Revision summary
Himalayan landslides are driven by tectonics, shattered rock, glaciers, and cloudbursts. Kedarnath 2013 and Chamoli show rain plus mountain structure. Western Ghat slides are monsoon, laterite, and slope cutting, as at Malin and in Kerala. Seismicity is primary in the Himalaya and secondary in the Ghats. NDMA maps must use different triggers for the two belts.
Model answer
Copper italics in this answer — like this — are the key facts. Each one is unpacked in the Facts & figures rail.
Introduction
Both belts slide, but they are not the same machine. The Himalaya is a young thrust mountain with earthquakes and deep rain on debris. The Western Ghats are an older scarp with laterite, monsoon cloudbursts, and hill-cutting for roads and estates.
Body
Himalayan causes
- Tectonics: the Main Central Thrust and frequent earthquakes, as in Chamoli, Sikkim 2011, and Nepal 2015, shatter slopes before rain even falls.
- Lithology: fractured schist, shale, and glacial till; river undercutting in gorges of the Alaknanda and Teesta.
- Climate: intense monsoon and cloudbursts, plus freeze–thaw at height; 2013 Kedarnath combined rain, moraine, and a lake outburst.
- Human load: hydropower cuts, Char Dham road widening, and unplanned hotels on colluvium.
Western Ghat causes
- Steep west-facing scarp and thick laterite or saprolite that loses strength when saturated, as in Malin 2014 (Pune district) and Kerala 2018–19.
- Extreme monsoon orographic rain, not Himalayan seismicity as the first cause.
- Land use: tea and plantation benches, quarry benches, and ghat-road hairpins that remove toe support.
- Coastal and midland laterite cliffs fail as debris flows more than as huge rock avalanches of the High Himalaya.
Contrast
- Himalaya: earthquake plus glacier plus thrust plus rain. Ghats: rain plus laterite plus slope cutting, with far weaker seismic trigger.
- NDMA landslide guidelines therefore need different maps: seismic-landslide for the north; rainfall-threshold and laterite for the west.
Flow diagram
flowchart TD H[Himalaya] --> EQ[Earthquakes thrusts] H --> G[Glacial debris rain] W[Western Ghats] --> L[Laterite saturation] W --> C[Road plantation cuts] EQ --> S[Landslide] L[L] --> S[S]
Conclusion
Himalayan slides start in a live collision belt. Western Ghat slides start in a monsoon-soaked scarp of weak weathered rock. Treat them as two hazard families, not one hill problem.
Quick related
Students also ask
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Mention the global occurrence of volcanic eruptions in 2021 and their impact on regional environment.
Next question on this syllabus topic (2021 · Q7). View answer →
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Do earthquakes cause Ghat landslides?
They can shake a wet slope, but the everyday Ghat killer is rain on laterite and cuts, not a thrust earthquake.
-
Is road building the only human cause?
No. Dams, hotels, quarries, and plantation benches all remove support or add water.
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