KATHMANDU, Sept 2 — A glacier break in Nepal on Wednesday unleashed a flood described as a “mud tsunami,” leaving thousands missing and a rising death toll, with dozens of bridges washed away and vast road sections obliterated in the rugged Himalayan terrain. The disaster has sharpened focus on the cascading threats a warming climate poses to mountain communities, according to reporting by ABC News’ Climate Team. Rescue efforts are being hampered by the destruction of transport links across the region.
The Himalayas hold more than 55,000 glaciers across the Himalayan, Karakoram, and Hindu Kush ranges—more ice and snow than any region outside the polar areas, earning the “third pole” nickname. That store of ice is destabilising as the region warms faster than the global average, data shows.
Umesh Haritashya, a glacier expert from the University of Dayton involved in an international investigation into the disaster, has logged more than 1,466 glacial lakes in the region, most formed since the second half of the 20th century. Their barriers of loose sediment and rock are unstable, officials noted. Lakes can fail directly, or avalanches and rockfalls can crash into them, generating displacement waves that overtop dams and trigger glacial lake outburst floods.
A second, less visible threat sits beneath the surface. Large areas of the Himalayas are permafrost—ground moisture that stays frozen year-round—and the ice acts like cement inside mountain slopes.
As permafrost thaws, previously frozen rock, sediment, and moraine material become unstable, raising the likelihood of landslides, debris flows, and rock-ice avalanches. “The ice plays the role of the glue between the rocks,” Haritashya said. “As the permafrost starts to thaw, these frozen ice pieces start to melt.
And once they melt, there is no longer glue that can hold the rocks together.” A study published this year by researchers from the School of Earth, Ocean and Climate Sciences at the Indian Institute of Technology Bhubaneswar concluded that a warming climate is shifting the 0-degree Celsius boundary where permafrost stays solid higher up the mountains. Snow cover in the Himalayas has shown a long-term decline from January 2022 to January 2025, though seasonal variation exists.
It is too early to determine what triggered Wednesday’s glacier break, but the glacier sat above 5,000 metres, where temperatures are generally cold enough to keep ice frozen year-round. Researchers are particularly concerned about cascading interactions: warming melts glaciers faster, opening slopes and changing their stability, while thawing permafrost destabilises steep slopes surrounding growing glacial lakes.
A rockfall or avalanche into a lake could trigger a glacial lake outburst flood, creating a dangerous chain reaction. Haritashya acknowledged the difficulty of communicating risk to communities. “It’s hard to tell people to move.
We know where the slope instability is, we know where the glacial lakes are, we know the area is warming faster. We need to figure it out to communicate properly to these communities so that they can understand the risk associated with it.” He added: “I know as a scientist, we all want you to be cautious until our data says that’s clear to attribute something to climate change.
But climate change is certainly playing a role in that area because we are seeing the frequency of these events occurring in these kinds of valleys.” The open question, researchers said, is whether some places may become too dangerous for human habitation.
