Ice Sheet Dynamics - Glacial Bottom Processes

Glacial Bottom Processes

Most of the important processes controlling glacial motion occur in the ice-bed contact—even though it is only a few meters thick. Glaciers will move by sliding when the basal shear stress drops below the shear resulting from the glacier's weight.

τ_D = ρgh sin α

where τ_D is the driving stress, and α the ice surface slope in radians.

τ_B is the basal shear stress, a function of bed temperature and softness.

τ_F, the shear stress, is the lower of τ_B and τ_D. It controls the rate of plastic flow, as per the figure (inset, right).

For a given glacier, the two variables are τ_D, which varies with h, the depth of the glacier, and τ_B, the basal shear stress.