Nepal and China warn that two debris-dammed lakes could burst after the Himalayan flood

Nepal and China issued matching warnings on Thursday that two lakes formed by this week's debris have no safe outlet. The first flood on Wednesday already killed about 390 people along the Nepal-Tibet border and left more than 1,400 unaccounted for. Officials on both sides now say the next pulse could arrive before the weekend is out.

China's Ministry of Water Resources put the volume of the lake at the confluence of the Chhochen Khola and Purepu Tsangpo at about 2 million cubic metres by Thursday morning. Another 3 million cubic metres, equal to roughly 1,200 Olympic pools, is forecast to flow in over the next three days. Peak inflow is expected around 1 September. Zhu Jinfeng, a researcher in the ministry's hydrology department, told CCTV that the water is still rising and so is the risk.

Nepal's disaster authority did not name a single site in its own notice. It said a lake formed by debris blocking a river at the flood zone is rising and could burst. Residents on the lower banks, passengers, and rescue crews were told to stay off the river edges.

What the first flood did

The Wednesday surge started after a glacier chunk broke off near the border and briefly dammed a river. The U.S. Geological Survey recorded a magnitude 5.2 event that it later described as a glacier collapse and debris flow, not a tectonic earthquake. A wall of water, ice, mud and rock several storeys high then tore down the Bhote Koshi corridor through Rasuwa and on toward the Trishuli and Narayani.

Nepal police and tourism officials said more than 500 of the 826 people listed missing on the Nepali side are foreign citizens. The named tallies circulating on Friday included 177 from India, 90 from the United States, 34 from Australia, 33 from Britain and 25 from Canada. China's count on the Tibet side stood at 558 missing, of whom at least 260 were foreign nationals. India's Ministry of External Affairs said about 290 Indian nationals remained uncontactable and that 84 had been rescued.

Hydropower plants along the same corridor were hit. Nepal later cut power sales to India from about 800 megawatts to about 400 megawatts. Grid India had recorded a 963.4 MW import peak from Nepal on 26 August, the day the flood struck.

Two rivers, one drainage

The Chhochen Khola and Purepu Tsangpo rise in Tibet and enter Nepal as part of the Bhote Koshi system that feeds the Trishuli, then the Narayani, then the Gandak in India. That is why a breach on the Tibetan side is not a local problem. Water that leaves the barrier lake has a prepared channel all the way to the Ganga plain.

Chinese rescue footage released by CGTN showed brown water pooling in a basin with no visible outlet. Bushes and trees were already underwater. The water pressed against a wall of stones and mud. Engineers on the Chinese side said they were running flood simulations for a possible outburst. Nepal told people along the Bhote Koshi, Trishuli and Narayani to stay clear until further notice.

Rain is still forecast

State media in Beijing, citing the water resources ministry, said rain over the coming week will add to the inflow. That is the mechanical problem. A debris dam is not engineered. It can fail at a weak point rather than overflow in a controlled way. When it fails, the stored volume leaves in minutes rather than hours.

Rescue work is already slow. Thick mud, broken roads and rain have kept helicopters and ground teams from some of the worst stretches. A magnitude 3.2 tremor in Nepal on Thursday night, about an hour after a magnitude 5.0 event in Tibet, added another interruption. Neither quake produced new casualty reports.

India has flown two C-130J loads totalling 47.5 tonnes of medicine and food and was preparing a third aircraft. Australia offered help after listing 34 citizens missing. South Korea sent a rapid response team for nine nationals.

The first flood showed how fast a blocked Himalayan river can empty. The second warning is about the same mechanism, still in place, with more water behind it. The next three days will decide whether the debris holds.