Ice-rock avalanche may have triggered Nepal flash flood, say scientists

Early analysis of seismic records has also identified unusual signals recorded during the period of the disaster but there was no immediate causal link established between seismic activity and the floods.

“The same site devastated by last year’s Rasuwa flood is once again under threat,” Qianggong Zhang, Head of Climate and Environmental Risks at ICIMOD, said in the press release. “An ice avalanche in the Lhende Khola is the suspected trigger, but the cause remains unconfirmed. With a blockage still lodged upstream on the Nepal-China border, authorities warn a second flood is imminent and evacuation orders are now in place for Jilong port,” it said.

An ice avalanche involves the sudden collapse and downhill movement of a large mass of ice from either a glacier that was hanging or from an ice-covered mountain.

ICIMOD noted the ‘exceptional speed and magnitude’ of the flood and added that water levels within 30 minutes reportedly rose as much as 9 metres on the Trishuli river at Galchhi and by seven metres at Malekhu. Galchhi and Malekhu are part of Dhading district and nearly 80 km from Kathmandu.

ICIMOD added that experts are assessing whether debris temporarily blocked the river at a narrow section, forming a landslide dam. Such blockage, it said, could create a ‘secondary hazard’ if impounded water is suddenly released.