The earth-shattering glacier break behind Nepal's flash flooding disaster

Nepal flash flood buries villages after earth-shattering glacier break Buildings, bridges and trucks look like toys, swept up in the gigantic mud wave, cascading down Nepal's Bhote Koshi River. The magnitude of the flooding, burying entire villages in its path, beggars belief. Climate scientists have been warning that the Himalayas are warming faster than the rest of the world, increasing the chances of a disaster of this scale. The source of the ice avalanche appears to be a glacier more than 5,000 metres up in the Langtang Himal mountain range. It sits just below the range's highest peak, Langtang Lirung, at 7,234 metres. This satellite image shows the mountainous terrain of the Himalayas before the collapse. NASA imagery captured after the avalanche shows a section of the glacier, hundreds of metres across, appears to have broken off. Elevation data shows the glacial rock fell more than 2 kilometres vertically into the valley below. Hundreds of people have been killed, and at least 1,500 are missing after the deadly flash floods struck villages in the border region between Nepal and Tibet on Wednesday. Despite initial suggestions that an earthquake may have triggered the disaster, the US Geological Survey has since confirmed the glacier collapse was so large it registered as a magnitude 5.2 seismic event and caused the devastation downstream. University of Tasmania glaciologist Poul Christoffersen said ice avalanches were known to occur in high-altitude environments where cold temperatures held glaciers in place. "These glaciers sit very steeply and high up in the head walls of the valleys as far up as you can get in these environments," he said. "There are emerging images to indicate perhaps that there could have been melting taking place, some liquid water starting to form, and opening up some cracks perhaps, but a large section of ice has simply fallen down." Professor Christoffersen said it was likely that millions of cubic meters of ice fell instantaneously into the valley below. "The friction and heat that are associated with this avalanche as it travels down create a valley; perhaps there is also damage to lakes along the way and water that's being funnelled into this process." Is this climate change? Soon after the disaster unfolded, questions were swirling about its cause and whether climate change was to blame. Scientists say while the ice avalanche can't be directly attributed to climate change at this point, warming temperatures are creating conditions that make events like these more likely. Ruth Gamble is a climate historian and director of La Trobe Asia, who has studied Tibet and Himalayan rivers for more than a decade. She's currently in Kathmandu, near where the landslip occurred, and was set to travel through the border pass that was wiped out by the flash flood in a few days. Dr Gamble said landslides were common in the region, but they were happening more often now. "Because I'm a historian, I look all the way back, and I know that there were outburst floods and landslides," she said. "I was looking at one yesterday that happened in 603 CE; we've got records of ones going back all that time. "But they were rare, the people saw them as being rare events and then what's happening now is every year there's more and more." Dr Gamble added that the fingerprints of climate change were all over this event. "Everyone can see, even non-scientists can see, that there's melting glaciers and melting ice and there's less snow and more rain and the rain's coming down faster all across the mountains," she said. "The conditions and the type of precipitation that's falling in the mountains are all changing so fast that denying that it's climate change takes a willful act to ignore all of the evidence." Melting reshapes mountains Research shows that higher temperatures in a warming climate are causing glaciers to melt and recede, increasing the chance of ice breaking away and causing a cascading event, like what's believed to have happened in Nepal. It also leads to more meltwater, which loosens up soils and destabilises the landscape, making avalanches more likely. Alpine communities rely on seasonal glacial melt for water, but too much warming can cause sudden, destructive flooding. Glaciologist and polar engineer Adrian McCallum at the University of the Sunshine Coast said this happened when glacial melt accumulated and formed a dam. "When that dam releases via whatever mechanism, glacial collapse or earthquake, then that's a bad thing," he said. "All of a sudden, you've got this large volume of water perched, poised up a valley about to run downstream and take everything out with it." Landscape part solid, part soup It's easy to think of mountains like the Himalayas as solid masses of rock, but much of what makes up the landscape is permafrost, ground that always remains below zero. Permafrost isn't just soil or rock, it's also moisture that remains frozen solid year-round, while the snow layer changes with the seasons. Warming temperatures can melt the snow and threaten the stability of the ground that was previously held together. As cracks open in the thawing permafrost, water from rain and ice melt can penetrate deeper inside the mountain. Melting permafrost can be problematic not only because of landslides, but also for building houses and infrastructure. "You used to be able to build it on solid frozen ground, but that frozen ground is no longer solid — it becomes part liquid, part solid, part soup," Dr McCallum said. "There are communities in Alaska which are having to be moved physically because the environment in which they're in is no longer essentially habitable. "Whole communities, if not cities, will potentially have to move or at great expense try and solidify their foundations, which is a huge task." An emerging pattern Glaciologist Dr Simon Cook says what happened in Nepal follows a spate of similar glacier avalanches in recent years. Just last year, a collapsing glacier buried an entire village in Switzerland. In July 2022, a part of the Marmolade Glacier in the Dolomites, in Italy, broke off, killing 11 mountaineers after unusually high air temperatures in the preceding months. Five years ago, in 2021, a massive portion of a hanging glacier and rock face detached from a Himalayan glacier in the Chamoli district of Uttarakhand, triggering a violent flash flood that left more than 200 people dead or missing. A recent study from Chinese researchers indicates ice avalanches on the Tibetan Plateau are increasing, with rising air temperatures since the early 21st century a key driver. This has sparked calls for more action to protect alpine regions from the impacts of climate change, such as improved monitoring of receding glaciers. "This is happening to people throughout this region all the time and a lot of them are people who live in villages and their voices don't get heard," Dr Gamble said. "It's almost as if you have disaster after disaster after disaster until it kind of impacts more international communities, and then people pay attention, but this is something that's every day for a lot of people in this region." Satellite images courtesy of USGS/NASA: Landsat 9, Google Earth. Elevation data is SRTM 30m. - Share options - Copy link - X (formerly Twitter)