October 13, 2017
EVERY 90 MINUTES OR SO, a crowd gathers on a wooden boardwalk as steam pours out of a crack in the ground. Soon enough, a spout of water, up to 184 feet high, erupts from the ground for about 90 seconds. And 90 minutes later, it happens all over again. Old Faithful is one of the most famous sights in Yellowstone National Park, but for all its popularity, we don’t know exactly how the predictable geyser works. Something is heating that water and forcing it out at regular intervals, but the exact mechanics have remained a mystery. Thanks to a new study, we now have a clearer picture of what things look like underground.