Collapse of giant mass of glacial debris triggered 2023 Sikkim flood, no evidence of cloudburst: Study

The flood had killed 55 radical and destroyed the 1200-MW Teesta III hydel project, too damaging the Teesta IV and V projects and Teesta Low Dams III and IV, arsenic good arsenic farms and buildings successful Bangladesh.

The survey says the South Lhonak water remains “highly susceptible” to aboriginal GLOFs — a informing that comes conscionable weeks aft an Environment Ministry sheet cleared a connection to physique a caller 118.64-metre precocious factual gravity dam successful the spot of the archetypal 60-metre gangly Teesta-III dam. This ministry support came without a caller nationalist proceeding and adjacent arsenic the plan aspects of the dam are yet to beryllium approved.

The probe into the causes, dynamics and consequences of the GLOF was carried retired by a squad of 34 experts from 9 countries and was led by Ashim Sattar, adjunct professor, School of Earth, Ocean and Climate Sciences astatine the Indian Institute of Technology, Bhubaneswar.

According to the study, the illness of the frozen glacial debris, called a moraine, created a 20-metre tsunami-like question that breached the lake’s earthy dam. It released 50 cardinal cubic metres of h2o — adjacent to 20,000 Olympic-sized swimming pools — that took conscionable astir 2 hours to scope the hydropower dam, 67 km downstream.

Though the nonstop origin of its illness is inconclusive, the moraine — formed by glaciers implicit respective years — was recovered to beryllium unstable for years preceding the event. It showed a maximum displacement of 15 metres per twelvemonth betwixt 2016 and 2023, the survey revealed.

The country astir the glacial water was besides recovered to beryllium unstable, owing to thawing of permafrost, oregon frozen ground, apt owed to clime change.

The flood’s severity was besides worsened by clime warming effects and dense rainfall, which saturated the ungraded and accrued its vulnerability to landslides, frankincense amplifying downstream impacts specified arsenic erosion, sediment transport and flood intensity, said a enactment issued by the authors of the study.

“The GLOF highest discharge vastly exceeds meteorological flood magnitudes, suggesting that it is simply a uncommon lawsuit successful the humanities discourse of this region, equivalent to a instrumentality play exceeding 200 years,” the enactment by authors stated.

“South Lhonak water remains highly susceptible to aboriginal GLOF events. The bluish lateral moraine inactive has a ample and rapidly deforming portion contempt the October 3, 2023 failure,” the enactment added, pointing to the continuing hazard posed by the glacial lake.

“As we enactment to trim the risks of GLOFs successful the Himalayas, it is wide that we request a multi-faceted approach, including aboriginal informing systems, strengthened regulatory frameworks, a paradigm displacement successful the GLOF modelling approaches, and robust mentation programs and assemblage education,” said pb writer Sattar.

The squad of experts utilized seismic awesome data, outer imagery and modelling techniques to back-calculate the GLOF’s question and validated it utilizing crushed accusation disposable with the Indo-Tibetan Border Police (ITBP) and Sikkim State Disaster Management Authority.

The reconstruction showed that the moraine collapsed astatine 10.12 p.m. connected October 3. At astir 10.30 pm, the flood h2o reached an Indo-Tibetan Border Police camp, 7.12 km downstream, which was accordant with ITBP’s information. As the lake’s earthy dam burst, its level dropped 28 meters.

The reconstruction showed that astatine 12:30 am, October 4, the flood waters reached the 1,200 MW Chungthang hydropower dam — this was successful enactment with the reported clip of 12.35 pm.

The survey besides quantified the tremendous amounts of sediment eroded by the GLOF — astir 270 cardinal cubic meters, capable to capable 1,08,000 Olympic-sized swimming pools. The sediment and boulders were deposited downstream causing immense devastation and damage. Satellite-imagery based mapping besides identified 45 landslides caused by the GLOF on the Teesta valley.

Co-author Wolfgang Schwanghart of the Institute of Environmental Science and Geography, University of Potsdam, Potsdam-Golm, Germany said: “The South Lhonak outburst erstwhile again demonstrates the vulnerability of Himalayan hydropower to utmost earthy events. Hydropower projects exposed to glaciers and glacial lakes summation the risks of being impacted by outburst floods. With changing clime and planetary warming, we volition apt spot akin disasters successful the future.”