Glacial collapse, not earthquake, triggered deadly Nepal floods, USGS says

The catastrophic flash floods that swept through parts of Nepal were caused by a glacial collapse rather than a magnitude 4.4 earthquake, as initially reported, the US Geological Survey has said.

The floods, which originated in Tibet on Wednesday, devastated Nepal’s Rasuwa and Dhading districts, killing 162 people. Around 750 others, including 133 Indian nationals, remain missing.

The USGS said a detailed assessment of data from nearby seismic stations, long-period seismic waves and satellite imagery found no evidence that an earthquake had occurred. Instead, the seismic activity was generated by collapsing glacial ice and the subsequent movement of debris.

The agency also revised the magnitude assigned to the seismic event from 4.4 to 5.2. It clarified that the measurement reflected the strength of the signals produced by the glacial collapse and debris flow, which caused catastrophic damage downstream.

Daniel Shugar, an associate professor of geomorphology at the University of Calgary in Canada, said the disaster appeared to have begun when a glacier collapsed from a cliff at an altitude of about 5,200 metres.

Shugar examined satellite images of the region captured before and after the floods and observed that glaciers in the area appeared to have lost a substantial amount of snow within 24 hours.

He suggested that melting snow and glacial ice may have allowed large quantities of water to seep beneath the glacier. This could have reduced friction at its base and destabilised it, eventually causing the glacier to collapse and unleash the destructive flow downstream.

With PTI inputs