Satellite observations have recorded that Joshimath has been sinking for the past four years. According to the French National Center for Scientific Research (CNRS), satellite images of the city of Uttarakhand between 2018 and 2022 have shown that its eastern part is shifting an average of about 10 cm every year due to the landslide crisis in Joshimath.
The French National Center for Scientific Research (CNRS), is the French state research organization and the largest fundamental science agency in Europe.
The Copernicus Sentinel programme, a cooperative mission developed in collaboration between Europe and the US, uses satellite observations to determine the movement of the surface, among other parameters. It also helps to calculate displacement over a wide area.
“The city is located on steep slopes and was built on unconsolidated soils known to be unstable for several decades,” says AUTh and CNRS-EOST in their consolidated report that conducted a displacement time series in the broader region of Joshimath from January 2018 to December 31, 2022. Suggests that surface displacement rates are being exacerbated over the past four years potentially by urbanization, including drainage disruption, uncontrolled water discharge, and slope scour.
Satellites reveal new details
Taken from the satellite data, a post on the Geohazards Exploitation Platform said that Joshimath town as well as the opposite slopes are showing signs of clear deformation, while the rest of the area seems relatively stable.
Two radar images of the same area that were collected at different times from similar vantage points in space can be compared with each other. Recent developments were tracked by the SURFACE MOTION MAPPING (SNAPPING) service for the Sentinel-1 mission on the Geohazards Exploitation Platform (GEP) to produce a ground deformation map covering a large spatial area.
SNAPPING provides the average velocities as well as the full displacement time series (ie, the evolution of motion over time) for each PSI (Persistent Scattering Interferometry).
Recent field observations here also showed complex subsidence patterns with both vertical and horizontal deformations, including subsidence of up to several centimetres, according to information released Thursday by Greece’s Aristotle University of Thessaloniki. It is supported by the Observatory des Sciences de la Terre ie Strasbourg, France, the School of Observatory and Earth Sciences.
Dave Petley, Vice-Chancellor of the Britain’s University of Hull, which provides observation and analysis on landslide occurrences around the world, said the situation would turn positive as summer begins.
Pointing to the above analysis made possible by Sentinel-1’s images, Petly says, this diagram clearly shows the different landslide units on which the city is built and the patterns of activity they display over long periods of time. This confirms that it is being displaced, not being decreased, as expected.
A sloping area is a clearly defined structure of soil or rock moving downward. This is due to the stress of the motion which is sufficient to produce permanent deformation.
The motion of such landslide complexes is very complex to understand and the rate of change we expect to occur over time. Thus, great care needs to be taken in interpreting the data for the different time phases over short periods of time.
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