The downslope movement of rock, soil or debris triggered by heavy rain, earthquakes or human activity. A major monsoon hazard in the Himalayas and Western Ghats.
phenomenaWhat is a Landslide?
A landslide is the downslope movement of rock, soil, or debris under the force of gravity. The term covers a wide range of events:
- Rockfall — Loose rocks tumbling down steep cliffs.
- Rockslide — Whole rock mass sliding along a fracture plane.
- Debris flow / mudslide — Saturated soil and rocks flowing rapidly down a slope.
- Earthflow — Slow flow of saturated fine-grained soil.
- Slump — Rotational failure of a slope.
- Creep — Imperceptibly slow downhill movement.
In South Asia, the most deadly type is the rain-triggered debris flow — when intense monsoon rainfall saturates a steep hillside, the soil loses cohesion and rushes downhill as a torrent of mud, rocks and uprooted trees, often burying entire villages in minutes.
What causes landslides
The fundamental cause is gravity acting on an unstable slope. Triggers:
Weather-related:
- Heavy or prolonged rainfall — saturates soil, increases pore-water pressure, lubricates failure planes. Responsible for ~80% of South Asian landslides.
- Cloudbursts — sudden 100+ mm/hour events can trigger flash-flood debris flows.
- Snowmelt — combined with rain in spring.
- Cyclone-driven rainfall — heavy rain hundreds of km inland can trigger landslides.
Non-weather:
- Earthquakes — Nepal 2015, Sikkim 2011, Pakistan 2005 triggered thousands of co-seismic landslides.
- Human activity — road-cutting, slope undercutting for construction, deforestation, unplanned terracing.
- Volcanic activity — rare in mainland South Asia, but possible.
Where landslides hit hardest in South Asia
Indian Himalayan states (highest frequency):
- Uttarakhand — Kedarnath 2013 (5,700+ deaths), Chamoli 2021, Rudraprayag yearly.
- Himachal Pradesh — Kullu, Manali, Mandi 2023 (~80 deaths).
- Jammu & Kashmir — Pir Panjal range during monsoon.
- Sikkim — South Lhonak GLOF 2023 (100+ deaths).
- Arunachal Pradesh — Sino-Indian border road slides.
Western Ghats:
- Kerala — 2018 floods (483 deaths, many from landslides); Wayanad 2024 (~400 deaths).
- Karnataka — Kodagu, Madikeri.
- Maharashtra — Konkan slopes, Talie, Raigad 2021.
- Tamil Nadu — Nilgiris, Coonoor.
Northeast India:
- Assam, Meghalaya, Tripura, Mizoram — annual monsoon landslides.
Nepal:
- Most landslide-prone country in South Asia per capita. 300–500 landslide deaths per year.
Pakistan:
- Khyber Pakhtunkhwa, Gilgit-Baltistan — Karakoram Highway frequently blocked.
- Murree, Galyat in eastern Punjab during heavy rain.
Bangladesh:
- Chittagong Hill Tracts — Rangamati, Bandarban — annual fatal landslides during monsoon.
Historic South Asian landslide disasters
- 1948 Darjeeling, India: 500+ deaths during cyclone.
- 1968 Kalimpong, India: 30,000 affected after Cyclone Burdwan rainfall.
- 2010 Attabad, Pakistan: 19 km² rockslide created a lake that drowned 20 villages.
- 2010 Leh cloudburst: 200+ deaths from debris flows.
- 2013 Kedarnath, Uttarakhand: cloudburst + glacial moraine collapse — 5,700+ deaths.
- 2014 Malin landslide, Maharashtra: village wiped out, 151 deaths.
- 2017 Rangamati, Bangladesh: 152 deaths after heavy rain.
- 2018 Kerala floods: 483 deaths including many from landslides.
- 2021 Chamoli, Uttarakhand: glacier-rock avalanche, 200+ deaths.
- 2023 Chooralmala-Mundakkai, Kerala: 30+ deaths.
- 2023 Himachal monsoon disaster: ~80 deaths from landslides + flash floods.
- 2024 Wayanad, Kerala: ~400+ deaths in a single debris flow.
Warning signs of an imminent landslide
If you live in or are visiting a mountainous area during monsoon, watch for:
- Cracks appearing in ground or walls
- Doors and windows that suddenly stick or jam
- Tilting trees or fence posts
- Unusual sounds — rumbling, cracking
- Sudden change in stream flow (clear water becoming muddy)
- New springs or wet patches on a hillside
- Bulging slopes
- Vehicles or buildings sliding even slightly
If you observe these, evacuate immediately to higher, stable ground — do not wait for official warnings, which may be too late.
Landslide safety
Before:
- Avoid building or living below steep slopes, especially loose-soil ones.
- Know your area’s landslide history.
- Plant deep-rooted vegetation to stabilise nearby slopes.
During heavy monsoon rainfall:
- Listen to weather bulletins and government warnings.
- Move to higher, level ground if rain has been intense for hours.
- Do not cross flooded valleys — they may carry debris flows.
After:
- Stay away from the slide area — secondary slides are common.
- Help check for trapped persons only if safe.
- Report damaged utilities (gas, water, electricity).
- Document damage for compensation.
Early warning and Indian system
The Geological Survey of India (GSI) operates a National Landslide Risk Management Centre. CWC and IMD issue rainfall-based landslide alerts for high-risk districts.
Newer technologies include:
- Satellite InSAR monitoring of slow ground movement.
- Doppler-radar rainfall thresholds for nowcast warnings.
- Smartphone landslide-alert apps in Sikkim and Uttarakhand.
Climate change and landslides
Three trends are increasing landslide risk:
- More intense rainfall events as the atmosphere warms (Clausius-Clapeyron: ~7% more water per °C).
- Glacial retreat and GLOFs — newly exposed slopes are unstable.
- Permafrost thaw in the high Himalayas — destabilising rock-ice slopes.
- Population pressure pushes settlements onto steeper, more vulnerable land.
Climate models project a 20–50% increase in landslide-triggering rainfall events in Himalayan and Western Ghats regions by mid-century.
Frequently asked questions
How much rain triggers a landslide? Thresholds vary by slope, soil and vegetation. Typical triggers: 70–100 mm in 24 hours, or 30–50 mm in 1 hour on already-saturated ground. A single dry-season storm rarely triggers slides; cumulative monsoon rainfall is more critical.
Are landslides predictable? Short-term triggers are increasingly predictable using radar-based rainfall nowcasting and slope-monitoring sensors. But the exact location and timing of slides remain difficult to forecast. Most warnings are area-wide, not pinpointed.
What’s the difference between a landslide and a mudslide? A landslide can involve any material (rock, soil, debris). A mudslide (or debris flow) specifically involves saturated fine-grained material flowing rapidly. Most fatal South Asian “landslides” are technically debris flows.
Can deforestation cause landslides? Yes — tree roots stabilise soil. Removing trees increases landslide risk by 5–10× on steep slopes within a few years. Many recent landslide disasters (Wayanad 2024, Chooralmala 2023) occurred in areas where forest had been cleared for plantations.
Where can I check landslide risk for my area? GSI publishes hazard maps. Mausam Online displays precipitation forecasts on every city page — useful as a leading indicator during monsoon. See Shimla, Dehradun, Kohima, Wayanad, Munnar.