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)
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.