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