Glacier surges can result when an ice dam, which is above the equilibrium length of the glacier, breaks from the forces of the excess ice that builds up behind the dam. It is shown that the high velocities of flow of surging glaciers cannot be due to the normal pseudo-plastic flow of glacier ice. Rather, the high velocities must result from a combination of sliding on the glacier bed and a fluidized block (or powder) flow resulting from melt water around the ice blocks in the interior and at the base of the ice mass. Various calculations are made to show the feasibility of the mechanisms proposed. The predictions are in line with the available observations on surging glaciers.