A team of scientists led by Dr Hsin-Hua Huang of California Institute of Technology in Pasadena and the University of Utah has discovered a reservoir of partly molten rock 19-45 km (12-28 miles) beneath the Yellowstone supervolcano. This magma body has a volume of 46,000 cubic km, approximately 4.5 times larger than the previously known upper-crustal magma reservoir.
Lion Geyser and Heart Spring in Yellowstone National Park. Image credit: Brocken Inaglory / CC BY-SA 3.0.
“The hot rock in the newly discovered, deeper magma reservoir would fill the 1,000-cubic-mile Grand Canyon 11.2 times, while the previously known magma chamber would fill the Grand Canyon 2.5 times,” explained Dr Jamie Farrell of the University of Utah, who is a co-author of the paper published in the journal Science.
Yellowstone is one of the largest known volcanoes in the world and the largest volcanic system in North America. The volcano is found above an intra-plate hot spot that has been feeding the magma chamber underneath Yellowstone for at least two million years.
During the past 2.1 million years, three massive volcanic eruptions have changed the face of the so-called Greater Yellowstone Ecosystem.
The first one occurred about 2.1 million years ago and was centered in what is now the western portion of Yellowstone National Park, extending to the area around Island Park, Idaho. The volume of volcanic rock produced by this eruption was about 2,400 times that produced by the Mt. St. Helen’s eruption of 1980.
The second great eruption, the smallest of the three great eruptions, occurred 1.3 million years ago in the western portion of the first eruption, near Island Park. The caldera left behind is referred to as the Island Park Caldera.
The third and most recent massive eruption occurred about 640,000 years ago in roughly the same area as the first eruption. It was a bit smaller than the first, but larger than the second eruption. The caldera created by it is referred to as the Lava Creek Caldera and largely overlaps the Huckleberry Ridge Caldera.
Dr Huang and his colleagues point out that the previously known upper magma chamber was the immediate source of these cataclysmic eruptions and that isn’t changed by discovery of the underlying magma reservoir that supplies the magma chamber.
This cross-section illustration cutting southwest-northeast under Yelowstone depicts the view revealed by seismic imaging. Scientists say new techniques have provided a better view of Yellowstone’s plumbing system, and that the supervolcano hasn’t grown larger or closer to erupting. Image credit: Hsin-Hua Huang / University of Utah.
They said these ancient eruptions were only the latest in a series of more than 140 as the North American plate of Earth’s crust and upper mantle moved southwest over the Yellowstone hotspot, starting 17 million years ago at the Oregon-Idaho-Nevada border.
In their study, Dr Huang’s team imaged the continuous volcanic plumbing system under Yellowstone.
“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,” Dr Huang said.
Contrary to popular perception, the magma chamber and magma reservoir are not full of molten rock. Instead, the rock is hot, mostly solid and spongelike, with pockets of molten rock within it.
“The study indicates the upper magma chamber averages about 9 % molten rock – consistent with earlier estimates of 5 – 15 % melt – and the lower magma reservoir is about 2 % melt,” Dr Huang noted.
The scientists emphasize that Yellowstone’s plumbing system is no larger – nor closer to erupting – than before, only that they now have used advanced techniques to make a complete image of the system that carries hot and partly molten rock upward from the top of the Yellowstone hotspot plume to the magma reservoir and the magma chamber above it.
They estimate the annual chance of a Yellowstone supervolcano eruption is 1 in 700,000.
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Hsin-Hua Huang et al. The Yellowstone magmatic system from the mantle plume to the upper crust. Science, published online April 23, 2015; doi: 10.1126/science.aaa5648
