A large part of Yellowstone National Park is a caldera, land that collapsed and crumbled after volcanic activity. Water seeps through the cracks and is heated by the magma below the surface. Pressure builds and steam and water burst to the surface in geysers.
The biggest and most famous is Old Faithful, so called because you can set your clock by its eruptions. It was a blustery day, which was great, but not so good for taking pictures that show just how high the water spout can be.
Whatever the weather, the geysers and steam pots make you feel like you’re walking through an ancient landscape. Which you are in most places. It’s just more obvious here.
Resident Alien -- Being Dutch in America 