USGS Says Glacial Collapse, Not Earthquake, Triggered Nepal Flash Floods
Fresh seismic analysis and satellite imagery indicate a glacier collapse and debris flow caused the devastating floods, with hundreds reported dead or missing.
Washington, Aug 27: The United States Geological Survey (USGS) has determined that a glacial collapse and subsequent debris flow, rather than an earthquake, triggered the devastating flash floods that struck Nepal after originating in Tibet.
The agency initially classified the seismic activity associated with the disaster as a magnitude 4.4 earthquake. However, further examination of data from nearby seismic stations, long-period seismic waves and satellite imagery led researchers to conclude that no earthquake had occurred.
The USGS has now assessed the seismic event at magnitude 5.2 and said it was generated by a glacial collapse followed by a debris flow that produced catastrophic impacts downstream.
The disaster on Wednesday caused widespread destruction in Nepal’s Rasuwa and Dhading districts. According to the figures cited in the report, 162 people were killed while another 750 remained missing, including 133 Indian nationals.
The revised assessment provides a clearer explanation of the powerful natural event that sent large volumes of water and debris downstream from the Tibetan region.
Daniel Shugar, an associate professor of geomorphology at the University of Calgary in Canada, said satellite imagery indicated that a glacier had rolled off a cliff at an elevation of about 5,200 metres.
Shugar compared satellite images taken before and after the disaster and observed substantial changes in snow and ice cover in the area.
He suggested that melting snow and glacier ice may have introduced significant quantities of water into the glacier. The water could have travelled down to the glacier bed, reducing friction and potentially contributing to the collapse.
The USGS said its updated assessment was based on multiple lines of evidence, including seismic observations and satellite imagery.
The findings shift the understanding of the disaster from an earthquake-related event to a cascading glacial hazard, highlighting the potential for rapidly developing floods and debris flows in high-altitude Himalayan regions.
