Nature and mechanics of the mount St Helens rockslide — avalanche of 18 May 1980

The bulging sector of the north slope of Mount St. Helens collapsed on 18 May 1980, triggered by an earthquake, thereby creating a tremendous mass movement. This movement in turn initiated volcanic eruptions resulting in the formation of an avalanche of debris. Limit equilibrium analysis of the slope suggests that failure was due to several culminating factors, including progressive strength losses prior to land slip, seismicity and gravitational movements.