Glacier Collapse Suspected in Nepal Flood Disaster as More Surges Remain Possible

A destructive flood near Nepal’s border with Tibet may have begun with a collapse of ice and rock high in the mountains, according to preliminary assessments cited by Live Science and Phys.org. The event sent mud and water through valleys, destroying buildings, uprooting bridges and sweeping away vehicles and parts of villages. Reports differed on the number of casualties. Live Science, citing Nepalese authorities and Chinese state media, said more than 330 people had died and more than 1,500 were missing, including 65 people from the United States. Phys.org, citing AFP, reported at least 165 deaths. The supplied reports did not explain the difference between the figures. The flooding initially appeared to involve an earthquake. The U.S. Geological Survey first recorded seismic activity associated with what was reported as a magnitude 4.4 earthquake, while another account described a magnitude 5.2 signal. After examining long-period seismic waves, the agency said the energy was instead generated by a glacial collapse and debris flow. Researchers at the International Centre for Integrated Mountain Development, or ICIMOD, said a rock-ice avalanche likely occurred in Nepal, blocking the Lhende River and producing a cascading flood. Live Science reported that satellite imagery placed the suspected collapse near an elevation of about 17,060 feet, or 5,200 meters, in the Lhende Kola river valley. The precise sequence remains uncertain. Jon Tunnicliffe, a river science researcher at the University of Auckland, said the material may have temporarily obstructed the river before releasing a larger surge laden with water and sediment. Nepal’s foreign minister initially suggested that an earthquake caused a landslide, which blocked a river until the obstruction failed. Phys.org also noted that experts had considered a glacial lake outburst flood as a possible mechanism, but the cause had not been conclusively established. A lack of substantial rainfall before the flooding was notable. Tunnicliffe said significant rain did not appear to be the trigger, while hydrologist Hatim Sharif told AFP that the absence of rainfall could make conventional flood-warning systems ineffective. Officials and researchers are concerned that the danger may not be over. Basanta Raj Adhikari of Nepal’s Tribhuvan University warned of possible second and third waves, and ICIMOD’s Qianggong Zhang said an upstream blockage could produce another flood. Authorities have urged people to remain away from the Bhotekoshi, Narayani and Trishuli rivers. Experts cautioned that climate change may be increasing hazards across the Hindu Kush Himalaya, where glaciers are retreating and permafrost is degrading. However, they said it is too early to attribute this specific collapse to climate change. Determining that connection would require further scientific analysis.