Land displacement has been continuously happening in Joshimath, shows satellite imagery analysis
The Hindu
Satellite measurements, analysed by European experts, show that Joshimath has been sliding at the rate of 3 to 10 cm per year over the past four years
While the recent damage to houses and structures in Joshimath have brought widespread attention to the its land subsidence, several experts say that geological changes affecting the town’s topography have been underway for many years.
An NRSC-ISRO report — that showed that Joshimath sank by 5.4 cms between December 27, 2022 and January 8, 2023 — sparked controversy and was taken down by the organisation after gag orders from the National Disaster Management Authority.
Dave Petley, a landslide expert and Vice Chancellor at the University of Hull in the U.K. quoted an analysis posted on a blog — authored by remote sensing and landslide experts at the Aristotle University of Thessaloniki, the Earth Science Observatory and School of the University of Strasbourg and the National Center of Scientific Research — which showed, via satellite measurements, that the surface displacement rate in Joshimath was between 3 cm and 10 cm per year (at different locations) over the past four years. It maintained that the Himalayan town is ‘sliding’.
The authors of the analysis, including geomorphologist Jean-Philippe Malet, claimed to have used satellite imagery and analysis based on the InSAR (Interferometric Synthetic Aperture Radar) to demonstrate the ‘sliding.’ InSAR is a technique used for mapping ground deformation using radar images of the Earth’s surface that are collected from orbiting satellites.
The Hindu has reached out to Mr. Malet for further details.
The conclusion of the analysis is that a clear deformation signal is visible at the town of Joshimath as well as on the opposite slopes, while the rest of the region seems relatively stable. It further added that it appears that two zones of the town have been continuously moving in the past four years, since 2018, on the downhill part of the slope.
Talking to The Hindu, Wolfgang Schwanghart, a geomorphologist from the University of Potsdam (Institute of Environmental Science and Geography) said that the analysis by the Aristotle University and CNRS-EOST researchers shows that different parts of the Joshimath area are moving at different velocities. The data dates back to 2018 and movements have perhaps been going on for longer than that. Some areas have experienced an acceleration of the movements since early 2022.
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