The Indian Space Agency (ISRO) activated the International Charter "Space and Major Disasters" to image the area of the disater in Uttarakhand (excellent visualisation here). Thanks to CNES and Airbus DS, Pléiades images (resolution: 70 cm in panchromatic, 2.8 m in multispectral) were acquired today 09 Feb 2021, two days after the event. These images show the detachment area with a clear rupture line of 550 m on the north face of Ronti.

This is a comparison with the latest Sentinel-2 image, before the flood.

 

Preliminary work by many scientists suggests that a rockslope failure released a mixture of rock and ice which created a potent flood in the valley of the Rishiganga River.

UPDATE 10 Feb 2021. A Pléiades stereo pair has been acquired (B/H = 0.12) which allowed us to generate a high resolution 3D model of the area.

Update 11 Feb 2021

Two elevation difference maps were computed by Etienne. A first one by differencing the above Pléiades DEM with the Copernicus 30 m resolution DEM

Then, D. Shean (Univ Washington) computed a pre-event DEM from WorldView-1 images which allowed a finer analysis. The estimated detached volume is 25 millions cubic meters.

Authors Etienne Berthier (CNRS/LEGOS) and Simon Gascoin (CNRS/CESBIO)

Acknowledgements Work carried out with the support of CNES, the International Charter for Major Spaces and Disasters and the DINAMIS program.

7 thoughts on “Pléiades images of the Uttarakhand disaster

  1. Dear colleagues,
    Thank you for your excellent work and for the images!
    I am interested in the detachment mechanism of the Chamoli landslide. Therefore, I would like to know the orientations (dip and dip direction) of the discontinuities (faults) bordering the detached block.
    Could you please let me know the orientation of the lower cross section given in "Elevation changes in the source area"? Is the diagram W - E or E - W oriented (line of sight to N or S)?
    Thank you for your help and best regards,
    Rainer Poisel

    1. Dear Rainer, the map is oriented with the north upward. The upper panel is the ~N-S cross section.

      1. Dear Simon,
        Could you please let me know the orientation of the lower panel? Is the cross section W - E (line of sight to N) or E - W oriented (line of sight to S)?

        Just to be sure: I assume the distances in both panels to be horizontal distances. Is this correct?

        Thank you for your help and best regards,
        Rainer Poisel

  2. Dear Simon,
    Thank you for your help!
    Using your information I managed to determine the orientations of the eastern and the western discontinuity forming the wedge. Moreover, these discontinuities can be found in the surrounding rock surface as well as the N-dipping plates of dark rock (presumably Biotite rich Para-gneisses in the Main Central Thrust Zone). It seems that these discontinuities do not extend into the dark rock and thus the wedge has been formed incompletely in the light rock (presumably Quartz-schists and Quartzites), being split by half by the contact plane between the light and the dark rock (hydraulic thrust?) and coming off the contact plane.
    Best regards and all the best,
    Rainer

    1. We are involved in a publication which will contain these results.. in the meantime I guess you can cite this page. Please let me know when your paper is available!

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