The catastrophic flooding along the Nepal-Tibet border was triggered by a massive collapse of ice and rock high in the Himalayas, not by an earthquake as initially believed. On August 26, part of a glacier and mountainside failed at an elevation of roughly 5,200 metres and plunged about 1,200 metres into the valley below. Nepali researchers estimate that the collapsing mass contained around five million cubic metres of ice and rock. As it descended, melting ice, water, mud, sediment and huge boulders combined into a rapidly expanding torrent that swept through the Lhende Khola, Bhote Koshi and Trishuli river systems. The US Geological Survey initially recorded the event as a magnitude 4.4 earthquake, but later analysis of seismic waves and satellite imagery showed that no earthquake had occurred. Instead, the glacier and debris collapse itself generated seismic energy equivalent to a magnitude 5.2 event. In some areas, river levels reportedly rose by as much as nine metres in around 30 minutes.
The scale of the disaster continues to grow. As of August 31, Nepali authorities reported 903 deaths and 4,247 people missing, while China reported another 16 deaths and 546 missing on the Tibetan side of the border. The Red Cross estimates that more than 90,000 people may have been affected. Among those still unaccounted for are 933 workers at 11 hydropower projects in the badly hit Rasuwa and Nuwakot districts, with hundreds feared trapped inside tunnels. Nearly 21,000 security personnel are involved in rescue operations alongside specialists from India and China. The torrent destroyed at least 19 bridges, around 40 kilometres of highway and infrastructure representing more than 10% of Nepal’s electricity-generation capacity. Rescue teams are using excavators and controlled explosions to reach blocked tunnels, while newly formed lakes, unstable glaciers and additional landslides continue to pose a risk of further flooding.
The deeper question is why such an event was able to occur. Scientists cannot yet say that climate change directly caused this specific collapse, but the Himalayan environment is changing rapidly. ICIMOD says the Hindu Kush-Himalaya region contains more than 63,700 glaciers and that between 1990 and 2020 they lost around 12% of their total area and 9% of their estimated ice reserves, while glacier wastage has roughly doubled since 2000. Rising temperatures accelerate melting, reduce snow cover and degrade mountain permafrost, which acts like a natural glue holding rock and ice together on steep slopes. These processes increase the background risk of avalanches, landslides and sudden floods. The disaster has also exposed weaknesses in monitoring and cross-border warning systems. Nepal is now pressing China for much more frequent data on rainfall, river levels and glacier movement, potentially every 10 minutes, in an effort to provide communities with earlier warnings before the next Himalayan disaster.
Sources: US Geological Survey (USGS), Reuters, ICIMOD, Nepal National Disaster Risk Reduction and Management Authority.
