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Sabancaya volcano, Peru in 2017

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.

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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Mount Tambora
Mount Tambora (or Tomboro) is an active stratovolcano, also known as a composite volcano, on Sumbawa island, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zones beneath it. This raised Mount Tambora as high as 4,300 m (14,000 ft), making it one of the tallest peaks in the Indonesian archipelago, and drained off a large magma chamber inside the mountain. It took centuries to refill the magma chamber, its volcanic activity reaching its peak in April 1815.

The 1815 eruption is rated 7 on the Volcanic Explosivity Index, the only such eruption since the Lake Taupo eruption in about 180 AD. With an estimated ejecta volume of 160 cubic kilometers, Tambora's 1815 outburst was the largest volcanic eruption in recorded history; the explosion was heard on Sumatra island (more than 2,000 km (1,200 mi) away).


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Wolfgang Waltershausen
Wolfgang Sartorius Freiherr von Waltershausen (December 17, 1809 – March 16, 1876) was a German geologist. Waltershausen was born at Göttingen and educated at the University of Göttingen. There he devoted his attention to physical and natural science, and in particular to mineralogy. Waltershausen's father, Georg, was a writer, lecturer and professor of economics and history at Göttingen, best known for his role of translator and popularizer of Adam Smith's Wealth of Nations.

During a tour in 1834-1835 Waltershausen carried out a series of magnetic observations in various parts of Europe. He then gave his attention to an exhaustive investigation of the volcano of Mount Etna, in Sicily, and carried on the work with some interruptions until 1843. The chief result of this undertaking was his great Atlas des Ätna (1858–1861), in which he distinguished the lava streams formed during the later centuries.

After his return from Mount Etna, Waltershausen visited Iceland, and subsequently published Physisch-geographische Skizze von Island (1847), Über die vulkanischen Gesteine in Sizilien und Island (1853), and Geologischer Atlas von Island (1853). Meanwhile he was appointed professor of mineralogy and geology at Göttingen, and held this post for about thirty years, until his death.

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Fusakichi Omori

Volcanoes topics

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Core topics: Volcano  • Volcanology  • Igneous petrology  • Lava  • Magma  • Decade Volcanoes  • List of volcanoes  • Plate tectonics  • Hotspot

Types of volcanoes: Fissure vent  • Shield volcano  • Lava dome  • Cinder cone  • Stratovolcano  • Supervolcano  • Submarine volcano  • Subglacial volcano  • Mud volcano

Types of eruptions: (Overview)  • Strombolian  • Vulcanian  • Peléan  • Hawaiian  • Surtseyan  • Plinian  • Submarine  • Subglacial  • Phreatic

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Wildfire
Credit: Mila Zinkova

Wildfire on the island of Hawaiʻi caused by pāhoehoe lava flowing on the coastal plain of Kīlauea. The new lava is moving across the old surface, which is covered with a roughly 1-inch (2.54 cm)-thick layer of moss. The burning moss generates the smoke visible in the image. This kind of fire cannot be easily prevented or suppressed.

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We'll just look at you. If you looked scared then we'll panic.

— Discovery channel crew, talking to volcanologist John Seach during filming at Yasur Volcano, 2000.


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Good articles: Abyssal plain  • Amak Volcano  • Anahim hotspot  • Axial Seamount  • Ben Nevis  • Bowie Seamount  • Crater Lake  • Davidson Seamount  • Ferdinandea  • Gareloi Volcano  • Geyser  • Glacier Peak  • Hawaii hotspot  • Hualālai  • Kohala (mountain)  • Lake Toba  • Minoan eruption  • Mount Adams (Washington)  • Mount Bailey  • Mount Baker  • Mount Cleveland (Alaska)  • Mount Edziza volcanic complex  • Mount Garibaldi  • Mount Hood  • Mount Kenya  • Mount Rainier  • Mount Redoubt  • Mount Tehama  • Mount Thielsen  • Mount Vesuvius  • Peter I Island  • Roxy Ann Peak  • Rùm  • Sakurajima  • Sangay  • Silverthrone Caldera  • Staffa  • Types of volcanic eruptions  • Volcanic ash  • Weh Island  • Wells Gray-Clearwater volcanic field  • Yamsay Mountain

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