This term is used to the rapid down-slope movement of a mass of material that moves as a unit and carries with it all the loose material above bedrock. Sometimes great masses of bed rock are also carried with the down-slope moving material.
In landslide the movement is sudden and the velocities of the moving mass are very high. Even though landslides are rare, but they have gained notoriety for the havoc played by them.
Landslides vary in their \intensity. In certain cases only loose materials lying on the bedrock are involved, while there are larger movements that detach massive rocks.
In certain especial cases landslides are so enormous that the volumes of the sliding rocks are measured in cubic kilometers.
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Whatever is there in their path is completely destroyed. Valleys are dammed up and soon converted into lakes. On certain occasions such dams are suddenly washed out producing most calamitous floods downstream.
Major rockslides occur mainly during the rainy season because the rain water lubricates the rock-mass and they become slippery.
The following are the causative factors of landslides: (i) steep slopes; (ii) lubrication by heavy rain; (iii) rocks that become slippery when wet; (iv) earthquakes; (v) removal of support by natural causes or by man; (vi) unnatural structures; and (vii) gravity.