Hot off the press

By | Science & Technology
Yellowstone National Park's Grand Prismatic hot spring Credit@Robert B. Smith and Lee J. Siegel

A team at the University of Utah has just announced the discovery of a vast magma reservoir underneath Yellowstone National Park in the United States. The results were published on Thursday in the journal Science and reports that the sizable chamber may fill the Grand Canyon 11.2 times over. This new reservoir of hot, partly molten rock lies 20-45 kilometres beneath the supervolcano and is more than four times larger than the magma chamber scientists were already aware of.

The Yellowstone Caldera is the biggest and most discussed supervolcano on the planet. Ever since the film ‘2012’ depicted the fictional fallout of its eruption, scientists (as well as the media) have been spellbound by the activity below the geothermal hot spot. The enormity of the park has appeared to puzzle researchers for decades, however new technology has helped US scientists make this substantial discovery.

The paper emphasises that even with this new finding, the probability of eruption at Yellowstone (which is around one in 700,000 annually) remains unaffected. “The magma chamber and reservoir are [the same size as] they have been, it’s just that we can see them better now using new techniques,” says postdoctoral researcher Jamie Farrell, a co-author of the study. The real achievement of the research is the way in which the scientists have managed to chart the volcanic arrangement completely using cutting-edge imaging technology called seismic imaging.

“For the first time, we have imaged the continuous volcanic plumbing system under Yellowstone,” explained lead author Hsin-Hua Huang. “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.” This means that geologists are now able to examine the underground network more closely and with more detail than ever before. This has the objective of providing a deeper understanding of the Yellowstone magmatic system to develop new models to predict seismic and volcanic activity more accurately and reliably than ever.

Seismic imaging operates similarly to a hospital CAT scan (a specialised X-ray examination). CAT scans produce very detailed and clear images of soft tissues of the body. Seismic imaging uses earthquake waves in replacement of X-rays to investigate beneath the Earth’s surface by exploiting how these waves move slowly through molten rock and more quickly through cold rock.

The technology revealed the presence of a colossal magma reservoir sitting underneath the magma chamber scientists already knew of. The research indicates that this newly revealed chamber siphons hot rock from the top of the Yellowstone plume that sits around 64 kilometres beneath the surface through cracks in the Earth’s crust. This is then moved into the smaller magma chamber above. The smaller chamber is what is emptied if the supervolcano erupts. Scientists believe this has happened three times in the past.

Schematic of magmatic system below Yellowstone Park's surface. Credit@Hsin-Hua Huang

Schematic of magmatic system below Yellowstone Park’s surface. Credit@Hsin-Hua Huang

In contrast with popular belief, the magma chamber and new reservoir are far from overflowing with molten rock. In reality, the paper shows that the hot rock is mostly solid or spongelike with small pockets of molten rock. Therefore, the molten rock presently underneath Yellowstone may only fill one quarter of the Grand Canyon – according to Farrell.

Discovery of the new chamber seems to answer an enduring mystery surrounding Yellowstone: Why does the soil emanate so much carbon dioxide, more than might be explained by gases from the magma chamber? This deeper magma reservoir had been hypothesised as an explanation, however only now has the technology been capable of supporting the theory. Huang’s unique approach of combining local and distant quake data enabled scientists to look more deeply into the structure of the system and comprehend it on an entirely new level, which might help predict future seismic activity as well as understanding past events more clearly.

What other types of Earth activity might the imaging technology be able to reveal?

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