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Yellowstone's Geologic Recycling Program
24 July 2001 7:00 pm
Yellowstone began recycling long before paper or plastic appeared on Earth. For more than a million years, new research shows, magma chambers beneath Yellowstone's volcanic caldera have been reusing rocks, with lava ejected in one eruption melting again and participating in subsequent giant eruptions hundreds of thousands of years later. The data suggest that volcanic activity in the area is on the wane--but a potentially apocalyptic new eruption could still happen.
The hot spot--an upwelling plume of hot mantle--beneath the Yellowstone Plateau caused massive and sudden eruptions 2.0 million, 1.3 million, and 0.6 million years ago--near "clockwork timing," according to geochemist Ilya Bindeman, the lead researcher of a team at the University of Wisconsin, Madison. Bindeman believes that Yellowstone may be once again poised for a disastrous event, perhaps within the next 100,000 years. Such an eruption would change the world's climate for years, and, Bindeman adds, might wipe out civilization.
To better understand the cycle of magma production, the researchers analyzed oxygen isotope ratios in quartz and zircon, water- and heat-resistant minerals, from volcanic rocks in the Yellowstone caldera. Because the tiny zircon crystals retain their isotopic signatures despite episodes of remelting, the researchers could date their cores at 0.8 million to 2.1 million years old. But the rocks were erupted less than 500,000 years ago, and younger outer layers of the same crystals were added later, indicating to researchers they'd been dipped repeatedly in molten magma. The material, they believe, was recycled as older volcanic rocks forming the roofs of magma chambers collapsed and remelted during eruptions, only to be reejected in the next volcanic outburst. The research appears in a paper in the July issue of Earth and Planetary Science Letters and another due out next month in the Journal of Petrology.
Because a more potent hot spot would be continually replenished from deep in the mantle, the researchers take the recycling as a sign that the cycle of volcanic activity in Yellowstone is calming down. But that "doesn't mean it's been turned off," cautions Robert Smith, a geophysicist at the University of Utah who works at the Yellowstone Volcano Observatory.