SLABS of rock more than a mile long were dislodged and swept up to seven miles in a series of underwater landslides set off by the earthquake that caused the Asian tsumani.

Dramatic images taken by a Royal Navy survey ship of the seabed beneath the Indian Ocean, 62 miles off the coast of Sumatra, show an “alien landscape” battered by the forces of nature.

The ferocity of the earthquake, which registered a magnitude of nine, shook underwater mountains and dislodged billions of tons of debris.

Enormous chunks of rock the size of St Mary’s, in the Isles of Scilly, were swept down ocean ridges and across plains at speeds estimated at more than 100mph. The images created by high-resolution sonar show gashes in plate tectonic ridges and mountains up to ten miles long and hundreds of yards wide.

One of the Earth’s geological plates was raised by 65ft in a matter of seconds, making water surge upwards and then outwards on the surface, causing the tsunami that devastated so many coastlines.

The point at which the Indian geological plate meets and disappears under the Eurasia-Burma plate can be seen in the images as the line where the ocean ridges meet plains. Little can be seen of the plate movement because one simply shifted, suddenly, farther beneath the other as the energy created by the earthquake a few miles away, deep under the ground, was released.

The point where the energy release was at its maximum, which was surveyed by HMS Scott, is known as the “prism toe”, and the surrounding landscape was irrevocably altered by the movement.

Captain Ian Turner, who commands the Royal Navy’s survey squadron, said as the sonar images were made public that they were an invaluable tool for learning about earthquakes and tsunamis. “From a scientific viewpoint the images of the seabed are no less exciting or significant than the images we saw recently being beamed back from space of the surface of Titan,” he said at the UK Hydrographic Office in Taunton, Somerset.

Commander Steve Malcolm, captain of HMS Scott, said that the underwater landscape had been transformed on a monumental scale. “It’s awesome,” he said. “To see the scale of it is incredible. It’s a very large area that has been affected by the earthquake.”

The ship’s 44-strong crew were joined by teams of scientists from the British Geological Survey (BGS) and the Southampton Oceanography Centre. The expedition was given permission by the Indonesian Government to sail in its waters.

HMS Scott explored a 110-mile by 25-mile section of the seabed where the tsunami started, at depths up to three miles.

Dr Dave Long, of the BGS, said: “We are looking at the sector that moved the most. The landslides are just one element of the tsunami. By looking back at the frequency of these events and the geology we hope in time that we will be able to predict and warn where earthquakes and tsunamis will take place.”

The survey pictures are the most detailed of the area and reveal underwater ridges higher than Ben Nevis and stretching for hundreds of miles along the seabed. Other features shown include canyons up to two miles deep.

Some of the features will be tens of thousands of years old but others, including many of the landslides, were created by the earthquake on December 26.

HMS Scott is the biggest of six Royal Navy survey ships and is the most advanced in the world. More than two thirds of the ocean floor, still less familiar to scientists than the moon’s surface, has yet to be mapped in the detail offered by the ship.

The crew were not directly involved in the relief effort for the tsumani victims but were proud to be “doing their bit” to collect data that may one day prevent a repeat of the huge death toll.

QUAKE EFFECTS

• The earthquake caused underwater landslides that left scars more than ten miles long and swept huge rocks distances of up to seven miles
• Tectonic plates shifted over a distance of 870 miles. The tsunami moved at speeds of up to 500mph
• The survey examined an area of 2,750 square miles

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