7 Dec 2011

Underwater volcanoes observed in South Pacific

1:03 pm on 7 December 2011

British scientists have released the most detailed survey to date of the most seismically active region of the planet - the South Pacific.

Using sonar to create images of the seabed, they have observed the process of underwater volcanoes being destroyed in the Tonga Trench.

The researchers are trying to understand the causes of the tsunamis that afflict the region.

The BBC's science correspondent says the pictures were created by sonar in waters up to 6km deep and expose how tectonic action is dragging giant volcanoes into a chasm in the seabed.

The volcanoes are strung across the ocean floor and are moving westward on the Pacific tectonic plate at up to 6cm per year.

One image shows a volcano nearest the edge of the abyss already starting to collapse.

The scene was captured along the Tonga Trench during a research expedition last summer.

The trench is a highly active fault line running north from New Zealand towards Tonga and Samoa. It forms the second deepest stretch of seabed in the world - reaching a depth of 10.9km.

The findings are to presented to the annual conference of the American Geophysical Union.

They are the result of a joint project by the universities of Oxford and Durham, funded by the Natural Environment Research Council.