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Encyclopedia > Stratovolcano
A cutaway diagram of a stratovolcano
A cutaway diagram of a stratovolcano
Mount St. Helens — a stratovolcano in the U.S. state of Washington — the day before the May 18, 1980 eruption that removed much of the top of the mountain
Mayon Volcano, a stratovolcano in the Philippines.
Mayon Volcano, a stratovolcano in the Philippines.
Mt. Kazbek in Georgia, a dormant stratovolcano in the Caucasus
Mt. Kazbek in Georgia, a dormant stratovolcano in the Caucasus
Popocatépetl, an active stratovolcano in Mexico
Popocatépetl, an active stratovolcano in Mexico

A stratovolcano, also called a composite volcano, is a tall, conical volcano composed of many layers of hardened lava, tephra, and volcanic ash. These kinds volcanoes are characterized by a steep profile and periodic, explosive eruptions. The lava that flows from them is viscous, and cools and hardens before spreading very far. The source magma of this rock is classified as acidic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite). This is in contrast to less viscous basic magma that forms shield volcanoes (such as Mauna Loa in Hawaii), which have a wide base and more gently sloping profile. Structure of a stratovolcano. ... Structure of a stratovolcano. ... Image File history File links Sthelens1. ... Image File history File links Sthelens1. ... For the mountain in California, see Mount Saint Helena. ... For the capital city of the United States, see Washington, D.C.. For other uses, see Washington (disambiguation). ... The 1980 eruption of Mount St. ... Image File history File links Download high-resolution version (1397x997, 1885 KB) Mayon Volcano overlooks a pastoral scene approximately five months before the volcanos violent eruption in September 1984. ... Image File history File links Download high-resolution version (1397x997, 1885 KB) Mayon Volcano overlooks a pastoral scene approximately five months before the volcanos violent eruption in September 1984. ... Mayon Volcano is an active volcano in the Philippines on the island of Luzon, in the province of Albay in the Bicol Region. ... Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Mount Kazbek, one of the chief mountains of the Caucasus, is located in modern-day Georgia, dominating the town of Kazbegi near the border with North Ossetia. ... The Caucasus Mountains are a mountain system between the Black and Caspian seas in the Caucasus region, usually considered the southeastern limit of Europe. ... Image File history File links Popocatépetl_sunrise. ... Image File history File links Popocatépetl_sunrise. ... Popocatépetl (commonly referred to as El Popo or Don Goyo) (IPA: ) is an active volcano and the second highest peak in Mexico after the Pico de Orizaba (5,610m). ... Puu Ōō, a cinder-and-spatter cone on Kīlauea, Hawaii Volcanic cones are among the simplest volcano formations in the world. ... Cleveland Volcano in the Aleutian Islands of Alaska photographed from the International Space Station For other uses, see Volcano (disambiguation). ... Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Tephra refers to air-fall material produced by a volcanic eruption regardless of composition or fragment size. ... Ash plume from Mt Cleveland, a stratovolcano Diamond Head, a well-known backdrop to Waikiki in Hawaii, is an ash cone that solidified into tuff Volcanic ash consists of very fine rock and mineral particles less than 2 mm in diameter that are ejected from a volcanic vent. ... Viscosity is a measure of the resistance of a fluid to deformation under shear stress. ... For alternative meanings see acid (disambiguation). ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... This page is about a volcanic rock. ... Grey, red, black, altered white/tan, flow-banded pumice dacite Dacite (IPA: ) is an igneous, volcanic rock with a high iron content. ... A sample of andesite (dark groundmass) with amygdaloidal vesicules filled with zeolite. ... Igneous rocks (etymology from Latin ignis, fire) are rocks formed by solidification of cooled magma (molten rock), with or without crystallization, either below the surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. ... Shield volcano A shield volcano is a large volcano with shallow-sloping side. ... For other uses, see Mauna Loa (disambiguation). ...


Although stratovolcanoes are sometimes called composite volcanoes, volcanologists prefer to use the term stratovolcano to distinguish among volcanoes because all volcanoes of any size have a composite (layered) structure — they are built up from sequential outpourings of eruptive materials. Stratovolcanoes are one of the most common types of volcanoes.


Information

Stratovolcanoes are a common feature of subduction zones, forming chains or 'arcs' along tectonic plate boundaries where oceanic crust is subsumed under continental crust (Continental Arc Volcanism, e.g. Cascade Range, central Andes) or another oceanic plate (Island arc Volcanism, e.g. Japan, Aleutian Islands). The magma that forms stratovolcanoes arises when water, which is trapped both in hydrated minerals and in the porous basalt rock of the upper oceanic crust, is released into mantle rock of the asthenosphere above the sinking oceanic slab. The release of water from hydrated minerals is termed "dewatering," and occurs at specific pressure/temperature conditions for specific minerals as the plate subducts to lower depths. The water freed from the subducting slab lowers the melting point of the overlying mantle rock, which then undergoes partial melting and rises due to its density relative to the surrounding mantle rock, and pools temporarily at the base of the lithosphere. The magma then rises through the crust, incorporating silica rich crustal rock, leading to a final intermediate composition. When the magma nears the surface it pools in a magma chamber under the volcano. The relatively low pressure of the magma allows water and other volatiles (CO2, S2-, Cl-) dissolved in the magma to begin to come out of solution, much like when a bottle of carbonated water is opened. Once a critical volume of magma and gas accumulates, the obstacle provided by the volcanic cone is overcome, leading to a sudden explosive eruption.#REDIRECT Bold Italic Bold text'Italic text Categories: Geology stubs | Plate tectonics ... The tectonic plates of the world were mapped in the second half of the 20th century. ... Age of oceanic crust Oceanic crust is the part of Earths lithosphere that surfaces in the ocean basins. ... The thickness of the Earths crust (km). ... “Cascades” redirects here. ... This article is about the mountain system in South America. ... An island arc is a type of archipelago formed by plate tectonics as one oceanic tectonic plate subducts under another and produces magma. ... Aleutians seen from space The Aleutian Islands (possibly from Chukchi aliat, island) are a chain of more than 300 small volcanic islands forming an island arc in the Northern Pacific Ocean, occupying an area of 6,821 sq mi (17,666 km²) and extending about 1,200 mi (1,900... For the cities, see Basalt, Colorado and Basalt, Idaho. ... Earth cutaway from core to exosphere. ... This article does not cite any references or sources. ... The melting point of a crystalline solid is the temperature range at which it changes state from solid to liquid. ... The tectonic plates of the lithosphere on Earth. ... World geologic provinces (USGS) Oceanic crust  0-20 Ma  20-65 Ma  >65 Ma Geologic province  Shield  Platform  Orogen  Basin  Large igneous province  Extended crust In geology, a crust is the outermost solid shell of a planet or moon. ... A magma chamber is a chamber typically between 1 km and 10 km beneath the surface of the Earth formed as rising magma forms a reservoir if it is unable to rise any further. ... Volatility in physics is a measure of the speed at which a chemical element or chemical compound evaporates. ... Effervescence from soda. ... Puu Ōō, a cinder-and-spatter cone on KÄ«lauea, Hawaii Volcanic cones are among the simplest volcano formations in the world. ... An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. ...


Bold text== volcanoes Hazards==

 In recorded history, explosive eruptions at subduction zone (convergent-boundary) volcanoes have posed the greatest hazard to civilizations.[1] Subduction-zone stratovolcanoes like Mount St. Helens and Mount Pinatubo typically erupt with explosive force, because the magma is too stiff to allow easy escape of volcanic gases. As a consequence, tremendous internal pressures mount as the trapped gases expand during ascent, before the pent-up pressure is suddenly released in a violent eruption. Such an explosive process can be compared to putting your thumb over an opened bottle of a carbonated drink, shaking it vigorously, and then quickly removing the thumb. The shaking action separates the gases from the liquid to form bubbles, increasing the internal pressure. Quick release of the thumb allows the gases and liquid to gush out with explosive speed and force.[1] 

As examples of the hazards of stratovolcanoes, consider two volcanoes on the western edge of the Philippine Plate that erupted in 1991. On June 15, Mount Pinatubo spewed ash 40 km into the air and produced huge pyroclastic flows and mudflows that devastated a large area around the volcano. Pinatubo, located 90 km from Manila, had been dormant for 600 years before the 1991 eruption, which ranks as one of the largest eruptions in the 20th Century.[1] Also in 1991, Japan's Unzen Volcano, located on the island of Kyushu about 40 km east of Nagasaki, awakened from its 200-year slumber to produce a new lava dome at its summit. Beginning in June, repeated collapses of this active dome generated destructive ash flows that swept down its slopes at speeds as high as 200 km per hour. Unzen is one of more than 75 active volcanoes in Japan; its eruption in 1792 killed more than 15,000 people--the worst volcanic disaster in the country's history.[1] For the mountain in California, see Mount Saint Helena. ... Mount Pinatubo is an active stratovolcano located on the island of Luzon in the Philippines, at the intersection of the borders of the provinces of Zambales, Tarlac, and Pampanga. ...  The Philippine plate, shown in dull red The Philippine Plate is an oceanic tectonic plate beneath the Pacific Ocean to the east of the Philippines. ... Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. ... Lahar from a March 1982 eruption of Mount St. ... For other meanings of the word, see Manila (disambiguation). ... In the distance, Mt. ...


While the Unzen eruptions have caused deaths and considerable local damage, the impact of the June 1991 eruption of Mount Pinatubo was global. Slightly cooler than usual temperatures recorded worldwide and the brilliant sunsets and sunrises have been attributed to this eruption that sent fine ash and gases high into the stratosphere, forming a large volcanic cloud that drifted around the world. The sulfur dioxide (SO2) in this cloud -- about 22 million tons -- combined with water to form droplets of sulfuric acid, blocking some of the sunlight from reaching the Earth and thereby cooling temperatures in some regions by as much as 0.5 °C.[1] An eruption the size of Mount Pinatubo could affect the weather for a few years; material ejected only into the troposphere will be washed away by rain and winds. A similar phenomenon occurred in April of 1815 with the cataclysmic eruption of Tambora Volcano on Sumbawa Island in Indonesia, the most powerful eruption in recorded history. Tambora's volcanic cloud lowered global temperatures by as much as 3 °C.[1] Even a year after the eruption, most of the northern hemisphere experienced sharply cooler temperatures during the summer months. In part of Europe and in North America, 1816 was known as the year without a summer. Atmosphere diagram showing stratosphere. ... Sulfur dioxide (or Sulphur dioxide) has the chemical formula SO2. ... Atmosphere diagram showing the mesosphere and other layers. ... This article is about precipitation. ... For the 1928 film, see The Wind. ... Mount Tambora (or Tomboro) is an active stratovolcano on Sumbawa island, Indonesia. ... Sumbawa is an Indonesian island, located in the middle of the Lesser Sunda Islands chain, with Lombok to the west, Flores to the east, and Sumba further to the southeast. ... The Year Without a Summer, also known as the Poverty Year and Eighteen hundred and froze to death was 1816, in which severe summer climate abnormalities destroyed crops in Northern Europe and the American Northeast. ...


Apart from possibly affecting climate, volcanic clouds from explosive eruptions also pose a hazard to aviation safety.[1] This was brought to attention during the 1982 eruption of Galunggung in Java; two Boeing 747 flew into the ash cloud, suffering temporary engine failure and structural damage. During the past two decades, more than 60 airplanes, mostly commercial jetliners, have been damaged by in-flight encounters with volcanic ash. Some of these encounters have resulted in the power loss of all engines, necessitating emergency landings. Luckily, to date no crashes have happened because of jet aircraft flying into volcanic ash.[1] Galunggung (Galoen-gong, Gunung Galunggung) is a stratovolcano on Java, Indonesia. ... This article is about the Java island. ... The Boeing 747, sometimes nicknamed the Jumbo Jet,[4][5] is a long-haul, widebody commercial airliner manufactured by Boeing in the United States. ...


Since the year A.D. 1600, nearly 300,000 people have been killed by volcanic eruptions.[1] Most deaths were caused by pyroclastic flows and mudflows, deadly hazards which often accompany explosive eruptions of subduction-zone stratovolcanoes. Pyroclastic flows are fast-moving, avalanche-like, ground-hugging incandescent mixtures of hot volcanic debris, ash, and gases that can travel at speeds in excess of 150 km per hour. Approximately 30,000 people were killed by pyroclastic flows during the 1902 eruption of Mont Pelée on the island of Martinique in the Caribbean.[1] In March-April 1982, three explosive eruptions of El Chichón Volcano in the State of Chiapas, southeastern Mexico, caused the worst volcanic disaster in that country's history. Villages within 8 km of the volcano were destroyed by pyroclastic flows, killing more than 2,000 people.[1] Pyroclastic flows sweep down the flanks of Mayon Volcano, Philippines, in 1984 A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. ... Mount Pelée (French: Montagne Pelée, Bald Mountain) is an active volcano on the northern tip of the French overseas département of Martinique in the Caribbean. ... 1982 is a common year starting on Friday of the Gregorian calendar. ... 1982 is a common year starting on Friday of the Gregorian calendar. ... El Chichón is an active volcano in northwestern Chiapas, Mexico. ... Location within Mexico Country  Mexico Capital Tuxtla Gutiérrez Municipalities 118 Largest City Tuxtla Gutiérrez Government  - Governor Juan José Sabines Guerrero ( PRD)  - Federal Deputies PRI: 7 PRD: 5  - Federal Senators PRI: 1 PRD: 1 PVEM: 1 Area Ranked 8th  - State 74,211 km²  (28,653 sq mi) Population (2005...


Ashfall is a threat to health (in terms of inhalation) and is only a threat to property with high enough accumulations (greater than 30 cm (1 ft) of accumulation is sufficient to collapse most buildings)


Mudflows (also called debris flows or lahars, an Indonesian term for volcanic mudflows) are mixtures of volcanic debris and water. The water usually comes from two sources: rainfall or the melting of snow and ice by hot volcanic debris. Depending on the proportion of water to volcanic material, mudflows can range from soupy floods to thick flows that have the consistency of wet cement.[1] As mudflows sweep down the steep sides of composite volcanoes, they have the strength and speed to flatten or bury everything in their paths. Hot ash and pyroclastic flows from the eruption of the Nevado del Ruiz Volcano in Colombia, South America, melted snow and ice atop the 5,390-m-high Andean peak; the ensuing mudflows buried the city of Armero, killing 25,000 people.[1] Lahar from a March 1982 eruption of Mount St. ... Space radar image of Nevado del Ruiz Nevado del Ruiz 2006 Nevado del Ruiz is an Andean stratovolcano in Caldas Department, Colombia. ... Armero is the name of a city in Colombia that was buried by ash after a nearby volcano erupted, killing about 23,000 people. ...


Lava flows are generally not a viable threat because generally lava will move slowly enough to allow people to move away; thus they are more of a property threat. However, Nyiragongo is dangerous because of its lava flows; its magma has extremely low silica content, making it more fluid than normal (even when comparing to Hawaiian lava) and thus less viscous. This is compounded by the extremely steep slope of Nyiragongo. Look up lava, Aa, pahoehoe in Wiktionary, the free dictionary. ... Mount Nyiragongo is a dormant volcano in the Virunga Mountains associated with the Great Rift Valley or East African Rift. ... Magma is molten rock located beneath the surface of the Earth (or any other terrestrial planet), and which often collects in a magma chamber. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... For other uses, see Viscosity (disambiguation). ... Mount Nyiragongo is a dormant volcano in the Virunga Mountains associated with the Great Rift Valley or East African Rift. ...


See also

  • List of stratovolcanoes

A list of stratovolcanoes follows below. ...

References

  1. ^ a b c d e f g h i j k l m Kious, W. Jacquelyne; Tilling, Robert I.. "Plate tectonics and people", This Dynamic Earth: The Story of Plate Tectonics. USGS. 

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