A vent on the surface of a volcanically active area, through which hot gases and vapours are emitted. The source of the gases is usually magma or hot groundwater. Gases emanating from fumaroles may include carbon dioxide, sulphur oxides, hydrogen sulphide, hydrogen chloride, and hydrogen fluoride. Their temperatures often reach hundreds of degrees. Fumaroles producing large amounts of sulphur are commonly referred to as solfatar; a fumarole rich in carbon dioxide is called a mofette.