Giant Underground Blob of Magma Puzzles Scientists

The Afar Rift in Ethiopia as seen from a helicopter. Credit: Graham Dawes View full size image

The Afar Rift in Ethiopia is marked by enormous gashes that signal the breakup of the African continent and the beginnings of a new ocean basin, scientists think.

The fractures appear eerily similar to seafloor spreading centers, the volcanic ridges that mark the boundaries between two pieces of oceanic crust. Along the ridges, lava bubbles up and new crust is created, slowly widening the ocean basin.

But a look deep beneath the Afar Rift reveals the birth announcements may be premature. “It’s not as close to fully formed seafloor spreading as we thought,” said Kathy Whaler, a geophysicist at the University of Edinburgh in Scotland.

 

Whaler and her colleagues have spotted 120 cubic miles (500 cubic kilometers) of magma sitting in the mantle under the Afar Rift. Hot liquids like magma like to rise, so the discovery is a conundrum.

“We didn’t expect this, because magma wants to pop up like a cork in water; it’s too buoyant compared to the surrounding medium in the mantle,” Whaler told LiveScience’s OurAmazingPlanet.

Models predict that at spreading ridges, magma should sit just under the rifts, in the crust. That’s what geoscientists see in the oceans, at places like the Mid-Atlantic Ridge and the Juan de Fuca Ridge. But not only is the giant pool at Afar extremely deep, but it is also mostly below the sleeping Badi volcano, many miles west of the scene of a 2005 series of underground magma intrusions, Whaler said.

“You just wouldn’t expect to have a blob of magma still underneath this other area,” Whaler said. “It’s one of the things we’re still having a lot of discussions about.”

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Giant Underground Blob of Magma Puzzles Scientists