A fumarole (Latin fumus, smoke) is an opening in Earth's (or any other astronomical body's) crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The name solfatara, from the Italian solfo, sulfur (via the Sicilian dialect), is given to fumaroles that emit sulfurous gases.
Fumaroles may occur along tiny cracks or long fissures, in chaotic clusters or fields, and on the surfaces of lava flows and thick deposits of pyroclastic flows. A fumarole field is an area of thermal springs and gas vents where magma or hot igneous rocks at shallow depth are releasing gases or interacting with groundwater. From the perspective of groundwater, fumaroles could be described as a hot spring that boils off all its water before the water reaches the surface.
A good example of fumarole activity on Earth is the famous Valley of Ten Thousand Smokes, which was formed during the 1912 eruption of Novarupta in Alaska. Initially, there were thousands of fumaroles in the cooling ash from the eruption, but over time most of them have become extinct. Fumaroles may persist for decades or centuries if they are above a persistent heat source, or disappear within weeks to months if they occur atop a fresh volcanic deposit that quickly cools. There are also an estimated four thousand fumaroles within the boundaries of Yellowstone National Park.
Another example is an array of fumaroles in the Valley of Desolation in Morne Trois Pitons National Park in Dominica.
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The formation called Home Plate at Gusev Crater, Mars that was examined by the Mars Exploration Rover (MER) named Spirit is highly suspected to be the eroded remains of an ancient and extinct fumarole.[1]
 Sulfurous fumaroles, Whakaari/White Island, New Zealand |
 Sulfur deposits near a fumarole |
 Fumarole at Rincón de la Vieja Volcano National Park, Costa Rica |
 Sampling gases at a fumarole on Mount Baker in Washington, USA. |
 At Námafjall, Iceland |
 Sulfur deposits on Vulcano (Eolian islands, Italy) |
SOLFATARA, a volcanic vent emitting vapours chiefly of sulphurous character, whence the name, from the Italian solfo (sulphur). The typical example is the famous Solfatara, near Puzzuoli, in the Phlegraean Fields, west of Naples. This is an old crater which has not been in active eruption since A.D. 1198, but which is continuously exhaling heated vapours, chiefly hydrogen sulphide, sulphur dioxide and steam. These issue from orifices in the crust, on the walls of which are yellow incrustations of sublimed sulphur, sometimes orange-red by association with arsenic sulphide, whilst the trachytic rocks of the volcano are bleached and corroded by the effluent vapours, with formation of such products as gypsum and alum. Sal ammoniac occurs among the sublimates. The term solfatara has been extended to all dormant volcanoes of this type; and a volcano which has ceased to emit lava or ashes but still evolves heated vapours, is said to have passed into the "solfataric stage." Examples are to be found in many volcanic districts. By French geologists the term soufriere is used instead of the Italian solfatara. (See VOLCANOES.)
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