Published online 17 December 2009 | Nature | doi:10.1038/news.2009.1150

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Erupting ocean volcano caught on film

Footage reveals lava flows and rock formation on the sea floor.

Underwater volcanoThe spectacular eruption of West Mata has been caught on film.NSF / NOAA

Footage of an eruption nearly 1,200 metres under the sea was unveiled today at a meeting of the American Geophysical Union in San Francisco, California.

The 50-plus hours of high-definition film, complete with background sound, represent one of the first times that lava has been caught flowing on the deep sea floor.

Taken at the West Mata volcano in the western Pacific, the footage is "spectacular", comments Katharine Cashman of the University of Oregon in Eugene — although it is not quite the first view of sea floor lava, she points out. Using the same remotely operated vehicle (ROV), named Jason, from the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts, Cashman's team had this April filmed the faint glow of lava from a much shallower sea floor volcano — Northwest Rota-1, at a depth of 500 metres.

But the footage (see video clips Mataeruption.mov">here and Mataeruption_zoom.mov">here) of the West Mata volcano, taken using the ROV Jason in May, captures this much deeper eruption and clearly shows actual lava flowing, says lead researcher Joseph Resing of the US National Oceanic and Atmospheric Administration, who is based at the Pacific Marine Environmental Laboratory in Seattle, Washington.

Lava lab

The ROV Jason "actually reached into the molten lava and pulled out a gob", says Resing, bringing back the first 'zero-aged' boninites: freshly erupted rocks from Earth's mantle that are magnesium- and silica-rich, like the ancient ocean rocks that compose Japan, for example. The West Mata volcano cone seems to channel a flow of older mantle that is rich in magnesium, whereas the lava from Northwest Rota-1 is more like the silica-rich lava from Mount St Helens volcano in Washington state.

The video also confirms geologists' theories for how rocks called pillow basalts form, showing that this happens when bubbles of hot magma expand and burst to form cascades, the surfaces of which are then cooled by the surrounding water to form pillow-shaped rocks. Pillow basalts are the most common rock form on Earth, making up ocean crust and appearing on continents after being plucked from the ancient sea floor by tectonic processes.

After the eruption

Researchers have observed huge spherical piles of pillow basalts at major spreading centres on the ocean floor, such as the mid-Atlantic ridge, for around 25 years but have never before caught their formation on film.

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Volcanic eruptions at such spreading centres, where new ocean crust is formed, can pump out huge volumes of magma over a few days. But capturing such an event on film has proved difficult because keeping a research vessel at the ready is incredibly expensive, and having to choose from more than 60,000 kilometres of ocean ridge that might erupt at any time makes aiming the cameras even more difficult, comments Christopher German of the Woods Hole Oceanographic Institution. Resing and his colleagues had to persuade funding agencies and tweak ship schedules to get to West Mata in time to film the flowing lava, after a cruise the previous November showed a chemical signature in the water column that indicated an ongoing eruption.

Richard Arculus, an igneous petrologist at the Australian National University in Canberra who was not involved in the work but who studies mineral-rich ridges nearby in the Lau Basin, says: "Really seeing how the lava flows work — the active processes — helps you understand what is happening." 

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