The driving force behind Yellowstone’s long and explosive volcanic history may not be as deep as once thought. A new study suggests that instead of a plume of hot mantle that extends down to Earth’s core, the real culprit is a subducting tectonic plate that began sinking beneath North America hundreds of millions of years ago.
Computer simulations show that movement of broken-up remnants of the ancient Farallon Plate could be stirring the mantle in a way that fuels Yellowstone, researchers report December 18 in Nature Geoscience. “The fit is so good,” says study coauthor Lijun Liu, a geodynamicist at the University of Illinois at Urbana-Champaign.
The giant supervolcano now beneath Yellowstone National Park, located mostly in Wyoming, has a 17-million-year history — much of it on the move. In that time, the locus of volcanism has moved northeastward from southwestern Idaho to its current location, where it most recently explosively erupted about 640,000 years ago. These shifting eruptions have created a track of volcanic craters resembling those created by the hot spot that formed the Hawaiian island chain. As a result, scientists have long suspected that a deep plume of magma originating from the core-mantle boundary, similar to the one that fuels Hawaii’s volcanoes, is the source of Yellowstone’s fury.
But the nature of the Yellowstone plume has been the subject of debate. “Usually with plumes, we can trace them to the core-mantle boundary,” says Robert Porritt, a seismologist at the University of Texas at Austin, who was not involved in the new work. To “see” Earth’s structure, seismologists use a technique called seismic tomography, which maps the interior using seismic waves generated by earthquakes. Particularly hot or liquid parts of the mantle slow some seismic waves known as shear waves. Tomographic images of mantle plumes such as the one beneath Hawaii show a low-velocity region that extends all the way down to the boundary between mantle and core, about 2,900 kilometers below Earth’s surface. Such deep plumes are thought to be necessary to provide sufficient heat for the volcanism.
“But at Yellowstone, we don’t have that…
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