The wave came without warning. A giant torrent of mud, water and ice, it smashed through buildings, swept away buses, snapped bridges into pieces and engulfed people who tried to run but were overtaken by its destructive force.
When it was over on Wednesday, at least 160 people had been killed and hundreds more had been left missing on the border between Nepal and Tibet, a rugged region of lush, green river gorges surrounded by the highest peaks in the world, in the snowy Himalayas.
Initial assessments by geologists and glaciologists indicated that an enormous chunk of ice — possibly 2,000 feet wide — had snapped off a glacier at an altitude of 17,000 feet and tumbled thousands of feet into a river valley below. Along the way, the avalanche pulverized itself into a fast-moving barrage of ice and rock that crushed everything in its path.
“The bottom looks like a bomb exploded — it’s just deposits from the broken-up glacier,” said Daniel Shugar, a geologist at the University of Calgary in Canada who studied satellite imagery of the disaster zone.
Shaking in the area, at first recorded as a 4.4-magnitude earthquake, was actually caused by the landslide itself, according to the United States Geological Survey. The shaking from the landslide ultimately registered at a magnitude of 5.2, the agency said.
Nepali officials said they had no advanced warning before violent floods of water and mud, unleashed by the avalanche, crashed through villages on the Bhotekoshi River, where thousands of people live.
“There was no rain in Nepal, so we were not expecting anything like this,” said Narendra Pariyar, the chief district officer of Rasuwa, one of the areas hit by the floods.
As many as 391 tourists, including 291 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 of Australia, the Netherlands, Malaysia and South Africa were also among the missing.
Surveillance video from the Gyirong port of entry, on the border between Nepal and the Tibet region of China, showed dozens of people running away moments before a huge mudslide obliterated a large building. It then enveloped the people and the camera recording the scene.
A second video from the border crossing captured another crowd sprinting down a road seconds before a titanic blast of mud swept away buses parked nearby, knocked down a building and engulfed everything in sight.
The Nepali police said at least 157 people in the country had been killed. At least 19 bridges and 24 miles of road, as well as schools and hydropower plants, were destroyed, Nepali officials said.
Chinese officials reported three deaths in Tibet, although the toll there was expected to rise. The Chinese state news agency Xinhua said there had been “significant” casualties at the Gyirong port of entry.
China’s leader, Xi Jinping, ordered the local authorities to “make every effort” to search for and rescue missing residents.
The disaster added to the challenges confronting Nepal’s recently elected government, led by Prime Minister Balendra Shah, a former rapper and mayor who is 36 and was lifted to power by a youth-led protest movement last year.
As rescue efforts got underway, the Nepali Army said it had mobilized 12 helicopters, set up a temporary hospital in the flood zone and evacuated at least 25 seriously injured people to the capital, Kathmandu. Nepal’s education minister, Sasmit Pokharel, said the country had also appealed for help from its larger neighbors, China and India.
The largest group of missing people, at least 100, were from India, according to Nepali and Indian officials. Many of them had been on a pilgrimage to Mount Kailash in Tibet, which is revered by many Hindus as the spiritual home of the god Shiva.
The influential Indian spiritual guru and entrepreneur known as Sadhguru said 77 people, on tours organized by his foundation, had been at an immigration center on the Nepal-Tibet border when the floodwaters hit.
“There has been no official information on the whereabouts of any of the people who were at the immigration office,” he wrote on social media. “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.”
Prime Minister Narendra Modi of India said on social media that he had expressed his condolences to his Nepali counterpart, Mr. Shah, and would provide humanitarian assistance as needed. The Indian Embassy in Nepal said it was coordinating with Nepal on rescue and relief efforts.
“The people of India stand in solidarity with their sisters and brothers in Nepal at this difficult time,” Mr. Modi said.
Scientists said warming temperatures caused by climate change may have accelerated the glacier’s collapse, although they cautioned that it was too early to determine a precise cause. Across the fast-warming Himalayas, melting glaciers are presenting dangerous new opportunities for avalanches and earthquakes to cause destruction.
In 2021, a Himalayan glacier broke off and caused major flooding in the northern Indian state of Uttarakhand, killing more than 100 people.
“This is one of the most devastating floods I can remember seeing in this region,” said Tenzing Chogyal Sherpa, an expert in atmospheric and water processes at Utrecht University in the Netherlands. He added that the disaster was a “brutal reminder” for those living in Himalayan valleys that changes in the climate mean “events like this may happen again.”
Reporting was contributed by Mujib Mashal Suhasini Raj, Sanjana Varghese, Maud Bodoukian, Lily Kuo, Pei-Lin Wu, Anupreeta Das and Amy Graff.
