Kheer Ganga's fury: Satellite images point to moraine breach behind Uttarkashi's Dharali disaster

Credit: ISRO

Fresh satellite images have laid bare the catastrophic aftermath of Tuesday’s flash floods in Uttarakhand, showing vast swathes of Dharali village smothered under layers of mud and debris. The images reveal entire buildings, roads and orchards submerged under sediment carried by the raging Kheer Ganga river, HT reported.

Satellite Insights Aiding Rescue & Relief Ops

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ISRO/NRSC used Cartosat-2S data to assess the devastating Aug 5 flash flood in Dharali & Harsil, Uttarakhand.

High-res imagery reveals submerged buildings, debris spread (~20ha), & altered river paths, vital for rescue teams on… pic.twitter.com/ZK0u50NnYF

— ISRO (@isro) August 7, 2025

The National Remote Sensing Centre (NRSC) of ISRO swiftly undertook a damage assessment utilising ultra high-resolution imagery from India’s Cartosat-2S satellites. By comparing satellite images captured after the disaster on August 7, 2025 with clear, pre-event data from June 13, 2024, analysts were able to determine the full scale and gravity of the devastation.

The images indicated that the deluge has partially blocked the Bhagirathi river downstream, disrupting its natural flow. A critical bridge and surrounding agricultural land appear inundated, compounding the challenges for rescue and recovery efforts.

Experts examining the images suggest the disaster may have been triggered by a glacial collapse upstream of Kheer Ganga. Anil Kulkarni, a scientist at the Divecha Center for Climate Change, noted in an internal briefing that the river originates from a glaciated area, where satellite imagery from 2022 showed a well-developed deglaciated valley.

“Outlet of the deglaciated valley is bounded by end moraine and a small river passes between it and the side wall,” Kulkarni stated, as cited by HT. He pointed to signs of past landslides in the moraine, which could have temporarily dammed meltwater, forming a lake. “The flash flood mudflow may have been caused due to the outburst of this lake,” he added.

The National Disaster Management Authority (NDMA) is awaiting clearer satellite images to confirm the exact cause. Safi Ahsan Rizvi, NDMA’s advisor for mitigation, said preliminary assessments indicate that a glacial snout at 6,700 metres detached recently, accumulating debris that was then loosened by heavy rainfall.

“Once critical mass was crossed, the massive collection of debris cascaded downstream with water in the Kheer Ganga, accelerating due to the steep gradient upto Dharali,” Rizvi explained, as cited by HT. He clarified that the affected area was not among the 195 glacial lakes previously categorised as ‘at-risk’ by the NDMA.