“When a mass of earth or rock slides down the slope along a definite zone of surface, the movement is called a landslide“. This movement takes place under gravity and is facilitated by moisture which acts a lubricating agent. The landslides start with slow movement along a slip surface followed by a rapid movement of the separated portion of the earth mass.
Causes of LandSliding
The factors which promote landslides are
The essential conditions which cause landslides are lack of supports in front and lubricant behind. Thus water is an important factor in causing landslides. you can also say that water is the main reason of landsliding.
It has been observed that majority of the earth or rock failures are confined to slopes. This indicates that slopes are directly responsible for landslides. As a rule steeper the slope greater is the instability of such a mass.
iii. Nature of Rocks
Unconsolidated sediments, such as clay, sand, gravel etc. can not stand permanently along slopes greater than their angles of repose (about 35o) and are likely to be affected by landslides. Where weak and slippery rocks like shale, volcanic tuff, phyllites or mica-schista are present, they are not likely to remain stable on steep slopes for a considerable period of time
iv. Structure of Rocks
Joints, fractures, shear zones and bedding planes usually become the slip surface in case of rock slides. Landslides are particularly common on hill slopes where dip of rock beds is also in the same direction.