Update 17 June 2021: these images were used in a study published in Science by Shugar et al. (2021) A massive rock and ice avalanche caused the 2021 disaster at Chamoli, Indian Himalaya, doi:10.1126/science.abh4455.
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.
The wall.. Impressive post-event image by @cnes @AirbusSpace Pléiades #Chamoli pic.twitter.com/vch2Ox4Qae
— Simon Gascoin (@sgascoin) February 10, 2021
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.
Thanks to @cnes & Pléiades images acquired this morning, we computed a high resolution DEM of the source area of the disaster. Maybe the first post-event high resolution topography. pic.twitter.com/5YmbEVzLgw
— Etienne Berthier (@EtienneBerthie2) February 10, 2021
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
Elevation changes in the source area of the #Chamoli landslide, #Uttarakhand. Massive 150 m loss, about 100 m on average. 10 Feb. 2021 Pléiades DEM was compared to the Copernicus 30 m DEM from ~2013. Data from @CopernicusLand @cnes @AirbusSpace. pic.twitter.com/q8xoBWoXpk
— Etienne Berthier (@EtienneBerthie2) February 11, 2021
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.
Elevation difference map & Pléiades digital surface model. Computed from #Worldview @Maxar by D. Shean @uwTACOlab and @EtienneBerthie2 #Chamoli pic.twitter.com/F9gzgYwDQa
— Simon Gascoin (@sgascoin) February 11, 2021
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.
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
Dear Rainer, the map is oriented with the north upward. The upper panel is the ~N-S cross section.
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
it is W (left) to E (right)
yes horizontal distance
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
Dear Simon,
May I use your images
– « Elevation changes in the source area » and
– « Orthoimage of the scar added contour lines from @CopernicusEU DEM »
in a paper quoting you? Which form of reference would you prefer (https://labo.obs-mip.fr/multitemp/pleiades-images-of-the-uttarakhand-disaster/ ?)?
Thank you for your help, best regards and all the best
Rainer
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!