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A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. Earth's volcanoes occur because its crust is broken into 17 major, rigid tectonic plates that float on a hotter, softer layer in its mantle. Therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging, and most are found underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, e.g., in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "plate hypothesis" volcanism. Volcanism away from plate boundaries has also been explained as mantle plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling diapirs with magma from the core–mantle boundary, 3,000 km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past one another.
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Erupting volcanoes can pose many hazards, not only in the immediate vicinity of the eruption. One such hazard is that volcanic ash can be a threat to aircraft, in particular those with jet engines where ash particles can be melted by the high operating temperature; the melted particles then adhere to the turbine blades and alter their shape, disrupting the operation of the turbine. Large eruptions can affect temperature as ash and droplets of sulfuric acid obscure the sun and cool the Earth's lower atmosphere (or troposphere); however, they also absorb heat radiated from the Earth, thereby warming the upper atmosphere (or stratosphere). Historically, volcanic winters have caused catastrophic famines.
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Vulcano (Sicilian: Vurcanu) is a small volcanic island in the Tyrrhenian Sea, about 25 km (16 mi) north of Sicily and located at the southernmost end of the eight Aeolian Islands. The island is 21 km2 (8 sq mi) in area, rises to 501 m (1,644 ft) above sea level, and it contains several volcanic caldera, including one of the four active volcanoes in Italy that are not submarine. The word "volcano" and its equivalent in several European languages derive from the name of this island, which in turn derives from Vulcan, the Roman god of fire.
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The Romans used the island mainly for raw materials, harvesting timber, and mining alum and sulfur. These were the principal activities on the island until the end of the 19th Century. After the Bourbon rule collapsed in 1860, a Briton named James Stevenson bought the northern part of the island, built a villa, reopened the local mines, and planted vineyards for making Malmsey wine. Stevenson lived on Vulcano until the last major eruption on the island happened in 1888. This eruption lasted the better part of two years, by which time Stevenson had sold all of his property to the local populace. He never returned to the island. His villa is still intact.
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The volcanic activity in the region is largely the result of the northward-moving African Plate meeting the Eurasian Plate. There are three volcanic centres on the island: At the southern end of the island are old stratovolcano cones, Monte Aria (501 m (1,644 ft)), Monte Saraceno (481 m (1,578 ft)) and Monte Luccia (188m (617 ft)), which have partially collapsed into the Il Piano Caldera. The most recently active centre is the Gran Cratere at the top of the Fossa cone, the cone having grown in the Lentia Caldera in the middle of the island, and has had at least nine major eruptions in the last 6000 years. At the north of the island is Vulcanello (123m (404 ft)), connected to the rest of it by an isthmus which is flooded in bad weather. It emerged from the sea during an eruption in 183 BCE as a separate islet. Occasional eruptions from its three cones with both pyroclastic flow deposits and lavas occurred from then until 1550, with the last eruption creating a narrow isthmus connecting it to Vulcano.
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Vulcano has been quiet since the eruption of the Fossa cone on 3 August 1888 to 1890, which deposited about 5 m (16 ft) of pyroclastic material on the summit. The style of eruption seen on the Fossa cone is called a Vulcanian eruption, being the explosive emission of pyroclastic fragments of viscous magmas caused by the high viscosity preventing gases from escaping easily. This eruption of Vulcano was carefully documented at the time by Giuseppe Mercalli. Mercalli described the eruptions as "...Explosions sounding like a cannon at irregular intervals..." As a result, vulcanian eruptions are based on this description. A typical vulcanian eruption can hurl blocks of solid material several hundreds of metres from the vent. Mercalli reported blocks from the 1888-1890 eruption fell in the sea between Vulcano and Lipari, several were photographed by him or his assistants that had fallen on the island of Vulcano.
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Volcanic gas emissions from this volcano are measured by a multicomponent gas analyzer system, which detects degassing of rising magmas before an eruption, improving prediction of volcanic activity.
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