Actually it crashes, falls, rolls, slides, slumps, flows, slips, and creeps downhill. Rockfalls happen off of cliffs and road cuts. Natural rock cliffs are usually quite stable except in areas of rapid erosion, but man-made cliffs are very unstable.
Landslides can be large and dangerous.
They commonly start out as a coherent mass but may break up into a flow if a long distance is covered. Another damaging slide was the Vaiont Dam Disaster in the Italian Alps on October 9, 1963. The 875 ft high dam was completed in 1960 and the reservoir took several years to fill. The dam held, but a 100m high wall of water sloshed over the dam and killed about 3000 people downstream. A debris flow is a water-fluidized flow of rock and soil that moves down slope.