Differentiate the causes of landslides in the Himalayan region and the Western Ghats.

Introduction

Landslides are mass movements of rock, debris, or earth down a slope and are triggered by a combination of natural and anthropogenic factors. In India, the Himalayan region and the Western Ghats are two major landslide-prone zones, but the  factors differ causing landslides due to distinct geological, climatic, and human-induced conditions.

Causes of Landslides in the Himalayan Region

Tectonic Activity: The Himalayas are seismically active due to the ongoing collision between the Indian and Eurasian plates. Frequent earthquakes destabilize slopes and act as direct triggers for landslides.

Topography: The steep terrain of the Himalayas, with high relief and unstable slopes, contributes to landslides.

Geological Structure: Presence of weak rock formations such the Himalayan geology makes slopes susceptible to landslides.

Glacial Activities: Melting glaciers can weaken slopes by loosening debris, leading to debris flows.

Monsoonal Rainfall: Heavy monsoonal rains and sudden cloudbursts lead to rapid slope saturation, reducing soil cohesion and triggering sudden and large-scale landslides.”

Climate Change: Shifting monsoon patterns, with the monsoon trough positioned north of its normal path, along with more frequent western disturbances, are causing anomalously heavy rainfall in the western Himalayas, particularly in Himachal Pradesh and Uttarakhand—intensifying landslide risk.

Deforestation and Human Activities: “Unscientific road construction, large hydroelectric projects, and rapid urban expansion disturb fragile slopes and increase vulnerability to landslides, especially in seismically active zones.”

Example:

Unseasonal and extreme rainfall in Himachal Pradesh and Uttarakhand during recent years has been linked to climate variability leading to landslides .

The 2013 Kedarnath tragedy involved cloudburst-induced landslides and flash floods.

Causes of Landslides in the Western Ghats.

Climate and Rainfall: The region receives prolonged and intense southwest monsoon rainfall, which gradually saturates the soil. This reduces friction and triggers slope failure, particularly in lateritic and clayey soils.

Slope - Any slope above 20° is vulnerable to slipping during heavy rain- Idduki District Landslide

Landslides are often triggered by unregulated quarrying, construction of roads and buildings on unstable slopes, and slope modification for plantations and tourism infrastructure. These activities disturb the natural slope stability, making the terrain vulnerable during intense monsoon rains.”

Anthropogenic activities have given rise to anomalous slopes and due to gravitational pull and rain, the overlaying material comes down. In the Western Ghats, if you have continuous rainfall for a couple of days, the soil gets soggy, leading to landslides.

Soil Erosion: Certain Regions -  soil has a high content of sand, which absorbs more water, takes a loose form, and is at risk of slipping down

Faults and Lineaments: Although geologically older and more stable, the Western Ghats also have zones with hidden faults and lineaments that weaken slope resistance over time, making them vulnerable during heavy rainfall episodes.

Examples :

2024 Wayanad landslides :

Intense and prolonged monsoon rainfall leading to rapid soil saturation and slope failure.

Unregulated land-use changes like deforestation, quarrying, and expansion of plantations and tourism infrastructure destabilized natural slopes.

Value Addition -

Idduku Landslide – Study by Kerala Disaster Management Authority

High intensity rainfall triggers the slope by saturating the overburden and slope materials thereby causing landslides.

These areas are covered by very thick layer of overburden material (mainly composed of clay rich lateritic soil). Also, the underlying rocks are highly weathered gneissic rocks. The Lateritic soil with higher clay content has high water retention capacity and less water draining capacity; thereby developing high water pressure in the slope material.

Reactivation of the paleo-landslide zones. Most of the paleo-landslides were left unprotected.

Note - the Gadgil report on the Western Ghats, released in 2011, classed most of Idukki and Wayanad districts as category 1 under eco-sensitive zones. In other words, they were the most vulnerable, where forest land is not to be used for agriculture or non-forest activities.

Conclusion

Effective landslide management demands region-specific strategies that respect local geography, climate patterns, and ecological limits. Without such tailored interventions, both natural triggers and human actions will continue to turn these fragile landscapes into disaster zones.