formulation of the problem suggests that a self-consistent solution can be found for the distribution of basal and vertical shear stresses.