Bhisma Raj Ojha, Kathmandu, Oct 26: A recent study conducted by the International Centre for Integrated Mountain Development (ICIMOD) has found the Dudh Koshi river basin and the Everest region – which was hit by five significant glacial lake outburst floods (GLOFs) in less than 50 years – as a flashpoint for GLOFs.
The study ICIMOD conducted on the 2024 GLOF in the Everest region showed a ‘devastating, and complex, chain reaction’ of geological and geomorphological factors amplified the destructive power of the flood that decimated the iconic high-altitude trekking village of Thame in Solokhumbu district of Nepal on 16 August 2024.
“The outflow fell 120 metres, amplifying its erosive power – and hit a second lake, whose moraine-dam then breached, leaving a hole 22-metre high (the height of an eight-storey building) and 51-metre-wide and releasing an additional 303,000 cubic metres of water. The combined waters transformed into a ‘hyper-concentrated flow of slurry’ as they swept downstream, transporting debris, including large boulders, 80km downstream and eroding riverbanks in its path,” stated the report.
Experts describe proactive risk management and mitigation as ‘urgent’ and ‘essential’ due to ongoing threat lakes pose to downstream communities.
“GLOFs are growing in severity and impact across the Hindu Kush Himalayas as temperature rise fuels the proliferation of glacial lakes, which now number 25,000 across the mountain region,” it said.
The report named ‘Thame Valley Glacial Lake Outburst Flood – Causes, Impacts, and Future Risks’ was co-authored by risk experts at ICIMOD, Sudan Bikash Maharjan, Tenzing Chogyal Sherpa, and Arun Bhakta Shrestha.
They confirmed after the study that a rock avalanche triggered a powerful displacement wave when it hit a glacial lake at 4,900 metres, causing the lake to breach and releasing 156,000 cubic metres of water.
A natural narrowing of the river channel (downstream of the Thyanbo outwash plain) combined with the draining of a temporary ponding of floodwaters tragically amplified the flood’s erosive force. This went on to cause erosion and landslides, and mobilised large quantities of debris as it moved towards and ultimately covered the entire half-a-kilometre wide valley floor near the Thame Village.
The flood caused extensive destruction, including homes, a school, a health post, a bridge, and damaging a hydropower plant, but thanks to the event’s occurrence in daylight and phased nature of the flood due to the ponding, no loss of life.
Nepal has seen over 90 GLOFs since the early 1920s, and the Everest region has withstood five significant events in less than 50 years – including the 1985 GLOF of Dig Tsho, which struck the neighbouring valley to the Thame event, wiping away a newly constructed hydropower plant.
“GLOFs are among the most destructive and prominent hazards in high-mountain regions. Capable of releasing millions of cubic meters of water and debris within hours, they can cause catastrophic damage downstream: unleashing torrents of water that obliterate communities, devastate infrastructure, and permanently reshape landscapes,” the authors underscored.
According to them, the accelerating impacts of climate change, particularly in the Hindu Kush Himalaya (HKH) region, are compounding these risks. The HKH, warming at an average of 0.28 degree Celsius per decade, is experiencing unprecedented glacier mass loss, which has increased by 65 percent in recent decades compared to earlier periods. This rapid glacier retreat has fuelled the proliferation of over 25,000 glacial lakes across the region, spanning the Amu Darya, Indus, Ganges, Brahmaputra, and Irrawaddy basins.
Remote sensing analyst at ICIMOD, Maharjan, observed, “The Hindu Kush Himalayas has more than 25,000 glacial lakes and Thame shows us that we need to spend much more effort in understanding and preventing the risks posed by even the relatively smaller lakes. In this case, the additional geological and morphological characteristics of a landscape intensified the impact of this climate-driven event to cause catastrophic damages, though mercifully – with no loss of life.”
In view of cryosphere analyst at ICIMOD, Sherpa, as climate extremes intensify, the Thame flood is both a stark reminder and a moment of reflection, showing how mountain communities are already bearing the brunt of climate-induced disasters. “In line with this year’s International Day for Disaster Risk Reduction theme on funding resilience, it reinforces the urgent need to invest in preparedness, strengthen scientific understanding, and support the people most at risk. Events like these also serve as crucial moments for understanding and communicating the realities of climate change, reminding us that the mountains are speaking, we just need to listen,” he reminded.
In addition to this, the study outlines several for urgent specific action in Thame itself – such as protecting tension cracks from direct flow or rapid infiltration of flood water, rain or snowmelt, supporting riverbanks from subsidence – as well as the development of a long-term flood risk management plan for the valley. It also advises on the growing urgency to bolster monitoring of high-altitude glaciated regions across the HKH.
Senior advisor at ICIMOD, Shrestha, further said, “The Thame case shows the glacial hazards are intensifying as the Hindu Kush Himalaya warms nearly three times faster than the global average. In the last two years alone, we have seen several high-altitude hazards including GLOFs, across the region. It points to two immediate needs: more hydrological and meteorological monitoring stations generating real-time information, and engineering measures including bank protection measures to reduce damages from future events.”
