BERKELEY, Calif., April 18 (UPI) -- Extra-hot magma from near Earth's core may rise thousands of miles to the crust via structures called "superplumes," scientists reported on Thursday.
Scientists at the University of California at Berkeley said new evidence suggest these massive plumes of magma may heat Earth's surface far more than previously believed, helping to feed dangerous volcanic hotspots and drive the motion of the continents. Their findings are reported in Friday's edition of the journal Science.
"The standard view is that only 10 percent of the heat available at the surface of the Earth comes from the core ... well, it could be double that," said geophysicist Barbara Romanowicz, director of the university's Seismological Laboratory.
Superplumes are gigantic upwellings of super-heated magma up to 3,000 miles wide that lurk some 1,800 miles below the surface in the Earth's lower mantle, the region nearest the planet's metallic core.
Scientists in the past have detected two superplumes, one seething below the volcanically active center of the Pacific and the other churning beneath Africa. These plumes are unusual because they are almost antipodal -- that is, they nearly point in exactly opposite directions, much like the north and south poles.
A number of studies indicate these superplumes rise at least 600 miles into the mantle. Until now, there was no convincing evidence of whether superplumes ascended any further up the remaining 1,200 miles of mantle to perhaps interact near the surface.
The researchers say they have direct indications that hot magma is rising up like a hot-air balloon to the very top of the mantle, below the crust.
"This could affect what we know of what ultimately drives the motion of the plates at the surface of the Earth, which creates earthquakes and volcanoes," Romanowicz told United Press International.
Romanowicz and her colleague Yuancheng Gung listened to sound waves from rumblings deep in the Earth. Sound waves travel more slowly through hot rock than they do through cold, so by listening to these "seismic waves" the researchers essentially developed 3-D pictures of heat inside the planet.
The scientists used two techniques to listen to seismic waves in vastly different layers of the Earth. Their methods have intimidating names such as elastic velocity tomography, used for the lower mantle, and attenuation tomography, targeting the upper mantle.
"If you want an analogy with a bell, elastic velocity tomography would be like finding the pitch of the bell ... the higher the velocity, the higher the pitch," Romanowicz explained.
"Attenuation tomography, which is far more difficult, measures how long you hear the signal -- how long you would hear the bell once you ringed it," she continued.
The findings seem to reveal that molten regions below the crust may be heated by superplumes.
"This is good work, but I think the interpretation is a bit speculative," cautioned geophysicist Gerald Schubert of the University of California in Los Angeles.
"(Romanowicz's) new data only cover the upper several hundred kilometers of the mantle. She's arguing there's a connection between her new data and the lower mantle, but it's a bit of a stretch. The data (are) certainly valuable, and if they can be extended beyond the regions she's already looked at, it'd be important."
(Reported by Charles Choi in New York.)
