Scientists from the International Centre for Integrated Mountain Development (ICIMOD), along with partner institutions in Nepal and China, are investigating whether an ice-rock avalanche from a high-altitude area could have triggered the massive flash flood and mudslide on the Nepal-Tibet border on Wednesday. ICIMOD is a Nepal-based intergovernmental institution leading the global effort to protect the Hindu Kush Himalaya (HKH) region.

On Wednesday morning, devastating flash floods struck Nepal’s Rasuwa district, downstream of Tibet, triggering water, sediment and boulders through Bhote Koshi and Trishuli rivers.

Rescuers use earthmovers to reach submerged houses after flash flooding along the Trishuli River in Nepal’s Nuwakot district

“Preliminary assessment based on video footage and information from affected areas suggests that a large volume of ice and rock debris may have entered the Lende Khola, a tributary of the Bhote Koshi river. Researchers say the event could have generated a sudden surge that carried water, sediment and large boulders downstream,” ICIMOD said in a press release issued on Wednesday evening.

Story continues below this ad

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.

Story continues below this ad

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.