The recent flood in Upper Mustang was caused by a glacial lake outburst flood (GLOF), according to HiRISK. Experts say this incident highlights the growing danger from glacial lakes forming at high altitudes due to melting glaciers. These lakes can burst suddenly and cause destructive floods, especially during warmer months. The event has raised concerns about the urgent need for better monitoring and early warning systems in Nepal’s mountain regions.

 KATHMANDU, July 13

The recent flood in Upper Mustang has been confirmed as a Glacial Lake Outburst Flood (GLOF), according to a rapid assessment by the HiRISK team. This incident has added to growing concerns about the danger posed by glacial lakes forming at high altitudes in Nepal’s Himalayas.

Satellite images taken on July 6 and July 12 revealed that a seasonal lake—formed by ice near an unnamed glacier at 5,900 meters—completely drained by July 8. This lake fed the Chhuhama River, a tributary of the Kali Gandaki. It had gradually grown to 0.016 square kilometers in recent weeks, but suddenly emptied out underneath the glacier over a stretch of more than 500 meters. The flood occurred around 5 PM on July 8.

Thanks to quick action by locals in Chumjung and Lo Manthang who noticed the flood and alerted others, people were evacuated in time, reducing possible injuries or deaths.

However, the flood destroyed four bridges and spread mud and debris up to 35 kilometers downstream. Damage is estimated at around Rs 15 million (approximately USD 100,000).

Experts say that the loose sediment beneath the glacier makes the area vulnerable to more floods, even from smaller lake bursts. Unlike other famous glacial lakes like Tsho Rolpa, which form at the front of glaciers, this Mustang lake formed on the side of the glacier and only appears during warmer months—making it a rare and risky type of GLOF.

This is now recorded as the third-highest glacial lake outburst flood ever documented in High Mountain Asia. The glacier involved has been retreating at about 20 meters per year since 2001. Since 2009, small lakes have regularly formed on its upper edges (5900–6100 meters), some of which still remain intact and may cause future disasters.

The Mustang flood happened just hours after another devastating glacial flood hit Rasuwagadhi in Rasuwa district on the morning of July 8. That flood swept away the Miteri Bridge, an important Nepal-China border crossing, and left at least 20 people missing. It also severely damaged roads, the customs office, a dry port, an EV charging station, and the Rasuwagadhi Hydropower Project. Over 60 vehicles—including EVs, container trucks, and Sino trucks—were swept away.

Following these twin disasters, ICIMOD (International Centre for Integrated Mountain Development) expressed deep concern about the rising threat of glacial floods in the Hindu Kush Himalaya region. ICIMOD confirmed that the Rasuwa flood was triggered by the sudden drainage of a supraglacial lake on the Purepu Glacier, which had been growing rapidly since December 2024 and burst in July 2025.

Nepal’s National Disaster Risk Reduction and Management Authority (NDRRMA) said a full understanding of the Rasuwagadhi flood’s cause will take more investigation.

With two major GLOFs within just 24 hours, experts are urgently calling for better monitoring, early warning systems, and disaster preparedness to deal with the increasing climate risks in Nepal’s high mountain regions.