What is a Fumarole?
A fumarole is a vent in the Earth’s surface from which steam and volcanic gases are emitted. A small amount of groundwater is heated by magma in the vent which bursts into steam and is forcefully expelled with other gases.
The hottest of Yellowstone's hydrothermal features are the fumaroles and can reach up to 280 degrees F. A plentiful water supply would help cool these features; however, steam vents are usually found on hillsides or higher ground, above the basin's water supply. They rapidly boil away what little water they contain, releasing steam and other gases forcefully from underground.