Landslide

Topic: Natural Hazards and Disaster Management in India · NCERT: Class 6, Ch 3 "Landforms and Life"; Class 7, Ch 3 "Climates of India"; Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 6 "Natural Hazards and Disasters: Causes, Consequences and Management"; Class 11, Ch 5 "Geomorphic Processes"

Meaning

A landslide is the fast movement of a large mass of rock, soil and debris down a slope, pulled by gravity. The mass breaks away along a failure plane (also called a shear plane), which is a weak surface between the moving mass and the firm ground below it.

Landslides look less dramatic than earthquakes, but they cause serious damage to the environment and the economy of hill areas. They are hard to predict because they depend on local conditions that change from one hillside to the next.

Explanation

How a landslide happens (cause → process → result)

• Heavy, continuous rain
• Water soaks into the soil and rock, so the slope gets heavier.
• The water also reduces the friction that holds grains and rock blocks together.

• The slope fails and the mass slides down.

• Earthquakes and volcanic shaking

• Shaking loosens rock on a slope.

• Areas hit by an earthquake stay unstable for years afterwards.

• Steep slopes and loose rock

• On a steep slope, gravity pulls harder along the surface.

• Unconsolidated rock (loose rock that is not packed together) gives way easily.

• Human causes: deforestation, mining, road building, unplanned building on hillsides and poor drainage.

• Cutting into a slope for a road removes the support at its foot (the toe).
• Water from blocked drains seeps into the slope.
• The weakened slope fails.

Why it is hard to predict

• Local factors control landslides: geology (rock type), geomorphic agents (running water, ice and wind that shape the land), slope steepness, land use, vegetation cover and human activity.
• These factors change over short distances, so monitoring is slow and costly.
• Landslides are one kind of mass movement (any movement of rock and soil down a slope under gravity). Other kinds include rock falls and debris flows.
• Debris flow: mud, boulders and uprooted trees mix with water and rush down stream valleys like a river of debris. This is what happened at Wayanad in 2024.

Why the Himalaya and the Western Ghats slide

Feature	Himalaya	Western Ghats and Nilgiris
Age and stability	Young fold mountains that are still rising and tectonically active (plates still move beneath them)	Old, stable block of the Peninsular plateau
Rock	Sedimentary and unconsolidated rocks that break easily	Hard crystalline rocks
Main triggers	Steep slopes, earthquakes, monsoon rain, road and dam building	Steep cliffs on the western face, very intense monsoon rain
Weathering	Freezing and thawing at height, plus erosion	Mechanical weathering from temperature change: rock heats by day, cools by night, then cracks and breaks apart
Result	Very frequent landslides	Landslides even though the rock is hard

Consequences and mitigation

• Consequences
• Roads and railways stay blocked for long periods.
• Rock falls damage houses, crops, and power and communication lines.
• River damming: debris blocks a river and a temporary lake forms behind it. When this natural dam bursts or the river changes course, floods follow downstream.

• Spatial interaction (travel and trade between places) becomes costly, which slows development in hill areas.

• Mitigation (steps to reduce how often landslides happen or how much harm they do; they must suit each area)

• Restrict roads, large dams and big settlements in high-vulnerability zones.
• Keep farming to valleys and gentle slopes.
• Carry out afforestation (planting forests on a large scale).
• Build bunds (low banks of earth or stone) to slow water flowing down the slope.
• In the north-east, use terrace farming in place of jhum. Jhum is shifting cultivation: farmers slash and burn forest, farm for a few years, then move on, leaving slopes bare. Terraces are flat steps cut into the hillside that slow runoff and hold the soil.

Where it occurs

• National extent: about 0.42 million sq km, or 12.6% of India's land area (not counting snow-covered areas), is landslide-prone (GSI) [2].
• Vulnerability zones (NCERT, Figure 6.9)

Zone	Areas
Very high	Young, unstable Himalaya; Andaman and Nicobar Islands; high-rainfall, steep Western Ghats and Nilgiris; the north-eastern region; areas often shaken by earthquakes; areas with heavy road and dam building
High	Same conditions but less severe. Covers all Himalayan states and north-eastern states, except the Assam plains
Moderate to low	Low-rainfall Trans-Himalayan Ladakh and Spiti (Himachal Pradesh); the Aravalis; rain-shadow parts of the Western and Eastern Ghats and the Deccan plateau (a rain shadow is the dry side of a mountain, away from the moist wind); mining and subsidence areas of Jharkhand, Odisha, Chhattisgarh, Madhya Pradesh, Maharashtra, Andhra Pradesh, Karnataka, Tamil Nadu, Goa and Kerala
Largely safe	Rajasthan, Haryana, Uttar Pradesh, Bihar, West Bengal (except Darjiling), Assam (except Karbi Anglong), and the southern coastal plains

• Repeat trouble spots: the road to Srinagar (Jammu and Kashmir) is often blocked by landslides. Rock falls keep hitting the Konkan Railway along the Western Ghats coast.
• Malpa landslide, 18 August 1998: Kali river valley, Pithoragarh district, Uttarakhand, where the Kali forms the India–Nepal border. About 220 people died, including Kailash Mansarovar Yatra pilgrims. Steep valley walls, weak rock and heavy monsoon rain caused the rockfall and debris that buried the village.
• Wayanad landslides, 30 July 2024: Mundakkai, Chooralmala and Punchirimattom villages in Wayanad district, Kerala, on the Western Ghats.
• These were debris flows, set off by extreme rain on soil already soaked by weeks of monsoon.
• Over 200 people died.

• The Centre told Parliament it had sent early warnings to Kerala on 23, 24 and 25 July 2024. On 26 July it warned of more than 20 cm of rain and possible deadly landslides [5].

• Mapping and warning systems

• National Landslide Susceptibility Mapping (NLSM), run by GSI, maps all landslide-prone hill areas at 1:50,000 scale. Landslide susceptibility means how likely an area is to slide. It covers the Himalaya, the Tertiary belt of north-east India (young, soft rocks) and the Western Ghats. That is parts of 19 states/UTs, about 4.3 lakh sq km, with 33,904 landslides checked on the ground [6].
• National Landslide Forecasting Centre (NLFC), run by GSI, was inaugurated on 19 July 2024. It warns of rain-triggered landslides using rainfall thresholds (the amount of rain beyond which slopes usually fail), Numerical Weather Prediction models (computer weather forecasts) and observed rainfall [6].
• Landslide Atlas of India by NRSC (ISRO) was released on 18 March 2023. It is an inventory of about 80,000 landslides (1998–2022) covering 17 states and 2 UTs and ranking 147 districts [3]. It used Resourcesat, Cartosat, Sentinel and other satellite images [3]. Rudraprayag (Uttarakhand) is the most exposed district, followed by Tehri Garhwal. Mizoram and Uttarakhand are among the most affected states.

Don't confuse with

• Land subsidence: the ground sinks downward in place, for example over mined coalfields at Jharia (Jharkhand), or at Joshimath (Chamoli, 2023). A landslide moves down a slope along a failure plane.
• Soil creep: a very slow, often unseen downhill movement of soil. A landslide is rapid.
• Avalanche: a mass of snow and ice sliding down a slope. A landslide is mainly rock, soil and debris.
• NLSM vs Landslide Atlas: the NLSM and the NLFC belong to GSI [6]. The Landslide Atlas of India was made by NRSC (ISRO) [3].

Prelims Hooks

• About 12.6% of India's land area (about 0.42 million sq km, not counting snow-covered areas) is landslide-prone, according to GSI [2].
• Landslide Atlas of India: made by NRSC/ISRO, released in March 2023, maps about 80,000 landslides (1998–2022) and ranks 147 districts [3]. Rudraprayag is the most exposed district.
• NLSM is mapped at 1:50,000 scale. GSI's National Landslide Forecasting Centre was inaugurated in July 2024 [6].
• Malpa (1998) is in Pithoragarh, Kali valley, and hit Kailash Mansarovar pilgrims. Wayanad (Kerala), 30 July 2024, was a set of debris flows.
• Trap: Ladakh and Spiti are in the moderate to low zone, not the very high zone, because they get little rain. Darjiling (West Bengal) and Karbi Anglong (Assam) are vulnerable hilly pockets inside states that are otherwise "safe".
• Trap: the Western Ghats have hard, stable rock but still fall in the very high zone. The reasons are steep cliffs, intense rain and weathering caused by temperature change.

Mains Points

• Distribution (GS-I): landslides cluster where weak geology meets heavy rain and human pressure.
• The young Himalaya and the north-east slide because of active tectonics and soft rock.

• The Western Ghats slide because of steep scarps (cliff faces) and intense orographic rain: moist wind is pushed up the mountain, cools, and drops heavy rain on the side facing the wind.

• Development versus fragile slopes (GS-III): Wayanad (2024) and nearby subsidence at Joshimath (2023) show how roads, tunnels, quarries and unplanned towns weaken unstable slopes.

• At Joshimath, the State stopped all building work, including the Tapovan-Vishnugad power project and the Helang-Marwari bypass [4].
• Wayanad brought back the debate on Ecologically Sensitive Areas (zones where mining, quarrying and big projects are restricted) under the Gadgil (2011) and Kasturirangan (2013) reports.

• Answer frame: carrying-capacity studies for hill towns, ESA zoning, and stricter environmental clearance for hydropower and highway projects.

• From relief to risk reduction (GS-III, Sendai Framework)

• Map the risk with GSI's NLSM at 1:50,000 and NRSC's Landslide Atlas [6][3].
• Forecast rain-triggered landslides through the NLFC [6].
• Plan land use in high-risk zones and follow the NDMA landslide guidelines (2009). Turn warnings into evacuations at the local level, and support this with afforestation, bunds, terracing, slope drainage and retaining structures.

Related concepts

• Landslide vulnerability zones
• Landslides in the Himalayas and Western Ghats
• Landslide mitigation
• Malpa landslide
• Landslide Atlas of India
• Land subsidence
• Joshimath land subsidence (2023)
• Wayanad landslides (2024)

Read more

• Landslides and land subsidence