Rock avalanches move downslope at speeds exceeding 200 km/hr (125 mi/hr) because when the soil expands and compresses, it lifts certain particles and drops them downslope a short distance.
Landslides are the common name for soil or rock avalanches. The most frequent type of avalanche, snowslides, can travel downhill more quickly than a skier. When an unstable snow mass detaches from a slope, a snow avalanche starts.
Rock avalanches are caused by the rapid breakup of initially intact, highly fast-moving rock masses during transportation. In mountainous areas, rock avalanches, which are unexpected rock slope failures marked by high velocities, lengthy runouts, and massive volumes, are among the most deadly and costly geological hazards.
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