Kathmandu, Nepal, 09 July 2025 - Scientists at the International Centre for Integrated Mountain Development (ICIMOD) have been mapping, and monitoring glacial lakes and glacial origin hazards since 1985 – when Dig Tsho lake in Khumbu, Nepal, knocked out a micro-hydro and caused nearly $3M of economic damages. The centre conducted the post-event assessment to this event and has now also conducted multiple major hazard assessments, including into disasters in Melamchi, Birendra Tal, Humla in Nepal and Chamoli, the South Lhonak disaster in Sikkim, India.
Frequency:
Experts at the centre state that they are shocked at the increased frequency of glacial origin hazards –
In the 2000s experts would anticipate a glacial origin flood to hit the Hindu Kush Himalaya region once every 5 to 10 years.
In two months - May and June 2025 alone saw three glacial origin floods hit the region, in Nepal (Limi), in Afghanistan (Andorab valley) and Pakistan (Chitral, Hunza).
Monday saw not just one, but two glacial origin floods strike Nepal: in Rasuwa, and in Upper Mustang.
A three-fold increase in GLOF risk across HKH is projected by the end of the 21st century.
“The acceleration of these types of events is completely unprecedented in the HKH region. We need to delve deeper into the triggers that are resulting in cascading impacts,” states Saswata Sanyal, ICIMOD Disaster Risk Reduction Lead.
Size no longer a determinant of potential danger:
What’s also new, say experts, is the devastation that small lakes, some so small, or hidden, that we didn’t even know they existed, are now causing.
ICIMOD has mapped and assessed lakes’ danger for decades. Size has previously been one of the criteria for analysis of potential danger, with only those greater than 0.02 km2 considered, and priority given to potential downstream impacts and moraine-dammed glacial lakes, since these are considered particularly unstable.
On this criteria, Nepal has 21 potentially dangerous lakes, 25 are in Tibet Autonomous Region of China, and 1 in India (ICIMOD 2020).
However, recent GLOF events have occurred by draining of newly formed (Supraglacial) ice dammed glacial lakes: this includes Monday's flood in Bhotekoshi Nadi in Rasuwa, and the rock avalanche in the bedrock dammed glacial lake and sequential breach of moraine dammed glacial lake in Thame, Everest region last year.
Researchers say it’s crucial that :
mapping and monitoring efforts increase
Potentially Dangerous Glacial Lakes inventories be more frequently updated
smaller, short-lived ice dammed lakes be analysed,
the dynamics of glacier retreat and lake formation be incorporated for more dynamic and accurate hazard assessment
What is a supraglacial lake?
Supraglacial lakes form on the surface of glaciers, particularly in debris-covered areas. They are highly dynamic and ephemeral, often beginning as small meltwater ponds that gradually expand and sometimes merge to form larger supraglacial lakes. The detection of these lakes largely depends on the spatial resolution of satellite imagery. Freely available satellite data, such as from Landsat and Sentinel-2, have limited resolution and can typically only identify lakes above a certain size threshold, potentially missing smaller or short-lived water bodies.
Early satellite pictures and analysis show that the lake that drained yesterday was a small pond in December 2024 and its size significantly grew in the month of June 2025.
Temperature’s role in rising glacial origin events
Temperature rise is known to play a key role in the increasing frequency glacial origin floods, in two key ways:
First the formation and gradual expansion of glacial lakes – a longer-term process driven by sustained warming.
Second, short-term temperature extremes on individual days can act as triggers for sudden events such as ice avalanches, ice calving, or slope failures related to permafrost thaw.
Floods carrying heavily debris-laden water, known as non-Newtonian flow, have significantly greater impacts than floods involving water alone. In recent events, such flows have become more common, with floods increasingly mixed with large volumes of sediment and debris, causing severe damage downstream.
Several factors may be contributing to this trend. One is the thawing of permafrost (previously frozen ground) which destabilizes the surface and makes it more susceptible to erosion by floodwaters. Another is the shift in precipitation patterns in periglacial areas where more rainfall (instead of snowfall) leads to increased runoff and excessive erosion. These changes are closely linked to climate change, particularly rising temperatures, which are altering both the quantity and the nature of what flows downstream.
‘These events are signals and symptoms of really rising temperatures, and are more destructive than normal flood due to the debris and steep topography’ states Sharad Prashad Joshi, cryosphere monitoring specialist at ICIMOD.
Extent of damage:
China - Nepal – 19 people missing 7 fatalities. 30MW of hydropower, 1 bridge, more than 100 EVs and blockage trade with China
How can we make communities safe?
Major investments are being made in disaster management in the region: ADB has started its BAR-HKH initiative in Nepal and Bhutan, which has a specific focus on mountain hazards
GCF just approved $36.1M for UNDP to lower four large glacial lakes in Nepal that ICIMOD had identified as of risk in its Potentially Dangerous Glacial Lake report: Thulagi, Lower Barun, Lumding Tsho, Hongu-2.
However apart from two lakes – Imja and Tsho Rolpa – we do not yet have the early warning systems or monitoring smaller sized lakes.
“We’re talking about a huge expanse of terrain where these sorts of lakes can develop, and the monitoring data and method to keep on top of pace of changes we’re now seeing simply does not yet exist,” says Qianggong Zhang, head of Climate and Environmental Risks at ICIMOD.
Resources
ICIMOD’s GLOF dashboard, compiles information on all recorded instances of glacial lake outburst floods (GLOFs) of High Mountain Asia starting from the 1830s. Aside from information on fatalities and injuries, the dashboard allows users to filter the GLOFs by country, river basin and lake type.
