Glacial collapse caused seismic activity, ‘catastrophic’ Nepal floods, USGS says

A glacial collapse triggered seismic activity that led to catastrophic downstream impacts in Nepal and Tibet, according to the US Geological Survey (USGS). The agency clarified that the seismic event initially reported as an earthquake was actually a glacial collapse and debris flow, causing devastating consequences downstream. At least 160 people lost their lives due to torrents of water and debris that swept downstream on either side of the Nepal-Tibet border, with hundreds more reported missing.

The disaster's immediate cause was initially unclear, with Nepal's Foreign Minister Shishir Khanal suggesting an earthquake triggered a landslide, subsequently blocking a river and causing the gushing of water downstream. Other theories proposed included a glacial lake flood or an ice avalanche. The USGS determined that a magnitude 5.2 seismic event occurred near the Nepal-China border on August 26 at 8:37am local time.

This seismic activity was initially reported as a magnitude 4.4 earthquake, but further analysis revealed it was a glacial collapse and debris flow, dispelling the notion of an earthquake occurrence. The exact sequence of events remains uncertain, but the disaster unfolded as torrents of water and debris swept downstream on both sides of the border.

Surveillance video from China showed a wall of mud and water crashing over a building, while in Nepal, a surge of water inundated villages and towns along the Bhote Koshi and Trishuli rivers. Initial reports described the disaster as a flood in Nepal and a mudslide in China. At least 165 people were reported dead, with 162 in Nepal and three in Tibet.

Chinese authorities stated that the disaster resulted in "major casualties" and reported 558 missing, including 260 foreigners. On the Nepalese side, authorities disclosed that 468 tourists, 393 of whom were foreigners, were unaccounted for, with Australians and citizens of other nationalities among the missing. Aid and assistance poured in swiftly after the scale of the disaster became apparent.

The United States pledged $500,000 in emergency aid, while the International Federation of the Red Cross and Red Crescent Societies donated $1.4 million. The organization's Nepal head, David Fisher, emphasized the priority of reaching affected communities for assistance. The European Union activated its Copernicus satellite surveillance system for recovery efforts and pledged further support, while the World Health Organization dispatched emergency medical supplies.

Neighboring India provided an initial 10 tonnes of humanitarian aid. The explanation for the calamity evolved but was ultimately linked to a collapsing glacier. Shortly after the flooding, Nepal's Foreign Minister Shishir Khanal attributed the disaster to an earthquake likely triggering a landslide, which blocked a river and led to downstream flooding.

China also reported a landslide, citing a debris surge hitting a border hub between Tibet and Nepal. The Nepali foreign minister's statement aligned with the USGS's initial report of an earthquake in Tibet north of the disaster zone. However, the USGS later revised its conclusion, asserting that the seismic activity initially reported as a quake was instead a glacial collapse and debris flow that caused the catastrophic downstream impacts.