Rheology of Ice in Shear Zones: Glacier Shear Margins

Fast glacier flow is accommodated primarily by slip at the bed and restrained in part by drag in the lateral shear margins. Lateral shear margins are bands of intense deformation that separate relatively fast-flowing ice from stagnant ice or rock. Drag in the shear margins is a function of the rheology of ice within the margins, which evolves in response to damage, heating, melting, and the development of crystallographic fabric, each of which depends on rates of local shearing and cumulative strain. Though fundamental to understanding glacier dynamics and to making reliable projections of future glacier states, our knowledge of the relative contributions of these rheological mechanisms is incomplete. We seek to understand the relative contributions of all mechanisms that can influence the effective rheology of shear margins, with a particular focus on the thermomechanics of the margins. In short, ice rheology is strongly dependent on temperature and liquid water content; the deformation of ice produces heat that warms cold ice and melts temperate, leading to feedbacks between deformation and softening.