Devastating flood in Nepal: Scientists reconstruct the disaster

The flood swallowed the valley within minutes, at speeds that sometimes exceeded 30 meters per second. Scientists are now reconstructing how 200 million cubic meters of rock and ice broke away from a Himalayan mountain and unleashed one of Nepal's worst disasters.

More than a week after the catastrophe, the provisional toll stood at 1,289 dead and 5,083 missing. The event began not with an earthquake or torrential rain, but with a collapse high on the Langtang Lirung massif.

At 8:37 a.m. local time on Aug. 26, at an altitude of 5,200 meters, a huge block of ice and rock detached from the mountain. It fell about 1,200 meters and generated a seismic signal measured at magnitude 5.2. The debris briefly blocked the Lhende River before the obstruction gave way.

The resulting flood struck the Nepal-China border post at Rasuwagadhi, carrying away most of the infrastructure before engulfing the valley. Scientists are calling for more detailed monitoring as glacier retreat and permafrost thaw weaken Himalayan slopes and make cascading disasters harder to anticipate.