KATHMANDU, JULY 13
The recent flood in Upper Mustang has been confirmed as a glacial lake outburst flood (GLOF), according to a Rapid Hazard and Risk Assessment (RHA) report published by HiRISK, raising fresh concerns over the increasing risk posed by high-altitude glacial lakes in Nepal.
According to the report, satellite images taken on July 6 and July 12 show a seasonal ice-dammed lake at 5,900 meters near an unnamed glacier feeding the Chhuhama River, a tributary of the Kali Gandaki, had completely drained by July 8. The lake had gradually expanded to 0.016 square kilometers in recent weeks before draining subglacially over 500 meters, triggering the flood around 5 PM on July 8.
Local residents in Chumjung and Lo Manthang noticed the incoming flood and alerted others, enabling early evacuation and helping reduce casualties, the report noted.
The GLOF destroyed four bridges and left sediment deposits as far as 35 kilometers downstream. Damages have been estimated at around Rs 15 million (approx. USD 100,000), report added. Experts warn that the loose sediments below the glacier make the area highly susceptible to further flooding, even from smaller lake breaches.
This glacial lake outburst is unique in itself. The lake had formed near the edge of the glacier at an altitude of around 5,900 meters. In comparison, the glacial lake that burst in Rasuwa flood was located on the surface of the glacier. Similarly, many other glacial lakes like Tsho Rolpa are formed in the frontal parts of glaciers. Due to its high elevation, this lake has been found to appear only during the warmer months, report stated.
This event is recorded as the third highest GLOF ever documented in High Mountain Asia, with the largest recorded in 1985 in the same region. The glacier itself has been retreating at about 20 meters annually between 2001 and 2025, and since at least 2009, lakes have started to form at the upper margins of the glacier, at elevations between 5900 and 6100 m a.s.l. These lakes tend to form seasonally. One of these lakes has drained rapidly on the 8th of July, after having grown steadily in preceding weeks to a relatively small size of 0.016 km2. The drainage happened over a distance of more than 500 m subglacially, according to the HiRISK report.
The HiRISK team has flagged multiple other ice-marginal lakes in the region that remain intact and could trigger future disasters. While local knowledge helped prevent worse outcomes in this case, no formal early warning system exists in the area.
The Mustang GLOF occurred just hours after another massive glacial flood hit Rasuwagadhi in Rasuwa district on the morning of July 8, sweeping away the Miteri Bridge-a vital cross-border link between Nepal and China-and leaving at least 20 people missing. The flood caused extensive damage to the Syafrubesi–Rasuwagadhi road section, Rasuwa Customs Office, a dry port yard, EV charging station, and the Rasuwagadhi Hydropower Project. Around 35 EVs, 23 container trucks, and six Sino trucks were also swept away.
Read Also: 20 missing in Rasuwagadhi flood, authorities urge caution amid widespread damage
Following this, the International Centre for Integrated Mountain Development (ICIMOD) voiced serious concern over the rise in glacial-origin floods in the Hindu Kush Himalaya (HKH) region. ICIMOD confirmed the Rasuwa flood was caused by the sudden drainage of a supraglacial lake on Purepu Glacier, north of Langtang Himal. The lake had rapidly expanded since it first appeared as a small pond in December 2024, breaching in July 2025.
The National Disaster Risk Reduction and Management Authority (NDRRMA) has stated that a full understanding of the Bhotekoshi flood in Rasuwa will only emerge after further investigation and analysis.
With two GLOFs occurring within 24 hours in Mustang and Rasuwa, experts stress the urgent need for monitoring, early warning systems, and preparedness to address the escalating climate-related risks in Nepal's high mountain regions.
