Earth is Sucking up its Own Water


Researchers have found that Earth is sucking up huge amounts of water. When tectonic plates collide under the ocean, they drag water down into the deep Earth and the process is absorbing about three times more water than previously estimated.

Earth's tectonic plates slide beneath another in a subduction zone. They squeeze water from Earth's surface and fuel volcanoes, which is then released back into the oceans with volcanic eruptions. These inputs and outputs drive a global deep-Earth water cycle. But until now, researchers did not know how much water is being dragged into the Earth's interior.

"This research shows that subduction zones move far more water into Earth's deep interior -many miles below the surface – than previously thought," said Candace Major from National Science Foundation's Division of Ocean Sciences. "The results highlight the important role of subduction zones in Earth's water cycle. "

To conduct this study, researchers selected the deepest ocean trench in the world and listened to the natural seismic rumblings of the earthquake using a network of instruments deployed across the Mariana Trench. The first-of-its-kind seismic study paints a more detailed picture of the Pacific Ocean's plate bending into the trench. As the plates collide and descending plate crawl ever deeper into the Earth's mantle, it brings the water along with it.

"Previous conventions were based on active source studies, which can only show the top 3-4 miles into the incoming plate," said Chen Cai from Washington University. "They could not be very precise about how thick it is, or how hydrated it is. Our study tried to constrain that. If water can penetrate deeper into the plate, it can stay there and be brought down to deeper depths."

The latest seismic images show an area at the Mariana Trench that extends almost 20 miles beneath the seafloor and holds a considerable amount of water.

"If other old, cold subducting slabs contain similarly thick layers of hydrous mantle, then estimates of the global water flux into the mantle at depths greater than 60 miles must be increased by a factor of about three," said researcher Doug Wiens.

"Does the amount of water vary substantially from one subduction zone to another, based on the kind of faulting that you have when the plate bends? There's been suggestions of that in Alaska and in Central America. But nobody has looked at the deeper structure yet like we were able to do in the Mariana Trench. "

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