Fumaroles are steam vents in the earth’s crust and are Yellowstone’s hottest geothermal feature. Black Growler Steam Vent, on the hillside in the picture, has measured 199 to 280 degrees F. Fumaroles are similar to hot springs because the ground water is heated up and rises through cracks in the bedrock. However, unlike a hot spring, the ground water under fumaroles does not reach the surface because they are usually located above the groundwater level on top of hillsides or higher ground. The steam from the heated groundwater and gases inside the earth’s crust rise through the cracks and are released through the fumarole, which many times results in a loud hissing noise. A variety of gasses are emitted but the most common are water vapor, carbon dioxide, and hydrogen sulfide which can contribute a putrid and pungent aroma to the fumaroles’ surrounding area.
Notice how the heat from Black Growler Steam Vent and the hot spring below have caused some of the surrounding trees and grasses to die:
Listen to the sound of the steam and gasses coming from the fumaroles at Paint Pot:
