A glacier flows because the ice within it deforms in response to gravity. The major controls on ice flow are temperature and shear stress, which is dependent on the ice thickness and the surface slope of the glacier. This can be summarized as:

where τ‎ is the shear stress at a point within the glacier, ρ‎ is the density of ice, g is the acceleration due to gravity, α‎ is the surface slope of the glacier, s is the surface elevation, and z is the elevation of a point within the glacier.

The basal shear stress is given by:

where τ‎ is shear stress, ρ‎ is the density of ice, g is the acceleration due to gravity, h is the thickness of the glacier, and α‎ is the surface slope of the glacier. See M. Bennet and N. F. Glasser (2009).