Not by Fire but by Ice



 Updated 15 December 2005      

Enormous Hydrothermal "Megaplume" 
Found in Indian Ocean

"A normal hydrothermal vent might produce something like 500 megawatts - 
this is producing 100,000 megawatts. It's like an atom bomb down there.”


12 Dec 05 - An enormous hydrothermal "megaplume" found in the Indian
Ocean serves as a dramatic reminder that underwater volcanoes likely play
an important role in shaping Earth's ocean systems, scientists report.

The plume, which stretches some 43.5 miles (70 kilometers) long, appears to
be active on a previously unseen scale.

"This thing is at least 10 times—or possibly 20 times—bigger than anything of its kind that's been seen before," said Bramley Murton of  the British National Oceanography Centre.

Scientists reported the finding last week at the fall meeting of the American Geophysical Union (AGU) in San Francisco . Researchers also announced newly discovered deep-sea hydrothermal fields in the Arctic Ocean and the south Atlantic .

The appearance of hydrothermal vents around the world suggests that they are a far more common part of the ocean system than once believed and could be a major influence on circulation patterns and ocean chemistry.

"I'd be surprised if in the next five years we didn't experience a mini-revolution in terms of finding these [fields] in places where they are not supposed to exist," said geophysicist Robert Reves-Sohn of the Woods Hole Oceanographic Institution.

Hydrothermal vents are volcanic hotspots that emit gasses and mineral-enriched water as hot as 760F (400C).

Megaplumes like the one found in the Indian Ocean are probably caused by undersea volcanic eruptions, though scientists aren't yet certain.

"Once formed they can possibly hang around for years," Murton said. The heat from such events could have a dramatic effect on ocean circulation, which plays a role in determining Earth's climate.

"The energy content is an order of magnitude greater [than ordinary plumes], and the thermal power may be many orders of magnitude greater," Murton said.

"A normal hydrothermal vent might produce something like 500 megawatts, while this is producing 100,000 megawatts. It's like an atom bomb down there.”

Regular hydrothermal fields stir the water for only a few hundred meters (about a thousand feet) above the ocean floor. "But these megaplumes can reach a column of 1,000 to 1,500 meters [3,280 to 4,920 feet], so it reaches right up into the midwater," he said.

But even the Indian Ocean megaplume may be small compared to larger underwater eruptions that have as yet gone undetected.

"We know when we look at the ocean floor that there have been much larger eruptions, so we can only speculate about what magnitude of event plumes would come from those."

The new data on hydrothermal fields and megaplumes underscores the fact that volcanic activity on the ocean floor remains a largely mysterious phenomenon.

"Ninety percent of the Earth's volcanic activity takes place underwater," Murton said. "Just because we can't see it doesn't mean it's not there."

Click here to see the rest of this article by Brian Handwerk of National Geographic News

        (Thanks to Charles Patrick and many other readers for telling me about this article.)


See also It's not global warming, it's ocean warming



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