Scientists have blamed climate change for the flash floods in Nepal, triggered by a glacial collapse that sent water rushing up to 650 feet high.
The disaster wiped out buildings and bridges along the Nepal-Tibet border, leaving what officials describe as devastation beyond imagination.
The United States Geological Survey initially reported the event as a magnitude 4.4 earthquake before confirming it was a glacial lake outburst flood. The USGS is a scientific agency of the US government that studies the landscape and natural hazards.
The agency told the BBC that additional analysis of nearby seismic stations, long period seismic waves, and satellite imagery led to the determination that the seismic event was instead a glacial collapse and debris flow, and that no earthquake had occurred.
Glacial collapse
Dr Wouter Buytaert, a reader in hydrology and water resources at Imperial College London, said climate change caused the glacier to break apart. Imperial College is a public research university in the United Kingdom.
"It is exactly the type of event that is triggered by climate change," he said. "Global warming shrinks glaciers, making it more likely for them to break apart. Land degradation, due to increasing wildfires, extreme weather, and unsustainable land use, destabilizes valley slopes and mobilizes rocks and sediment."
"In mountain regions with steep slopes and narrow valleys, this creates the perfect conditions for events such as this," he said.
Warming warnings
The flood arrived one month after researchers at Kathmandu University, an autonomous public institution in Nepal, published a study in the journal Frontiers in Climate warning that global warming could spark glacial collapses in the Himalayas.
"Across the Himalayan region, warming rates exceed the global average, intensifying climate-related hazards and associated losses contributing to the melting of glaciers and increasing the risk of GLOF [glacial lake outburst floods]," the researchers wrote.
A glacial lake outburst flood occurs when a water reservoir near or beneath a glacier is suddenly released. The rushing water can carry huge amounts of mud, rocks, and debris downstream, damaging farmland, settlements, roads, and bridges. They are a significant hazard in mountainous regions including the Himalayas, Alps, and Andes.
Rising flood risks
Dr Adrian McCallum, a glaciologist and polar engineer at the University of the Sunshine Coast in Queensland, Australia, said the floods were probably glacial lake outburst floods, which are becoming increasingly common in global alpine regions.
"I'm yet to fully appraise myself of the situation, but these floods are probably 'glacial lake outburst floods' (GLOFs); these are increasingly common in alpine regions globally as our climate changes," he said.
"As glaciers melt and recede, ice turns to water, the water is stored (temporarily) behind natural moraine dams, but when those dams breach, tremendous amounts of water can be released down a valley, taking out everything in its path," he said.
Dr Ella Gilbert, a climate scientist at the British Antarctic Survey, the UK's national polar research institute, said climate heating is destabilising Himalayan glaciers, with the rate of ice loss doubling since 2000.
"We can't say definitively yet what the links to climate change are, but we know that climate heating is destabilising glaciers in the Himalaya, with the rate of loss doubling since 2000," she said. "When glacier stability is undermined, sudden failures can occur, leading to horrible incidents like this one."
"Mountain glaciers worldwide are under threat from climate heating, particularly those in tropical regions," she said. "The higher temperatures rise, the greater the risk of sudden and devastating collapse."
Vulnerable topography
The Kathmandu University researchers wrote that Nepal, a mountainous, landlocked and least developed country in the eastern Himalayas, is highly vulnerable to climate change due to its complex topography, fragile ecosystem and limited ability to adapt.
"The vulnerability is exacerbated with increased frequency and intensity of climate-induced disasters, such as floods, landslides, glacier retreat and glacier lake outburst floods (GLOF), among others, leading to loss and damage," the researchers wrote.
At least 45 glacial lake outburst floods have occurred across 39 lakes in Nepal, with several resulting in loss of life, according to the study.
Extreme weather probabilities
Scientists warn that these events will become more frequent as temperatures continue to rise.
"Nepal is already experiencing significant climate-induced loss and damage across multiple sectors at the current level of global warming," the researchers warned.
"An event specific climate attribution study for September 2024 extreme rainfall in central Nepal shows that in a 1.3°C warmer world, the intensity of the rainfall was approximately 10% higher and the probability of occurrence about 70% greater."
"With temperature exceeding 1.5°C, the risk of floods, glacier melt, GLOFs and droughts would significantly increase," they added.
Early warning systems
With the true extent of the devastation only just beginning to emerge, scientists hope the disaster will trigger the development of future warning systems.
Dr Nader Naderpajouh, an expert in risk and resilience at the University of Sydney, a public research university in Australia, said the implementation of future warning systems is feasible with current state-of-the-art technology.
"At least the buildup of water can be an early warning sign for downstream communities, a form of seasonal warning for preparation," he said. "Such communications and preparations can save lives and reduce the impact at scale."
He added that with global warming, there is an expectation that similar patterns of disasters will recur.
"We can benefit from the implementation of a warning system, similar to those triggered for tsunami warnings after 2004's tsunami," he said.
