Environment

Yellowstone Supervolcano Had A Violent, Dramatic Origin

February 12, 2016 | by Robin Andrews

Photo credit: A battle between a tectonic slab and a mantle plume decided the fate of the supervolcano. Fredy Thuerig/Shutterstock

The Yellowstone supervolcano in Wyoming may have had quite a dramatic origin. As a new study due to be published in the journal Geophysical Research Letters reveals, a gargantuan tectonic slab would have shielded the upper crust from a molten plume. This would have influenced the formation of Yellowstone’s magma chamber for millions of years.

Roughly every 650,000 years, the vast magma reservoir concealed beneath Yellowstone’s 72-kilometer-long (44-mile) caldera (cauldron-like crater) bursts through a rupture onto the surface. A recent study concluded that this reservoir of molten rock is up to 600 cubic kilometers (about 145 cubic miles) in size. That’s 240 million Olympic swimming pools of liquid fire – the question is, how did it all get there?

For a long time, volcanologists have assumed that this enormous magma chamber could have only originated from a mantle plume, a “hotspot” beneath the crust that provided a constant source of magma-generating heat. However, seismic surveys of this part of the mantle have revealed “anomalies,” large regions of the mantle that may in fact be descending (subducting) tectonic slabs.

A team of geoscientists at the University of Illinois decided to run simulations on the university’s Blue Waters supercomputer to investigate the possibility that one or more of these slabs would have inhibited the rise of a mantle plume. By taking into account the descent speed of the subducting slabs and their mechanical properties, along with the types of possible plumes that could have been rising up to greet it, the researchers produced a range of possibilities.

Importantly, all of them concluded that one particular subducting slab would have always gotten in the way of any mantle plume. This means that a plume may not have played as significant a role in the formation of Yellowstone’s magma chamber as previously thought.

One of the computer simulations that shows the plume (red) eventually breaking through the subducting slab (green). The text in the white boxes represents the timeline in Ma – millions of years ago. Leonard & Liu/Geophysical Research Letters

At this point, one of several things could have happened. In one version of simulated events, the slab successfully impeded the rise of the plume. Although it would have damaged the slab, even a plume with a remarkable 700-kilometer (435-mile) diameter would have been stopped in its tracks.

Another more likely possibility is that the subducting slab was eventually overcome by the hellish mantle upwelling, piercing through a weak spot in the rock, perhaps along a hinge point. This only happened 15 million years ago – relatively young in geological terms – after a prolonged battle between the rocky shield and the mantle plume.

This plume would have been considerably weaker by the time it penetrated the slab, meaning that it still would not have played as vital a role in the formation of Yellowstone’s underlying magma. Ultimately, this study points out that the origin of Yellowstone may be far more mysterious than anyone previously thought.

“The majority of previous studies have relied on conceptual, idealized models, which are not physically and geologically accurate,” said Lijun Liu, a geology professor at the University of Illinois and one of the study’s coauthors, in a statement. “I know people like simple models, but the Earth is not simple.”

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