Satellite imagery reveals scale of destruction from Nepal-Tibet flash floods

Satellite images show devastation along Trishuli River

High-resolution satellite imagery has confirmed the scale of destruction along Nepal's Trishuli River following this week's flash floods, with structures and settlements wiped off the map, as reported by ABC Australia and BBC News.

The floods, triggered by a glacier collapse, sent a torrent of water and debris surging through the valley, destroying villages, bridges and hydroelectric power stations. Satellite images from US-based commercial provider Vantor show the devastation stretching from the Nepal-Tibet border downstream through several communities.

At the Rasuwagadhi border point between Nepal and Tibet, a large multi-storey building and surrounding infrastructure have been completely destroyed. Vantor imagery captured in April 2024 showed the border facility with large buildings, a basketball court and other structures; images after the flood show almost all structures gone, with the area appearing reduced to its bedrock, as reported by ABC Australia.

Death toll and missing

Officials in Nepal have reported more than 550 people killed, with hundreds more missing, according to BBC News. ABC Australia reported at least 392 deaths and hundreds still missing, including at least 39 Australians. The discrepancy in figures reflects the ongoing search and rescue efforts.

The floodwaters rose by up to nine metres within just 30 minutes, catching people by surprise and leading to widespread destruction, ABC Australia reported. CCTV footage captured the moment the wall of water hit, with people fleeing as buildings were overwhelmed.

Communities destroyed

Satellite images reviewed by BBC Verify show multiple villages along the Trishuli River heavily damaged or destroyed. The village of Timure, a few miles south of the border, has now largely disappeared, with most houses on the steep valley slopes gone or covered in mud.

Further downstream, the low-lying areas of Syapru Besi have been swept away, leaving mud and debris. ABC Australia reported the village covered by mud, rock and other debris, with houses and other structures, including a bridge and hydroelectric power station, disappeared.

The town of Trishuli, about 45km (28 miles) downstream from the border, suffered severe damage. Satellite imagery shows an entire neighbourhood washed away. Verified videos show a bridge collapsing as the river surged forward, with footage from inside a bus capturing people crying out, as reported by BBC News.

The damage and mud extend more than 2.5km (1.5 miles) upstream, reaching 100m (330 ft) above the area first hit, according to BBC News' review of satellite imagery. Simon Gascoin, a researcher from the Center for Spatial Studies of the Biosphere, noted in an online post that Sentinel-2 imagery showed the flood surged up sloping terrain for at least 2.5 kilometres, ABC Australia reported.

Cause and aftermath

The disaster is believed to have been triggered by part of a Himalayan glacier breaking off and crashing into the river below, as reported by ABC Australia. The glacier has fallen away, carving a path of rock and debris, with trees and vegetation stripped at the base of the landslide.

Satellite images show the formation of a barrier lake at the base of the landslide, 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 it was not possible to determine from the images how stable the barrier was or how likely the lake was to drain suddenly. He said there was no significant increase in its surface area between Wednesday and Thursday, despite water continuing to flow into the lake. He noted a visible drainage channel, suggesting some water was already escaping downstream, and added that the volume was "not alarmingly large" and appeared to have stabilised.

The extent of damage on the Tibetan side of the border remains unclear. The region is strictly controlled and foreign media access is heavily restricted, according to BBC News. BBC Verify has so far been unable to find verifiable footage from the area.

The satellite imagery, published by Vantor as part of its Open Data Program, is intended to help aid authorities establish where best to focus their efforts to locate the missing, rescue survivors and recover the dead, as reported by BBC News.

Perspectives

Nepalese authorities: Official figures cite more than 550 dead with hundreds missing, reflecting the ongoing scale of the disaster and search-and-rescue challenges.

Chinese authorities: Have warned that the barrier lake formed at the base of the landslide poses a major risk of further flooding and has hampered rescue efforts.

Glaciology expert (Dr Argha Banerjee): Assesses the barrier lake as not alarmingly large and appearing stabilised, but notes uncertainty about its stability and drainage, while observing visible drainage already occurring downstream.