Fumarole

A fumarole (ultimately from the Latin fumus," smoke") is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrogen chloride, and hydrogen sulfide. The steam forms when superheated water vaporizes as its pressure drops when it emerges from the ground. The name solfatara, from the Italian solfo, sulfur (via the Sicilian language, compare Solfatara (volcano)), is given to fumaroles that emit sulfurous gases.