Source: NIE
Context: Severe land subsidence in Chamoli’s Nanda Nagar, Uttarakhand has destroyed seven buildings and left 16 others at risk, forcing evacuations and triggering panic among residents.
About Land Subsidence:
What it is?
- Land subsidence is the gradual settling or sudden sinking of the Earth’s surface due to movement of underground materials.
- It may occur naturally or be induced by human activities.
Regions Affected:
- Globally: Parts of the US (Chesapeake Bay, Louisiana), China, Indonesia, Iran.
- In India: Joshimath (Uttarakhand), Chamoli, Himachal Pradesh, Delhi NCR (due to groundwater depletion).
- Current hotspot: Chamoli’s Nanda Nagar (Uttarakhand Himalayas).
How Land Subsidence Happens?
- Tectonic Setting: In regions like the Himalayas, active plate convergence (Indian Plate pushing into Eurasian Plate) creates fractured and unstable bedrock. These weak zones allow ground layers to sink more easily.
- Lithology (Soil & Rock Type): Fine-grained alluvial soils, loess deposits, or unconsolidated sediments compact when water is removed. Clay-rich layers are especially prone to shrinkage.
- Hydrology (Water Movement): Over-extraction of groundwater lowers the water table. Pore pressure in sediments drops, causing soil grains to compress, leading to vertical sinking.
- Geomorphic Processes: Heavy rainfall, floods, and glacial meltwater infiltrate slopes, adding weight and reducing shear strength. This destabilises the slope–valley system.
- Anthropogenic Impact: Mining, tunneling, hydropower projects, and unregulated construction disturb the natural load balance and accelerate downward movement.
Implications:
- Humanitarian: Displacement of families, loss of homes, trauma.
- Infrastructure: Cracks in roads, collapse of buildings, damage to utilities (pipelines, power lines).
- Economic: Rehabilitation costs, loss of tourism, strain on state disaster relief funds.
