There are four basic types of mass movement – fall, slide, flow and creep. The pull of gravity working on a mass until it falls, Glides, flows and creeps is the most dominant factor in each case.
There is of course, close relationship between moisture content and rate of movement of surface material. The process of mass movement may be rapid as in case of a landslide or very slow and sluggish as happens in case of soil creep down the gentle slope.
It is to be pointed out that the role of slopes in all types of mass movement is very important. In addition, earthquakes and volcanic eruptions also hold place of eminence among various forces creating mass movements.
Rockfall refers to a process by which small blocks of rock become detached from a cliff face and fall nearly vertically down-slope producing rattling sound over other loose rock and debris.
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Loose blocks are generally produced where the rock has suitable joints so that the freeze and thaw action, and differential expansion and contraction easily take place. The rocks or their fragments involved in rockfall show a lot of variance in their size.
It is to be pointed out that rockfalls are common in steep, mountainous areas, where one finds cone-shaped accumulations of rock fragments at the base of the cliffs forming talus cones.
In spring rockfalls are more common. Spring is the season when alternate periods of freezing and thawing loosen the rock particles with the result that they are more susceptible to force of gravity and fall.
A debris avalanche may be called a misnomer. The correct and more meaningful term for this particular phenomenon would be debris slide. Actually the term avalanche creates confusion and leads one to think of snow and ice movement.
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Truly speaking, the term debris avalanche refers to a sudden downhill movement of debris due to saturation by torrential rain.
The extreme danger of a debris avalanche results from tremendous velocity and absence of any warning system. Because of a debris avalanche, cities are buried and thousands of persons are killed.