View of a glacier shear margin seen from the NASA DC-8 on the Nov. 1 survey of the Ronne Ice Shelf grounding line. Therefore margin is the point where fast-flowing glacier ice meets slow-moving ice or rock (in this case, ice attached to the Dufek Massif in Antarctica’s Pensacola Mountains). Credit: NASA / Maria-Jose Viñas

Fast glacier flow is accommodated primarily by slip at the bed. And restrained in part by drag in the lateral shear margins. Therefore Lateral shear margins are bands of intense deformation that separate relatively fast-flowing ice from stagnant ice or rock. Also drag in the shear margins is a function of the rheology of ice within the margins, which evolves in response to damage, heating, melting. Also and the development of crystallographic fabric, each of which depends on rates of local shearing and cumulative strain.

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