A landslide is defined as the movement of a mass of rock, debris, or earth down a slope. Landslides are a type of “mass wasting,” which denotes any down-slope movement of soil and rock under the direct influence of gravity.

Landslide Vulnerability Zones in India:

• Very High Vulnerability Zone: Highly unstable, relatively young mountainous areas in the Himalayas and Andaman and Nicobar, high rainfall regions with steep slopes in the Western Ghats and Nilgiris, the North-Eastern regions, along with areas that experience frequent ground- shaking due to earthquakes, etc. and areas of intense human activities, particularly those related to construction of roads, dams, etc. are included in this zone.
• High Vulnerability Zone: Areas that have almost similar conditions to those included in the very high vulnerability zone are also included in this category. The only difference between these two is the combination, intensity and frequency of the controlling factors. All the Himalayan states and the states from the North-Eastern regions except the plains of Assam are included in the high vulnerability zones.
• Moderate to Low Vulnerability Zone: Areas that receive less precipitation such as the Trans-Himalayan areas of Ladakh and Spiti (Himachal Pradesh), undulated yet stable relief and low precipitation areas in the Aravalli, rain shadow areas in the Western and Eastern Ghats and Deccan plateau also experience occasional landslides. Landslides due to mining and subsidence are most common in states like Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala.
• Other Areas: The remaining parts of India, particularly states like Rajasthan, Haryana, Uttar Pradesh, Bihar, West Bengal (except district Darjeeling), Assam (except district Karbi Anglong) and coastal regions of the southern states are safe as far as landslides are concerned.

Measures to mitigate the effect of landslides:

• Need of area-specific measures: Restriction on construction and other developmental activities such as building of roads and dams in the high vulnerability zones should be strictly enforced.
• Horizontal drain to dewater the landslide areas: A horizontal drain can be used to drain water to reduce pressure on the soil. Holes are drilled into a cut slope or embankment. They are then encased with a liner comprised of slotted-plastic or perforated-metal.
• Afforestation drive: Positive actions like promoting large-scale afforestation programmes and construction of bunds to reduce the flow of water can be taken to mitigate the impact of landslides.
• Ground anchor walls: Reaction blocks are anchored to slopes or existing retaining walls to stabilize them. The blocks are often placed in a row pattern across the slope or wall.
• Reducing pressure on vulnerable areas: Limiting agriculture to valleys and areas with moderate slopes, and control on the development of large settlements in the high vulnerability zones should be enforced.
• Measures for North-Eastern states: Terrace farming should be encouraged in the North- Eastern hill states where jhumming (slash and burn/shifting cultivation) is still prevalent.

Landslide hazard is one of the more difficult ones to address, as it involves extensive risk analysis and geotechnical investigations, in addition to risk maps. For critical infrastructure, the non structural mitigation measures for reducing consequences such as warning system, evacuation plans, and restriction of construction should be given importance along with structural mitigation measures to reduce the impact on operational activity during such a hazard.