One of the most popular attractions in Yellowstone National Park is Old Faithful—the iconic geyser that erupts every 90 minutes like clockwork. Its unusual regularity makes it famous, but now it’s also helping scientists understand the physics behind geysers across the world.
A team of scientists from the University of Savoie in France and their colleagues recently identified a large, secret chamber in the rocks beneath the geyser, a finding that radically changed the understanding of how eruptions occur. The discovery was made thanks to a set of seismic data collected in the 1990s and a modern acoustic technique most often used to locate whales or submarines. Based on the sound of popping bubbles in the geyser captured in the seismic record, the researchers identified a 60-cubic-metre cavern 15 meters below the ground and off to one side of the geyser.
The cavity serves as a compressible reservoir, causing water in the smaller main vent to bob up and down like a spring. These oscillations influence water pressure and help the geyser boil in the early stage of an eruption.
The discovery "totally changes our perspective of the physics of how geysers work," Shaul Hurwitz, a hydrologist with the US Geological Survey in Menlo Park, California, told New Scientist. He added that he hopes the innovative acoustic technique will be used to help map the inside of other geysers and volcanoes as well.