Utilization of ICESat-2 and Pleiades Stereo Datasets for assessments of Changes in Elevation in Complex Himalayan Terrain due to the Rockslide at Trishul Mountain Range near Ronti Glacier, Chamoli

Openly accessible space-borne lidar, ICESat-2 datasets along with Pleiades stereo datasets provide a unique opportunity for estimation and monitoring of fragile sites in relatively inaccessible complex terrain for their changes in elevation and state. Two sets of over 100 lidar points (footprints) from ICESat-2 Track ID: 1354, dated 27 March 2019 were chosen in the flood-impacted Rishiganga and Dhauliganga valleys, i.e. at the place of the rock slide and a confluence Junction on the downstream side towards the severely affected Raini Village. These two locations depict the large-scale changes that occurred due to the flash flood initiated by the rockfall on 7th February 2021. The pre-and post- datasets from Google Earth optical images depict the large variations that occurred due to the event. Digital elevation model generated from Pleiades stereo datasets acquired on 10th February 2021 (post-event), is used for analysis with ICESat-2 datasets (pre-event). Before the event at the analyzed junction location, there was a width of about 30m channel with boulders and had tree-covered surrounding slopes. After the event lot of mud and debris have accumulated in a width of about 300 m without tree cover. The trees got unearthed in the processes involved in the event. The analysis shows a clear sign of erosion on the banks and the accumulation of debris along the river channel as well. The analysis depicted an accumulation of debris that raised the elevation from 0.1m to 44.86m at places with an average of 11.34m. Whereas the erosion varies from 0.15m - 15.76m with an average of 4.85m, mainly on the eroded river banks.