A stratovolcano, also called a composite volcano, is a tall, conical volcano composed of many layers of hardened lava, tephra, and volcanic ash. Volcanic cones are among the simplest Volcano formations in the world Plate tectonics and hotspots Divergent plate boundaries At the Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures Tephra is air-fall material produced by a volcanic eruption regardless of composition or fragment size Volcanic ash consists of small Tephra, which are bits of pulverized rock and glass created by volcanic eruptions less than in diameter These kinds of 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. Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. The source magma of this rock is classified as acidic, having high to intermediate levels of silica (as in rhyolite, dacite, or andesite). In Computer science, ACID ( Atomicity Consistency Isolation Durability) is a set of properties that guarantee that Database transactions are The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide This page is about a volcanic rock For the ghost town see Rhyolite Nevada, and for the satellite system see Rhyolite/Aquacade. Dacite ( deɪsaɪt) is an igneous, volcanic rock with a high iron content For the extinct cephalopod genus see Andesites. Andesite (ˈændəsaɪt is an igneous, Volcanic rock, of intermediate 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. Igneous rocks (etymology from Latin ignis, fire are rocks formed by solidification of cooled Magma (molten rock A shield volcano is a large Volcano with shallow-sloping sides Mauna Loa is the largest volcano on earth and one of five volcanoes that form the Island of Hawaii in the U

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.

A cutaway diagram of a stratovolcano

Mount St. Helens — a stratovolcano in the U. Mount St Helens is an active Stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States S. state of Washington — the day before the May 18, 1980 eruption that removed much of the top of the mountain

The Mayon Volcano, the most active stratovolcano in the Philippines. Washington ( is a state in the Pacific Northwest region of the United States. The 1980 eruption of Mount St Helens, a volcano located in Washington state in the United States was a major volcanic eruption. The Mayon Volcano is an active Stratovolcano in the Philippines on the Island of Luzon, in the province of Albay The Philippines ( Filipino: Pilipinas, officially known as the Republic of the Philippines (fil ''Republika ng Pilipinas'' RP

Mt. Kazbek in Georgia, a dormant stratovolcano in the Caucasus

Popocatépetl, an active stratovolcano in Mexico

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. Mount Kazbek (მყინვარწვერი Mqinvartsveri) is a dormant Stratovolcano and one of the chief Mountains of the Caucasus. Georgia ( საქართველო, Sakartvelo) is a Transcontinental country in the Caucasus region situated at the dividing line between This article is about the terrestrial Eurasian mountain range Popocatépetl (commonly referred to as Popo, El Popo or Don Goyo) (popokaˈtepetɬ is an active Volcano and at 5426 m The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. In Geology, a subduction zone is an area on Earth where two tectonic plates meet and move towards one another with one sliding underneath the other Plate tectonics (from Greek τέκτων tektōn "builder" or "mason" describes the large scale motions of Earth 's Lithosphere Oceanic crust is the part of Earth's Lithosphere that surfaces in the Ocean basins The continental crust is the layer of granitic, Sedimentary, and Metamorphic rocks which form the Continents and the areas of shallow seabed g. Cascade Range, central Andes) or another oceanic plate (Island arc Volcanism, e. The Andes form the world's longest exposed Mountain range. They lie as a continuous chain of highland along the western coast of South America. A volcanic arc is a chain of volcanic islands or Mountains formed by Plate tectonics as an oceanic Tectonic plate subducts under g. Japan, Aleutian Islands). For a topic outline on this subject see List of basic Japan topics. The Aleutian Islands (possibly from Chukchi aliat, " Island " are a chain of more than 300 small volcanic islands forming a Volcanic 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. Basalt (bəˈsɔːlt ˈbeisɔːlt ˈbæsɔːlt is a common Extrusive Volcanic rock. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided The asthenosphere (from an invented Greek a + ' sthenos "without strength" and Greek word σφαίρα (sphera meaning globe is the 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 melting point of a solid is the temperature range at which it changes state from solid to Liquid. The lithosphere (IPA, from the Greek λίθος for "rocky" + σφαίρα for "sphere" is the solid outermost shell of a rocky Planet. The magma then rises through the crust, incorporating silica rich crustal rock, leading to a final intermediate composition. In Geology, a crust is the outermost solid shell of a planet or moon When the magma nears the surface it pools in a magma chamber under the volcano. A magma chamber is a large underground pool of molten rock lying under the surface of the earth's crust The relatively low pressure of the magma allows water and other volatiles (CO₂, S^2-, Cl^-) dissolved in the magma to begin to come out of solution, much like when a bottle of carbonated water is opened. Volatility in the context of Chemistry, Physics and Thermodynamics is a measure of the tendency of a substance to Vaporize. Once a critical volume of magma and gas accumulates, the obstacle provided by the volcanic cone is overcome, leading to a sudden explosive eruption. 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.

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. Mount St Helens is an active Stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States Mount Pinatubo is an active Stratovolcano located on the island of Luzon 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. The Philippine Plate is a Tectonic plate beneath the Pacific Ocean to the east of the Philippines. 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. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically 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. The City of Manila ^[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. Mount Unzen ( jp 雲仙岳 Unzendake) is an active volcanic complex of several overlapping Stratovolcanoes also known as a Composite volcano 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]

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 stratosphere is the second major layer of Earth's atmosphere, just above the Troposphere, and below the Mesosphere. 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. The troposphere is the lowest portion of Earth's atmosphere. It contains approximately 75% of the atmosphere's mass and almost all of its Water vapor and Rain is Liquid precipitation. On Earth it is the condensation of atmospheric Water vapor into drops heavy enough to fall often making it to 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. Mount Tambora (or Tomboro) is an active Stratovolcano, also known as a Composite volcano, 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 The Republic of Indonesia ( (Republik Indonesia is a Country in Southeast Asia. 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. The Year Without a Summer, also known as the Poverty Year, The Year There Was No Summer or Eighteen hundred and froze to death

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. Galunggung, Galoen-gong, or Gunung Galunggung is an active Stratovolcano in West Java, Indonesia. Java (Jawa is an Island of Indonesia and the site of its Capital city Jakarta. WikipediaWikiProject Aircraft. Please see WikipediaWikiProject Aircraft/page content for recommended layout 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]

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. A pyroclastic flow (also known as a pyroclastic density current) is a common and devastating result of some volcanic eruptions. 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. Mount Pelée ( French: Montagne Pelée, or "Bald Mountain" is a dormant Volcano on the northern tip of the French Overseas department Martinique is an Island in the eastern Caribbean Sea, having a land area of 1128 km² ^[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. Year 1982 ( MCMLXXXII) was a Common year starting on Friday (link displays the 1982 Gregorian calendar) Year 1982 ( MCMLXXXII) was a Common year starting on Friday (link displays the 1982 Gregorian calendar) El Chichón is an active Volcano in northwestern Chiapas, Mexico. Chiapas is the southernmost state of Mexico, located towards the southeast of the country The United Mexican States ( or commonly Mexico (ˈmɛksɪkoʊ () is a federal constitutional Republic in North America. Villages within 8 km of the volcano were destroyed by pyroclastic flows, killing more than 2,000 people. ^[1]

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 Ashfall Fossil Beds of Antelope County in northeastern Nebraska are among the rare preservation sites called Lagerstätten which preserve ecological A lahar is a type of Mudflow / Landslide composed of Pyroclastic material and Water that flows down from a Volcano, typically 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. Nevado del Ruiz, also known as Mount Ruiz, is an Andean Stratovolcano in Caldas Department, Colombia. Colombia (kəˈlʌmbɪə officially the Republic of Colombia () is a country in northwestern South America. Armero tragedy Armero, or Armero-Guayabal, is a municipality in the Tolima Department, Colombia. ^[1]

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. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures 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. Mount Nyiragongo is a Stratovolcano in the Virunga Mountains associated with the Great Rift Valley. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet The Chemical compound silicon dioxide, also known as silica or silox (from the Latin " Silex " is an Oxide Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. This is compounded by the extremely steep slope of Nyiragongo. Mount Nyiragongo is a Stratovolcano in the Virunga Mountains associated with the Great Rift Valley.

See also

• List of stratovolcanoes

References