Fountain Paint Pots, Yellowstone National Park

A mud pot (technically known as solfatare) is a hot spring or fumarole formed in high-temperature geothermal areas where water is in short supply. The little water that is available rises to the surface at a spot where the soil is rich in volcanic ash, clay and other fine particulates. The thickness of the mud usually changes along with seasonal changes in the water table.

The mud takes the form of a viscous, often bubbling, slurry. As the boiling mud is often squirted over the brims of the mud pot, a sort of mini-volcano or "mudvolcano" starts to build up, sometimes reaching heights of 3-5 feet.

The mud is generally of white to greyish color, but is sometimes stained with reddish or pink spots from iron compounds. When the slurry is particularly colorful, the feature is then called a "paint pot".

The geothermal areas of Yellowstone National Park contain several notable examples of both mud pots and paint pots.