The dam had been contentious from the start. It was the largest to be built in India's far northeastern Sikkim state, and had been operating since 2017 as part of the country's effort to use hydroelectric power. Early Wednesday, Lhonak Lake overflowed and tore through the Teesta 3 dam downstream, flooding a valley, killing at least 41 people, and causing widespread destruction, reports the AP. CBS News reports bridges were destroyed and the sole highway into the rest of India has been damaged. Warnings of this very outcome had dogged the lake for years: There was a 2021 paper; other warnings preceded that in 2019, 2013, and 2001. And yet "there were no early warning systems installed," said a rep for the NGO South Asian Network for Rivers, Dams and People.
The New York Times flags that 2021 paper by Indian glaciologist Ashim Sattar, which foretold of the possibility that a flood wave coming from South Lhonak Lake could overwhelm the town of Chungthang and cause "substantial damage to the hydropower dam site." The dam was more than damaged—it was swept away. The Times reports scientists call what happened a "glacial lake outburst flood" (GLOF). It explains: "The Himalayas are full of potential GLOFs, as many as 7,500 of them. ... As deadly as GLOFs are, they can be predicted. And they are predicted to get worse" due to climate change.
That's due to a combination of factors: rising temps are melting glacial ice, causing glacial lakes to grow in size; monsoons are becoming both more intense and more erratic; and the permafrost under the Himalayan ice cap is softening, who can cause "soil and snow lose their grip on each other," triggering avalanches. The Times reports an avalanche is what happened this week, with snow, ice, and boulders careening down a mile and into Lhonak Lake, triggering the GLOF. CNN reports as much as 60% of the lake's water poured out of it.
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"There are more than 54,000 glaciers across the Hindu Kush Himalayan region and very few of them are monitored, which means that such disasters will continue to increase," a UN climate scientist told CBS News. As far as monitoring goes, Reuters reports a system was finally being put in place at Lhonak Lake but wasn't ready for use. "The fact it happened just two weeks after our team was there was completely bad luck," said project member and geoscientist Simon Allen of the University of Zurich. Though a camera and instruments were in place, the tripwire sensor that would signal a burst was coming was a step "the Indian government was not prepared to do ... this year, so it was being done as a two-step process," he said. Had it been completed, a warning could have been issued 90 minutes before the lake burst. (More climate change stories.)
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