Collapsed glacier likely caused devastating Nepal-Tibet floods, scientists say

Preliminary investigations have pointed to a collapsed glacier as the cause of the flash flood on the Nepal-Tibet border, highlighting the matter of rapidly melting Himalayan ice, scientists have informed the BBC.

Key points

• One analysis published by ICIMOD, external earlier this year identified that the Hindu Kush Himalaya glaciers are now losing ice at double the rate since 2000.
• This caused a "large volume of ice and rock debris" to enter the Lende Khola, a tributary of the Bhote Koshi river.
• According to Dr Cook, there have been similar incidents of floods and landslides caused by glacier collapses in India, Switzerland and Italy over recent years.
• Nevertheless, the US Geological Survey then clarified that the disaster was caused by a "glacial collapse".
• Scientists afterwards estimated that the impact of the collapse was equivalent to 15 atomic bombs.

Initial reports of an earthquake led plenty of to believe that a tremor had caused a landslide. It in turn caused the flood that has killed at least 177 residents.

Nevertheless, the US Geological Survey then clarified that the disaster was caused by a "glacial collapse". It is when a glacier or part of a glacier disintegrates.

Notably, the impact of the collapsed glacier hitting the bottom of a valley was so powerful that it registered a magnitude of 5.2, according to USGS data and scientists who have analysed the event.

Dr Simon Cook, a glacier expert with the University of Dundee, informed the BBC his team had detected that the lower part of a glacier in Nepal near the Langtang Lirung peak – which is approximately 15km (9 miles) west of the site of the floods – had collapsed.

He estimated that the glacier collapsed in a northwesterly direction and then travelled westwards downstream. What we know regarding deadly Nepal-Tibet floods. Video demonstrates scale of flash flood hitting Nepal-Tibet border.

Notably, an analysis, externalby the International Centre for Integrated Mountain Development (ICIMOD), an intergovernmental scientific institution, discovered there could have been "an ice-rock avalanche originating from a high-altitude area".

This caused a "large volume of ice and rock debris" to enter the Lende Khola, a tributary of the Bhote Koshi river. It in turn generated a sudden surge in the river carrying water, sediment and sizeable boulders downstream.

For context, the centre discovered that water levels in rivers downstream rose between seven to nine metres within a span of 30 minutes, and a number of water monitoring stations were washed away or damaged.

Meanwhile, the area is flanked by steep mountains, and videos of the flood show debris and water funnelled down the river at a rapid pace. It is unclear what caused the glacier to collapse on Wednesday.

But scientists for years have cautioned of melting ice and permafrost in the Himalayas due to warming temperatures and climate change.

One analysis published by ICIMOD, external earlier this year identified that the Hindu Kush Himalaya glaciers are now losing ice at double the rate since 2000. This in turn exacerbates dangers such as flooding.

In 2021, a sizeable chunk of a Himalayan glacier collapsed in the valley of Chamoli in northern India, sending a cascade of debris and water downstream that killed 200 residents. Scientists afterwards estimated that the impact of the collapse was equivalent to 15 atomic bombs.

Even in Nepal, the same region saw flooding last year caused by a glacial lake in Tibet bursting.

Mohd Farooq Azam, a specialist with ICIMOD, remarked the increasing frequency of hazards in the cryosphere – or the frozen parts of the Earth – "is becoming more visible than ever before. The pace of change is so rapid that current efforts are struggling to keep up."

While it is tough to say whether any single event is caused by climate change, "when you look at the pattern of these events, you do think climate change could have an impact, " stated Dr Cook.

"The logic is that with a warming planet, you will see shrinking glaciers, lots of snow melt. The permafrost that is partially holding some mountainsides together is warming and thawing and degrading."

"So you are going to get more landslides, debris flows, glacial meltwater, lake outbursts, glacier collapses, because climate warming ultimately destabilises these high mountain environments."

Taken together, the developments around collapsed glacier likely caused devastating Nepal point to a situation that is still moving, and the coming days should bring more clarity.