The down-slope gravitational movement of a body of rock or earth as a unit owing to the failure of the material is known as a landslide. Landslide, also called landslip. It may be induced by natural agencies, e.g., heavy rain, earthquake, or it may be caused by human over-interference with the slope-stability. Earth flow, mass movement, mudflow, rotational slip, and avalanches are all examples of landslides.
Landslides are rarely on a scale comparable to seismic or volcanic events. Moreover, many of the larger landslides are slow-moving so while destructive to propert — they present little threat to life. The intensity and magnitude of the landslide, however, depends on the geological structure, angle of dip of the slope, nature of sedimentary rocks, and the human interaction with the slope.
The 5 major causes of landslide are:
Earthquakes are the most important cause of landslides in the folded mountainous areas (Himalayas, etc.). In India, landslides are more frequent in the folded mountains of the Tertiary Period. In the Kashmir Valley, an earthquake of 1905 resulted in landslides in the Lesser and the Greater Himalayas in which several thousand people lost their lives.
2 Rainfall and Snowfall
The occurrence of heavy or continuous rainfall may lead to heavy landslides in the areas of steep slopes where National Highways and roads have been constructed. The Nashri area between Batote-Ramban-Ramsu and Banihal (Jammu and Kashmir State) is frequently subjected to landslides. The landslides in this region are particularly severe during the rainy and winter seasons when the vehicular traffic is disturbed for several days. In Malin village, Pune district, 44 houses were destroyed killing nearly a hundred people and over 200 feared trapped on 30 July 2014. Environmentalists say large scale deforestation has made the are a vulnerable (Times of India, 31.7, 2014).
3. Mining Quarrying, and Road-cutting
The continuous extraction of coal, minerals, and stones from the mines and quarries and development of roads by cutting the steep slopes in the folded mountains create a conducive condition for the occurrence of landslides. Such landslides may be observed throughout the Himalayas and in the Eastern and Western Ghats.
4. Loading by Construction of Houses
Unplanned growth of towns and cities in the hilly areas without testing soil and rocks is also an important cause of landslides. The eastern slope of Nainital (Uttarakhand) is sinking because of the heavy load of hotels and residential structures.
Deforestation and other human activities also induce landslides. Most of the landslides are small involving some blocks up to a few metres across. But some are large enough to cause a catastrophe. They may bury roads, building, and other structures. The adverse effect of landslides can be reduced by checking deforestation on mountain slopes, following building codes for such areas, and by avoiding construction of buildings on steep slopes.