SOURCE :- THE AGE NEWS
To many who survived the disaster that struck parts of Nepal and China, the threat came out of the blue.
Most of the region had seen little or no rain. The skies over much of the region were blue and clear. Suddenly, a mass of ice, mud, water, debris and rock began to barrel along narrow Himalayan canyons, obliterating the towns and villages, bridges and power stations, farms and schools that were nestled along the riversides and valley floors.
This disaster, overwhelming everything in its path with terrifying power and force, is complex and difficult to analyse. Here is what we know so far – and what remains uncertain.
Unravelling the trigger
So inaccessible are many of the high peaks of the region that experts are still trying to piece together exactly what caused the disaster, relying not only on survivor accounts and vision posted on social media, but satellite imagery and seismic monitoring data.
What is known is that a magnitude 5.2 seismic event occurred near the Nepal-China border at 8.37am local time. It registered as a 4.4 earthquake, but later the United States Geological Survey reported that the seismic activity detected was likely the avalanche itself, rather than an avalanche caused by an earthquake.
“The root cause of this disaster is already known, although there is a lot of misinformation and some uncertainty,” wrote Dave Petley, a leading British earth scientist for Eos, an online journal for the American Geophysical Union.
“There has been some speculation, and indeed official comments, that the trigger was an earthquake. This is likely to be a misinterpretation of the data; the seismic signal is almost certainly the rock ice avalanche and debris flow, not a tectonic event.”
This analysis lends weight to early reports that the “snout” of a glacier on the side of Mt Langtang Lirung, the highest peak of the Langtang Himal, a range of the Nepalese Himalayas, had broken free and fallen over a kilometre into the valley beneath.
Earth scientist Dan Shugar, an associate professor at the University of Calgary, told Reuters that satellite imagery seemed to show that a large amount of snow had melted in the 24 hours before the disaster.
“Some of the glaciers in the valley were covered in snow yesterday and today they are mostly bare ice. So in other words (and I haven’t seen any weather station data yet), it was probably warm,” he said.
“What I can see in this morning’s satellite imagery from Planet Labs, the lower part of a glacier broke off at about 5200 metres and crashed onto the valley floor about 1200 metres below,” Shugar said.
The force of that mass falling that far would have been catastrophic, Dr Anil Kulkarni, a distinguished scientist with the Divecha Centre for Climate Change at the Indian Institute of Science, told this masthead.
“The moment it hits the ground with such an explosion, it gets converted into water,” Kulkarna said.
“All that potential energy [in the mass of rock and ice] converts into kinetic energy and liquid in a very short period of time,” said Kulkarni, who has also been studying satellite images of the disaster zone captured before and after the collapse as part of the international response to the disaster.
“It would have been a very potent mass coming down from the mountain.”
This mass of ice, mud, water, debris and rock then began its violent passage downwards through villages clinging to valley walls and riversides.
Swept away in seconds
Among the first hit was the border town of Timure in Nepal’s Rasuwa District. Vision posted on social media shows a wall of mud, water and rock slamming into the village.
“It looked as though a river that had been frozen suddenly burst its banks. The entire village of Timure was out of sight,” a helicopter pilot who flew to Timure for the rescue operation told the Kathmandu Post. He was unable to lend aid because there was no safe place to set-down.
A river port obliterated
Ram Kumar Adhikari, the manager of the tour company Alpine Eco Trek that was leading a party of 12 British tourists through the region, said it lost contact with two guides at 8.42am, shortly after the group crossed through the river town of Gyirong Port.
“The whole area was swept away by the flood. Even the Tibet immigration office.”
Horrifying CCTV footage captured what some described as an inland tsunami, estimated to be 20 metres high, smashing into the town, a tourism hotspot that is also part of a pilgrim route.
Survivor Kalpana Malla, who saw her father, mother, sister and sister’s children lost to the flood, told the BBC her family didn’t stand a chance against the fury of the flood.
“They could not escape, there was no chance at all. This flood took everything, but my son and I climbed the rooftop of a house and survived somehow,” she said.
Another survivor, Bhawani Prasad Neupane, told Nepal News that at around 8.40am as he ate breakfast, he heard news that the nearby town of Timure had been destroyed and rushed outside.
“While looking toward Betrawati, a terrifying sound suddenly echoed. Along with the roar, it looked as if a massive whirlpool was sweeping through. The whole village shook.
“It felt like an earthquake was happening. Right before our eyes, the market and the settlement were devastated. An event we could not even have imagined took place.
As the mass of debris and water continued on its path, it found its way through the Bhote Koshi River into the Trishuli River, the International Centre for Integrated Mountain Development, a regional intergovernmental body, has reported.
It said that water levels on the river at the Galchhi area downstream rose by as much as nine metres within 30 minutes, while levels at Malekhu increased by seven metres over a similar period.
It said several water monitoring stations along the Trishuli River were damaged or washed away and that experts were now exploring the possibility that debris temporarily blocked narrow sections of the river, only to later break and cause further carnage.
An ongoing threat
Though much of the early analysis of the disaster focuses on the seismic movement detected in the minutes before the flash flood began its destruction, there is also evidence of movement in the hours beforehand.
This might have destabilised the glacier in question. Some scientists have not ruled out the possibility that a glacial lake might also have collapsed, contributing to the flood that flashed through the valleys, though Petley does not believe this was a factor.
Whatever the proximate cause, there is broad agreement that climate change is the catalysing force.
Nepal’s glaciers have lost almost a third of their volume in the past 30 years, the United Nations reported in 2023. “The rooftops of the world are caving in,” said UN chief Antonio Guterres at the time.
Dr. Basanta Raj Adhikari, a Nepalese expert in disaster risk and geomorphology, told this masthead that as glaciers and the permafrost that holds them in place melt due to global warming, glaciers begin to detach from mountainsides.
“That’s why we are experiencing very extreme events like these every year,” he said.
In 2023, heavy rainfall caused flooding and landslides in Himachal Pradesh. The ensuing series of disasters would eventually kill at least 72 people.
Dr Neera Shrestha Pradhan, who leads the water program at International Centre for Integrated Mountain Development noted the region is known as the world’s third pole, because its glaciers hold the largest volume of permanent snow and ice on earth outside the Arctic and Antarctica.
As warming is more pronounced at altitude, its glaciers are melting faster than those at sea level, she said.
Over the coming 25 years, experts expect disasters to happen with increasing frequency. “There will be too much water for some time; floods, flash floods, glacial lake outburst floods, leading to landslides and this multi-hazard and cascading, compounding series of risks.”
Later, in around 2050, the period of peak water will subside because so much of the ice and snow will have been lost, says Pradhan. Then the region is expected to suffer from water shortages, potentially crippling the region’s farming and hydroelectricity output.
Those that live high in the Himalayas, she warns, are as vulnerable to the accelerating threat of climate change as those fighting off the seas on the world’s lowest-lying islands.
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