Everest region hotspot of cryosphere-linked hazards, ICIMOD study says

Kathmandu, Oct 14 (PTI) A new study published on Tuesday concluded that a “devastating, and complex, chain reaction” of geological and geomorphological factors amplified the destructive power of a glacial lake outburst flood last year in the Everest region.

The flood decimated the iconic high-altitude trekking village of Thame in Solukhumbu, Nepal on August 16, 2024.

‘Thame Valley Glacial Lake Outburst Flood — Causes, Impacts, and Future Risks’, authored by risk experts at the International Centre for Integrated Mountain Development (ICIMOD), concludes 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.

This 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, 80 km downstream and eroding riverbanks in its path.

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, according to the study report.

The flood caused extensive destruction, including houses, a school, a health post, a bridge, and damaged a hydropower plant.

However, thanks to the event’s occurrence in daylight and phased nature of the flood due to the ponding, no life was lost, according to the ICIMOD report.

Nepal has witnessed 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.

“The Hindu Kush Himalaya, warming at an average of 0.28 degree Celsius per decade, is experiencing unprecedented glacier mass loss, which has increased by 65 per cent in recent decades compared to earlier periods,” points out the report.

“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.” Sudan Maharjan, Remote Sensing Analyst at ICIMOD and one of the authors of the report, said: “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.” The Thame disaster is the latest in a series of events to reinforce the need to translate cryosphere and disaster related science into actionable policy. PTI SBP GSP GSP