Landslides

A landslides is the downward movement of rock, soil, debris or earth material along a slope under the influence of gravity. It may occur suddenly or slowly, depending on slope condition, rainfall, geological structure, vegetation cover and human interference.

• Landslides are not only geological events. They are also linked with climate, land use, infrastructure planning, deforestation, river erosion and disaster governance. In India, they are a recurring hazard in the Himalayas, North-East, Western Ghats and parts of the Eastern Ghats
• Landslides occur when the driving force acting on a slope becomes greater than the resisting force. The resisting force is provided by soil strength, vegetation roots, rock structure and slope stability. When rainfall, earthquakes, road-cutting, river erosion or construction weakens the slope, failure takes place.
• They are often described as secondary disasters because they may be triggered by heavy rainfall, earthquakes, cloudbursts, glacial lake outburst floods, river erosion or human disturbance.

Major Types

Falls

Falls occur when rocks or debris detach from steep slopes or cliffs and fall freely. They are common along road-cut slopes, mountain highways and unstable rocky terrain.

Slides

Slides involve the movement of soil or rock along a defined surface. They may be rotational, where the movement occurs along a curved surface, or translational, where material moves along a relatively flat plane.

Flows

Flows occur when water-saturated soil, mud or debris moves like a fluid. Debris flows and mudflows are especially dangerous because they move rapidly and can bury settlements, roads and agricultural land.

Creep

Creep is the slow, gradual movement of soil downslope. It may not appear dramatic initially, but over time it can damage roads, buildings, retaining walls and pipelines.

Complex Landslides

Many major landslides involve a combination of fall, slide and flow. Himalayan and Western Ghats landslides often become complex because of heavy rainfall, steep slopes, fractured rocks and human disturbance

Causes of Landslides

• Heavy Rainfall: Intense or prolonged rainfall saturates soil, increases pore-water pressure and weakens slope stability. Example: In the 2024 Wayanad landslides, heavy rainfall saturated hill slopes and triggered massive debris movement.
  
• Earthquakes: Seismic shaking disturbs weak slopes and loosens fractured rocks and soil. Example: The 2015 Nepal earthquake triggered thousands of landslides across the Himalayan region.
  
• River Erosion: Fast-flowing rivers cut the base of slopes, removing support and making the upper slope collapse. Example: In Uttarakhand, rivers like Alaknanda and Bhagirathi often erode valley slopes, causing landslides along roads and settlements.
  
• Weak Geological Structure: Fractured rocks, loose soil, fault lines and steep slopes naturally increase slope failure risk. Example: The Darjeeling-Sikkim Himalayas face frequent landslides due to fragile geology and steep terrain.
  
• Snowmelt and Glacial Activity: Rapid snowmelt or glacial lake outburst floods saturate slopes and trigger debris movement. Example: The 2021 Chamoli disaster in Uttarakhand involved sudden high-mountain mass movement linked with rock-ice and glacial processes.
  
• Unscientific Road Construction: Hill cutting without retaining walls, slope stabilisation and drainage weakens slopes. Example: Landslides along the Char Dham road corridor in Uttarakhand are often linked with road widening and slope cutting.
  
• Deforestation: Removal of trees reduces root binding, increases runoff and makes soil loose. Example: In Kerala’s Western Ghats, loss of natural vegetation has increased slope instability in several hill areas.
  
• Unregulated Construction: Buildings, hotels and houses on unstable slopes add extra load and disturb natural drainage. Example: Joshimath in Uttarakhand witnessed land subsidence and slope instability linked with fragile geology, construction pressure and drainage issues.
  
• Mining and Quarrying: Blasting, excavation and removal of slope material weaken rock structure and create loose debris. Example: Quarrying in Kerala’s Western Ghats has been repeatedly associated with landslide vulnerability.
  
• Hydropower and Tunnelling Projects: Tunnelling, blasting, dam construction and muck dumping disturb fragile slopes and drainage channels. Example: Hydropower zones in Uttarakhand have seen repeated concerns over slope failures in fragile Himalayan terrain.
  
• Poor Drainage: Blocked drains, leaking pipes or badly designed drainage allow water to collect inside slopes, weakening soil. Example: Hill towns like Shimla and Darjeeling face monsoon landslide risks due to poor drainage and unplanned construction.
  
• Slope Agriculture: Terracing, over-irrigation and removal of natural vegetation on hill slopes disturb soil stability. Example: Parts of North-East India with jhum cultivation face erosion and local landslide risk.
  
• Tourism Pressure and Urbanisation: Hotels, roads, parking areas and commercial buildings overload fragile hill slopes and block drainage. Example: Manali, Mussoorie, Gangtok and Nainital face increasing landslide vulnerability due to tourism-driven construction.
  

Landslide-Prone Areas in India

India’s landslide vulnerability is concentrated mainly in:

• North-Western Himalayas: Jammu and Kashmir, Ladakh, Himachal Pradesh, Uttarakhand
• Eastern Himalayas: Sikkim, Darjeeling region of West Bengal
• North-East India: Arunachal Pradesh, Assam, Meghalaya, Nagaland, Manipur, Mizoram, Tripura
• Western Ghats: Kerala, Karnataka, Tamil Nadu, Maharashtra and Goa
• Eastern Ghats: parts of Andhra Pradesh, Odisha and Tamil Nadu

The Geological Survey of India estimates that around 0.42 million sq km, or about 12.6% of India’s land area, is prone to landslides. This includes the Himalayas, North-East and Ghats regions.

The NDMA notes that landslides are a chronic problem in Darjeeling, Sikkim and the North-Eastern states, while the Western Ghats and Nilgiris also face serious slope instability, especially along steep slopes and lateritic formations.

Landslide Atlas and Mapping

The Landslide Atlas of India, prepared by NRSC/ISRO, is an important national-level database. It contains a geospatial inventory of around 80,000 landslides mapped during the period 1998–2022. It covers landslide-vulnerable regions in 17 states and 2 Union Territories, mainly in the Himalayas and Western Ghats.

The atlas ranked 147 districts based on their exposure to landslides using socio-economic parameters. This is important because landslide risk is not determined only by physical hazard; it also depends on population, infrastructure and economic exposure.

The NDMA also hosts the National Landslide Hazard Atlas of India, which is used for hazard awareness, planning and risk reduction.

Disaster Management Framework

Hazard Zonation

Landslide-prone areas must be mapped according to hazard intensity. Scientific zonation helps identify safe and unsafe areas for housing, roads, schools, hospitals and other infrastructure.

Monitoring and Early Warning

Rainfall thresholds, ground movement sensors, satellite monitoring, drones and community reporting can help provide warnings. However, early warning systems for landslides are more difficult than for cyclones because landslides are highly localised.

Land-Use Regulation

Construction should be restricted in high-risk zones. Hill towns need slope-sensitive planning, carrying-capacity studies and strict building regulation.

Engineering Measures

Important structural measures include:

• retaining walls
• rock bolting
• slope terracing
• drainage channels
• check dams
• debris barriers
• bioengineering
• controlled blasting
• safe muck disposal

Engineering works must be based on geological investigation, not only immediate repair.

Eco-Restoration

Afforestation, grass cover, slope vegetation, watershed treatment and protection of natural drainage reduce erosion and improve slope stability.

Community Preparedness

Local people are often the first responders. Community awareness, evacuation routes, warning protocols and village-level disaster plans are essential in hill regions.

NDMA Approach

NDMA’s landslide management framework emphasises a shift from ad hoc response to systematic risk reduction. Earlier, landslide management was often limited to debris removal and temporary restoration of roads. NDMA guidelines call for a more scientific approach based on hazard assessment, vulnerability analysis, monitoring, early warning, regulation, capacity building and long-term mitigation.

The Landslide Risk Management Strategy, 2019 focuses on hazard mapping, monitoring and early warning, awareness, capacity building, research and risk reduction planning.

Key Concerns

• Development projects often proceed without adequate slope-stability assessment.
• Road widening in hill areas frequently ignores drainage and muck-disposal norms.
• Hill towns are expanding beyond their ecological carrying capacity.
• Landslide data is still fragmented across agencies.
• Early warning systems are limited and not uniformly operational.
• Local bodies often lack technical capacity for hill-area planning.
• Post-disaster reconstruction often restores damaged infrastructure without reducing future risk.
• Climate change is increasing rainfall variability and extreme events.

Way Forward

• Landslide management must move from relief-centric response to risk-sensitive development. Mountain infrastructure should be planned with proper geological investigation, slope treatment, drainage design and environmental safeguards.
• Hill-area land-use planning must become stricter. Construction in unstable zones, river erosion zones and steep slopes should be regulated. Carrying-capacity studies should guide tourism and urban expansion in Himalayan and Western Ghats towns.
• Detailed landslide susceptibility mapping should be integrated into district planning, road alignment, hydropower approvals and urban development. GSI’s meso-scale mapping and ISRO’s Landslide Atlas should be used actively by state governments and local bodies.
• Nature-based solutions must be combined with engineering solutions. Slope vegetation, watershed management and restoration of natural drainage are as important as retaining walls and rock bolts.
• Community-based preparedness is essential because landslides often occur suddenly. Local warning systems, evacuation drills, village disaster plans and school-level awareness can reduce casualties.
• Post-disaster recovery should follow the principle of build back better, where damaged roads, houses and public infrastructure are reconstructed in safer locations or with improved resilience.

Conclusion

Landslides are not merely natural accidents. They are the result of the interaction between fragile terrain, intense rainfall, geological instability and human interference. In India, the rising frequency of landslide disasters shows the need for scientific planning in hill regions.

A sustainable approach must combine hazard mapping, early warning, slope-sensitive infrastructure, ecological restoration, strict land-use regulation and community preparedness. In fragile mountain ecosystems, disaster management cannot be separated from development planning.