GYIRONG, Tibet — Two days after a collapsing Himalayan glacier unleashed a torrent of ice, rock and mud across the China-Nepal frontier, the disaster entered a more uncertain phase on Friday as a newly formed lake began overflowing above the shattered Gyirong border crossing.

Chinese authorities briefly withdrew rescuers and vehicles after the lake, held back by an unstable wall of debris, accumulated more than 2.5 million cubic meters of water. Nepalese officials separately reported that the lake had begun breaching its banks and ordered rescuers and residents to move uphill.

By midday, China said the immediate risk had become manageable and allowed rescue operations to resume. But “manageable” did not mean resolved. Rain was forecast to continue, the valley walls had been severely eroded, and satellite imagery showed another barrier lake expanding upstream without a visible outlet. Nepal said the danger would persist until both lakes had drained.

A Threat Changing by the Hour

Chinese hydrologists estimated that another three million cubic metres of water could enter the first lake over several days, with peak flows expected around Sept. 1. Engineers have used drones, aerial surveys and three-dimensional modelling to track the lake because damaged roads and unstable cliffs have made conventional access nearly impossible.

The most likely outcome may be a gradual release rather than a catastrophic rupture. Scientists consulted by the BBC said the young lake appeared relatively shallow and could drain naturally as the summer melting season ends. Even a modest discharge, however, could scour already weakened slopes, trigger fresh landslides or send another debris-laden surge through the narrow valley.

That secondary danger has repeatedly interrupted the search for survivors. Chinese rescuers reaching the Gyirong complex on Friday found the principal border facilities almost entirely destroyed. On the Nepalese side, helicopters were temporarily grounded and relief convoys carrying supplies for isolated communities were blocked when river levels rose.

The toll continued to climb. By Friday, Nepal had reported at least 579 deaths and 1,924 people missing. Chinese reporting placed the death toll in Tibet at seven, with at least 558 people still unaccounted for. At least 540 missing people were foreign nationals, many of them pilgrims traveling toward Mount Kailash. The figures remain provisional and may change as communications are restored.

Not a Conventional Glacial-Lake Flood

Early accounts described Wednesday’s disaster as a possible glacial-lake outburst flood. Satellite and seismic analysis now points to a more complex sequence.

A large section of ice and rock appears to have detached from the northern slopes of the Langtang Lirung massif, falling roughly 1,200 meters before accelerating through the valley. Chinese geological investigators estimated that the resulting debris flow traveled at about 50 meters a second and continued for more than 20 kilometers.

Scientists writing for the European Geosciences Union said satellite images showed no large glacial lake at the source before the collapse. The event was therefore probably not a conventional glacial-lake outburst but a high-energy ice-and-rock avalanche that temporarily blocked rivers, entrained water and sediment, and created unstable lakes afterward. Seismic signals initially interpreted as an earthquake were most likely generated by the collapse itself.

The immediate trigger remains under investigation. Researchers caution against attributing a single collapse directly to climate change. Yet the broader conditions are difficult to ignore: glaciers in the Langtang region have been thinning and retreating rapidly, while warming can increase meltwater, expose steep ice faces and weaken frozen rock. The disaster illustrates how a single failure can become a chain reaction — glacier collapse, debris flow, river blockage, flash flood and then renewed flooding from temporary lakes.

A Cross-Border Emergency With Wider Consequences

China has deployed firefighters, military aircraft, engineering teams and heavy-lift drones, while allocating 120 million yuan in central disaster-relief funding. Beijing has also ordered intensified monitoring of glacial lakes and landslide-prone slopes across the region.

Nepal has relied primarily on its own military, police and emergency services and has, for now, declined offers of foreign search-and-rescue teams. Kathmandu says domestic forces can manage the operation, although it continues to accept humanitarian supplies and technical support. China, India, the United States, Britain, Japan, South Korea and other governments have offered assistance.

The humanitarian emergency extends far beyond the border post. The Red Cross estimates that at least 93,000 people require urgent assistance. The World Health Organization reported damage to six health facilities, while the United Nations warned of growing needs for food, clean water and sanitation. The International Federation of Red Cross and Red Crescent Societies has launched a 25 million Swiss franc appeal.

For now, the central challenge is no longer a single wall of water but an unstable landscape. Rivers have shifted, slopes have been stripped of support, roads and warning stations have disappeared, and temporary lakes continue to form behind debris.

The first flood lasted hours. Managing the hazards it left behind may take months — and has become a test of whether two countries sharing the same mountain watershed can also share warnings quickly enough to protect those living below.

Sources: Xinhua, Reuters, IFRC