Revealing what triggered the destructive Flash Floods at Chamoli in 2021
- Arpit Shah
- Jul 6, 2021
- 4 min read
Updated: 14 hours ago
The Chamoli Disaster refers to the flash floods that occurred on 7 February 2021 in the outer Garhwal Himalayas within the mountainous state of Uttarakhand, India.
Imagine being struck by a torrent of rock hurtling at 90 km/h (56 mph)—some of the boulders within the flow were over 20 metres in diameter!
The 13.2 MW Rishiganga Small Hydro Project, located about 15 kilometres upstream, was obliterated in seconds. The debris-laden mass then surged downhill and struck the 520 MW Tapovan-Vishnugad Hydro Project, located 10 kilometres downstream, at speeds approaching 60 km/h (37 mph). The force was sufficient to catastrophically damage the under-construction power plant, block its tunnels, and fatally trap 140 workers inside.
In total, 204 people lost their lives, along with 20 hectares of forest, bridges, critical infrastructure, and residential settlements.
In the days following the disaster, media reports speculated widely about its cause—glacier bursts, landslides, or a combination of both. The definitive cause, however, was established last month (10 June 2021) by a group of 53 researchers, who published their findings in the prestigious academic journal Science. Shortly thereafter, the Geological Survey of India independently reached the same conclusion (29th June 2021).
The flash floods were triggered by a rock and ice avalanche, formed by the sudden collapse of a glacier-covered rock mass measuring approximately 1,500 metres in length, 500 metres in width, and 180 metres in thickness, from the steep northern face of Ronti (Raunthi) mountain.
The glacier-covered rock experienced a near-free fall for much of its initial 2-kilometre descent. When the estimated 27 million cubic metres of material—comprising roughly 80% rock and 20% ice—impacted the valley floor at Ronti Gad, the energy released was equivalent to the detonation of 15 Hiroshima atomic bombs. This immense energy instantaneously melted snow and ice, generating a highly mobile slurry of water and debris that travelled 35 kilometres downstream, devastating everything in its path—including the two hydropower projects.
A detailed account of the Chamoli disaster is presented in this BBC article, which prompted me to independently examine the source of the avalanche. My findings, derived from Sentinel-2 optical satellite imagery, are captured in the video below and in the two comparison sliders that follow.
Slider 1: Source view on 21 May 2020 (one year prior) vs 5 February 2021 (two days prior)
Slider 2: Source view on 5 February 2021 (two days prior) vs 31 May 2021 (~four months later)
One cannot help but wonder how different the outcome might have been had Ronti Peak been actively monitored prior to 7 February 2021. So many precious lives could have been saved.
“Hindsight is a wonderful thing, but foresight is better—especially when it comes to saving life, or some pain.” — William Blake
In perspective, this is not a far-fetched proposition. Displacement of the glacier-covered rock mass on Ronti Peak was detected as early as 2016. Moreover, the wisdom of constructing critical infrastructure in fragile Himalayan terrain has long been questioned by experts. At the very least, a robust Early Warning System (EWS) should have been in place from a risk-management standpoint.
Uttarakhand’s history is replete with floods, landslides, and forest fires, and notably, the two destroyed hydropower projects had themselves been impacted by floods on multiple occasions in the past. If you read this article written by Sunita Narain—a member of an inter-ministerial group assessing issues related to the Ganga River—you will be left aghast by the planning and sanctioning of hydropower projects in a state that hosts all five headstreams of the River Ganges, a lifeline for 650 million people downstream.
It is also critical to acknowledge the role of climate change in this disaster. January 2021 was the warmest January in Uttarakhand in six decades, and the region experienced heavy snowfall followed by an abrupt rise in temperatures between 4 and 6 February 2021. These conditions likely weakened the structural integrity of the glacier-covered rock mass on Ronti’s steep face, setting the stage for the catastrophic collapse on 7 February.
The unfortunate reality is that while terabytes of satellite imagery are acquired every day, much of it goes unanalyzed. This is precisely where the value of automated detection and classification algorithms becomes evident.
Explore more of my independent Remote Sensing work here.
ABOUT US - OPERATIONS MAPPING SOLUTIONS FOR ORGANIZATIONS
Intelloc Mapping Services, Kolkata | Mapmyops.com offers a suite of Mapping and Analytics solutions that seamlessly integrate with Operations Planning, Design, and Audit workflows. Our capabilities include — but are not limited to — Drone Services, Location Analytics & GIS Applications, Satellite Imagery Analytics, Supply Chain Network Design, Subsurface Mapping and Wastewater Treatment. Projects are executed pan-India, delivering actionable insights and operational efficiency across sectors.
My firm's services can be split into two categories - Geographic Mapping and Operations Mapping. Our range of offerings are listed in the infographic below-
A majority of our Mapping for Operations-themed workflows (50+) can be accessed from this website's landing page. We respond well to documented queries/requirements. Demonstrations/PoC can be facilitated, on a paid-basis. Looking forward to being of service.
Regards,
