Land Subsidence

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Context:

Almost a week after cracks appeared in many roads and hundreds of houses of Joshimath, Uttarakhand, authorities declared it a landslide and subsidence-hit zone.

What is Land Subsidence?

Land subsidence is a gradual settling or sudden sinking of the Earth's surface due to the removal or displacement of subsurface earth materials. The principal causes include: aquifer-system compaction associated with groundwater withdrawals. drainage of organic soils.
It can happen for a host of reasons, man-made or natural, such as the removal of water, oil, or natural resources, along with mining activities. Earthquakes, soil erosion, and soil compaction are also some of the well-known causes of subsidence.

What can be the reasons behind Joshimath’s subsidence?

The exact reason behind Joshimath land subsidence is still unknown but experts suggest that the incident might have occurred because of unplanned construction, over-population, obstruction of the natural flow of water and hydel power activities.
Not only this, the area is a seismic zone, which makes it prone to frequent earthquakes.
As per the reports, residents have also blamed NTPC’s Tapovan Vishnugad Hydro Power Project for the incident. They allege that the tunnel had water seepage “from a punctured aquifer, leading to the drying of water sources in Joshimath. Experts suggest that it could be one of the reasons for the collapse of the area.
Reports have also pointed out that subsidence in Joshimath might have been triggered by the reactivation of a geographic fault — defined as a fracture or zone of fractures between two blocks of rock — where the Indian Plate has pushed under the Eurasian Plate along the Himalayas.