It is useful to identify slump because it often recurs
in the same place or on nearby slopes. Thus, a slope that
shows evidence of past slump is not a good place to build
a house.
During a rockslide, or rock avalanche, bedrock
slides downslope over a fracture plane. Characteristically,
the rock breaks up as it moves and a turbulent mass of
rubble tumbles down the hillside. In a large avalanche,
the falling debris traps and compresses air beneath and
within the tumbling blocks. The compressed air reduces
friction and allows some avalanches to attain speeds of
500 kilometers per hour. The same mechanism allows a
snow or ice avalanche to cover a great distance at a high
speed.