Satellite images taken before and after a deadly flash flood near Nepal's border with Tibet reveal a dramatic change in the landscape: green mountainside visible before the disaster is now covered by a broad expanse of brown debris and sediment.

The imagery, provided by Planet Labs, has offered early clues about how the disaster may have started. Experts examining the pictures believe the lower section of a glacier broke away high in the mountains and plunged hundreds of metres into the valley below, likely carrying or entraining rock and sediment as it fell.

Early reports raised an earthquake as a possible trigger, but the US Geological Survey later said the recorded seismic activity came from the collapse itself rather than a separate earthquake, according to news agency reports.