Everywhere on the earth’s surface, materials are always acted upon by the force of gravitational attraction. This force of gravity plays an important role in the removal of broken rock debris from high elevations and on steep slopes.
Evidence of the down-slope movement of rock and regolith is found almost universally. Abundant evidences show that on most slopes at least a small amount of down-hill movement is going on constantly.
The movement of rock debris and regolith on slopes is subject to a large variety of processes, some of which act in a slow and continuous manner whereas others a sudden and catastrophic way.
The various kinds of down-hill movements of coherent masses of rock-debris, occurring under the pull of gravity, are collectively known as ‘Mass-wasting’ or ‘Mass-movement’. It constitutes an important process in denudation of the continental surfaces.
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types of mass-movement
C.F.S. Sharpe made one of the first attempts at classification of the various types of mass-wasting (‘Landslides & Related Phenomena, Columbia University Press, 1938). He recognized four major classes of mass-wasting as follows:
I. Slow-flowage
(a) Soil creep.
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(b) Talus creep.
(c) Rock creep
(d) Rock-glacier creep.
(e) Solifluction.
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II. Rapid-flowage
(a) Earth-flow
(b) Mud-flow
(c) Dabris avalanche.
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III. Landslides
(a) Slump.
(b) Debris slide.
(c) Debris fall.
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(d) Rockslide.
(e) Rockfall.
IV. Subsidence.
From the above classification, fundamentally mass-movement occur through ‘flowage’ and ‘sliding’, which may be so slow that the movement is imperceptible or too rapid like catastrophic slumping an rockfalls.