Plastic flow

Plastic flow (or creep) of ice around an obstacle clearly must contribute to flow of a glacier past the obstacle. Weertman suggested that this plastic flow is enhanced owing to the high stresses on the obstacle. He thus assumes that the speed with which ice moves past the obstacle by this process, Sp, is proportional to t and to the creep rate obtained by using the stress difference from Equation (7.1) in the flow law:

where b is a dimensionless constant of proportionality. Note that dimen-sionally et is a speed.

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Figure 7.3. Relation between sliding speed and obstacle size for regelation, 5r, plastic flow, Sp, and their sum, 5.

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