Three days of floods later, Nepal fears a new lake could burst again. Here's why

Three days of flash floods and mudslides have struck the Nepal-China border, and officials now warn a newly formed lake upstream could burst within days. Here is the science behind the disaster and the fresh flood alert.Floodwater and debris choke the Bhotekoshi valley after a glacier collapse triggered a deadly flash flood on the Nepal China border.Three days of flash floods have now struck the Nepal-China border, and the danger is not over.A glacier collapse on August 26 sent a deadly wall of water down Nepal's Bhotekoshi river, a mudslide the same morning buried China's Gyirong Port crossing, and now, with the region already exhausted, scientists say a new lake upstream could burst within three days and send a fresh pulse downstream.WHAT CAUSED THE BHOTEKOSHI FLOOD IN NEPAL?Nepal's Department of Hydrology and Meteorology (DHM) says the flood was not caused by rain. Satellite images point to a huge chunk of glacier, most likely on the north face of Langtang Lirung, breaking away at roughly 5,200 metres and crashing about 1,200 metres down into the Lhende river, a tributary of the Bhotekoshi.The falling ice and rock blocked the narrow valley like a natural dam, then burst, sending a thick, muddy wall of water, ice and boulders racing towards Rasuwa, Nuwakot, Dhading, Gorkha and Chitwan. WHY WAS THERE ANOTHER DISASTER ON THE CHINA SIDE?The same morning, a separate mudslide struck near Gyirong Port in China's Xizang region, a key trade crossing with Nepal. China's state broadcaster CCTV said mud there lay more than five feet deep in places, cutting roads and communications.As of Thursday morning, three people had been confirmed dead and 558 remained missing on the Chinese side, prompting President Xi Jinping to order an all-out search and rescue effort. Officials have not yet formally confirmed whether the mudslide and the Bhotekoshi flood share a single source.IS ANOTHER FLOOD ABOUT TO HIT NEPAL? China's Ministry of Water Resources says a barrier lake has formed near the confluence of the Chhochen Khola and Purepu Tsangpo rivers, holding about 2 million cubic metres of water by Thursday morning and already overflowing. Another 3 million cubic metres could flow in over the next three days, raising a high risk of breach.Chinese engineers are running flood simulations to prepare for the possibility, while Nepal has told residents along the Bhotekoshi, Trishuli and Narayani rivers to stay off the banks until further notice.HOW BIG WAS THE FIRST FLOOD WAVE?DHM data shows the surge crossed into Nepal around 9 am on Wednesday and peaked at Devghat in Chitwan by late afternoon, flowing at nearly 5,850 cubic metres a second.Around 20 million cubic metres of extra water passed through Devghat, several times the volume of the 1985 Dig Tsho glacial flood in the Everest region, as the wave travelled almost 170 kilometres downstream in a matter of hours.WHY DOES THIS KEEP HAPPENING IN THE HIMALAYAS?This is the second such flood on this exact stretch in just fourteen months, after a July 2025 event linked to a lake sitting on top of a glacier.The International Centre for Integrated Mountain Development says Himalayan glacial lakes have risen from around 1,900 to over 2,600 since 2005, as the region warms faster than the global average, making sudden, destructive floods increasingly common on both sides of the border.- EndsPublished On: Aug 27, 2026 17:30 IST