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A fumarole (Latin fumus, smoke) is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrogen chloride, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from the ground. 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.
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. The Valley of Ten Thousand Smokes, for example, 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.
There are an estimated four thousand fumaroles within the boundaries of Yellowstone National Park.
In April 2006, a fumarole killed three Ski Patrol workers east of Chair 3 at Mammoth Mountain Ski Area in California. The workers were overpowered by toxic fumes (a mazuku) that had accumulated in a crevasse they had fallen into.
Fumaroles emitting sulfurous vapors form surface deposits of sulfur-rich minerals; places in which these deposits have been mined include:
Sulfur deposits on volcano in the Aeolian Islands, Italy
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