A magma reservoir under the Yellowstone supervolcano has been discovered to contain enough magma to fill the Grand Canyon 11 times over, according to a new study. However, geologists say that's no reason to believe an eruption is imminent.

This magma chamber beneath Yellowstone National Park is more than four times larger than the one previously known to geologists. The newly discovered basin of soft, hot rock lies between 12 and 28 miles beneath the ground.

"For the first time, we have imaged the continuous volcanic plumbing system under Yellowstone," said Hsin-Hua Huang of the University of Utah. "That includes the upper crustal magma chamber we have seen previously plus a lower crustal magma reservoir that has never been imaged before and that connects the upper chamber to the Yellowstone hotspot plume below." 

Contrary to the popular image of magma chambers and reservoirs, they are not filled with molten rock. In actuality, smaller pockets of liquid rock are scattered throughout a sponge-like matrix of hot, semi-molten stone.

A new investigation of the supervolcano reveals the upper chamber is composed of around nine percent molten rock, consistent with previous estimates of between five and 15 percent. The newly discovered lower reservoir only contains around two percent melted rock, according to researchers.

Supervolcanoes are classified as volcanoes capable of producing eruptions containing more than 240 cubic miles of rock and other debris. The last time the Yellowstone supervolcano erupted, 640,000 years ago, the event sent debris flying across North America. No eruption of a supervolcano has taken place in the course of written history, leaving only prehistoric evidence of these massive events.

The discovery of this vast underground magma chamber underlying Yellowstone, brought about by new seismic-imaging techniques, is no reason for alarm — or even thinking an eruption is more likely than before. Geologists say there isn't evidence that the reservoir is growing larger, and the chances of a massive eruption during a given year remain around one in 700,000.  

The Yellowstone supervolcano has erupted at least three times in the ancient past — two million, 1.2 million, and 640,000 years before our own time. It is the largest supervolcano on Earth, and the last eruption released more than 8,000 times the debris ejected during the 1980 explosion of Mt. St. Helens. The Long Valley in California is home to the second-largest of these geographical features, followed by the Valles Caldera, located west of Sante Fe, New Mexico.

Genetic and fossil evidence suggests that just a few thousand humans survived a cataclysmic event around 74,000 years ago. The timing would correlate with the eruption of the Toba Caldera in Indonesia. The last supervolcano eruption on Earth was 27,000 years ago, at Taupo, on the northernmost island of New Zealand.

Discovery of the larger, lower magma chamber under Yellowstone was profiled in the journal Science.

Photo: Frank Kovalchek | Flickr

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