Landslides are generally classified into slides, falls and flows. Slides move as large bodies by slipping along one or more failure surfaces. Falls of rock or soil originate on cliffs or steep slopes. Large rockfalls can be catastrophic events. An earthquake off the coast of Peru in 1970 started a rockfall which accelerated to more than 170 miles per hour and buried more than 18,000 people.
Flows are landslides that behave like fluids.
Mudflows involve wet mud and debris. Earthflows involve wet, claylike material. Solifluction is the downslope flow of soil that occurs on arctic and alpine hillsides when thawed ice or snow saturates the soil cover. Landslides commonly occur with other major natural disasters, such as earthquakes and floods. The 1980 eruption of Mount St. Helens in Washington was preceded by the development of a large landslide on the north side of the volcano.