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Volcanic vent from which steam and volcanic gases issue. The major source of the steam emitted by fumaroles is groundwater heated by magma. Carbon dioxide, sulfur dioxide, and hydrogen sulfide are usually emitted directly from the magma. A fumarole rich in sulfur gases is called a solfatara; a fumarole rich in carbon dioxide is called a mofette.
This entry comes from Encyclopædia Britannica Concise. For the full entry on fumarole, visit Britannica.com.