2023 Sikkim flood disaster decoded by IIT scholar

BHUBANESWAR: A catastrophic Glacial Lake Outburst Flood (GLOF) struck Sikkim’s Upper Teesta Basin on October 3, 2023, originating from
South Lhonak Lake (5,200 m).
The flood travelled 385 km downstream, causing 55 deaths, 70 missing persons, and extensive damage to infrastructure.

A study published in ‘Science’, led by Dr. Ashim Sattar from IIT Bhubaneswar, brought together 34 experts from nine countries to analyse the disaster. Using seismic data, satellite imagery, and modelling, they identified the trigger—a landslide of frozen ground at 22:12:20 IST—releasing water equivalent to 20,000 Olympic-sized pools and causing a ~28 m lake level drop.
The study revealed that the part of the land that collapsed had been unstable for years, showing movement with a maximum velocity of 15 m annually from 2016 to 2023. GLOF modelling showed the flood reached Chungthang by 12:30 AM IST on October 4, destroying the 1200 MW Teesta III hydropower project and impacting Teesta V, Teesta VI, and Teesta Low Dams III and IV.
“Teesta V and VI remain non-functional,” noted co-author Rajeev Rajak. Co-author Wolfgang Schwanghart says, “Himalayan hydropower remains vulnerable to such extreme events, emphasizing the need for climate-adaptive risk mitigation.”
The flood eroded enormous volume of sediment—enough to fill 108,000 Olympic-sized pools—which was deposited downstream, devastating areas including Chungthang, Dzongu, Dikchu, Singtam, Bardang, Rangpo, Melli, Teesta Bazaar, and Geli Khola. High-resolution satellite imagery identified 45 landslides along the valley, damaging 200 buildings and 6.4 km of NH-10, isolating communities at places after the event.
Road slumping persisted for months, notably at the Naga landslide.
“Anticipating future GLOFs requires understanding cascading hazards like landslides and sediment mobilization,” said co-author Kristen Cook.
Published in the journal Science, the study brought together 34 global experts who used seismic data, satellite imagery, and modelling to track the flood’s path.
Dr. Sattar emphasized the need for urgent action, including robust hazard mapping, improved early warning systems, and stronger community preparedness.
The study also highlighted IIT Bhubaneswar’s expertise in remote sensing technology, crucial for evaluating natural hazards like coastal erosion, cyclones, and heatwaves in Odisha. “Scientific assessments and climate-adaptive strategies are essential to protect vulnerable communities from future disasters,” he said.