Purple badge with silhouette mountain and word "Geology" over image of a rock mountaintop overlooking other mountains.
Geology sets the stage of everything that happens in Yellowstone. It is also quite dynamic, with some features changing on a daily basis.

Explosive Past

About 631,000 years ago, Yellowstone exploded in a massive volcanic eruption. It blew volcanic ash and gas into the air.

As the underground magma reservoir emptied, a giant crater, or caldera, formed.

Take a look at what is beneath Yellowstone.

Cross-section of earth showing the crust (A), mantle (B), core (C), and a hotspot (D)
  • Crust (A) is the layer of rock that we walk on, is very thin, and made of solid rock.
  • Mantle (B) is very hot, often consisting of rocks in molten form. Sometimes hot melted rocks called lava come out to the surface of the earth.
  • Core (C) is divided into two parts: the liquid inner core and the solid outer core. Rapidly circulating liquid metal releases heat through the outer core and into the overlying mantle.
  • Hotspot (D) is a relatively small, very hot region of magma (molten rock from the mantle) that is close to earth's surface.

Antique Ashes

The last highly explosive Yellowstone eruption was approximately 174,000 years ago. It created what is now the West Thumb of Yellowstone Lake.

►Check it out!

Look at the map of ash fallout from the previous three major eruptions. If you live in the US, does your state have ash from the Yellowstone super volcano?

Map of Lower 48 of US showing three different ash-falls in gray shades.
Purple map overlain by three shades of gray the cover the majority of the US with text that asks, "Is the volcano still active?"

Yes. The heat undeneath the park fuels many of the hydrothermal features. Earthquakes (1,000 to 3,000 per year) reveal activity below ground. The University of Utah Seismograph Stations track this activity closely. Visit the university's seismograph web page to see real-time monitoring data.

Child wearing a winter hat and coat looking out across a deep, aqua-green hot spring.
Kids & Youth

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Last updated: February 9, 2022

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Mailing Address:

PO Box 168
Yellowstone National Park, WY 82190-0168



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