  A numerical model was developed for simulating the formation of U-shaped
glacial valleys by coupling a two-dimensional ice flow model with an erosion
model for a transverse cross section. The erosion model assumes that the
erosion rate varies quadratically with sliding speed. We compare the
two-dimensional model with a simple shallow-ice approximation model and show
the differences in the evolution of a pre-glacial V-shaped valley profile using
the two models. We determine the specific role of the lateral shear stresses
acting on the glacier side walls in the formation of glacial valleys. By
comparing the model results with field data, we find that U-shaped valleys can
be formed within 50 ka. A shortcoming of the model is that it primarily
simulates the formation of glacial valleys by deepening, whereas observed
valleys apparently have formed mainly by widening.
