Fumaroles or steam vents are the hottest hydrothermal features in the park.
Hot springs are the most common hydrothermal feature in the park.
Yellowstone National Park has approximately half of the world's geysers and most of them, including Old Faithful, are located in the Upper Geyser Basin.
Mudpots are acidic features with a limited water supply. Microorganisms convert hydrogen sulfide gas coming up from deep within the earth to sulfuric acid, which breaks down rock into clay minerals.
P.O. Box 168
Yellowstone National Park, WY
Recorded information. For road and weather information,
please dial 307-344-2117.