Nepal’s Major Flood Analyzed as Caused by Rock Wall Collapse, Not a Glacial Lake

The major flood that occurred last month on the border between Nepal and China was analyzed to have started not because a glacial lake burst, but because a massive rock wall and glacier on a mountain slope at an altitude of over 5,000 meters collapsed together. The international research network WWA announced this conclusion on the 17th after combining satellite data with weather, glacier, and geological information. According to the researchers, the accident occurred when a rock wall and glacier covering an area of about 2 km² collapsed all at once on the north face of Langtang Lirung. After falling into the valley, this material drew in water and sediment, growing into a massive debris flood that reached an area about 22 km away in just seven minutes. At first, the possibility of a glacial lake collapse was also raised, but the analysis confirmed that the collapse began on the mountain first. The study did not conclude that climate change directly caused this disaster, but it said it is highly likely that warming made the mountain slope more unstable. Due to climate change, temperatures in July and August, just before the accident, rose by about 1.5 degrees Celsius, and as ice melted in the highlands, the force holding the rocks together weakened. Glacier retreat and permafrost thaw were also identified as factors that increased the risk of slope collapse. The researchers emphasized that this case shows the need to expand disaster monitoring systems in highaltitude regions. They explained that integrated monitoring is needed to track not only glacial lakes and rivers, but also changes in glaciers, permafrost, and mountain slopes.