Viral CCTV footage timestamped 10:59:53 shows a dark wall of water, mud, boulders, ice and rock surging down the valley from behind buildings on the Chinese side of the border. The video, analysed by the BBC, provides the first clear visual evidence of the destruction. Satellite imagery and electronic immigration records from Nepal's Rasuwagadhi border post are helping authorities piece together events.
The only surviving staff member of the border post, Tika Ram Pokharel, who was in Kathmandu taking an exam when the flood hit, told the BBC the crossing was unusually busy that day. The area is a historic travel route between Kathmandu and Tibet, used by pilgrims travelling to Mount Kailash, traders, truck drivers, customs officials, tourists and border residents.
Kathmandu-based hydrologist Ajay Dixit described the region as geologically vulnerable, characterised by deep gorges and steep rivers that flow at high velocity, carrying heavy sediment and boulders.
More than 100 Indians may have been in or near the crossing when the flood struck, according to India's foreign ministry, which has confirmed at least 275 Indians missing in Nepal. Nepal's immigration department is continuing its efforts to account for those caught in the disaster.