Saturday 20 December, 2014

New images of Pacific Ocean capture destruction of underwater mountains

Published On: Wed, Dec 7th, 2011 | Geology | By BioNews

New images from the depths of the Pacific Ocean have revealed the destruction of massive underwater mountains as one of Earth’s most violent processes.

The pictures, which expose how tectonic action is dragging along giant volcanoes into a chasm in the seabed, were created by sonar in waters up to 6km (4mi) deep.

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

The extraordinary scene was captured along the Tonga Trench during a research expedition last summer, which was the result of a joint project by the universities of Oxford and Durham, funded by the Natural Environment Research Council.

Where the Pacific plate collides with the Indo-Australian plate, it is forced downwards into the trench, a subduction zone, and the volcanoes are carried with it.

The trench, reaching a depth of 10.9km, forms the second deepest stretch of seabed anywhere in the world, easily large enough to hold Mount Everest.

One of the images shows the volcano nearest the edge of the abyss, the next to be destroyed, already starting to collapse.

With frequent earthquakes, the region is vulnerable to tsunamis and one aim of the research is to understand whether the destruction of the volcanoes adds to the risk.

One theory is that the volcanoes add friction to the movement of the two plates which leads to a greater build-up of tension and consequently to a more explosive quake.

Another is that by shearing into blocks as they collapse, the volcanoes provide a kind of buffer easing the subduction process.

According to Tony Watts of Oxford University, joint leader of the project, the earthquakes are less frequent at the precise point where the volcanoes enter the trench.

“When you see size of these features you’d think they’d cause massive earthquakes and disruption – and that was our starting hypothesis,” the BBC quoted Watts as saying.

“But we found that the volcanoes were highly fractured before they entered the trench – which is very important for what happens after they enter the system,” he said.

Analysis so far has not determined the precise impact of this process.

The study has been presented at the annual conference of the American Geophysical Union.

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