Most visitors to Yellowstone National Park are interested in what they can see—geysers like Old Faithful that spew superheated water and steam into the air. But scientists are more intrigued by what they can’t see: the underfoot, underground plumbing system that makes all these dramatic eruptions possible.
Now, they have a much clearer picture of what’s happening below Yellowstone’s surface. Using a helicopter equipped with a special electromagnetic instrument, researchers mapped the Earth’s composition as far as 8,200 feet—about a mile and a half—underground at the country’s first national park, according to a paper published in March in the journal Nature.
“This is the biggest survey of any hydrothermal system that's been collected,” Carol Finn, a geophysicist with the U.S. Geological Survey and one of the study’s authors, tells Wired’s Matt Simon.
Their survey is a boon to fields like microbiology and geochemistry, which focus on the tiny microbes that can survive in Yellowstone’s scalding hot springs and the geological processes that create their world, and for understanding potentially hazardous hydrothermal steam explosions that can create huge gaping craters in the park. It’s also important for considering how the use of geothermal energy outside the park, such as to produce electricity or heat for homes and businesses, could affect Yellowstone’s geysers and hot springs. Although geothermal energy is widespread (for instance, most homes in Iceland are heated this way), harnessing natural geysers can also be destructive. New Zealand’s Wairakei Basin, for example, once resembled Yellowstone in its bubbling geysers, but an industrial effort to capture its energy for electricity completely silenced the entire region.
But perhaps most importantly, the map fills an important knowledge gap between what’s happening on the surface and what’s happening in the magma bodies that extend three to 30 miles below ground.
“It’s like a mystery sandwich—we know a lot about the surface features from direct observation and a fair amount about the magmatic and tectonic system several kilometers down from geophysical work, but we don’t really know what’s in the middle,” Steven Holbrook, a geophysicist at Virginia Tech University and one of the study’s authors, says in a statement.
To visualize Yellowstone’s subsurface layer, scientists flew a helicopter over the park with an 80-foot-diameter, hexagonal electromagnetic ring dangling underneath. That device, called SkyTEM, sent out electromagnetic pulses that traveled below the surface and bounced back up again, similar to a radar signal. After analyzing that data, researchers had a subsurface picture of the rocks, clay and thermal liquid below Yellowstone.
“If we picture the helicopter flying over a football field, we could picture one sounding being taken at the back of the home end zone, the next one at the 20-yard line, the next one at midfield, then one at the other 20-yard line and finally one at the back of the visitor’s end zone,” Holbrook tells Gizmodo’s Isaac Schultz. “Then we put those soundings next to each other over very long transects, and we get a picture of layers in the subsurface—how deep they are, which way they’re dipping and so forth.”
Though scientists are only just beginning to explore the survey in great detail, already they’re curious about one new mystery the map shows: Old Faithful and the Upper Geyser basin are six miles apart, but they appear to share a hydrothermal source below the surface. That finding could have important implications for understanding the behavior of the geyser and the basin, as well as the specialized microorganisms and bacteria that live in Yellowstone. That, in turn, may help paint a richer picture of how Earth’s early life forms emerged and evolved during the planet’s early history.
“If you're interested in asking the question, ‘What would early forms of life be doing?’ well, let's look at contemporary chemosynthetic life in a hot spring in a hydrothermal system like Yellowstone,” Eric Boyd, a geomicrobiologist at Montana State University who was not involved in the study, tells Wired.