One of the world’s deepest-diving robot submarines has returned from its first mission with spectacular images of giant holes on the seabed and evidence of underwater avalanches.

Autosub6000, which was developed by British scientists, descended almost three miles below the surface to investigate a submarine canyon north of the Canary Islands.

Its next mission is to investigate the Lisbon earthquake of 1755, one of Europe’s worst natural disasters, in which more than 10,000 people died.

The successful first dive this week formed part of a research expedition investigating potential threats to Western European coasts from tsunamis, giant landslides and earthquakes.

On its return to the surface, 24 hours after its launch, it provided scientists with three-dimensional images showing holes in the sea floor the size of Wembley Stadium - evidence of giant underwater avalanches in the past, and a potential cause of tsunamis in the future.

The robot’s success was a relief to its creators. A previous underwater autonomous vehicle (AUV) developed from the same £10 million research programme was dispatched to investigate the underside of the Antarctic ice shelf in 2005 but never returned. “It’s always slightly nerve-racking launching an AUV,” Steve McPhail, the team leader, said.

Unlike most undersea robots, the £1.5 million submarine dives without cables connecting it to the surface, travelling for up to 330km (205 miles) before returning to the surface to rendezvous with the Royal Research Ship James Cook.

Autosub6000, which was developed at the National Oceanographic Centre, Southampton, can dive to a depth of 6,000 metres – nearly four miles – allowing it to reach 93 per cent of the world’s seabed.While spiralling downwards on the journey from ship to seabed, the craft can be sent off track by tides and currents, so Autosub6000 receives an acoustic position correction from its mother ship once it has arrived on the ocean floor.

Speaking to The Times from the James Cook, 200 miles southwest of Portugal, Russell Wynn, the expedition’s chief scientist, said: “This new technology is allowing us to image the sea floor in unprecedented detail, and is providing valuable information about the huge scale and immense power of these giant submarine flows.”

More than 95 per cent of the sea floor is known only from crude bathymetric data, whose resolution can miss mountains. Autosub6000 travelled at 100 metres above the seabed to scan a 16 sq km area with its onboard multi-beam sonar, and returned an image that shows objects as small as 2m wide.

The increased resolution allows the UK-led research team, involving scientists from Spain, Portugal and Russia, to drill cores accurately above and below the avalanche scars, known as scours, and so discover how and when many landslides have occurred.

“We have found that giant landslides are actually quite rare around the Canary Islands, with no major activity in the last 15,000 years,” Dr Wynn said.

“At the moment we don’t even know where the Lisbon quake originated,” he added. “We hope that new data from the deep ocean will provide information about the potential future threat to coastal communities.”

The research expedition began in the Canary Islands on August 5 and is scheduled to finish in the UK on September 3. The last stop on the journey is in the Bay of Biscay, where Autosub6000 will investigate the origins of the catastrophic megaflood that burst through the Straits of Dover, creating the British Isles hundreds of thousands of years ago.

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