Two new lakes sit above the Bhote Koshi after Wednesday's ice-rock collapse

Two lakes have formed at the source of the ice-rock avalanche that sent a flood down the Bhote Koshi-Trishuli system on 26 August. Krishna Vatsa, a member of India's National Disaster Management Authority, told The Hindu on Friday that one lake covers 19.80 hectares and the other 7.28 hectares. He said there are moraines at the site and that no reliable volume estimate is yet in Indian hands.

Satellogic imagery taken at 04:22 UTC on 27 August showed a lake of about 20.25 hectares in the Lhende Khola region, at 28°17′39.0″N, 85°30′38.9″E, near the Nepal-Tibet line. The 70-centimetre resolution frame is one of the few hard measurements available to agencies that cannot put people on that slope.

China's Ministry of Water Resources gave a different unit and a warning. It estimated 1.5 to 2 million cubic metres already held behind debris at the confluence of the Chhochen Khola and the Purepu Tsangpo, and said another 3 million cubic metres could flow in over three days. State television put the Friday morning figure at about 2.5 million cubic metres and called the breach risk high. A Chinese military drone on Friday filmed an avalanche that dropped an estimated 50,000 cubic metres of ice into the barrier lake.

What a barrier lake is, and why this one matters

A barrier lake forms when rock, ice and mud dam a river. Wednesday's flood began when a glacier collapsed into the headwaters and drove a wave of debris down the valley. The same debris has now plugged the channel again. Qianggong Zhang, who leads climate and environmental risk work at the International Centre for Integrated Mountain Development in Kathmandu, said the new dammed lake had begun to outflow on Friday. He put the stored volume in the range of a few million cubic metres and noted that the valley section below has a limited elevation drop. That geometry can cut peak discharge. It does not remove the risk to the settlements and hydropower works that were already stripped on Wednesday.

Nepal's disaster authority said the river is blocked upstream and that flood risk remains until both lakes drain. One lake was overflowing on Friday. Satellite frames showed a second, larger water body without a visible outlet, which means pressure may still be building. Rescuers were pulled back from parts of the corridor when the water rose.

The death toll from Wednesday's flood was still moving on Friday. Al Jazeera cited 584 confirmed deaths and more than 2,400 people missing across Nepal and Tibet. Mathrubhumi put Nepal's count at 579. Earlier MEA briefings in New Delhi spoke of hundreds dead and of 320 Indian nationals still uncontactable. The numbers will keep changing as bodies are pulled from mud. The lake risk is a separate clock.

Why the monitors cannot promise a warning

Vatsa was blunt about the gap. Agencies can see the lakes. They cannot yet measure depth or the strength of the debris dam. High-resolution optical satellites need a clear sky and a pass. Radar helps through cloud but does not give volume by itself. Ground sensors in that catchment were not built for a collapse of this size. Early-warning sirens downstream can buy minutes if a cable holds. They cannot stop a second pulse.

Gyirong Port, the main land crossing between Nepal and Tibet, sat several kilometres below the new barrier. CCTV in China placed the debris dam more than 10 kilometres from the port. The port was already buried on Wednesday. A second release would travel the same path, through the same broken bridges and hydropower intakes.

India has sent aircraft with tents, pumps, medicines and the offer of Bailey bridges. The scientific job on Saturday is narrower: keep the two lakes on a satellite watch, compare Friday's frames with Saturday's, and say whether the second basin has found an outlet. Until that outlet is visible and the first lake is falling, the Bhote Koshi corridor stays on a flood clock that started on Wednesday and has not yet run out.