Landslide is a collective term used to describe various types of movement of the slope forming materials i.e. rock, earth, artificial materials or a combination of these materials. It can be delineated as “downward movement in the slope under the influence of gravity with a velocity ranging from very slow to very rapid”.  Landslides are not an isolated phenomenon, they can occur virtually anywhere. Orthodox philosophy about landslide was that it only occurs in steep slopes but with passage of time and research it has been noticed that it can influence gentle slope too. One can experience this hazard on land as well as under the water. About 12% Indian land is prone to landslides . Recently, there was landslide in Uttarakhand's Chamoli district where a part of mountain collapses after heavy rains.

Causes of landslides

• It occurs when the consequence of a complex field of forces (stress is a force per unit area) active on a mass of rock or soil on the slope. It happens due to geological causes, morphological causes, physical causes and human causes. There are two parameters that determine the landslides are as follows:

1. 1. Increase of shear stress: It happen due to the removal of lateral and underlying support; increase of lateral forces as well as load; transitory stresses like blasting, earthquakes etc.; and geological movement.
   2. Decrease of material strength: It happens due to the weathering, pore water pressure and changes in structure.

• The incidents of landslides increasing day by day due to the over urbanisation, massive deforestation, construction and development work in landslide prone areas.
• Slope instability due to removal of lateral and underlying support.
• Indiscriminate chopping down of trees.
• Slash and burn cultivation practices in hills
• Road construction and mining activities.
• With increasing population pressure, there is an increase in grazing activities, urbanization which reduces dense natural evergreen forest cover.
• Due to these activities the ecological balance is disrupted, thereby resulting in loosening of the soil.
• Under conditions of heavy rain, there is increased and substantial soil erosion and frequent landslides.

Impact of landslide

• Lead to economic decline: Landslides have been verified to result in destruction of property. If the landslide is significant, it could drain the economy of the region or country. After a landslide, the area affected normally undergoes rehabilitation. This rehabilitation involves massive capital outlay.
• Decimation of infrastructure: The force flow of mud, debris, and rocks as a result of a landslide can cause serious damage to property. Infrastructure such as roads, railways, leisure destinations, buildings and communication systems can be decimated by a single landslide.
• Loss of life: Communities living at the foot of hills and mountains are at a greater risk of death by landslides. A substantial landslide carries along huge rocks, heavy debris and heavy soil with it. This kind of landslide has the capacity to kills lots of people on impact.
• Affects beauty of landscapes: The erosion left behind by landslides leaves behind rugged landscapes that are unsightly. The pile of soil, rock and debris downhill can cover land utilized by the community for agricultural or social purposes.
• Impacts river ecosystems: The soil, debris, and rock sliding downhill can find way into rivers and block their natural flow. Many river habitats like fish can die due to interference of natural flow of water. Communities depending on the river water for household activities and irrigation will suffer if flow of water is blocked.

Landslide in different parts of India

• The Northern Himalyan region is badly affected by landslide problems of a bewildering variety. Landslides in the Darjeeling district of West Bengal as also those in Sikkim, Uttarakhand, Himachal Praesh, Mizoram, Tripura, Meghalaya, Assam, Nagaland and Arunachal Pradesh pose chronic problems, causing recurring economic losses worth billions of rupees.
• A different variety of landslides, characterized by a lateritic cap, pose constant threat to the Western Ghats in the South, along the steep slopes overlooking the Konkan coast besides Nilgiris, which is highly landslide prone.
• Some spectacular events of tragedies are reported as Varnavat landslide, Uttarkashi District, Malpha landslide Pithoragarh district, Okhimath landslide in Chamoli district, UK and Paglajhora in Darjeeling district as well as Sikkim, Aizawl sports complex, Mizoram. These are some of the more recent examples of landslides.

National Landslide Risk Management Strategy and its component

• It was decided that NDMA will constitute a Task Force of experts for formulation of National Landslide Risk Management Strategy. The concept was widely discussed in NDMA and a Task Force comprising of six Sub-Groups was constituted to formulate important documents related to the strategy on 17th June 2016.
• The strategy document clearly brings out the message for the need to strengthen and mainstream landslide disaster preparedness, mitigation, response and relief mechanism through mapping, early warning system (EWS), awareness generation, capacity building, formulation of mountain zone regulations / policies and mitigation of problematic landslides.
• Landslide Hazard Zonation - It covers aspects of reliability and validation of landslide zoning maps in Indian scenario and proposes future plan of activities for landslide zoning.
• Landslide Monitoring and Early Warning System - The strategy document highlights the past work,best practices and present status in the field of Landslide Early Warning System (LEWS), rainfall threshold based modelling, ground based wireless instrumentation and real time monitoring system for landslide prediction, earthquake triggered landslide, monitoring mechanism of landslides and gap areas in landslide monitoring and development of early warning system.
• Awareness Programmes - The strategy spells out need of awareness programmes, review of past work and best practices, identification of gaps, as well as recommendations and implementation strategies.
• Capacity Building and Training of Stakeholders – Strategy document highlights the past work, gaps, implementation strategy, financial implications and monitoring mechanism for capacity building and training in landslides.
• Preparation of Mountain Zone Regulations and Policies - The strategy describes the formulation of land-use policies and techno legal regime, updation and enforcement of building regulations, review and revision of BIS code, guidelines for landslide management and proposed amendment in town and country planning legislations.

Conclusion:

Protection of life and properties from landslide disaster is indispensable in creating a safe environment for the society. The national imperative towards safety due to landslide initiation is increasing in view of the higher rate of human settlement in the mountain slope across the country. Landslides are significant amongst those hazards that can be disastrous to human life and property. It is estimated that economic loss due to landslides may reach between 1-2% of the gross national product in many developing countries. Evaluating and mitigating the landslide hazard and risk is a major challenge for the technocrats and decision makers in India and in other developing world as 80% of the reported fatalities due to landslide is within the developing countries.