Nepal floods were triggered by Himalayan ice-rock avalanche, report says

A preliminary scientific report says Nepal's August 26 floods were triggered by an ice-rock avalanche in Langtang-Lirung. The finding rules out heavy rainfall and a glacial lake outburst as the main cause while deepening concern over Himalayan hazards.Image used for representational purposes onlyA preliminary report by Nepalese scientists has said the devastating floods that tore through the Bhotekoshi-Trishuli corridor on August 26 were triggered by a massive ice-rock avalanche in the high Himalayas, and not by conventional rainfall. The report, commissioned by the Nepal Environment Society and released on Sunday, said the disaster was also not caused by a glacial lake outburst flood.As bodies continued to be recovered, authorities said on Monday that the death toll from the flash floods had risen to 903. The disaster caused widespread damage across northern and central Nepal and also hit power infrastructure, with a preliminary assessment putting economic losses at around Rs 3 trillion.According to the study, a huge mass of ice, rock and debris fell from around 5,200 metres in the Langtang-Lirung area of Rasuwa and entered the Lhende River. The surge then moved downstream through the Bhotekoshi and into the Trishuli, creating a powerful debris-laden flood, My Republica reported.The researchers said the ice-rock mass began falling from the northern part of Langtang-Lirung at around 8.37 am on Wednesday. It moved down steep terrain from about 5,200 metres before reaching the Lhende River at around 2,930 metres. The report said satellite images showed major geographical changes across about 10 square kilometres, while a section of glacier covering around 0.56 square kilometres had broken away. The researchers analysed satellite imagery, hydrological and meteorological data, terrain features, and changes in elevation and slope along the river system, and found no evidence of a glacial lake outburst flood.The study said the ice-rock mass travelled about 22 kilometres to Rasuwagadhi in just over seven minutes, at an estimated average speed of 46.3 metres per second, or 167 kilometres per hour. Its speed later dropped to around 73 kilometres per hour between Rasuwagadhi and Betrabati, and to about 22 kilometres per hour further downstream. Even after slowing, the flow continued to carry large quantities of rock, sediment and soil, the report said. The researchers also found that river level and flow in the Rasuwagadhi and Syafrubesi areas had 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 around 7 am.The study said there was no evidence of exceptionally heavy rainfall in the upper watershed that day, weakening the assumption that the disaster was caused solely by extreme rainfall or a cloudburst. However, experts said further field investigation was needed to establish the precise geological mechanism, the contribution of melting ice, and whether the river was temporarily blocked upstream.The floods also caused extensive damage to hydropower infrastructure. Citing preliminary Nepal Electricity Authority data, the study said 13 hydropower projects and one solar project were affected, taking around 431 MW of generation capacity out of the system. It added that while detailed sector-wise assessments were still under way, a preliminary government assessment had estimated economic losses at around Rs 3 trillion.In sum, the preliminary findings linked Nepal's deadly August 26 floods to a fast-moving ice-rock avalanche in the Langtang-Lirung area, while ruling out both a glacial lake outburst flood and exceptionally heavy rainfall as the main cause.With PTI Inputs- EndsPublished By: India Today Web Desk Published On: Aug 31, 2026 10:30 IST