Cracks are visible due to sinking ground around a house in Joshimath, Uttarakhand. file | photo credit: special arrangement
while the recent Damage to houses and structures in Joshimath Many experts say that geological changes affecting the topography of the city have been going on for many years.
A report by NRSC-ISRO – which showed that Joshimath sank by 5.4 cm between December 27, 2022 and January 8, 2023 – sparked controversy and was later removed by the organisation. Gag Order of National Disaster Management Authority,
Dave Petley, a landslide expert and vice-chancellor of the University of Hull in the UK, cited an analysis posted on a blog – written by remote sensing and landslide experts at the Aristotle University of Thessaloniki, the Earth Sciences Observatory and the University of Strasbourg’s School of Remote Sensing and Landslides – and the National Scientific Research Center – which showed through satellite measurements that the surface displacement rate at Joshimath was between 3 cm and 10 cm per year (at different places) in the last four years. It said that the Himalayan city is ‘sliding’.
The authors of the analysis, including geomorphologist Jean-Philippe Mallet, claim to have used satellite imagery and analysis based on 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.
Hindu For more details contact Mr. Malet.
‘Areas moving at different velocities’
The conclusion of the analysis is that Joshimath town as well as the opposite slopes show a clear deformation signal, while the rest of the region appears relatively stable. It further added that it appears that the two zones of the city have been moving continuously on the steeper side of the slope over the past four years, since 2018.
talking to HinduGeomorphologist Wolfgang Schwanghardt of the University of Potsdam (Institute of Environmental Science and Geography) said the analysis by researchers from Aristotle University and CNRS-EOST shows that different parts of the Joshimath region are moving at different velocities. The data is from before 2018 and the movement has probably been going on longer than that. Some areas have experienced a spurt in movements since early 2022.
The analysis states that surface displacement rates are higher on the eastern side of the slope with values in excess of 10 cm per year and a second zone also appears on the western side with displacement rates of up to 3 cm per year. The rest of the slope, mostly in the upper parts, shows an average velocity of less than 2 cm per year.
“The values are averages over large areas, and therefore, we cannot exclude that some areas have remained stable while others have moved at a more rapid rate which may explain why some buildings are more severely damaged than others.” The authors provide important data for understanding the kinematic behavior of the landslide, thus providing important information that will hopefully lead to a better understanding of its causes,” he said.
‘Landslide prone’
Mr Schwanghart himself co-authored another study by Indian and international scientists in 2022, which said it identified over 300 “fully or partially road-blocking landslides” between Rishikesh and Joshimath. Gone, which is at a distance of 250 kms. Passes between Tehri, Pauri, Rudraprayag and Chamoli districts of Uttarakhand. The study is currently under review for publication.
Mr Schwanghart said, the road in the given section is highly prone to landslides, which have been described earlier and attributed to the fragility of the slopes of the area, concentrated rainfall and frequent seismicity.
As per the government’s assessment, as of Friday, over 863 houses were found damaged in the town, of which 181 were in the danger zone. Over 900 people have been rehabilitated in temporary shelter homes by the state government since January 5.