BENGALURU, India (AP) — A flash flood in Nepal on Wednesday was likely caused by a large section of a glacier that broke off and temporarily dammed a river, according to preliminary investigations by scientists. This event may have led to a surge of water downstream several hours later.
Scientists are currently analyzing satellite and ground-level data to determine the exact cause of the flood, which resulted in hundreds of fatalities and many missing individuals, including foreigners and pilgrims.
The U.S. Geological Survey reported a magnitude 5.2 glacier collapse that sent debris downstream, impacting local communities. This assessment was based on data from nearby seismic stations, long period seismic waves, and satellite imagery.
Jakob Steiner, a geoscientist at the University of Graz in Austria, stated, "A lower part of a glacier has really come off. If you look at the imagery it's like someone cut with a huge knife through the whole lower part and it fell off."
Steiner noted that the mass of glacial ice dropping from a significant height could have created a sound similar to an explosion, leading to the ensuing chaos.
While scientists caution against drawing direct connections between global warming and the flood, they acknowledge that rising temperatures due to human activities, such as fossil fuel combustion, increase the likelihood of such disasters, particularly in the rapidly warming Himalayan region.
Saswat Sanyal, a disaster risk reduction specialist at the Kathmandu-based International Centre for Integrated Mountain Development, remarked, "We have to be cautious and not draw a connection yet. However, rising temperatures are changing the Hindu Kush Himalaya region and melting glaciers."
The floods have displaced hundreds and caused significant damage to infrastructure, including hydropower dams, roads, buildings, and bridges. Water levels in rivers in the affected area rose by as much as 9 meters (29.5 feet) within 30 minutes due to the surge from the glacial detachment.
Preliminary evidence indicates that a large volume of ice and rock may have fallen into the Lhende Khola, a tributary of the Bhote Koshi River, potentially displacing water and sediment, which contributed to the powerful surge downstream. Researchers are investigating whether debris temporarily blocked the river before the impounded water burst through, exacerbating the flood.
The region has a history of destructive mountain hazards, with previous floods and avalanches occurring in the area. The Hindu Kush Himalaya is warming rapidly, leading to significant changes in glaciers, snow cover, and mountain slopes, according to climate scientists.
This mountain range holds the largest volume of snow and ice outside polar regions, with over 63,000 glaciers feeding at least 10 major Asian river systems, supporting the livelihoods of billions. However, approximately 78% of the glacier area between 4,500 and 6,000 meters above sea level is highly vulnerable to warming.
Steiner stated, "What happened yesterday is unfortunately the new normal. It's going to get worse from here onwards." The last decade has been the hottest on record, with projections indicating that up to 50% of all glaciers, excluding those in Greenland and Antarctica, could be lost by 2100 if global warming is limited to 1.5 degrees Celsius (2.7 degrees Fahrenheit).
Research indicates that glaciers in the region are melting at an accelerating rate, with ice-loss rates doubling since 2000. Melting glaciers can lead to the formation of glacial lakes, increasing the risk of sudden floods.
As glaciers retreat, previously insulated mountain rock becomes exposed to warmer temperatures, rain, and cycles of freezing and thawing, which can destabilize slopes. Sanyal suggested that the recent events in Nepal may be indicative of cascading hazards, where an avalanche or glacier collapse leads to debris flows, river blockages, and flash floods.
Steiner noted that about 10% of Nepal's power production is located in the valley affected by the disaster, raising concerns about the adequacy of warning systems for residents and visitors following previous disasters. The landscape has attracted millions of tourists annually in recent years.
Scientists emphasize the need for improved early warning systems, better monitoring, and faster cross-border information sharing as temperatures rise and mountain landscapes become increasingly unstable. However, monitoring the numerous glaciers and steep slopes across the Himalayan region presents significant challenges.
"We don't have hours," Sanyal said. "We have sometimes a few minutes to actually prepare." Steiner added that some regions of Nepal have reached a point where they are too risky for habitation. He expressed frustration that previous disasters have not prompted sufficient governmental action to address these risks, stating, "I'm not super optimistic that from tomorrow onwards there will be clear solutions. We know what can be done, but various stakeholders need to coordinate and make things happen."