Introduction
Landslides are among the most destructive forms of natural disasters that occur due to the downward and outward movement of slope-forming materials like rocks, debris, and soil under the influence of gravity. In India, landslides are a recurrent hazard, especially in the mountainous and hilly terrains that cover a significant portion of the country. Among the most vulnerable regions are the Himalayan region in the north and the Western Ghats in the peninsular south-west. Although both regions experience frequent landslides, the underlying causes differ substantially due to variations in their geology, climate, vegetation, human activities, and geomorphic settings.
This article aims to provide a detailed differentiation of the causes of landslides in the Himalayan region and the Western Ghats. By examining natural and anthropogenic triggers, this analysis will help in understanding how geography, geology, and human activity interact differently in these two zones to create similar disasters.
Understanding Landslides: A Brief Background
Before diving into regional differences, it is essential to understand that landslides are usually caused by a combination of factors:
- Geological factors – such as rock composition, fault lines, and soil stability.
- Geomorphological factors – like slope steepness, weathering, and erosion.
- Climatic factors – particularly rainfall, snowfall, and temperature changes.
- Seismic factors – earthquakes and tremors that destabilize slopes.
- Human-induced factors – deforestation, road construction, mining, and unplanned settlements.
The Himalayas and the Western Ghats, though both prone to landslides, differ in their geological history and environmental setup. The Himalayas are young fold mountains, tectonically active and seismically unstable, whereas the Western Ghats are old block mountains of the Deccan plateau, geologically stable but highly vulnerable due to monsoon rainfall and human encroachments.
Causes of Landslides in the Himalayan Region
The Himalayas are globally recognized as one of the most landslide-prone regions. Their geology, combined with intense climatic conditions and human interventions, makes them extremely vulnerable.
1. Geological and Tectonic Factors
- Young Fold Mountains: The Himalayas are among the youngest mountain ranges in the world, formed by the collision of the Indian and Eurasian plates. The rocks are weak, fractured, and structurally unstable.
- Fault Lines and Seismicity: Major thrusts like the Main Central Thrust (MCT) and Main Boundary Thrust (MBT) run across the Himalayas. Frequent earthquakes and tectonic movements destabilize slopes and trigger landslides.
- Unconsolidated Rock Material: The rocks are not well-consolidated due to their young age, making them highly susceptible to weathering and sliding.
2. Geomorphological Factors
- Steep Slopes: The Himalayas have steep gradients, which make gravitational pull stronger on soil and rock masses.
- Intense Weathering: Freeze-thaw cycles in higher altitudes cause physical weathering, loosening rocks and soil.
- River Erosion: Major rivers like the Ganga, Yamuna, and Brahmaputra cut deep valleys and undercut slopes, destabilizing hill flanks.
3. Climatic Factors
- Heavy Rainfall: The Himalayan foothills receive intense monsoonal rains, which saturate soil, increase pore water pressure, and cause slope failure.
- Snowmelt: In summer, rapid snowmelt adds to soil moisture, creating instability.
- Cloudbursts: Sudden, localized heavy rainfall events are common in Uttarakhand, Himachal Pradesh, and Jammu & Kashmir, triggering massive landslides.
4. Seismic Factors
- Frequent Earthquakes: The Himalayas fall in seismic zones IV and V, making them highly earthquake-prone. Tremors loosen rock masses, leading to landslides even weeks after the quake.
5. Human-Induced Factors
- Deforestation: Large-scale clearing of forests for agriculture, roads, and urbanization reduces root strength, leading to soil erosion.
- Road Construction and Hydropower Projects: Widening highways (like the Char Dham project) and tunneling for dams destabilize slopes.
- Unplanned Settlements and Tourism: Rapid urbanization in towns like Shimla, Manali, and Joshimath leads to overloading of slopes.
- Mining and Quarrying: Extraction of minerals destabilizes hill slopes further.
Example: The 2013 Kedarnath disaster in Uttarakhand was caused by heavy rainfall, glacier outburst, and landslides, worsened by human encroachment and hydropower projects.
Causes of Landslides in the Western Ghats
The Western Ghats, though geologically older and stable compared to the Himalayas, also face frequent landslides, particularly during the monsoon season. The causes here are different due to the unique setting of the region.
1. Geological and Tectonic Factors
- Old Block Mountains: The Western Ghats are much older (formed during the break-up of Gondwana land) and are made of hard basalt and granite rocks. They are not tectonically active like the Himalayas.
- Lateritic Soils: The region has thick lateritic and weathered soils that easily become saturated and unstable during monsoon.
- Plateau Margins: The escarpment-like steep western face of the Ghats makes the slopes prone to failure.
2. Geomorphological Factors
- Moderately Steep Slopes: Compared to the Himalayas, slopes are less steep, but where they are sharp, erosion is severe.
- Intense Weathering: Due to the tropical climate, chemical weathering is common, weakening rock structures.
- River Action: West-flowing rivers with short courses cut gorges and valleys, undercutting slopes in high rainfall areas.
3. Climatic Factors
- High Monsoonal Rainfall: The Western Ghats are one of the wettest regions in India, receiving up to 7,000 mm of rainfall annually (e.g., Mawsynram and Agumbe regions nearby). Prolonged rainfall leads to waterlogging, slope failure, and debris flow.
- Absence of Snowmelt: Unlike the Himalayas, snowmelt is not a factor. Rainfall is the dominant cause.
4. Seismic Factors
- Low Seismic Activity: The Western Ghats are not located in major seismic zones, so earthquakes rarely trigger landslides here.
5. Human-Induced Factors
- Deforestation for Plantations: Large areas of natural forests have been converted into tea, coffee, and rubber plantations. These monoculture plantations reduce soil binding capacity.
- Quarrying and Mining: Illegal quarrying of laterite and granite rocks destabilizes slopes. Kerala, Goa, and Karnataka are most affected.
- Infrastructure Development: Road cutting, tunneling, and building dams in ecologically fragile zones increase landslide vulnerability.
- Urbanization: Expansion of towns like Wayanad, Kodagu, and Nilgiris has led to unscientific slope construction.
Example: The 2018 Kerala floods saw widespread landslides across the Western Ghats, particularly in Idukki and Wayanad, due to intense rainfall coupled with quarrying and deforestation.
Comparative Analysis: Himalayas vs. Western Ghats
| Aspect | Himalayas | Western Ghats |
|---|---|---|
| Geological Age | Young fold mountains (tectonically unstable) | Old block mountains (tectonically stable) |
| Tectonic Activity | Highly active, earthquakes frequent | Low tectonic activity, minimal seismic risk |
| Rock Structure | Weak, unconsolidated, fractured rocks | Hard basalt and granite, but weathered |
| Slopes | Very steep, unstable | Moderately steep, localized instability |
| Climatic Trigger | Heavy rainfall, snowmelt, cloudbursts | Prolonged monsoon rainfall |
| Seismic Factor | Major cause of landslides | Negligible role |
| Human Activities | Road construction, hydropower, urbanization, deforestation | Quarrying, plantations, deforestation, infrastructure expansion |
| Main Example | Kedarnath disaster (2013) | Kerala landslides (2018) |
Educational Significance
Understanding the differentiated causes of landslides in the Himalayan region and Western Ghats is crucial for:
- Disaster Preparedness – Early warning systems need to be tailored regionally.
- Infrastructure Planning – Roads, dams, and towns should consider geological differences.
- Environmental Conservation – Protecting forests and reducing quarrying are critical.
- Community Awareness – Local populations must be educated about slope safety.
- Policy Formulation – Differentiated regional strategies for landslide mitigation.
Conclusion
While both the Himalayas and the Western Ghats are prone to landslides, the causes vary significantly due to differences in geology, tectonics, climate, and human interventions. In the Himalayas, tectonic instability, steep slopes, earthquakes, and snowmelt combine with human interference to make the region extremely vulnerable. In contrast, the Western Ghats, though geologically stable, are threatened mainly by intense monsoon rainfall, deforestation, quarrying, and unsustainable land use practices.
Addressing landslides requires region-specific solutions: seismic-resilient infrastructure and controlled development in the Himalayas, and stricter environmental regulations against quarrying and deforestation in the Western Ghats. Only through scientific planning and ecological sensitivity can the landslide menace in both regions be reduced.
