Floodwaters and mud crashed through Himalayan river valleys and swallowed villages on Wednesday, creating a cross-border crisis in Nepal and the Chinese territory of Tibet, with an unknown number of people swept away or buried.
Thousands of people live in riverside settlements downstream from the flooding, and hundreds are dead or missing, including foreign tourists. At least 19 vehicle bridges and 40 kilometers of roads have been swept away, according to a statement from Nepal’s prime minister.
Here’s what to know about the flash floods.
Where did the floods hit?
The torrents rushed through the valley of the Trishuli River, which is flanked by steep mountains and straddles the border between Tibet and the Rasuwa district of Nepal.
Officials in Nepal reported 157 deaths. The Chinese state news agency Xinhua reported that a mudslide killed at least three people and left 265 people missing. The agency said there had been “significant” casualties at the Gyirong Port in China, where footage released by state media showed surging waters and mud overwhelming buildings, uprooting trees and rendering roads impassable.
Video and images from Nepal showed the debris-choked river wiping out bridges, and towns partially buried in mud.
Gyirong Port, a small town with a border crossing into Nepal, is within the Tibetan Autonomous Region, an area that the Chinese government keeps under tight control as part of efforts to quash any dissent over its control of Tibet. The authorities invested in the port, about 40 miles north of Kathmandu, Nepal’s capital, as part of efforts to incorporate Tibet into China’s signature Belt and Road infrastructure project, through trade with Nepal and India.
From there, the Trishuli flows southwest across Nepal.
How can a flash flood happen without heavy rain?
Officials were caught off guard by the floods on Wednesday because it was not raining, according Narendra Pariyar, the chief district officer of Rasuwa.
Nepal’s foreign minister, Shisir Khanal, said the government had received preliminary information that an avalanche had occurred Wednesday morning in the affected region. Landslides in the region caused shaking intense enough to initially register as a 5.2.-magnitude earthquake, according to the U.S. Geological Survey.
The disaster was likely set off at least in part by an enormous chunk of ice snapping off a glacier and cascading thousands of feet to the valley below, according to an initial assessment by a group of geologists and glaciologists. The phenomenon is known as an ice avalanche.
The scientists said the impact released vast amounts of energy that pulverized the ice into a significant volume of floodwater.
Flash floods are usually caused by extremely heavy rainfall from thunderstorms, according to the U.S. National Weather Service. But there are other triggers, such as landslides or other events that displace large amounts of water.
Wednesday’s ice avalanche appeared to mirror a similar event in India in 2021, when a Himalayan glacier broke and caused major flooding in the northern Indian state of Uttarakhand, killing more than 100 people.
Who are the missing tourists?
Hundreds of travelers, including 391 foreigners, have been reported missing in Nepal, the country’s tourism board said in a statement. They included more than 100 visitors from India, a dozen Britons and at least three Americans. Citizens from Australia, the Netherlands, Malaysia and South Africa were also among the missing.
Among the large number of Indian nationals missing is a group of pilgrims from India’s south. Mount Kailash in Tibet is a sacred site for multiple faiths, including Hinduism.
Sadhguru, an influential Indian spiritual guru and entrepreneur whose Isha Foundation organizes pilgrimage tours to Mount Kailash, said 77 people participating in its tours were at the immigration center on the Nepal-Tibet border when the floodwaters came.
“There has been no official information on the whereabouts of any of the people who were at the immigration office,” he said. “We are working with the authorities to see if we can get to the location and stand ready to be part of the rescue efforts.”
How common are landslides in the region?
Despite lower-than-average rainfall across the country this monsoon season, local media noted heavy rains in multiple hilly regions that caused deadly landslides and flash floods earlier this month.
In 2024, intense rains caused floods and landslides that killed hundreds in Nepal, including in the densely populated region around Kathmandu, the capital.
Nepal is prone to landslides and floods when heavy monsoons collide there with some of the world’s tallest mountains, including Mount Everest.
But the warming climate has made weather events more dangerous and deadly, causing frequent flooding from melting glaciers. Climate change has also intensified rainfall. At the same time, rapid development and haphazard construction have added to the risk that lives will be lost in natural disasters.
Reporting was contributed by Lily Kuo, Suhasini Raj, Hari Kumar, Leo Sands and Pranav Baskar.