Yellowstone is one colossal volcano and 640,000 years ago one of its eruptions collapsed the land leaving a significant depression in the earth known as the Yellowstone Caldera. Over hundreds and thousands of years the caldera filled with lava repeatedly and created the volcanic plateau that is much of the central part of the park. At Mud Volcano you come face to face with one of the resurgent domes. The eastern hills comprise Sour Creek Dome. Resurgent domes are areas of active ground deformation where the land moves up or down with the fluctuation of the magma chamber below. Scientists monitor these domes closely for information about ongoing volcanic activity. Unsurprisingly, many of the park's geysers, hot springs, mud pots, and fumaroles are near or within the caldera. The short hike will take 1-2 hours around Mud Volcano and the trail has boardwalks and pavement. This loop trail begins and ends at the same parking lot though at different trailheads. If you have a high tolerance for foul smells, this is a fantastic sight to see.