Concept

Fumarole

Summary
A fumarole (or fumerole) is a vent in the surface of the Earth or other rocky planet from which hot volcanic gases and vapors are emitted, without any accompanying liquids or solids. Fumaroles are characteristic of the late stages of volcanic activity, but fumarole activity can also precede a volcanic eruption and has been used for eruption prediction. Most fumaroles die down within a few days or weeks of the end of an eruption, but a few are persistent, lasting for decades or longer. An area containing fumaroles is known as a fumarole field. The predominant vapor emitted by fumaroles is steam, formed by the circulation of groundwater through heated rock. This is typically accompanied by volcanic gases given off by magma cooling deep below the surface. These volcanic gases include sulfur compounds, such as various sulfur oxides and hydrogen sulfide, and sometimes hydrogen chloride, hydrogen fluoride, and other gases. A fumarole that emits significant sulfur compounds is sometimes called a solfatara. Fumarole activity can break down rock around the vent, while simultaneously depositing sulfur and other minerals. Valuable hydrothermal mineral deposits can form beneath fumaroles. However, active fumaroles can be a hazard due to their emission of hot, poisonous gases. A fumarole (or fumerole; from French fumerolle, a domed structure with lateral openings, built over a kitchen to permit the escape of smoke) is an opening in a planet's crust which emits steam and gases, but no liquid or solid material. The temperature of the gases leaving the vent ranges from about . The steam forms when groundwater is superheated by hot rock, then flashes (boils due to depressurization) as it approaches the surface. In addition to steam, gases released by fumaroles include carbon dioxide, sulfur oxides, hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. These have their origin in magma cooling underground. Not all these gases are present in all fumaroles; for example, fumaroles of Kilauea in Hawaii, US, contain almost no hydrogen chloride or hydrogen fluoride.
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