The collapse of a 14.7-million cubic metre mass of rock, ice and sediment into the South Lhonak glacial lake was the set off behind the devastating 2023 Sikkim flood that destroyed a hydropower dam on the Teesta, reveal the findings of a year-long examine revealed within the prestigious Science journal on Friday.
Crucially, the examine discovered no proof of a “triggering cloudburst occasion” within the neighborhood of the lake. The Sikkim authorities had informed the Nationwide Inexperienced Tribunal final yr {that a} cloudburst had probably preceded the glacial lake outburst flood (GLOF).
The flood had killed 55 individuals and destroyed the 1200-MW Teesta III hydel mission, in addition to damaging the Teesta IV and V tasks and Teesta Low Dams III and IV, in addition to farms and buildings in Bangladesh.
The examine says the South Lhonak lake stays “extremely prone” to future GLOFs — a warning that comes simply weeks after an Setting Ministry panel cleared a proposal to construct a brand new 118.64-metre excessive concrete gravity dam within the place of the unique 60-metre tall Teesta-III dam. This ministry approval got here and not using a contemporary public listening to and even because the design points of the dam are but to be authorised.
The investigation into the causes, dynamics and penalties of the GLOF was carried out by a group of 34 consultants from 9 nations and was led by Ashim Sattar, assistant professor, College of Earth, Ocean and Local weather Sciences on the Indian Institute of Expertise, Bhubaneswar.
In line with the examine, the collapse of the frozen glacial particles, referred to as a moraine, created a 20-metre tsunami-like wave that breached the lake’s pure dam. It launched 50 million cubic metres of water — equal to twenty,000 Olympic-sized swimming swimming pools — that took nearly two hours to achieve the hydropower dam, 67 km downstream.
Although the precise reason for its collapse is inconclusive, the moraine — shaped by glaciers over a number of years — was discovered to be unstable for years previous the occasion. It confirmed a most displacement of 15 metres per yr between 2016 and 2023, the examine revealed.
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The world across the glacial lake was additionally discovered to be unstable, owing to thawing of permafrost, or frozen floor, possible resulting from local weather change.
The flood’s severity was additionally worsened by local weather warming results and heavy rainfall, which saturated the soil and elevated its vulnerability to landslides, thus amplifying downstream impacts corresponding to erosion, sediment transport and flood depth, mentioned a be aware issued by the authors of the examine.
“The GLOF peak discharge vastly exceeds meteorological flood magnitudes, suggesting that it’s a uncommon occasion within the historic context of this area, equal to a return interval exceeding 200 years,” the be aware by authors acknowledged.
“South Lhonak lake stays extremely prone to future GLOF occasions. The northern lateral moraine nonetheless has a big and quickly deforming zone regardless of the October 3, 2023 failure,” the be aware added, pointing to the persevering with hazard posed by the glacial lake.
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“As we work to scale back the dangers of GLOFs within the Himalayas, it’s clear that we’d like a multi-faceted strategy, together with early warning methods, strengthened regulatory frameworks, a paradigm shift within the GLOF modelling approaches, and sturdy preparation applications and group schooling,” mentioned lead creator Sattar.
The group of consultants used seismic sign knowledge, satellite tv for pc imagery and modelling strategies to back-calculate the GLOF’s motion and validated it utilizing floor data out there with the Indo-Tibetan Border Police (ITBP) and Sikkim State Catastrophe Administration Authority.
The reconstruction confirmed that the moraine collapsed at 10.12 pm on October 3. At round 10.30 pm, the flood water reached an Indo-Tibetan Border Police camp, 7.12 km downstream, which was in keeping with ITBP’s data. Because the lake’s pure dam burst, its degree dropped 28 meters.
The reconstruction confirmed that at 12:30 am, October 4, the flood waters reached the 1,200 MW Chungthang hydropower dam — this was in keeping with the reported time of 12.35 pm.
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The examine additionally quantified the big quantities of sediment eroded by the GLOF — about 270 million cubic meters, sufficient to fill 1,08,000 Olympic-sized swimming swimming pools. The sediment and boulders have been deposited downstream inflicting immense devastation and harm. Satellite tv for pc-imagery based mostly mapping additionally recognized 45 landslides brought on by the GLOF alongside the Teesta valley.
Co-author Wolfgang Schwanghart of the Institute of Environmental Science and Geography, College of Potsdam, Potsdam-Golm, Germany mentioned: “The South Lhonak outburst as soon as once more demonstrates the vulnerability of Himalayan hydropower to excessive pure occasions. Hydropower tasks uncovered to glaciers and glacial lakes improve the dangers of being impacted by outburst floods. With altering local weather and international warming, we’ll possible see related disasters sooner or later.”
