How a glacier collapse may have caused Nepal-Tibet disaster

A huge piece of ice that fell thousands of metres from a glacier into a river below may have unleashed the disaster in Nepal and Tibet that killed at least 180 people.

Here is what experts believe happened so far:

Glacier collapse

A glacier collapse in Nepal’s mountains near Tibet appears to have triggered the disaster.

“A large chunk of glacier fell from about 5,200 metres… into a valley,” said Simon Cox, principal scientist at New Zealand’s GNS Science.

It “transformed into this raging mass of debris… where it picks up rocks and sediment and trees and anything in the way and fires it on down through the canyon,” he told AFP.

The wall of water first impacted a border post, as documented in terrifying CCTV footage showing mud and debris engulfing the area as people fled before it.

It then travelled downstream into Nepal, flooding villages and bringing down bridges and buildings.

Seismic activity

The glacier collapse was large enough to register as a seismic event, initially mistaken for an earthquake.

But after further analysis, the US Geological Survey determined “that the seismic event was instead a glacial collapse and debris flow, and that no earthquake had occurred”.

The collapse registered as a 5.2-magnitude “seismic event”, which took place at 8:37am local time (7:52am PKT).

Estimating just how much of the glacier collapsed will take time, Cox said, but it could range from “half a million cubic metres to tens of million cubic metres”.

Glofs

Early speculation suggested a glacial lake outburst flood, or Glof, a growing risk as glaciers melt due to climate change.

A Glof occurs when a fragile debris wall holding back a lake of glacier melt suddenly collapses, unleashing the water behind it.

Some experts suggested a Glof might have been involved.

“Water does flow within glaciers and flows beneath glaciers,” said Adrian McCallum, a glaciologist at the University of the Sunshine Coast.

“But to my mind, the only reason why a large volume of water should all of a sudden flow down a valley is because it has been released,” he told AFP.

And even for those receiving a warning, options would be limited, said Hatim Sharif, a hydrologist at the University of Texas San Antonio.

“Running will not help,” nor will trying to flee by vehicle, he told AFP, because the mud and water moving at high speed form a lethal combination “like liquid concrete.”

The only solution is to climb up a hill, at least 20 feet (six metres), he estimated.

Climate change

While it is hard to immediately attribute any individual glacial event to climate change, the warming planet is a constant background stress on these ancient ice rivers, experts say.

Glaciers are retreating globally, creating disaster risks but also depriving downstream communities of vital water sources.

“The biggest way to mitigate the risk would be to reduce our greenhouse gas emissions to limit warming,” said Vargo.

Header image: A drone view shows mud covering buildings and property following devastating floods at Trishuli in Nuwakot district, Nepal, on Aug 27, 2026. — Reuters