Yellowstone National Park is a dynamic hotspot of geology in action. A vast swath of the southwestern part of the park is a volcanic caldera formed by an eruption that sent about 600 cubic miles of ash across much of what are now the western United States. (By comparison, this was about 2,400 times more material than Mt. St. Helens sent up in its impressive explosion in 1980.) Geologic features throughout much of the park highlight what heat, water, minerals, and time can create. Yellowstone has the largest collection of hydrothermal features on the planet.
Heated waters surface and flow, changing direction and volume over time. The effects can be stunning. The top two photos are from Mammoth Hot Springs in the northeast corner of the park.
Vistas can be filled with steam from fumaroles, holes in the earth’s crust through which steam escapes. If I’ve got the details right, in most places the earth’s crust is over 20 miles deep. In Yellowstone it’s about 3 miles thick, closer to the earth’s surface than in most other parts of the world. There are about 10,000 features known to exist in Yellowstone’s geyser basins.
The geothermal features in Yellowstone are so unique that it was designated a United National Biosphere Reserve site in 1972.
In parts of the park it seems as if everywhere you look something is steaming, boiling, or erupting. I’ve never seen so much amazing, restless earth before.