For decades, researchers in and around Yellowstone National Park have used seismic waves — imagine giving the region an MRI — to map the hot mush below the Earth’s surface.
Now a group of scientists from across the country have added solar storms and lightning to the diagnostic toolkit, tapping into the Earth’s natural electricity to further refine the image of what lies up to 30 miles below its crust.
“The challenge we face in geology, is there are very few direct observations of what’s actually happening deep beneath the surface. Drilled holes only give you a pinprick or tiny view of what’s happening, and the deepest drill hole only goes down that far. So we have to find other ways to look at what’s happening beneath the surface, and now we have a few,” said Michael Poland scientist-in-charge at the U.S. Geological Survey Yellowstone Volcano Observatory. “And that’s pretty darned cool.”
The study, recently published in the prestigious journal Nature, adds information to the constant speculation about when the Yellowstone caldera could once again erupt. The newly clarified picture suggests that a mass-scale eruption is likely tens or even hundreds of thousands of years away.
Answering questions with electricity
While the Yellowstone region offers plenty of action to study above ground, including thousands of small earthquakes, explosive geysers, gurgling hot pots, and wild pools of psychedelic colors, it’s actually a remarkably difficult system to study underground.
Very little penetrates the ground, and even less penetrates 20 to 30 miles below ground. Researchers have made breakthroughs using seismology, but when Oregon State University Geophysics Professor Adam Schultz and a team of scientists finished mapping the geo-electric structure of the U.S., they turned their sights specifically to the Yellowstone region.
The method they used is called magneto-telluric, and as is the case with most geophysics, it’s complicated.
To explain, Schultz harkens back to high school physics classes where teachers loop a coil of wire around a battery and another around a voltmeter. When the two move close to each other, the voltmeter registers electricity. That’s electromagnetic induction, and it’s akin to what he and a team of researchers did in Yellowstone.
Ninfa Bennington, a research geophysicist at the Hawaiian Volcano Observatory and lead author on the paper, said the process is also similar to how an electronic toothbrush charges. If you touch the charger with your hand you will not be electrocuted, but a coil in your toothbrush creates an electromagnetic field which enables electricity to flow from a coil in the charger.
Now think of magma as your toothbrush and the sky as the charger. Electricity caused by solar storms in the ionosphere, a layer of rarified gasses best known for occasionally producing stunning light shows such as the Aurora Borealis, can penetrate deep into the earth. The team also harnessed electricity from lightning, which strikes somewhere on Earth roughly every two seconds and creates an electromagnetic signal that’s trapped between the ground and the atmosphere.
“Magma is a great conductor of electricity,” Bennington said. “As the electromagnetic field goes around the Earth, the really conductive material in the Earth produces a secondary current.”
The researchers then monitored the electrical signals that conductive material like magma sends back to the Earth’s surface.
What they could map from the experiment was that nestled underneath geysers, bison, elk and wolves is not a big bubble of magma waiting to burst but a lot of individual pockets of mush relatively isolated from one another.
Poland likens it to hardening concrete.
“Even if the concrete is not completely solidified, you can walk on it. It’s not going to flow, because it’s really bound up. This particular study supports the seismic work saying ‘yeah, there’s a lot of hot rock down there, but it’s mostly solid,” Poland said.
So it’s not something that’s ready to blow.
The study also more clearly identified a pocket of melt in the northeast part of the caldera that is connected to a deeper source of magma, which Bennington called a “heat engine.” While that pocket could, sometime far in the future, erupt, right now “there’s too low a percentage of magma to produce an eruption,” she said.
And because the more western portion of the caldera is no longer connected to a heat source, it will, over geologic time, begin to cool.
A stable system
For the researchers studying Yellowstone, and anyone reading this, the takeaway is clear: The Yellowstone caldera isn’t likely to massively explode in our lifetime, our children’s, or possibly humanity’s.
We know the caldera has made three impressive eruptions in its history, 2.1 million years ago, 1.3 million years ago, and about 631,000 years ago, reshaping the area’s landscape. What everyone wants to know is when it will happen again. And while the last one seems like a very long time ago, Poland said the system is not actually “ready to blow again” as many like to tell each other around campfires and at bars.
Forestalled global destruction aside, what’s most exciting for Poland, who has studied the system for decades, is it gives researchers another way to understand what’s happening underground. Combine this work with other studies and scientists have an increasingly rich, more vivid view beneath the Earth’s surface
And Schultz reassures people that all those exciting geysers, gurgling hot pots, and steaming pools will not fade, certainly not anytime soon.
“This is still not the most stable, boring piece of ground in the world,” he said. “And that’s what makes it interesting.”
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