TYPES OF LANDSLIDES

Landslides are extremely complicated and varied nomena. They differ in terms of sliding, flowing, creel toppling or speed of movement so markedly that
extremely difficult to combine all these diagnostic pheJ ena into a standard taxonomy. Classifications of lands have been attempted by T.H. Nilsen (1979), R.J. E (19'73), AJ. Nemcock (1972), AW. Skempton and
Hutchinson (1964), and D.J. Varnes (1978). The sel advanced by Varnes has received widest acceptance
1. Rotational slide It is a classic form of land: Some cases produce multiple regressive phenomena when continued instability produces new head carps to develop progressively up the slope.
2. Translational slide It involves relatively flat, planar movement following the surface. This type of movement is found in bedding planes made of sedimentary or metamorphic rocks dipping in the direction of slope.
3. Roto-translational slide It is a complex type where a combination of slip along a circular arc and a flat plane is found.
4. Soil-slab failure In this case, a slab of saturated regolith is converted into a thick liquid. So the speed of landslide accelerates to as high as 10m/sec.
5. Debris slide or avalanche It occurs in surface deposits of granular materials. The surface of rupture is almost parallel to the inclination of bedrock.
6. Debris flow It occurs when debris is saturated with water. When rigid solid also fallsalongwith the sliding mass, the phenomenon is called plug flow.
7. Falls These take place through air; for example,
jointed weathered rock falls from vertical cliffs.
8. Topples After detachment from cliffs the outward
rotation of angular blocks and rock columns cause toppling.
9. Mudflow It contains 20 to 80 per cent fine sediments saturated with water. Friction is caused by viscous move­ment that generates enough power to carry even large boulders.
10. Soil creep It is the least destructive of landslide phenomena. Creep is slow and superficial.

P.E. Kent (1966) proposed a hypothesis based on fluidisation of rock mass. He said that accumulated stress within rock particles causes compression of air in the pore spaces. This results in a fast-moving stream of debris. A. Heim (1932) held elasto-mechanical collisions responsible for landslides. His emphasis was on exchange of stresses between solid particles rather than fluids.