by Bob Henson, Yale Climate Connections
August 28, 2026

Rescue efforts in Nepal and Tibet in the wake of a massive rock-and-ice avalanche and flood early on Wednesday, August 26, were halted on Friday after water was observed flowing over a dam from an impromptu lake formed by the disaster itself. Officials and residents are concerned about yet more disastrous flooding across the devastated region, although China state media reported that the situation had stabilized later in the day, according to the BBC. Long-term human-caused warming of the planet has destabilized glaciers and permafrost in the Himalayas, setting the stage for disasters like this one.

The most recent death tolls as of this writing – according to the BBC, at least 547 in Nepal and five in Tibet – are virtually certain to end up far below the ultimate tally of those killed. Even the numbers reported missing – more than 2,400, according to a Wikipedia page on the event – only reflect those people for whom reports have been filed. Grim videos make it clear that many people were swallowed by the flood within minutes, and the destruction of transport corridors and communication towers makes it impossible to know how many killed and missing persons have yet to be tallied.

This geophysical disaster has unusual international impact in that the Himalayas are a major draw for tourists and mountaineers from across the globe. Among those missing in Nepal are at least 575 foreign nationals from 36 countries, including at least 65 from the United States.

How glacier collapse led to disaster

An earthquake wasn’t the direct cause of the tragedy as had been initially thought. In fact, the detected earthquake – initially classified by the U.S. Geological Survey as a magnitude 4.4 near the border of central Nepal and Tibet to its north – was reclassified by USGS as a magnitude 5.2 landslide. In other words, it was a glacier collapse and landslide that triggered the earthquake, not the reverse: “Additional analysis of long period seismic waves indicate that the seismic energy was instead generated by a glacial collapse and debris flow,” the USGS reported.

Along with the planet as a whole, the Himalayas have been experiencing a climate warmed by human fossil-fuel burning for decades. Warming temperatures have destabilized glaciers and permafrost, and they have intensified precipitation rates across the region.

Satellite data confirm the hypothesis that a glacier collapse caused the catastrophe, as shown in a detailed analysis by Levan Tielidze, a postdoctoral researcher in glacial geomorphology at Monash University, that was published on Friday at The Conversation.

Tielidze opens his account with this description: “On August 26 a glacier collapsed in the Langtang region of Nepal near the China border, triggering an ice and rock avalanche. This apparently entered the Lhende Khola, a tributary of the Bhote Koshi river, where it either caused or contributed to a temporary blockage. When this burst, a catastrophic flash flood travelled almost 100 kilometers downstream.”

It appears the core nature of this event was a phenomenon often referred to as a rock-ice avalanche, a threat that’s been looming larger in recent years. When the front edge of a huge glacier collapses, the descending ice and the rock below quickly mix into a horrific sludge that morphs into a giant wave of water, mud, rock, and other debris cascading down a mountain valley. As summarized by Wikipedia, the debris flow in Nepal is estimated to have traveled at speeds of around 110 mph (180 km/hr). After having pushed roughly 4.3 mi (7 km) downstream from its origin, the flood wave was as deep as 2,600 feet (800 meters). The flood devastated communities that were perched as high as 270 feet (80 meters) above the normal river level.

How Switzerland’s Birch Glacier collapse differed from this one

A recent rock-ice avalanche that grabbed attention worldwide was the Birch Glacier collapse in Switzerland on May 28, 2025, the most destructive in modern Swiss Alps history. That event, which inundated the town of Blatten shortly after timely warnings led to its evacuation, appears to have been one of a subset of rock-ice avalanches described by Andreas Kääb at the University of Oslo and colleagues in a 2021 paper in The Cryosphere as “sudden large-volume detachments of low-angle mountain glaciers.”

However, the Nepal/Tibet disaster doesn’t fall into that sub-category. “Definitely no!” said Mylène Jacquemort, a glaciologist at ETH Zurich who coauthored the Cryosphere paper, in an email. Jacquemort added, “It was a large rock avalanche with a glacier on top.”

Even if the Blatten disaster isn’t a direct analog to the cataclysm in Nepal and Tibet, it does have instructive elements, as discussed in an excellent analysis of this week’s disaster from Renato Colluci at Severe Weather Europe:

Blatten is important because it shows how rapidly one process can feed another. Progressive rock failure loaded and destabilized a glacier; the glacier and rock mass collapsed together; the avalanche crossed the valley floor; and the deposit dammed a river, creating a secondary flood hazard. A 2026 study in the Journal of Rock Mechanics and Geotechnical Engineering reconstructed the event as a domino-style rock and ice avalanche, with about 5.5 million cubic meters of progressive rock collapse preceding the sudden release of roughly 8.3 million cubic meters of mixed rock and ice.

Glacier collapse on a warming planet

Many local and regional factors – including weather and climate as well as landscape change – can lead to catastrophic glacier collapse. It’s clear that temperatures are warming over the long term globally, and at even higher rates across glaciated Northern Hemisphere locations such as the Rockies, Alps, and Himalayas. We also know that occasionally disastrous glacier collapses have been recorded for centuries. So it’s helpful to think of long-term warming from fossil fuel use not as “causing” any particular collapse, but more as setting the preconditions for the kind of events that emerge from geographic and climatic conditions that can vary sharply over space and time.

It’s certainly been a warm year and a warm summer across central Nepal and adjoining parts of Tibet. Global analyses from NOAA show unusual warmth focused on eastern Nepal and much of western China for the month of July, as well as for the year to date (January-July), with record warmth for 2026 thus far across large parts of nearby China.

In a Bluesky post, Jeff Berardelli shared his graphing of August temperatures over the affected region. The trace below represents long-term trends across a grid box 19 miles (31 kilometers) wide, centered on a point near the landslide.

Much work remains to be done on the myriad factors driving glacier collapse. Among these is better characterizing the state of permafrost across the Himalayas, since the ongoing and future destabilization of that undergirding layer (as analyzed earlier this year in an npj Natural Hazards paper) may be an important piece of the puzzle.

It’s clear enough already that people and societies around the Northern Hemisphere’s high-mountain glaciers have plenty to worry about in the coming years – and that the world at large must stand ready to help these vulnerable people and places.

Jeff Masters contributed to this post.

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