In this theory it is assumed that a stagnant ice block or dam develops in the lower regions of a glacier. Ice gradually builds up above the dam while the dam itself becomes thinner by ablation. Eventually the upper end of the stagnant ice block crumbles from the force of the ice above it, and much of the glacier is changed from a state of compression to one of tension. The breaking of the ice dam results in the glacier rapidly becoming broken into a mass of blocks or powdered ice. The apparent viscosity of the broken-up glacier is much less than that of bulk ice, so high velocities of flow are possible, and a phenomenon similar to a mud flow results. This theory explains why some glaciers repeatedly surge yet appear stagnant between surges. The broken-up appearance of surging glaciers and the delayed surging of tributaries are explained. Additional substantiating observations on several of these phenomena are presented.