A mud pot bubbles in the Artists Paint Pots area of Yellowstone National Park.
A mud pot, according to the National Park Service, is a hot spring "containing a relatively small amount of acid water. Acid breaks down the surrounding rock into clay, which mixes into the water. Mud consistency ranges from thick to thin, depending on the amount of water present. Abundant surface water in winter and spring thins the mud, creating a soupier mud pot. During the drier months of summer and autumn, mud pots often become thicker and sometimes dry up altogether."