French for noxious gas and similar to the Italian word mofeta, meaning “noxious exhalation,” a mofette is a type of fumarole (a vent in the Earth’s surface from which gases erupt) characterized by its high carbon dioxide emissions at temperatures much below the boiling point. Mofette refers both to the opening itself and to the gas emitted, which, along with carbon dioxide, can contain oxygen, nitrogen, and water vapors. Mofettes indicate a late stage in minor volcanic activity, such as in the Phlegraean Fields near Naples; at Auvergne in central France; in Java; and at Yellowstone National Park.

Kim Barnes