The catastrophic flash flood that struck Nepal’s Himalayan border region on Wednesday is suspected to have been triggered by an earthquake followed by a massive ice-rock avalanche, according to preliminary assessments.
A magnitude 4.4 earthquake was recorded in the region shortly before the disaster. The German Research Centre for Geosciences said the quake occurred approximately seven minutes before the time captured on security footage showing the flood reaching the border area.
Initial satellite analysis by Nepal’s National Disaster Risk Reduction and Management Authority indicates that a mass of snow and rock fell into the Lhende Khola river, around 20 kilometres northeast of the Nepal-China Rasuwagadhi border crossing.
Scientists believe the avalanche may have blocked the river, causing water and debris to accumulate behind the natural barrier. When the blockage gave way, a sudden surge of water, mud, rocks and sediment rushed downstream through the Lhende Khola and into the Bhote Koshi river system.
The resulting wall of water and debris swept through settlements, destroying buildings, roads, bridges and power infrastructure along its path.
However, authorities have stressed that the precise sequence of events has not yet been conclusively established. Scientists are investigating whether the magnitude 4.4 earthquake destabilised the mountainous terrain and triggered the avalanche. They are also examining whether a glacial lake outburst contributed to the disaster.
Heavy rainfall does not currently appear to have been the main trigger. Nepalese experts said there had been no significant rainfall in the Rasuwa area immediately before the disaster, while the sudden nature of the flood was more consistent with the rapid release of water from an upstream blockage.
Authorities have also warned that the danger may not be over. A blockage remains upstream on the Lhende Khola, raising concerns that another sudden flood could occur. (Newswire)