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WSU and UI researchers say there’s more magma beneath Yellowstone caldera than previously thought

UPDATED: Tue., June 12, 2018

New research from Washington State University and the University of Idaho suggests scientists have been significantly underestimating the amount of heat generated by Yellowstone’s caldera.

From geysers to hot springs, most of the famous features at Yellowstone National Park owe their existence to the volcanic hot spot that sits below the park. Melted rock in the earth’s mantle seeps into a shallow magma reservoir below the earth’s surface.

“All the heat that drives all the famous hot springs and geysers, ultimately all of that originates in the mantle,” said Jerry Fairly, a geologist and professor at the University of Idaho.

Figuring out how much magma is keeping that system running, and how much heat it puts out, has been an ongoing challenge for scientists.

Geologists at WSU and UI have come up with a new technique to measure how quickly magma is recharging the Yellowstone caldera, bringing scientists closer to getting an accurate picture of the engine heating up the volcano.

“It gives us a better understanding of how magma is created in the caldera and sustained,” said Peter Larson, a geologist and professor at WSU’s School of the Environment.

The team spiked Yellowstone hot springs with “heavy water,” so named because the hydrogen atoms in the water have a neutron in them, making them heavy. They detailed their findings in a paper published earlier this month in the journal Geosphere.

The heavy water acted as a tracer, allowing the team to figure out the rate at which water flows out of the hot springs by measuring the concentrations of heavy water over time. The springs are recharged with hot water from underground, so scientists can measure the amount of heat entering them by knowing the rate water leaves and is replaced.

“That has to be balanced by the heat being carried into the crust way underneath Yellowstone,” Larson said.

Using heavy water has an advantage over other common tracers, like table salt or dyes, that can have visual or environmental impacts on the park.

During field work in 2014, the team also worked to measure heat loss through the sides of hot springs. Because some water seeps into the soil and back down into the aquifer, measuring heat only based on what comes out of the stream underestimates the thermal energy in the system.

“All those pieces are necessary in order to understand how much material is being recharged to the volcano,” said Jerry Fairley, a University of Idaho professor of geology who helped lead the project.

Based on their accounting, the actual amount of magma under the caldera may be as much as double of what scientists previously thought.

“What our work did is really showed that there’s a lot of heat unaccounted for if you just measure the hot water coming out,” Larson said.

The lead author of the paper was WSU graduate student Nick McMillan, who was one of Larson’s students.

Though the heat measurement doesn’t help predict when the caldera might erupt next, it does help researchers better understand the system driving the park’s thermal attractions.

“It gives us a better idea of how to monitor and keep an eye on Yellowstone,” Larson said.

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