Nearly 20,000 Glacial Lakes Span The Himalayas As Warming Takes Its Toll; Detailed Risk Analysis Hasn't Even Begun

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The death of a glacier is widely understood to be a tragedy, a loss reversible only on geological time scales, mourned like the death of a species. But before a glacier is gone — while it is still in the process of dying — it represents not just a loss, but a threat. The problem is the meltwater. As a glacier shrinks, it sheds water that gathers in the earthen bowl where the ice once sat, forming a lake. But the dirt and rock around this bowl are loose, crumbly. And so maybe one day there is a landslide. Maybe a chunk of the glacier’s remaining ice breaks off and plummets into the water.

What happens next? Picture doing a cannonball into an aboveground swimming pool, said Daniel Shugar, an expert on glacial floods at the University of Calgary. Except you don’t just make a giant splash; you blow out an entire wall of the pool. “It would drain within seconds,” Dr. Shugar said. Water plunges down the valley, picking up speed but also sand, silt, gravel and boulders. It becomes a slurry so thick that it knocks down buildings. This is the way some of the largest floods in Earth’s history, ancient deluges that reshaped entire landscapes, took place. More recent floods have taken their own staggering toll: In northern India in 2023, a chunk of partially frozen earth half a mile long collapsed into a lake, creating a 65-foot tsunami that barreled down the mountains, killing dozens of people and destroying a hydropower dam.

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When you think of a glacier, you probably imagine an expanse of white: stately, solid, pristine. Dr. Watson and his team crossed the face of Nepal’s longest glacier, the Ngozumpa, and found it to be a river of dirt, boulders and milky-gray water. Ice is still there, beneath the debris that crumbles off the mountains. But as it melts, more and more of the glacier’s surface is liquid: puddles that you could step across at first, then ponds, then lakes. Now, the lakes are joining up, transforming the landscape into a maze of ribbonlike waterways.

Dr. Watson stood at the edge of one lake and steered a robot across its surface. A program on his phone showed the water’s depth. “Fifty meters, the deepest I’ve seen,” he said. Then, five minutes later: “I think we’re up to 67 meters,” or around 220 feet. In recent decades, satellites have allowed scientists to watch glacial lakes expand and proliferate in ever-increasing detail. There were 19,300 of these lakes across the Himalayas as of 2020, nearly 1,700 more than in 1990, by one recent estimate. Their total area grew 10 percent.

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https://www.nytimes.com/interactive/2025/11/14/climate/glacier-melt-himalayas.html