Landslide is rapid movement of rock, soil and vegetation down the slope under the influence of gravity. These materials may move downwards by falling, toppling, sliding, spreading or flowing. Such movements may occur gradually, but sudden sliding can also occur without warning. They often take place in conjunction with earthquakes, floods and volcanic eruptions. The extent and Intensity of landslide depends upon number of factors- Steepness of the slope, amount of vegetation cover, tectonic activity, bedding plane of the rocks etc.
Types of Landslides
- Falls: Abrupt movements of materials that become detached from steep slopes or cliffs, moving by free-fall, bouncing, and rolling.
- Creep: Slow, steady downslope movement of soil or rock
- Debris flow: Rapid mass movement in which loose soils, rocks, and organic matter combine with water to form slurry that then flows down slope. Usually associated with steep gullies
- Mudflow: Rapidly flowing mass of wet material that contains at least 50% sand-, silt-, and clay-sized particles
- Flows: General term including many types of mass movement, such as creep, debris flow, mudflow etc.
Causes of Landslides
- Geological causes: Weak, sensitive and weathered material, presence of joints and fissures, variation in physical properties such as permeability.
- Morphological causes: Tectonic or volcanic uplift, erosion due to wind and water, higher deposition of load on the slope or its crest, removal of vegetation.
- Physical causes: Intense rainfall, earthquake/volcanic eruption, rapid snow melt/freeze
- Anthropogenic causes: Excavation of the slope or its toe, deposition of load on the slope, drawdown of reservoir, deforestation, mining, irrigation and artificial vibration.
Landslide Prone areas in India
As per Geological Survey of India, about 0.42 million sq.km covering nearly 12.6% of land area of India is prone to landslide. Major landslide prone areas in India:
- Western Ghats and Konkan Hills (Tamil Nadu, Kerala, Karnataka, Goa and Maharashtra)
- Eastern Ghats (Araku region in Andhra Pradesh)
- North-East Himalayas (Darjeeling and Sikkim)
- Northwest Himalayas (Uttarakhand, Himachal Pradesh, J&K).
Himalayan mountain ranges and hilly tracts of North-Eastern region are highly susceptible to slope instability due to the immature and rugged topography, fragile rock conditions, high seismicity resulting from proximity to the plate margins, and high rainfall. Extensive anthropogenic interference, as part of developmental activities, is another significant factor.
Similarly, the Western Ghats, though located in a relatively stable domain, experiences landslides due to number of factors- steep hill slopes, high intensity rainfall and anthropogenic activities. The Nilgiris hills located at the convergence zone of the Eastern Ghats and the Western Ghats experiences a number of landslides due to high intensity and protracted rainfall.
Impact of Landslides
Short run: Loss and damage to property, loss of lives, Destruction to agricultural crops, Damages to Vegetation, Obstruction of vehicular movement leading to Traffic jam, temporary loss of livelihood for the poor people etc.
- Increase in the sediment load of the river which can lead to floods.
- Reduce the effective life of hydroelectric and multipurpose projects by adding an enormous amount of silt load to the reservoirs.
- Loss of cultivable land and infrastructure.
- Environmental impact in terms of erosion and soil loss
- Demographic impact in terms of relocation of population towards other areas.
- Frequent disruption of transportation networks leads to geographical isolation and hence perpetuates under-development.
- Challenges of responding to landslide disasters:
a) Majority of landslide prone habitations are in remote locations in hinterlands of Himalayas, North-Eastern and on Western and Eastern Ghats. Thus, it becomes a difficult for district administration and NDRF and SDRF teams to reach locations in short span.
b) Most landslides occur during rainy season when weather conditions coupled with poor visibility makes it difficult for relief operations to continue using helicopters.
NDMA Guidelines for Landslide Disaster Management
- Landslide hazard, vulnerability & risk assessment: Delineating areas susceptible to landslide hazards and to assess the resources at risk.
- Early warning systems for landslides: Continuous monitoring of movements, development of stresses and the transmission of this data at regular time intervals.
- Investigations for Landslide risk assessment: multi-disciplinary investigations of landslide risk assessment leading to formulation of Standards to mitigate impact of landslides.
Landslide Risk Mitigation and Remediation
- Restricting development in landslide-prone areas through land use planning.
- Laying down standards to be followed for excavation and construction.
- Protecting existing developments through restraining walls and rock anchors.
- Slope Stabilization measures: Generally, include works involving modification of the natural landslide conditions such as topography, geology, ground water, and other conditions that indirectly control portions of the entire landslide movement. These include drainage improvement works, soil/debris removal works etc.
- Landslide insurance and compensation for losses
Regulation & Enforcement: State governments/SDMAs will adopt the model techno-legal framework for ensuring compliance with land use zoning and landslide safety issues in all development activities and plans.
Awareness and Preparedness: Comprehensive awareness campaigns targeting different groups of people living in landslide prone areas should be conducted systematically.
Capacity Development (Including Education, Training and Documentation):
- Introduction of curriculum related to Disaster Management, including Landslides in the Schools
- Training of the Administrators to plan, respond and mitigate the impact of Landslides
- Technical institutes located in vulnerable areas should develop adequate technical expertise on the various subjects related to landslide management.
Immediate Response: Put in place Standard Operating Procedure (SoP) which should ensure coordinated and sustained action from various agencies in the aftermath of landslides
R&D: Government should encourage, promote, and support R&D activities to address current challenges, offer solutions, and develop new investigation techniques, with the application of the latest developments in remote sensing, communications, and instrumentation technologies.