Joshimath sank 5.4cm in just 12 days
Source: By The Indian Express
Satellite images released by ISRO’s National Remote Sensing Centre on 13 January 2023 show that Uttarakhand’s Joshimath witnessed a rapid sinking of 5.4cm in just 12 days — between 27 December 2022 and 8 January 2023.
The quick subsidence stands in contrast to the slow-paced sinking of the area that was recorded between April and November 2022. According to the government agency’s report, during these seven months, Joshimath sank up to just nine centimetres.
The report also added that rapid subsidence occurred in the central part of the city. “Crown of the subsidence is located near Joshimath-Auli road at a height of 2180 m”, it mentioned.
The images and report have come just days after cracks appeared in many roads and hundreds of houses in the city, which has now been declared as a landslide and subsidence-hit zone by the authorities. So far, a total of 168 families have evacuated to temporary relief centres.
What exactly is subsidence?
Subsidence is the “sinking of the ground because of underground material movement”, according to the National Oceanic and Atmospheric Administration (NOAA). 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.
The US-based agency’s website said that this phenomenon can “happen over very large areas like whole states or provinces, or very small areas like the corner of your yard.”
Why is Joshimath sinking?
The exact reason behind the land subsidence in Joshimath is still unknown, but experts suggest that it might have been caused by unplanned construction, overpopulation, 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 tremors. Warning bells for Joshimath were first sounded about 50 years ago in the MC Mishra committee report, which pointed to unplanned development in the area that already had natural vulnerabilities.
According to experts, Joshimath city has been built on ancient landslide material — meaning it rests on a deposit of sand and stone, not rock, which doesn’t have a high load-bearing capacity. Moreover, the lack of a proper drainage system could also have contributed to the sinking of the area. The accumulated water seeps into the rocks below, softening them.
Apart from the aforementioned possible reasons, reports have 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.
