Page 13 - ScienceIndia Magazine March 2021
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            Above: Route map of the February 7 flash flood. Right: The highlighted glacial ice mass — 500 x 700m — broke off and created flash floods
per a report of the National Institute of Disaster Management (NIDM), the 2013 flash floods had occurred due to very heavy rainfall in the region on June 16, followed by Chorabari Glacial Lake outburst and possible landslides on June 17, devastating the Kedarnath region completely. That remains the worst Himalayan tragedy of our times.
The Himalayas are the youngest mountain ranges on the earth, made up of uplifted sedimentary and meta- morphic rocks. The Himalayas are also tectonically very active, further making the mountain ranges very unstable, frag- ile and susceptible to natural hazards. The International Centre for Integrated Mountain Development in Nepal in its studies has consistently pointed out the rapid building up of glacial lakes in the region. As a result of global warming, melting of glaciers has increased and this has led to the formation of glacial lakes. The mountains weakened by landslides holding the lakes are a fright- ening prospect.
The most recent flash flood oc- curred in Uttarakhand near the Ta- povan area in Chamoli district about 10.15 am on Sunday, February 7, in the
environs of the Nanda Devi National Park, a UNESCO World Heritage Site in the outer Garhwal Himalayas in the state. The Rishi Ganga river originates from the Nanda Devi Biosphere Reserve (NDBR), established in 1982 around the peak of Nanda Devi (7,816 m). Satel- lite imagery shows a clear scar of 500 m width and 800 m length (approxi- mately) moving downwards, with a probable breaking of small glacial lake, sufficient to grease away the large ice mass downstream a narrow valley of loose mountain soil. This mass travelled 24 kilometres down from the slopes of Nanda Ghunti, a 6,300 m peak on the south-western rim of the Nanda Devi sanctuary, to an altitude of 1,900 m (4 km of altitude fall allowing ice mass to face very high thermal shocks to melt) resulting in flash floods and claiming many lives. The disaster caused flooding in the Chamoli district, most notably in the Rishi Ganga river, the Dhauli Ganga river, and in turn the Alaknanda, the major headstream of the river Ganga.
This tragedy again reminds us that the fragile, geologically active Himala- yan region cannot be taken for granted.
received the videos of the flash floods in the Tapovan area on WhatsApp. It was a terrible sight even to imagine but keeping cool was important. From a few of the videos, I tried to understand the flow of water from the movement of boulders, and the viscosity (thickness) of the fluid (water) in the river. On prima facie analysis, I could make out that for the initial five minutes of the video made by a mobile phone camera, there was a
On the fateful day, I immediately
MARCH, 2021 SCIENCE INDIA 13
         Images Courtesy: Dr Sanjeev Kumar Joshi/ DRDO

























































































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