Page 14 - ScienceIndia Magazine March 2021
P. 14

     UTTARAKHAND FLOODS
 ITBP personnel involved in relief work after the flash flood in Chamoli district in February
flow of muddy water (more water, less soil). Afterwards, there was a consistent flow of thick mud (less water, more soil), which was clear because of the move- ment of boulders along with thick mud. The distinction of water and mud flow was done through various conditions of solid-liquid interaction scenario.
Taking reference of the initial ob- servation of videos where I could clear- ly visualise water flow and then mud flow, I could playback the imagination with concepts of science. The total path length from the Nanda Ghunghti Gla- cier to Tapovan area is around 24 kms in which ice mass, water, boulders, trees and soil flowed. There may be a small landslide underneath the hanging glacier blocking the flow of water from Trishul Glacier overnight, of which some traces can be seen at the place where the gla- cial mass had fallen, thereby breaking glacial lake.
A glacial block of approx. 500 x 700 sq m size with an approximate thickness of 10 m, constructing approximately 02 million cubic metres of ice mass along with a big rock portion, broke off from an altitude of 6,300 m and came down
The sudden altitude variation creating thermal shock to ice mass helped in melting it, creating large water content
 14 SCIENCE INDIA MARCH, 2021
the valley with a very high velocity along a slope of 340, travelling approximately 2.8 km. It was forced to stop immedi- ately at 3,880 m, restricting its natural flow due to obstruction from the other sides of the mountains.
This very high kinetic energy hit the glacial ice boulders. As a result, the soil and rocks may not only have broken the small lake created overnight but also al- lowed pressure melting of glacial ice due to sudden restriction posed in its path. The air burst of rock mass created dust all around. This pressure melting would have then further caused the greasing ef- fect and may have lubricated both sides of the valley, allowing complete mass to flow downstream under gravity.
The flow route of Raungti Nala is narrow and full of loose soil mass, trees, boulders and rocks with numer- ous twists and turns. The large ice mass along with rocks and debris, when achieved terminal velocity, would have
further faced heavy friction and hence, melted into water, thereby increasing the water content. The terminal veloc- ity achieved may have further created vacuum, thereby taking dust coming out of airburst of rocks along the flow path. The sudden altitude variation cre- ating thermal shock to ice mass further helped in melting it, creating large water content. Till this time, the water content was in backstage and ice mass, boulders, eroded soil and debris were in the front creating erosion. Further, loose soil eroded from both the banks of Raungti Nala, gaining further momentum due to boulders and ice chunks.
This whole mass travelled down nonstop with terminal speed, up to 8.5 km distance, till it reached the conflu- ence of Raungti Nala and Rishi Ganga river having semi-circular path towards Dhauli Ganga confluence point. Here, Rishi Ganga river meets at the tangent of that semi-circular path. When the
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