Landslide: Types, Causes, Impact & Remedial steps

• A landslide is the sudden downslope movement of a mass of rock, debris or earth, along with its soil and plant cover, under gravity.
• It is both a natural and a human-made hazard. Heavy rain and earthquakes set it off, and road cutting, mining and building on slopes make it more likely.
• About 0.42 million sq km of India, nearly 12.6% of its land, is prone to landslides, chiefly in the Himalaya, the north-eastern hills and the Western Ghats.

Natural Hazards and Disasters

Hazard, Disaster and Vulnerability

• A hazard is a dangerous condition or threat, natural or man-made, that can hurt or kill people or damage property, livelihoods and the environment.
• A natural hazard is the threat of a naturally occurring event that would harm people. A natural disaster is what follows when that threat actually strikes and does the harm.
  • Put simply, a hazard is a threat and a disaster is an event.
  • A disaster is a serious disruption of a society, with human, material or environmental losses beyond the society’s capacity to cope using its own resources.
• Vulnerability is how far a person, community, structure or area is likely to be damaged by a given hazard.
  • It joins physical exposure, such as nearness to a steep slope, with the social and economic ability to withstand and recover.
• A rough global estimate gives the scale of these events: every year the world endures lakhs of thunderstorms, thousands of floods, hundreds of landslides and earthquakes, and scores of cyclones and volcanic eruptions.
• In India, the law on the subject is the Disaster Management Act, 2005, amended in 2025. The national framework for disaster management rests on it.
  • The Disaster Management (Amendment) Act, 2025 received assent on 29 March 2025. It lets the national and State authorities prepare disaster plans directly, and provides for disaster databases and urban disaster management authorities.

Types of Hazards

• Hazards can be grouped by origin and process in three ways. These groupings overlap, and landslides appear in all of them.

• Epidemics are often listed with weather hazards because they follow floods and heat. Their agent, however, is biological.
• Landslides fit the socio-natural class best. Nature supplies the slope and the rain, and roads, tunnels, mines and quarries raise their frequency and their toll.

Landslides

Meaning and Nature

• A landslide moves rock, soil and vegetation down a slope. It may be set off naturally, by heavy rain or an earthquake, or by human over-interference with slope stability.
  • People break rock to build roads, railways, buildings and tunnels. This loosens the slope and invites failure.
• Mass movement or mass wasting is the wider term for all gravity-driven downslope transfer of material. Mass movement includes slow creep, while landslide is the everyday word for its rapid forms.
• Earth flow, mudflow, rotational slip and avalanches are common forms named under the landslide family.
  • The terms used for slope movements follow from the kind of material and the kind of motion.
• Landslides are usually local events, rarely on the scale of major seismic or volcanic events. Their intensity and magnitude depend on:
  • the geological structure, including joints, folds and faults;
  • the steepness of the slope and the angle of dip of the beds;
  • the nature of the sedimentary rocks and the state of weathering;
  • the vegetation cover;
  • human interaction with the slope.
• Onset: a slope may creep for a long time, but the failure itself often arrives without warning.
  • Exact prediction is hard. Zones of high risk can still be marked from geology, hydrology, vegetation and the record of past slides.
  • Landslides often combine with other hazards: earthquakes, floods and volcanic activity.

• The block diagram shows three forms side by side:
  • Slump: a rotational slide along a curved glide plane, with a scarp at the head, backward-rotated blocks and a bulging toe.
  • Rock fall: rock dropping from a cliff to collect as talus.
  • Debris flow: a wet mass running down a chute and spreading at its toe, where it can pond water.

Landslide Dam

• When a slide on a valley wall reaches the valley floor, it can partly or wholly block the river channel. This accumulated debris, holding back the river, is called a landslide dam.
• The hazard comes in two stages. Upstream land is drowned by the rising lake, and downstream land is flooded when the weak dam gives way.
  • Gohna Lake (1893–94): a slide in September 1893 dammed the Birahi Ganga, a tributary of the Alaknanda. The dam partly failed in August 1894.
    • Engineers had watched the lake and run a telegraph line down the valley, so villagers could be moved in time.
  • In the Brahmaputra basin, rock falls can dam a river briefly and then release a flood.

Types of Landslides

• The standard scheme was set out by David J. Varnes (1978) and revised by David M. Cruden and David J. Varnes (1996) and by Oldrich Hungr, Serge Leroueil and Luciano Picarelli (2014).
  • It sorts movement by type of motion and type of material: rock, debris (mostly coarse) or earth (mostly fine).

Causes of Landslides

• The major causes are grouped below, with Indian examples.
• Rainfall and snowfall:
  • Heavy or continuous rain saturates the slope, adds weight and lubricates the failure surface. This is most damaging on steep slopes where National Highways and other roads have been cut.
  • The overbearing weight of snow, ice and seeped water on soft, permeable rock leads to slipping. Freezing and thawing break rock so that it rolls downhill.
  • The Nashri area, between Batote, Ramban, Ramsu and Banihal in Jammu and Kashmir, slides often. It is worst in the rainy and winter seasons, when traffic can be held up for several days.
  • The Wayanad disaster of 2024 followed extreme rain on a steep headwater slope.
• Earthquakes and volcanic eruptions:
  • Earthquakes are a leading trigger in folded mountain areas. In India, landslides are more frequent in the fold mountains of the Tertiary Period, above all the Himalaya.
    • The Kangra earthquake of 4 April 1905, also felt in the Kashmir valley, set off landslides in the Lesser and Greater Himalaya and took thousands of lives.
    • The Uttarkashi earthquake of 1991 cracked Varunavat Parvat. These cracks fed the slides that hit Uttarkashi town in 2003.
  • Volcanic eruptions also trigger landslides in mountainous regions.
• Mining, quarrying and road cutting:
  • Continuous extraction of coal, minerals and stone, and roads cut across steep slopes in the fold mountains, create conditions for failure.
  • Such landslides occur throughout the Himalaya and in the Eastern and Western Ghats.
  • Road building alone is costly. One estimate puts the debris from each kilometre of mountain road at 40,000–80,000 cubic metres. It slides downhill, kills vegetation and chokes streams.
• Loading by construction of houses:
  • Unplanned growth of hill towns, without testing soil and rock, is an important cause.
  • Nainital (Uttarakhand) is the classic case. Its eastern slope is described as sinking under the load of hotels and houses, and the town has a long record of slope failure, from Sher Ka Danda in 1880 to the Balia Nala slide on its southern edge.
  • Joshimath (Uttarakhand) saw land subsidence and cracks in hundreds of buildings in January 2023.
• Deforestation:
  • Clearing trees removes the roots that bind the soil, and so destabilises the slope.
  • Most slides are small, with blocks up to a few metres across. Some are large enough to be catastrophic, burying roads, buildings and other structures.
• Other natural causes: rivers oversteepen a slope by cutting at its base. Near the sea, as on the Kanara coast, waves undercut the cliffs until the overhanging rock falls.
• Causes can also be sorted into four groups:

Impact of Landslides

• Effects are severe but local. They spread far only when a river or a main road is cut.

• Floods: blocked rivers cause flash floods, a frequent event in the upper Ganga and Brahmaputra courses.
  • Rain, landslides and floods are closely tied in the mountains. The combined flood hazard can reach far downstream.
• Casualties depend on place and time. The toll is heaviest where dense settlement lies down the slope.
• Elements at risk: houses perched on steep ground or at the foot of a slope, and those where a hill stream reaches the valley; buildings without suitable foundations; roads, communication lines and buried utilities.
• Hill farming and livelihoods: in Uttarakhand, a central team reporting on the landslides of 1998 described several effects:
  • terraced fields destroyed beyond repair;
  • water channels breached and choked, cutting off irrigation;
  • roads closed for long spells, cutting villages off from supplies;
  • some villages left unfit for habitation.
• Notable events:

• Wayanad, 30 July 2024: the Minister of State for Home told Parliament on 1 April 2025 that 298 people had died, on the count reported by the Kerala government.
  • The Centre classed it as a calamity of severe nature in December 2024.
• Dharali, Uttarkashi, 5 August 2025: a sudden debris-laden flood down the Kheer Gad buried much of the village. The district administration’s count on 13 August was one confirmed dead and 68 missing.
  • Its cause was disputed. The first official reports spoke of a cloudburst, while geologists pointed to a slide or a blocked valley. The State ordered a technical inquiry.

Vulnerability Profile of India

• Extent: older official accounts say the hazard affects at least 15% of the land area, about 0.49 million sq km.
  • The Geological Survey of India figure, used in the national strategy of 2019, is about 0.42 million sq km or 12.6%, leaving out snow-covered areas.

• Where they occur:
  • Geodynamically active belts: the Himalaya and the Arakan–Yoma belt of the North-East.
  • Relatively stable areas: the Meghalaya Plateau, Western Ghats and Nilgiri Hills.
• The Nilgiri Hills, where the Eastern and Western Ghats converge, carry innumerable slide scars. They receive intense, protracted rain, and their overburden is sensitive to over-saturation.
• Vulnerability zones recognised in India:

• Zonation mapping: maps of prone ground have served India since the 1980s.
• National Landslide Susceptibility Mapping Programme: begun by the Geological Survey of India in 2014–15. It covered about 4.3 lakh sq km at 1:50,000 (Lok Sabha, July 2024), grading ground as high, moderate or low.
  • The Survey has since moved to 1:10,000 and 1:5,000 mapping of 200 critical sectors (Lok Sabha reply, PIB, 20 August 2025).
• Landslide Atlas of India: a document giving details of landslides in the landslide provinces, including damage assessment of specific sites. It was prepared by the National Remote Sensing Centre (NRSC) of the Indian Space Research Organisation (ISRO) and released in 2023.
  • It maps about 80,000 landslides, 1998–2022, and ranks 147 districts in 17 States and 2 Union Territories by exposure.
  • Rudraprayag ranks first for exposure, followed by Tehri Garhwal. Mizoram (12,385) and Uttarakhand (11,219) record the most slides.

Mitigating the Risk

Landslides Mitigation Strategy

• Identify and manage: hazard zones must be identified and specific slides stabilised and managed, with monitoring and early warning at selected sites.
• Hazard mapping locates ground commonly prone to failure, so that settlements can avoid it. Measures should always be area-specific.
• Land-use control: restrict construction and other development such as roads and dams; limit agriculture to valleys and moderate slopes; and control large settlements in high-vulnerability zones.
  • Denuded slopes should be replanted with suitable species, and natural drainage must not be blocked by roads, buildings and canals.
• Retaining walls: relatively rigid walls that support soil laterally, so it stays at different levels on the two sides. They are built along roads and on the Konkan railway line.
• Surface drainage works: these check movement by keeping out rain water and spring flow.
• Engineered structures: strong foundations help buildings resist ground movement. Pipes and cables should be flexible enough to move with it.
• Vegetation: raising tree cover is the cheapest and among the most effective measures. It binds the topsoil to the layers below and cuts run-off and soil erosion, so checking deforestation on mountain slopes matters most.
• Building rules: follow building codes for such areas and avoid construction on steep slopes.
• NDMA Guidelines for Landslides rest on nine pillars:
  • Landslide hazard, vulnerability and risk assessment
  • Multi-hazard conceptualisation
  • Landslide remediation practice
  • Research and development, monitoring and early warning
  • Knowledge network and management
  • Capacity building and training
  • Public awareness and education
  • Emergency preparedness and response
  • Regulation and enforcement

What Measures Should Be Taken

• Resilience building: develop resilience against geo-hazards arising from natural processes, environmental degradation and human activity. This calls for a network of sensors for real-time monitoring and data collection.
• Technology for monitoring:
  • Web-based sensors: rain gauges, piezometers, inclinometers, extensometers, InSAR (Interferometric Synthetic Aperture Radar) and total stations, placed first in dense and built-up zones.
  • Integrated Early Warning System (EWS): artificial intelligence and machine learning (AI, ML) could predict hazards and give communities time to act.
    • The Geological Survey built a regional prototype under the LANDSLIP project and has given operational forecasts since the 2025 monsoon, through its National Landslide Forecasting Centre at Kolkata.
• A Himalayan States Council has been proposed: a common platform for the disaster authorities of the Himalayan States, to pool knowledge, experience and resources. It would work on:
  • Simulation and hazard assessment: modelling scenarios from natural processes, environmental degradation, climate and human activity.
  • Knowledge dissemination: sharing findings across States, since the region is diverse and varied.
  • Ecosystem protection: promoting sustainable practice and responsible resource use.
• Sustainable socio-economic development: the region’s glaciers, springs, minerals, energy sources and medicinal plants offer real potential, which must be balanced against ecological preservation.
• Environmental considerations: town planning suited to mountain terrain, with limits on heavy construction, effective drainage, scientific slope cutting and retaining walls.
• Building codes and assessment: high-resolution mapping of towns and their load-bearing capacity should underpin codes, where slides and earthquakes are both likely.
• Sustainable tourism: this can reduce pressure through environmental awareness, conservation and respect for biodiversity and ecosystems.
  • It can also give local communities income and social benefits, which raises their capacity to cope with hazards.
• Sustainable government projects: environmental assessment, eco-friendly technology, involvement of local communities, wider stakeholder awareness and coordination among government sectors.

Initiatives Taken by the Government

• Allocation under the NLRM Project: Rs 378 crore for eight north-eastern States; Rs 139 crore each for Uttarakhand and Himachal Pradesh; Rs 100 crore for Maharashtra; Rs 72 crore each for Karnataka and Kerala; Rs 50 crore each for Tamil Nadu and West Bengal.

Snow Avalanches

• An avalanche is a mass of snow, often with ice and rock, hurtling down a mountain slope. By material, avalanches are snow, debris or rock types.
• Causes: fresh snow slipping off older snow in winter; partly thawed snow rolling down in spring; and glacier edges breaking off.
• Prone areas: the snowy Western Himalaya.
  • Jammu and Kashmir and Ladakh: higher reaches of the Kashmir and Gurez valleys, Kargil, Ladakh and some main roads.
  • Himachal Pradesh: Chamba, Kullu–Spiti and Kinnaur.
  • Uttarakhand: parts of Tehri Garhwal and Chamoli.
• Effects: damaged and blocked roads, overturned retaining walls, and wrecked structures in the path.
  • Mana, Chamoli, 28 February 2025: an avalanche struck a road workers’ camp. The Lok Sabha was told that eight died and 46 were rescued.
• Hazard zones are marked in three colours:

• Control measures are of two kinds:
  • Hardware (structures):
    • Prevention: avalanche forest, stepped terraces, control piles and fences, suspended fences, and structures that stop snow cornices.
    • Protection: fences, retaining walls, deflecting structures, snow sheds over roads, and earth mounds and piles that slow the flow.
  • Software:
    • Prediction and forecasting, with evacuation guidance. The Defence Geoinformatics Research Establishment issues danger-level warnings.
    • Clearing dangerous snow on hazardous slopes by blasting or labour.
• Past events in the National Centre for Disaster Management manual (2001): Himachal Pradesh, March 1978 (30 dead); Lahaul and Spiti, March 1979 (237); Jammu and Kashmir, December 1982 (100) and March 1988 (70); Ladakh, December 1984 (27 soldiers).
  • Road blockage recurs too: the Tinku avalanche in Himachal Pradesh blocked a road for 40 days in 1991.