Fumarole

Fumaroles near the summit on Mount Damavand, Iran
Sulfureous fumaroles, Whakaari/White Island, New Zealand
Fumaroles in Nisyros, Greece

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.

Etymology

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