Satellite imagery reveals scale of devastation from Nepal flash flood triggered by glacier collapse

New satellite imagery has revealed the scale of the devastation along Nepal's Trishuli River caused by Wednesday's deadly flash flood, triggered by a glacier collapse.

Before-and-after images show how sections of the valley, where a torrent of floodwater and debris surged through, destroyed villages, bridges and hydroelectric power stations.

More than 550 people have been killed, Nepalese officials say, with hundreds more missing.

Among the worst-hit locations reviewed by BBC Verify was a key Nepal-Tibet border crossing, which was engulfed by a rush of floodwater and captured on camera.

The satellite imagery from US-based intelligence firm Vantor, shows the site has been almost entirely washed away. Shocking CCTV footage showed the moment as the deluge of water swept over buildings as people tried to escape.

Damage and mud can be seen more than 2.5km (1.5 miles) upstream, reaching 100m (330 ft) above the area it first hit.

A few miles further south is the village of Timure, which has now largely disappeared.

The walls of the valley at this point are steep, reaching up to 50m above the water line. The image shows most of the houses perched on this slope are now gone or covered in mud.

One of the larger villages to be struck by the full force of the flood was Trishuli, where some of the earliest verified footage of the disaster emerged from.

A satellite image of the town and surrounding agricultural land, which is about 45km (28 miles) downstream from the border, show an entire neighbourhood has been essentially washed away.

Verified videos of the town show a bridge collapsing as the river surges forward. At the very same moment from ground level, footage filmed from inside a bus shows people crying out in distress and trying to flee as they see the water rushing down the river.

Other dramatic videos show people sheltering inside a house, peering over the edge of a balcony as they watch a torrent of floodwater wash away almost everything around them, knocking large metal debris and a vehicle toward the building.

Somehow the house remains intact and survivors can be seen in a second verified video standing surrounded by mud once the floodwater had receded.

Imagery from satellite provider Planet Labs released today has also provided a clearer view of the disaster's origins at the collapsed glacier, the moment of which has been captured on a verified drone video.

The satellite image shows an enormous chunk of the glacier has fallen away, carving an enormous path of rock and debris where water rushed through the valley.

At the base of the landslide, trees and other vegetation have been stripped at a height of more than 300m above the riverbed.

This destructive path continues westwards along with the swelled river, before heading southwards.

Satellite images also show the formation of a barrier lake at the base of the landslide's path, which Chinese authorities have warned poses a major risk of further flooding and has hampered rescue efforts.

Dr Argha Banerjee, a glaciologist at the Indian Institute of Science Education and Research, told BBC Verify that it was not possible determine from the images how stable the barrier was or how likely the lake was to drain suddenly.

But he said there was no significant increase in its surface area between Wednesday and Thursday, despite water continuing to flow into the lake.

Dr Banerjee said there was a visible drainage channel, which suggests some water was already escaping downstream, adding that the its volume was "not alarmingly large" and appeared to have stabilised.

The extent of the damage on the Tibetan side of the border remains unclear. It is a strictly controlled region which China annexed in the 1950s, where foreign media access is heavily restricted. BBC Verify has so far been unable find verifiable footage from the area.

The satellite imagery - which only provides an initial glimpse into the damage of the flood - has been published by Vantor as part of its Open Data Program to help aid authorities establish where best to focus their efforts to locate the missing, rescue survivors and recover the dead.

Additional reporting Shruti Menon, Merlyn Thomas and Alex Murray. Graphics by Mesut Ersoz and Mike Hill.