Determining conditions that allow a shear margin to coincide with a Röthlisberger channel

The mass loss from the West Antarctic Ice Sheet is dominated by numerous rapidly flowing ice streams, which are separated from stagnant ice in the adjacent ridges by zones of concentrated deformation known as shear margins. Because the discharge from a single ice stream depends sensitively on the ice stream width, determining the physical processes that control shear margin location is crucial to a full understanding of ice stream dynamics. Previous work has shown that the transition from a deforming to an undeforming bed within a shear margin concentrates large stresses on the undeforming bed beneath the ridge. In this paper we investigate how the presence of a drainage channel collocated with the transition from a deforming to an undeforming bed perturbs the stress field within the shear margin. We show that the channel limits the maximum shear stress on the undeforming bed and alters the yield strength of the till by changing the normal stress on the ice‐till interface. By comparing the maximum stress with the till strength, we show that the transition from a deforming to an undeforming bed can occur across a channel whenever the water flux in the channel exceeds a critical value. This critical flux is sensitive to the rheology and loading of the shear margin, but we conclude that there are some scenarios where the transition from a deforming to an undeforming bed can be collocated with a drainage channel, though this configuration is probably not typical.