Fumarole

opening in or near a volcano, through which hot sulphurous gases emerge

A fumarole (Latin fumus, smoke) is an opening in the crust of the Earth, often in the neighborhood of dormant volcanoes, where steam and gases come out, for instance carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide.

Sulfureous fumaroles at the Solfatara crater, one of the 24 craters of the Phlegraean Fields, Naples
Fumaroles near the summit on Mount Damavand, Iran
Sulfureous fumaroles on Whakaari/White Island, New Zealand
Fumaroles in Nisyros, Greece

Etymology

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The name solfatara (from the Italian solfo, sulfur), is given to fumaroles with sulfurous gases.