You probably know that Yellowstone National Park’s iconic Old Faithful, which fires geysers up to 180 feet in the air, gets its kick from underlying magma that heats and propels water. You know that because scientists know that: By firing seismic waves into the ground and analyzing what bounces back, and by parsing the chemistry of Old Faithful’s discharge, they can surmise that a magma chamber three miles deep is the engine driving Yellowstone’s world-famous attractions. But what exactly all that water under tourists’ feet — the hydrothermal plumbing system, as scientists call it — is doing has so far been a mystery.
“We did not have any pictures of [the area] between the surface and the magma at all, ”Says Carol Finn, a research geophysicist at the US Geological Survey. “So although a lot of the geochemistry was known, no one’s ever seen a picture of: How does the water flow? Where does it go? Where does it mix?”
Now, thanks to an 80-foot-diameter electromagnetic ring dangling underneath a helicopter, Finn and her colleagues have mapped the plumbing underneath Yellowstone’s boisterous geysers. “This is the biggest survey of any hydrothermal system that’s been collected,” says Finn, lead author of a paper describing the work that was published today in the journal Nature.
That airborne loop generated an electromagnetic field, which in turn generated a current in the ground, which was then sensed by the loop. “All these things together can tell us how well electricity is conducted in the ground: It’s not conducted well with dry rocks, and it’s conducted well with wet rocks or clays,” says Finn.
This allowed the researchers to map the composition of the Earth down to a mile and a half deep, which you can see in the cross section above. Red means the material is dry, and blue means it’s wet.