As the death toll from the catastrophic flooding in Nepal and Tibet rises above 900, scientists say there were troubling signals in the days before the disaster that suggested the region was on the brink of collapse.
Last Wednesday, a violent surge of ice, snow and rock tore through the steep valleys along the Tibet-Nepal border, devastating communities in its path.
Researchers currently believe the disaster was triggered by a glacier collapse, after a vast section of ice measuring roughly 1,000 to 1,300 metres wide broke away and plunged into the valley below.
Experts now say monitoring equipment had already detected signs that conditions were becoming dangerously unstable two days before the deadly flood struck.
The Himalayan region is heating faster than the global average, specialists warn, putting pressure on glaciers and ice formations that would normally remain locked in place.
Dr Hamish Pritchard, a glaciologist with the British Antarctic Survey, said he operates temperature sensors in and beside a lake at an altitude of 5,100 metres, around 10 km from the glacier.
According to Dr Pritchard, last Wednesday — the day the devastating flood occurred — brought the warmest lake temperature recorded there this year. Two days earlier, sensors also logged the highest ground temperature seen in the past two years.
‘These high temperatures would have weakened the snowpack, filled crevasses with water and thawed the bonds between ice and rock that hold these glaciers in place,’ he said.
As the death toll for the devastating flooding in Nepal and Tibet climbs above 900, experts have revealed the ominous warning signs that hinted disaster was imminent
Scientists initially suspected that the flooding had been triggered by a magnitude 5.2 earthquake that was detected on August 26.
However, it was later discovered that this seismic event was actually the impact of a massive glacier collapse on the Langtang-Lirung mountain.
This sent ice and rock cascading down the mountain, mixing with sediment left by previous floods, and temporarily blocking the Lhende Khola River.
That caused a large lake to temporarily form before it broke through in a devastating flood.
As of today, 903 people are confirmed dead in Nepal, in addition to 16 in Tibet.
More than 4,000 are also reported missing in Nepal, with another 500 in Tibet.
With recovery efforts ongoing, scientists are now starting to understand the conditions that made the flooding more likely.
Dr Pritchard says: ‘This happened in the middle of the monsoon season when heavy snow and rain fall in this region, making this the peak season for avalanches.
Scientists say that temperatures in a nearby mountain lake were at their highest on record, just two days before the glacial collapse triggered flash flooding. Pictured: Satellite images before (left) and after (right)
Experts say the flood occurred at the height of monsoon season, which would have saturated the soil and filled the rivers downstream. Pictured: A vehicle trapped by mud along the banks of the Trishuli River
‘The heavy rain would have saturated the soil and filled the rivers downstream, setting the scene for such a disaster, and these conditions are made much more likely by climate change that is causing rapid retreat of Himalayan glaciers.’
The terrain in the northern half of Nepal is extremely steep, making it highly susceptible to landslides, rockfalls, and ice cliff collapses.
When glaciers flow over steep slopes, they fracture into features known as seracs, inherently unstable ice cliffs.
However, climate change is now threatening to further destabilise these already perilous conditions.
Glaciers sit on a layer of permafrost, ground that remains frozen all year, which helps maintain their stability.
As temperatures warm, parts of this permafrost are beginning to thaw, loosening rocks and mud that create a serious risk of catastrophic collapse.
In Nepal, this means that similar rockslides, glacial collapses, and floods are becoming increasingly common.
In April 2015, an earthquake released a major avalanche on the south face of the same Langtang-Lirung mountain, which destroyed Langtang village and caused many casualties.
Experts say that human-caused climate change has made this kind of disaster more likely by melting the glaciers and thawing the permafrost. Pictured: Damaged buildings on the Likhu River
As of today, 903 people are confirmed dead in Nepal, in addition to 16 in Tibet. More than 4,000 are also reported missing in Nepal, with another 500 in Tibet
Professor Maria Shahgedanova, a climate scientist from the University of Reading, says: ‘The failed glacier retreated by approximately 450m between 1990 and 2020, potentially reducing the mechanical support provided by the glacier to the underlying rock slope.’
Since the start of the Industrial Revolution, the global average temperature has risen by 1.4°C (2.52°F), but this warming is not evenly distributed.
The Himalayas have been warming far faster than the global average, leading to rapidly accelerating glacier melting.
The latest comprehensive assessment of glaciers using satellite data from 1976 to 2024 found that melt rates have increased everywhere on Earth besides Iceland.
In High Mountain Asia, which includes the Himalayas, the rate of melting in the last decade has been 25 per cent faster than the long-term average.
This increased melting makes serac collapses more likely, destabilises the permafrost, and leads to the growth of large lakes at the feet of glaciers.
These glacial lakes are held back by fragile natural dams of sediment from previous floods that can suddenly break, causing destructive glacial lake outburst floods.
Professor Hugh Sinclair, of the University of Edinburgh, adds: ‘No single event can be attributed to climate change, but the trend is worrying. Melting is driving collapse of the high Himalayan glacial valleys, and this is likely to accelerate with global warming.’
