Landslides in the Himalayas and Western Ghats

Topic: Natural Hazards and Disaster Management in India · NCERT: Class 11, Ch 5 "Geomorphic Processes"

Meaning

A landslide happens when a large mass of rock, soil and debris moves quickly down a slope because of gravity. It breaks away along a weak surface called a failure plane (or shear plane). The Himalaya slides often because the mountains are young, still rising and made of weak rock. The Western Ghats and Nilgiris are made of hard, stable rock, yet they also slide because of steep cliffs, very heavy monsoon rain and rock that cracks as it heats and cools.

This matters because both regions fall in India's very high landslide vulnerability zone. Disasters like Malpa (1998), Joshimath (2023) and Wayanad (2024) show how weak slopes, heavy rain and human building together cost lives, block roads and slow development in hill areas.

Explanation

How a landslide happens (cause → process → result)

• Heavy, continuous rain
• Water soaks into soil and rock, so the slope becomes heavier.
• Water also cuts 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 earthquakes 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: cutting forests (deforestation), mining, building roads, 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 slope becomes weak and fails.

• Local factors control landslides. These are rock type, geomorphic agents (running water, ice and wind that shape the land), slope, land use, vegetation and human activity.

• These factors change from one hillside to the next.
• So landslides are hard to predict, and monitoring them is slow and costly.

Why the two mountain regions slide

Feature	Himalaya	Western Ghats and Nilgiris
Age and stability	Young fold mountains, still rising and tectonically active (plate movement still goes on 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 caused by temperature change: rock heats by day and cools by night, so it cracks and breaks apart
Result	Landslides are very frequent	Landslides happen even though the rock is hard

• Western Ghats rain: moist monsoon wind hits the mountain and is pushed up. The rising air cools, its water vapour condenses, and very heavy rain falls on the western side (the windward side). This is orographic rain.

Types seen in these regions

• Rockfall and debris burial: at Malpa (1998), rock and debris fell from steep valley walls and buried the village.
• Debris flows: at Wayanad (2024), mud, boulders and uprooted trees mixed with water. They rushed down stream valleys like a river of debris.
• Land subsidence (a related hazard): the ground surface sinks, slowly or suddenly. At Joshimath (2023), a town built on old landslide debris began to sink and crack.

Consequences

• Roads and railways stay blocked for long periods.
• Rock falls damage houses, crops, and power and communication lines.
• River damming and diversion
• Debris falls into a river channel and blocks it.
• A temporary lake forms behind the blockage.

• The natural dam bursts or the river changes course, and floods follow downstream.

• Travel and trade between places (spatial interaction) become costly. This slows development in hill areas.

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 prone to landslides (GSI) [2].
• Very high zone: the young, unstable Himalaya; Andaman and Nicobar Islands; the high-rainfall, steep-sloped Western Ghats and Nilgiris; the north-eastern region; areas often shaken by earthquakes; and areas with heavy road and dam building.
• High zone: all Himalayan states and north-eastern states, except the Assam plains.
• Moderate to low zone: Trans-Himalayan Ladakh and Spiti (Himachal Pradesh), which get little rain; the Aravalis; and the 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 wind).
• Vulnerable pockets in "safe" states: Darjiling district (West Bengal) and Karbi Anglong (Assam).
• Named examples:
• Malpa, Kali river valley, Pithoragarh district, Uttarakhand, on 18 August 1998. The Kali forms the India–Nepal border here. About 220 people died, including pilgrims on the Kailash Mansarovar Yatra.
• Mundakkai, Chooralmala and Punchirimattom, Wayanad district, Kerala (Western Ghats), on 30 July 2024. Over 200 people died.
• Joshimath, Chamoli district, Uttarakhand, above the Alaknanda valley, in January 2023. A strip about 350 metres wide was affected [4].
• The road to Srinagar (Jammu and Kashmir) is often blocked by landslides.

• Rock falls repeatedly hit the Konkan Railway along the Western Ghats coast.

• Most exposed districts and states (Landslide Atlas): Rudraprayag (Uttarakhand) is first, followed by Tehri Garhwal. Mizoram and Uttarakhand are among the most affected states.

• Mapping and warning systems:
• National Landslide Susceptibility Mapping (NLSM) by GSI is mapped at 1:50,000 scale. Landslide susceptibility means how likely an area is to slide. NLSM covers the Himalaya, the Tertiary belt of north-east India (young, soft rocks) and the Western Ghats. It spans parts of 19 states/UTs, about 4.3 lakh sq km, and 33,904 landslides have been checked on the ground [7].
• National Landslide Forecasting Centre (NLFC) 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 (NWP) models (computer weather forecasts) and observed rainfall [7].
• Landslide Atlas of India by NRSC (ISRO) was released on 18 March 2023. It maps about 80,000 landslides from 1998 to 2022, covers 17 states and 2 UTs in the Himalaya and Western Ghats, and ranks 147 districts by exposure [3]. It used Resourcesat, Cartosat, Sentinel-1 and 2 and other satellite images [3].

Don't confuse with

• Land subsidence: the ground sinks downward, for example over coal mines at Jharia (Jharkhand) and Raniganj (West Bengal), or at Joshimath. A landslide is a mass moving down a slope along a failure plane.
• Himalaya vs Western Ghats rock: the Himalaya slides because of weak, young, sedimentary and unconsolidated rock and active tectonics. The Western Ghats have hard, stable crystalline rock and slide because of steep cliffs, intense rain and temperature-driven weathering.
• Ladakh and Spiti vs the rest of the Himalaya: they are Himalayan but fall in the moderate to low zone because they get little rain. They are not in the very high zone.
• Debris flow vs rockfall: a debris flow (Wayanad) is a fast, water-soaked mix of mud, boulders and trees moving down stream valleys. A rockfall (Malpa) is rock dropping from steep valley walls.

Prelims Hooks

• 12.6% of India's land area (about 0.42 million sq km, not counting snow-covered areas) is landslide-prone (GSI) [2].
• Landslide Atlas of India: released by NRSC/ISRO in March 2023. It 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 [7].
• Place–district pairs: Malpa (1998) → Pithoragarh, Kali valley. Joshimath (2023) → Chamoli, with the Tapovan-Vishnugad project linked [5]. Wayanad (2024) → Kerala, debris flows.
• Trap: the Western Ghats have hard, stable rock yet sit in the very high zone. Ladakh and Spiti are only moderate to low.
• Trap: Darjiling (West Bengal) and Karbi Anglong (Assam) are landslide-prone pockets inside otherwise "safe" states.

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.

• The Himalaya and Western Ghats both fall in the very high zone, but for different reasons.

• Development vs fragility (GS-III): Joshimath (2023) and Wayanad (2024) show how roads, tunnels, quarries and unplanned towns weaken unstable slopes.

• At Joshimath, the town sits on old landslide debris and has poor drainage. All building work was stopped, including the Tapovan-Vishnugad power project and the Helang-Marwari bypass road [5].
• Wayanad revived the debate on Ecologically Sensitive Area (ESA) zoning under the Gadgil (2011) and Kasturirangan (2013) reports. ESAs are zones where mining, quarrying and big projects are restricted. The Centre told Parliament it had sent early warnings to Kerala from 23 to 26 July 2024 [6].

• 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 [7][3].
• Forecast rain-triggered landslides through the NLFC [7], and turn warnings into local evacuations.
• Mitigation: limit roads, large dams and big settlements in high zones. Keep farming to valleys and gentle slopes. Promote afforestation (planting forests on a large scale), bunds (low earth or stone banks that slow runoff), slope drainage and retaining structures.
• In the north-east, replace jhum (shifting cultivation: slash-and-burn farming that leaves slopes bare) with terrace farming (flat steps cut into the hillside that hold the soil).

Related concepts

• Landslide
• Landslide vulnerability zones
• Landslide mitigation
• Malpa landslide
• Landslide Atlas of India
• Land subsidence
• Joshimath land subsidence (2023)
• Wayanad landslides (2024)

Read more

• Landslides and land subsidence