opening in or near a volcano, through which hot sulphurous gases emerge
Sulfureous fumaroles, Whakaari/White Island, New Zealand
Fumarole in Greece

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

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