There are four types of hydrothermal features in Yellowstone National Park: hot springs, mudpots, steam vents and geysers.
Red Spouter, found along the Fountain Paint Pot Trail in the Lower Geyser Basin, originated with the Hebgen Lake earthquake in 1959. It actually exhibits the behavior of fumaroles, hot springs and mudpots. In the spring and early summer its pools splash muddy water that sometimes has a red tone. Later in the summer and fall, when the water table is lower, Red Spouter becomes a hissing fumarole.
Video: Yellowstone Park Foundation