A glacial lake outburst flooded Mustang after a lake in Lomanthang Ward No. 4 burst. The flood, known as a GLOF, flowed into the Chuwa River in Chumjung village. This event is the third-highest elevation GLOF in the Himalayan region, with the highest recorded in 1985 nearby.

The Department of Hydrology and Meteorology is working to confirm a glacial lake outburst. Meteorologist Binod Parajuli indicated that initial findings suggest a glacial lake outburst likely occurred. Amrit Thapa, a Nepali glaciologist from the University of Alaska, confirmed the glacial lake outburst in Lomanthang. The Department reported no significant rainfall in Mustang before the flood. Thapa noted the glacier feeding the Kali Gandaki River has been retreating at an average rate of 20 meters per year. Historical data shows the glacier's source, originally a glacial lake, was at an elevation of 5,700 meters above sea level.

Since 2009, the upper edge of the glacier has been retreating, leading to the formation of new lakes between elevations of 5,900 to 6,100 meters. These lakes freeze in winter and melt into water bodies in summer. One such lake, estimated to be 0.016 square kilometers in size, burst last Tuesday, causing a glacial flood in Lomanthang.

The formation of lakes at the upper surface of glaciers, rather than the lower parts, is a new phenomenon in the region. Experts suspected a glacial lake outburst, rather than rainfall, as the cause of the flood due to the minimal rainfall in high Himalayan districts like Mustang. The flood occurred at around 5 PM on Tuesday, July 8, 2025, in the Chuwa River near Chumjung village in upper Lomanthang Ward No. 4. Despite

more severe damage in Rasuwa, the Department and the National Disaster Risk Reduction and Management Authority had focused their investigations there, somewhat overlooking the event in Lomanthang.

Locals promptly alerted downstream areas about the flood, preventing casualties. Lomanthang Rural Municipality Vice Chairperson Chhyumi Bista Gurung confirmed successful evacuation of at-risk settlements due to early warnings. Ward Chair Chhiring Dhindu Gurung and local officials inspected the glacial lake breach site. High-risk settlements downstream were evacuated in time, and four bridges in the lower valley were damaged. Debris from the flood reached up to 35 kilometers downstream from the lake.