The geology of Yellowstone National Park is some of the most interesting in the world. Nowhere else on earth is there a place with so much geothermal activity in one place, from hot springs and geysers, to mud pots, fumaroles and other features.

The reason for Yellowstone's unique geological features is caused by the molten rock that is only three miles below the surface, which is incredibly close to the surface in geologic terms.

Hot Springs
Many of Yellowstone's hot springs and geothermal pools are brightly colored with blues, oranges, reds, and other colors. These colors are caused by the pool's water temperature, mineral content, algae, light refraction, and absorption by of the light by suspended particles in the water itself.

Geysers
Geysers are hot springs that erupt steaming water violently into the area. The eruptions are caused by pressure building up and releasing periodically. Some geysers erupt continuously, others are inactive for months or even years. Yellowstone Park has over 150 active geysers.

Mud Pots
A hot spring caused by heated water and caustic chemicals mixing with clay and soft stone to create a thick, bubbling cauldron of chemical activity and sulfurous smells.

Fumaroles
Also known as "dry geysers" are holes in the ground where water vapor and other gases are expelled from the earth often causing the ground to tremble and producing a strong roaring sound