Introduction
Landslides are mass movements of soil, rock, and debris down a slope due to gravity, often accelerated by rainfall, earthquakes, or human interventions. They pose a serious geological hazard, particularly in mountainous regions, causing loss of life, damage to infrastructure, disruption of transportation, and environmental degradation.
India, with its diverse topography, experiences frequent landslides, especially in the Himalayan region. While landslides also occur in the Western Ghats, their frequency and intensity are markedly lower. Understanding the causes behind this discrepancy requires an examination of geological, geomorphological, climatic, and anthropogenic factors.
This essay critically analyzes why the Himalayas are more landslide-prone than the Western Ghats, exploring natural and human-induced factors, regional case studies, and implications for disaster management and sustainable development.
1. Geological Factors
1.1 Young and Tectonically Active Mountains
- The Himalayas are geologically young, formed around 50 million years ago due to the collision between the Indian Plate and the Eurasian Plate.
- Young mountains are structurally unstable due to faults, folds, and fractures.
- Continuous tectonic activity generates earthquakes, which weaken rock masses and trigger landslides.
Western Ghats Comparison:
- Western Ghats are ancient mountains, part of the Precambrian shield.
- They are geologically stable, with hard igneous and metamorphic rocks, showing minimal tectonic activity.
- Hence, landslides occur less frequently in the Western Ghats.
1.2 Rock Type and Soil Characteristics
- Himalayan slopes are composed of unconsolidated sediments, shale, sandstone, and loose alluvium, which are prone to weathering and mass movement.
- The presence of highly jointed and fractured rocks reduces slope stability.
- In contrast, Western Ghats have igneous rocks like basalt and granite, which are dense, cohesive, and less prone to sliding.
2. Geomorphological Factors
2.1 Steep Slopes
- The Himalayas are characterized by very steep slopes, especially in regions like Uttarakhand, Sikkim, and Himachal Pradesh.
- High slope angles increase gravitational stress, making soil and rock more likely to slide.
Western Ghats Comparison:
- Western Ghats have gentler slopes, rarely exceeding 30–40°, which naturally reduces landslide risk.
2.2 Rapid Elevation Changes
- Elevation in the Himalayas changes dramatically over short horizontal distances, causing high potential energy for slope failure.
- Rivers and glaciers carve deep valleys, creating oversteepened slopes.
- Western Ghats have gradual elevation changes, minimizing slope instability.
2.3 Himalayan River and Glacier Activity
- Himalayan rivers are fast-flowing and erosive, undercutting slopes and destabilizing valleys.
- Glacial retreat and snowmelt contribute to saturation of slopes, increasing landslide susceptibility.
- In the Western Ghats, rivers are smaller, slower, and less erosive, reducing slope destabilization.
3. Climatic Factors
3.1 Intense and Concentrated Monsoon Rainfall
- Himalayas experience heavy rainfall during the southwest monsoon, sometimes exceeding 3000–4000 mm annually in areas like Cherrapunji and Sikkim.
- Sudden cloudbursts and prolonged rainfall saturate soil, reduce cohesion, and trigger landslides.
- Western Ghats receive moderate to heavy rainfall, but it is more evenly distributed and slopes are generally more stable.
3.2 Snow and Freeze-Thaw Action
- High-altitude Himalayan regions experience freeze-thaw cycles, where water freezes in cracks and expands, weakening rocks.
- This increases mechanical weathering, making slopes more prone to collapse.
- Western Ghats, being tropical, do not experience freeze-thaw cycles, reducing this risk factor.
4. Vegetation and Land Cover
4.1 Deforestation in the Himalayas
- Rapid population growth, agricultural expansion, and timber extraction have led to significant deforestation in Himalayan foothills and slopes.
- Loss of vegetation reduces root reinforcement, decreasing slope stability.
- Exposed soil is more susceptible to erosion and landslides during heavy rains.
4.2 Vegetation in Western Ghats
- Western Ghats are densely forested, with tropical evergreen and deciduous forests covering slopes.
- Strong root systems enhance soil cohesion, naturally protecting slopes from mass movement.
- Forest cover acts as a buffer against rainfall-induced slope failure.
5. Human-Induced Factors
5.1 Road Construction and Urbanization
- Himalayan regions are increasingly developing roads, highways, and hydropower projects.
- Road cuts, slope excavation, and construction disturb natural slopes, creating artificial oversteepening.
- Examples: NH-34 landslides in Uttarakhand and Darjeeling hill roads.
5.2 Terrace Farming and Land Use Changes
- Terrace farming and conversion of slopes into agriculture change the natural drainage and load distribution.
- Mismanaged irrigation further saturates soil, increasing landslide risk.
5.3 Mining and Quarrying
- Sand, gravel, and stone quarrying in Himalayan valleys destabilize slopes.
- Large-scale extraction for urban and road construction amplifies landslide frequency.
Western Ghats Comparison:
- Western Ghats have limited large-scale mining and road cuts, reducing anthropogenic triggers.
6. Seismic Activity
- The Himalayas lie in the highest seismic risk zone (Zone V) of India, due to the collision of tectonic plates.
- Earthquakes induce sudden slope failure, often resulting in massive landslides.
- Examples: 2015 Nepal earthquake and 1991 Uttarkashi earthquake triggered large landslides.
Western Ghats Comparison:
- Western Ghats fall in seismically stable Zone II–III, with minimal earthquake activity.
- Low seismicity contributes to fewer landslides.
7. Case Studies of Frequent Landslides in the Himalayas
- Uttarakhand (2013 Kedarnath Disaster):
- Heavy rainfall combined with deforestation and steep slopes caused massive landslides and flash floods, destroying settlements and infrastructure.
- Heavy rainfall combined with deforestation and steep slopes caused massive landslides and flash floods, destroying settlements and infrastructure.
- Darjeeling Himalayas:
- Landslides frequently occur due to road cuts, monsoon rainfall, and weak rock formations, disrupting transportation and local economy.
- Landslides frequently occur due to road cuts, monsoon rainfall, and weak rock formations, disrupting transportation and local economy.
- Sikkim (2011 Sikkim Earthquake):
- Triggered landslides in fragile slopes with loose rocks and saturated soil, emphasizing the role of seismic activity.
Western Ghats Example:
- Landslides are sporadic and mostly minor, limited to hilly districts of Kerala, Karnataka, and Maharashtra, caused by localized heavy rainfall rather than tectonic activity.
8. Summary of Causes for Higher Landslide Frequency in the Himalayas
| Factor | Himalayas | Western Ghats |
|---|---|---|
| Age of mountains | Young, tectonically active | Old, stable |
| Slope gradient | Very steep | Moderate |
| Rock type | Fragile, unconsolidated | Hard, igneous/metamorphic |
| Rainfall | Intense, concentrated | Moderate, evenly distributed |
| Seismicity | High (Zone V) | Low (Zone II–III) |
| Glacial activity | Present, contributes to instability | Absent |
| Freeze-thaw cycles | Present | Absent |
| Vegetation | Degraded, deforested | Dense, intact |
| Human activities | Roads, terraces, hydropower | Limited, controlled |
Conclusion: The Himalayas’ combination of young geology, steep slopes, intense rainfall, seismic activity, and human interventions makes them far more prone to landslides than the geologically stable, well-vegetated, and less tectonically active Western Ghats.
9. Implications
9.1 Human Safety and Settlement Planning
- Settlements in fragile Himalayan slopes face high landslide risk.
- Disaster management strategies must identify high-risk zones, restrict construction, and relocate vulnerable communities.
9.2 Infrastructure Development
- Roads, railways, and hydropower projects are vulnerable.
- Engineers must use retaining walls, slope stabilization, and proper drainage to minimize landslide hazards.
9.3 Environmental Conservation
- Afforestation, soil conservation, and controlled land use reduce landslide risk.
- Maintaining natural vegetation in the Himalayas is crucial for slope stabilization.
10. Conclusion
The Himalayas experience more frequent landslides than the Western Ghats due to a combination of natural and anthropogenic factors:
- Young, tectonically active mountains with weak and fractured rocks.
- Steep slopes and rapid elevation changes.
- Intense monsoon rainfall and snowmelt.
- Deforestation and unplanned human activity.
- High seismic activity and glacial influence.
In contrast, the Western Ghats’ geological stability, gentle slopes, dense forest cover, and low seismicity reduce landslide frequency.
Understanding these factors is crucial for disaster management, urban planning, infrastructure design, and environmental conservation. Sustainable development in the Himalayas requires a scientific approach to slope management, forest conservation, and controlled human activity to reduce landslide hazards.
