mofette, ( French: “noxious fume”) , also spelled
moffettefumarole, or gaseous volcanic vent, that has a
temperature well below the boiling point of water, though above
the temperature of the surrounding air, and that is generally
rich in carbon dioxide and perhaps methane and other
hydrocarbons. When the winds are right, the issuing gases may
drift and settle into nearby hollows or small valleys and cause
the asphyxiation of animals and birds wandering in the areas.
Such potentially deadly hollows have been noted in the Absaroka
Range near Yellowstone National Park in Wyoming, U.S., and at
the base of Iceland’s Hekla volcano.