31 August,2026 11:50 AM IST | Kathmandu (Nepal) | mid-day online correspondent
Death toll rises to 903, over 4,200 still missing. Pic/ PTI
The devastating flash floods that swept through Nepal's Bhotekoshi-Trishuli corridor on August 26 were triggered by a massive ice-rock avalanche in the high Himalayas, rather than conventional heavy rainfall, according to a preliminary report by Nepalese scientists.
The report, commissioned by the Nepal Environment Society (NES), was released on Sunday.
The findings come as the death toll from the disaster rose to 903, with authorities continuing to recover bodies from affected areas.
According to the study, a huge mass of ice, rock and debris fell from an altitude of around 5,200 metres in the Langtang-Lirung area of Rasuwa and entered the Lhende River.
The resulting surge travelled downstream through the Bhotekoshi River and into the Trishuli, creating a powerful, debris-laden flood that devastated towns and villages across northern and central Nepal, reported PTI.
The study concluded that the disaster was not caused by a glacial lake outburst flood (GLOF).
Researchers analysed satellite imagery, hydrological and meteorological data, terrain characteristics and changes in elevation and slope along the river system. They found no evidence of a GLOF.
According to PTI, the report said the ice-rock mass began falling from the northern part of Langtang-Lirung at around 8.37 am on August 26. It descended steep terrain from about 5,200 metres before reaching the Lhende River at around 2,930 metres.
Satellite imagery showed major geographical changes across nearly 10 square kilometres, while a glacier section covering approximately 0.56 square kilometres had broken away.
The ice-rock mass travelled around 22 kilometres to Rasuwagadhi in just over seven minutes, reaching an estimated average speed of 46.3 metres per second, or approximately 167 kmph, according to the study.
Its speed subsequently dropped to around 73 kmph between Rasuwagadhi and Betrabati and to approximately 22 kmph further downstream. Despite slowing, the flow continued carrying large quantities of rock, sediment, and soil, PTI reported.
As per PTI, the study also found no evidence of exceptionally heavy rainfall in the upper watershed on the day of the disaster, weakening the assumption that extreme rainfall or a cloudburst alone caused the floods.
Researchers noted that river levels and flow rates in the Rasuwagadhi and Syafrubesi areas had actually declined several hours before the flood arrived.
At Rasuwagadhi, the average water level fell between 5 am and 8 am, while the flow at Syafrubesi began declining at around 7 am.
Despite identifying the ice-rock avalanche as the likely trigger, experts said further field investigations are required to establish the precise geological mechanism behind the event.
Researchers also said more work is needed to determine the contribution of melting ice and whether the river was temporarily blocked upstream before the sudden surge.
The disaster also caused extensive damage to Nepal's hydropower infrastructure.
Citing preliminary data from the Nepal Electricity Authority, the study said 13 hydropower projects and one solar project were affected, taking around 431 MW of generation capacity out of the system.
The study, citing a preliminary government assessment, estimated the overall economic losses at around Rs 3 trillion, although detailed sector-wise assessments are still underway, PTI reported.
(With PTI inputs)
