Catastrophic mass movements are large and rapid mass wasting events such as landslides, rockslides, and rock avalanches. Although they are often believed to occur with no warning, catastrophic mass movements are often preceded by subtle changes such as rock creep that foreshadow their occurrence. Because of their speed and size, catastrophic mass movements are often fatal events.

One of the most notable catastrophic mass movements to have occurred during recorded times was associated with the May 18, 1980 eruption of Mount St. Helens. Magma movement produced a bulge on the north side of the volcano that failed as a series of three large landslides during a magnitude 5.2 earthquake on May 18, and was immediately followed by the well-known eruption. The volume of the material removed by the landslides is estimated to have been about 2.3 km³. The landslides broke apart as they began to move and traveled downhill...