What Is a Fumarole?

A fumarole is an opening in the Earth's crust, typically found near active volcanoes, geothermal areas, and hot springs, through which steam and volcanic gases such as sulfur dioxide, hydrogen sulfide, carbon dioxide, and hydrogen fluoride escape from underground magma chambers. The word comes from the Latin "fumariolum," meaning smoke hole. Fumarole temperatures range from below 100°C (low-temperature fumaroles) to over 900°C near active volcanic vents. They are found worldwide at volcanic hotspots — Iceland's Hverir geothermal area, Yellowstone's Roaring Mountain, and Italy's Solfatara crater near Naples are famous examples. Geologists monitor fumaroles because changes in gas composition or temperature can signal impending volcanic activity.