An initial assessment suggests that an ice avalanche blocked the Lhende river, triggering the sudden flood in the Bhotekoshi river, according to Rijan Bhakta Kayastha, a professor at Kathmandu University and climate researcher.

Speaking to Kantipur, Kayastha said the assessment was based on preliminary findings and discussions with scientists in Nepal and China. He said an ice avalanche appears to have fallen into and blocked the Lhende river, causing water to build up before bursting downstream.

“There is information that an ice avalanche from the Nepal side blocked the Lhende river,” Kayastha said. “An earthquake also occurred on the Tibetan side around the same time.”

According to the US Geological Survey, a magnitude 4.4 earthquake struck Tibetan territory at 8:37 am, about 47 kilometres north of Gosainkunda.

Kayastha said it could take several days to determine whether a glacial lake had also burst. The possibility is being considered because glacial lakes have burst in the same area in the past.

A similar sudden flood struck the Bhotekoshi river on July 8, 2025. The Department of Hydrology and Meteorology concluded at the time that a glacial lake outburst had caused flooding in the Lhende river near the Nepal-China border in Rasuwa. An analysis using Sentinel satellite imagery indicated that the flood was triggered by the bursting of a glacial lake.

Kayastha said the area contains several large glacial lakes and that the Lhende river had been blocked in a similar incident last year.

“There are large glacial lakes in that area,” he said. “The Lhende river was also blocked last year. The initial assessment this time is also that an ice avalanche and possibly a glacial lake outburst caused the flood.”

Kayastha ruled out heavy rainfall as the main cause, saying the sudden nature of the flooding pointed to a burst of water from an upstream blockage.

“This was not a regular flood. Looking at the nature of the flooding, it appears to have come as a sudden burst,” he said.

Shanti Mahat, spokesperson for the National Disaster Risk Reduction and Management Authority, said the agency had also received preliminary information that an ice avalanche had blocked a river. The information came through the International Centre for Integrated Mountain Development (ICIMOD), which obtained it from sources in China.

“We have not received any official information yet,” Mahat said. “But ICIMOD has shared the information it received from the other side with us. This is only an initial assessment. We are focused on rescue and relief efforts for now. The cause will become clearer gradually.”

The Department of Hydrology and Meteorology also said a glacial lake outburst may have occurred somewhere in Nepal or Tibet.

In a special update on the Rasuwa flood, the department said there had been no heavy rainfall in the Rasuwa area on Tuesday or Wednesday. It said significant rainfall was not expected on Wednesday either, with rain-bearing clouds expected to develop only from Thursday.