Nepal’s Glaciers Will Flood Again. Can Scientists Predict the Next One?
The Himalaya is one of many places around the world home to glaciers that are increasingly becoming unstable as the planet warms.
Tragedy struck Nepal and China this Wednesday when a maelstrom of water, rock, and mud erupted down a Himalayan river valley, sweeping away countless houses, bridges, roads, and people—and burying many more under a viscous slurry. Although scientists are still determining precisely what happened, initial assessments indicate that glacial fragments, along with the nearby section of a cliff, broke away thousands of feet above the ground, dropping the equivalent of 70 Great Pyramids of Giza down into the valley all at once.
Although this specific catastrophe was unanticipated, this type of hazard—the rapid, violent collapse of a glacier—is becoming par for the course in a rapidly warming world. Anthropogenic climate change is thawing glaciers at an unparalleled pace. Melt them enough, and those dangling precariously atop mountains will smash into whatever resides below.
The Himalaya is far from the only place with elevated glaciers: everywhere from Norway and New Zealand to Iceland and Chile have these cryogenic time bombs perched on their highest peaks. “All the world's glaciated regions are vulnerable due to rapid warming and accelerated melting,” says Mohan Bahadur Chand, a glaciologist at Kathmandu University in Nepal and National Geographic Explorer. And depending on where they are, a glacial collapse could unleash anything from a sudden flash flood to a skyscraper-high megatsunami.
“But it’s not all doom and gloom,” said Alton Byers, a National Geographic Explorer and glacier hazards expert at the University of Colorado, Boulder, in an email. Some treacherous glaciers, when properly monitored, show signs when they’re about to crumble—meaning thousands of lives can be saved under the right circumstances.
But will they be enough to help millions survive our planet’s increasingly warm future?
The Explosive Power of a Glacier
Glaciers can be found on every single continent. When those stuck atop mountain ridges thaw, crack, and collapse, they can cause a range of potentially lethal mass movements, from ferocious outpourings of meltwater to terrifying avalanche-landslide hybrids.
If a glacier disintegrates in a tall fjord, it can create what’s known as a megatsunami. In 2023, a gargantuan rock-ice avalanche in eastern Greenland splashed down into the confined waters below, creating waves 650 feet high that shredded the fjord’s rocky walls to pieces.
In 2025, a similar collapse took place in an Alaskan fjord, creating a 1,580-foot-high megatsunami; that’s three times the height of the Washington Monument. The Alaskan fjord is often frequented by cruise ships. It was only because the megatsunami happened in the early hours that the fjord was mercifully empty at the time.
Sometimes, glaciers break apart in less remote locations. Last May, a large piece of the Birch glacier in the Lötschen Valley of the Swiss Alps snapped, generating a rock-ice avalanche that smothered most of the village of Blatten in 20 million tons of debris.
The recent collapse in the Himalaya offers another nightmarish example. On Wednesday, something dislodged on the north face of the peak of Langtang Lirung, on the Nepal-Tibet border. “There was a collapse of a large piece of bedrock that was sitting below the glacier,” says Kristen Cook, a geomorphologist at the Université Grenoble Alpes in France. “The ground underneath the glacier collapsed and took the glacier with it.”
The breakneck speed of the freefalling ice then caused it to melt. It’s also possible that the rock briefly dammed the Lhende River, forming a temporary lake—a dam that was suddenly breached. “Though the timing, size of the damming, and volume of water are not yet confirmed, this could be the most likely reason for the floods,” says Chand.
No single disaster can be solely attributed to higher atmospheric temperatures. But here, the high-altitude permafrost—“the cryospheric glue that’s held the snow/ice/rock together for millennia,” says Byers—has likely been weakened by our warming world.
In fact, global warming has been cited as a key contributing factor for all these glacier-related collapse events. The equation is straightforward. “As the temperature increases, glacier melting accelerates, and glacial lake formation and other factors make the mountain unstable, along with fragile geology,” says Chand.
Forecasting the Next Glacial Cascade
If Earth’s skies and oceans continue to warm unabated, the next few decades will be unpleasant. Both the frequency, and possibly the magnitude, of these glacial hazards, will rise. “We do expect more instabilities in high mountains,” says Cook. “This event [in Nepal] was an exceptionally large one. But much smaller collapses of this type will certainly continue to occur.”
The Himalaya doesn’t have a monopoly on glacial dangers.
“The Andes, especially the Cordillera Blanca in Peru, started to experience devastating glacial lake outburst floods as early as the 1940s,” says Byers, partly a consequence of these glaciers being at lower elevations and subject to faster, earlier temperatures rises. Some engineering work—including digging draining ditches—has been implemented to try and stave off future torrents. But those protective measures can’t stop the glaciers from thawing and breaking apart.
But the Himalaya is particularly vulnerable, says Cook: the region has a high number of glaciers atop very steep slopes, above similarly steep river valleys—valleys often filled with infrastructure. And as well as the threat of glacial collapses, a 2019 study found that 210 glacial lakes potentially threaten human settlements with sudden flash flooding events.
That doesn’t mean humanity is defenseless. Aside from lofty goals of stabilizing glaciers by limiting greenhouse emissions, scientists have recently been able to save countless lives from a glacial collapse. The 2025 avalanche that buried the Swiss village of Blatten was a disaster, but nobody from that village perished: the locals, and their animals, had been evacuated nine days before the collapse took place.
Benjamin Bellwald, a natural hazards researcher at the Norwegian Geotechnical Institute–and a native of Blatten—explains that the glacier in question was known to be problematic since the 1990s. By early 2025, increasingly frequent rockfalls from the glacier put scientists and policymakers on alert. Thanks to the watchful eye of the residents, along with a suite of scientific monitoring technology, evidence pointed to a glacial collapse sooner rather than later.
“A very clear and open communication resulted in a smooth evacuation, so that ultimately no resident of Blatten died,” says Bellwald. The economic damages were steep—around $400 million—but lives that could have been lost without a warning were saved.
Can this system apply to the Himalayan glaciers too? Potentially, yes. Byers explains that work is underway with the authorities in Nepal to identify the sites of future glacial outbursts, along with the development of hazard maps and community preparedness plans.
There are, however, some sizable caveats. “The Himalayas are obviously a very large region to monitor, making it more challenging compared to the Alps,” says Bellwald. Even if you prioritize a smaller number of especially sketchy-looking glaciers, based on what scientists know about them already, it’s not like each one will give off the same warning signals before a collapse event.
But such warning systems could work, if the imperiled country deploys “highly sophisticated, continuous monitoring,” says Chand. Unfortunately, the relative wealth afforded to the Swiss is often not available to others. “Developing countries in the Hindu Kush Himalaya are facing greater challenges.”
One especially pervasive problem is the “unregulated construction and urbanization on rivers and flood plains subject to catastrophic floods,” says Byers. The busier these areas are, the higher the future death tolls will ultimately be.
There’s plenty of work left to be done. Crucially, nobody yet knows exactly when, or where, the next glacial collapse or flash flooding event will appear. There is, for now, only one certainty. “More and more disasters are coming,” says Chand.
