Joshimath – Satellite data shows the town was sinking at a rate of 6 cm for the past 18 months

'We have been looking at the satellite data since 2015, but the analysis would take some time,' a scientist told DH

Over the last 18 months, the hill town of Joshimath has been sinking at a very high rate of 6-6.5 cm every year, a new study has shown.

Indian space scientists on Tuesday presented satellite images showing what they described as a “significant” subsidence rate in Joshimath for over 18 months – between July 2020 and March 2022.

The finding comes at a time when several teams of experts are conducting studies in the popular tourist centre after hundreds of houses and a few hotels developed deep cracks making them unsuitable for living and forcing the Uttarakhand administration to evacuate nearly 4,000 people.

"Joshimath is sinking at a rate of 6-6.5 cm per year as per the satellite images. The reason could be manifold. We have been looking at the satellite data since 2015, but the analysis would take some time,” a scientist at Indian Institute of Remote Sensing, Dehradun told DH.

While breaching of an underground water source appears to be the immediate trigger behind such deep cracks, scientists are not sure about what is causing such a breach.

“Water is being discharged at a rate of 400-500 litres per minute and there is no slowing down. We are not sure what the source of the water is,” geologist Piyoosh Rautela, executive director at Uttarakhand Disaster Management Authority said.

As the origin of the water source remains unclear, scientists at Wadia Institute of Himalayan Geology, Dehradun too are conducting experiments to see if the water is being released from a ground aquifer – a water-bearing rock – or from some underground streams.

Joshimath, the gateway to the holy shrines of Badrinath and Hemkunt Sahib, is situated in a geologically and tectonically fragile zone. But irrespective of its vulnerability, big-time construction activities including tunnelling through the rocks for a mega-hydro power plant and widening of the road under the Char Dham project were going on.

"Being situated in close proximity to major tectonic discontinuities, Joshimath has been showing signs of distress due to the burgeoning anthropogenic pressure. The area reportedly shows signs of continuous ground subsidence and the same has been recorded earlier,” Rautela and fellow geologist MPS Bisht wrote in a 2010 correspondence in Current Science, flagging how a tunnel boring machine employed by the National Thermal Power Corporation pierced an underground aquifer in December 2009.

Joshimath has been declared a land subsidence-hit area after huge cracks developed in houses and other structures, roads and ground. The National Crisis Management Committee also reviewed the situation on Tuesday.

Uttarakhand Chief Secretary apprised the NCMC that the operation of the Joshimath-Auli ropeway has been discontinued and construction works in and around the Joshimath municipality area have been stopped till further orders. A team of officials from the Union Home Ministry and National Disaster Management Authority has also reached Joshimath to ascertain the location of underground water accumulation in the subsidence zone.