Glacial lake may have caused Nepal floods, hydraulic analysis suggests

A temporary glacial lake may have unleashed the extreme flood that struck Nepal’s Trishuli River, according to a hydraulic analysis by Korea’s Construction and Building Technology Institute. The proposed sequence is stark: an initial glacier collapse formed a lake, then a second collapse breached it and sent a vast volume of water downstream.

Senior researcher Kim Won’s report analyzed the August 2026 flood. It estimated that a major surge began about nine kilometers downstream from the Nepal-Tibet border between 8:40 and 8:55 a.m. The flow may have reached 11,000 tonnes per second, raising the water level by 12 meters and moving downstream at about 14 meters per second.

The surge continued through several monitoring points. At Galchhi, 81 kilometers downstream, the water level rose 8.85 meters between 10:20 and 10:50 a.m. At Maleku, 100 kilometers downstream, it rose 7.13 meters between 11:10 and 11:40 a.m. At Devghat, 168 kilometers downstream, Nepal’s hydrometeorological authorities recorded a peak flood flow of 5,850 tonnes per second and a total passing volume of 57.4 million tonnes. The excess above the normal base flow totaled 19.96 million tonnes.

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The huge flood volume, water level and flow speed that suddenly appeared upstream may have caused this disaster.

Kim estimates that a glacial lake of roughly 20 million tonnes formed upstream and then collapsed. Because satellite images taken before the flood showed no lake, he believes it may have appeared only shortly before the disaster, perhaps after a first glacier collapse. He said the alternative explanation, a flood caused directly by glacier collapse without an intervening lake, appears less likely given the volume and speed of the water.

Kim described the event as an extreme situation that could not have been anticipated, but warned that climate-driven extreme rainfall could produce similar disasters in South Korea. He proposed new response systems for extreme events and evacuation plans for riverside cities, low-lying areas and underground spaces.

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This flood was an extreme situation that could not have been anticipated, but South Korea cannot guarantee that a similar disaster will not occur if climate change brings extreme rainfall.