Landslides are simply defined as the mass movement of rock, debris or earth down a slope and have come to include a broad range of motions whereby falling, sliding and flowing under the influence of gravity dislodges earth material. They often take place in conjunction with earthquakes, floods and volcanoes. At times, prolonged rainfall causing heavy block the flow or river for quite some time. The formation of river blocks can cause havoc to the settlements downstream on it’s bursting.

In the hilly terrain of India including the Himalayas, landslides have been a major and widely spread natural disaster the often strike life and property and occupy a position of major concern

One of the worst tragedies took place at Malpa Uttarkhand (UP) on 11th and 17th August 1998 when nearly 380 people were killed when massive landslides washed away the entire village. This included 60 pilgrims going to Lake Mansarovar in Tibet. Consequently various land reform measures have been initiated as mitigation measures.

The two regions most vulnerable to landslides are the Himalayas and the Western Ghats. The Himalayas mountain belt comprise of tectonically unstable younger geological formations subjected to severe seismic activity. The Western Ghats and nilgiris are geologically stable but have uplifted plateau margins influenced by neo- tectonic activity. Compared to Western Ghats region, the slides in the Himalayas region are huge and massive and in most cases the overburden along with the underlying litho logy is displaced during sliding particularly due to the seismic factor.

Incidences of Landslides in India

Region	Incidences of Landslides
Himalayas	High to very high
North-eastern Hills	High
Western Ghats and the Nilgiris	Modern to high
Cattle lost	Low
Vindhayachal	Low

Landslides Zonation Mopping is a modern method to identify landslides prone areas and has been in use in India since 1980s

The major parameters that call for evaluation are as follows:

•	Slope-Magnitude, length and Direction
•	Soil thickness
•	Relative relief
•	Land use
•	Drainage- pattern and density
•	Landslide affected population

Causes of Landslides

Landslides can be caused by poor ground conditions, geomorphic phenomena, and natural physical forces and quite often due to heavy spells of rainfall coupled with impeded drainage.

A Checklist of Causes of Landslides Ground Causes

•	Weak, sensitivity, or weathered materials
•	Adverse ground structure (joints, fissures etc.)
•	Physical property variation (permeability, plasticity etc)

Morphological Causes

•	Ground uplift (volcanic, tectonic etc)
•	Erosion (wind, water)
•	Scour4. Deposition loading in the slope crest5. Vegetation removal (by forest fire, drought etc)

Physical Causes

•	Prolonged precipitation
•	Rapid draw- down
•	Earthquake
•	Volcanic eruption
•	Thawing
•	Shrink and swell
•	Artesian pressure

Settlement policy Drawing upon the kerala study in parts of Western Ghats (referred to earlier), it has been felt that while permanent settlement should be avoided in high-risk zones, site selection even in moderately safe zones, especially in plateau edge regions should be made with caution. Diversion of stream channels in upper slopes, especially above settlement should strictly disallow. Adequate provision should made to ensure drainage of storm water away from the high sloping terrain so as to reduce over saturation, Any contour bounding, or terracing adopted for seasonal cultivation or initiation of plantations in slopes of >16o above settlement should have sufficient provision for storm water drainage. Further, in such areas the existing natural drainage channels and hallows are to be meticulously maintained without any attempt at blocking, division or modification.