This article uses HTML markup . (February 2019)
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.
In geology, the crust is the outermost solid shell of a rocky planet, dwarf planet, or natural satellite. It is usually distinguished from the underlying mantle by its chemical makeup; however, in the case of icy satellites, it may be distinguished based on its phase.
Earth is the third planet from the Sun and the only astronomical object known to harbor life. According to radiometric dating and other sources of evidence, Earth formed over 4.5 billion years ago. Earth's gravity interacts with other objects in space, especially the Sun and the Moon, Earth's only natural satellite. Earth revolves around the Sun in 365.26 days, a period known as an Earth year. During this time, Earth rotates about its axis about 366.26 times.
Lava is molten rock generated by geothermal energy and expelled through fractures in planetary crust or in an eruption, usually at temperatures from 700 to 1,200 °C. The structures resulting from subsequent solidification and cooling are also sometimes described as lava. The molten rock is formed in the interior of some planets, including Earth, and some of their satellites, though such material located below the crust is referred to by other terms.
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. km deep in the Earth. Volcanoes are usually not created where two tectonic plates slide past one another.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
Plate tectonics is a scientific theory describing the large-scale motion of seven large plates and the movements of a larger number of smaller plates of the Earth's lithosphere, since tectonic processes began on Earth between 3 and 3.5 billion years ago. The model builds on the concept of continental drift, an idea developed during the first decades of the 20th century. The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s.
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which eventually become rift valleys. Most active divergent plate boundaries occur between oceanic plates and exist as mid-oceanic ridges. Divergent boundaries also form volcanic islands which occur when the plates move apart to produce gaps which molten lava rises to fill.
Convergent boundaries are areas on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other causing a process known as subduction. The subduction zone can be defined by a plane where many earthquakes occur, called the Benioff Zone. These collisions happen on scales of millions to tens of millions of years and can lead to volcanism, earthquakes, orogenesis, destruction of lithosphere, and deformation. Convergent boundaries occur between oceanic-oceanic lithosphere, oceanic-continental lithosphere, and continental-continental lithosphere. The geologic features related to convergent boundaries vary depending on crust types.
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.
A jet engine is a type of reaction engine discharging a fast-moving jet that generates thrust by jet propulsion. This broad definition includes airbreathing jet engines. In general, jet engines are combustion engines.
An operating temperature is the temperature at which an electrical or mechanical device operates. The device will operate effectively within a specified temperature range which varies based on the device function and application context, and ranges from the minimum operating temperature to the maximum operating temperature. Outside this range of safe operating temperatures the device may fail. Aerospace and military-grade devices generally operate over a broader temperature range than industrial devices; commercial-grade devices generally have the narrowest operating temperature range.
A turbine is a rotary mechanical device that extracts energy from a fluid flow and converts it into useful work. The work produced by a turbine can be used for generating electrical power when combined with a generator. A turbine is a turbomachine with at least one moving part called a rotor assembly, which is a shaft or drum with blades attached. Moving fluid acts on the blades so that they move and impart rotational energy to the rotor. Early turbine examples are windmills and waterwheels.
The word volcano is derived from the name of Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn comes from Vulcan, the god of fire in Roman mythology.The study of volcanoes is called volcanology, sometimes spelled vulcanology.
Vulcano or "Vulcan" 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.
The Aeolian Islands are a volcanic archipelago in the Tyrrhenian Sea north of Sicily, named after the demigod of the winds Aeolus. The islands' inhabitants are known as Aeolians. The Aeolian Islands are a popular tourist destination in the summer and attract up to 200,000 visitors annually.
Vulcan is the god of fire including the fire of volcanoes, deserts, metalworking, and the forge in ancient Roman religion and myth. Vulcan is often depicted with a blacksmith's hammer. The Vulcanalia was the annual festival held August 23 in his honor. His Greek counterpart is Hephaestus, the god of fire and smithery. In Etruscan religion, he is identified with Sethlans.
At the mid-oceanic ridges, two tectonic plates diverge from one another as new oceanic crust is formed by the cooling and solidifying of hot molten rock. Because the crust is very thin at these ridges due to the pull of the tectonic plates, the release of pressure leads to adiabatic expansion (without transfer of heat or matter) and the partial melting of the mantle, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans; therefore, most volcanic activity on the Earth is submarine, forming new seafloor. Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed; for example, Iceland.
Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramafic cumulates. The crust overlies the solidified and uppermost layer of the mantle. The crust and the solid mantle layer together constitute oceanic lithosphere.
An adiabatic process occurs without transfer of heat or mass of substances between a thermodynamic system and its surroundings. In an adiabatic process, energy is transferred to the surroundings only as work. The adiabatic process provides a rigorous conceptual basis for the theory used to expound the first law of thermodynamics, and as such it is a key concept in thermodynamics.
A mantle is a layer inside a planetary body bounded below by a core and above by a crust. Mantles are made of rock or ices, and are generally the largest and most massive layer of the planetary body. Mantles are characteristic of planetary bodies that have undergone differentiation by density. All terrestrial planets, a number of asteroids, and some planetary moons have mantles.
Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges, under the continental plate, forming a deep ocean trench just offshore. In a process called flux melting, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating magma. This magma tends to be extremely viscous because of its high silica content, so it often does not attain the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed. Typical examples are Mount Etna and the volcanoes in the Pacific Ring of Fire.
Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced to sink due to gravity into the mantle. Regions where this process occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the average rate of convergence being approximately two to eight centimeters per year along most plate boundaries.
In igneous petrology and volcanology, flux melting occurs when water and other volatile components are added to hot solid rock. In engineering and metallurgy, flux is a substance, such as salt, that produces a low melting point mixture with a metal oxide. In the same way, the addition of water and other volatile compounds to rocks composed of silicate minerals lowers the melting temperature of those rocks.
Magma is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural satellites. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma is produced by melting of the mantle and/or the crust at various tectonic settings, including subduction zones, continental rift zones, mid-ocean ridges and hotspots. Mantle and crustal melts migrate upwards through the crust where they are thought to be stored in magma chambers or trans-crustal crystal-rich mush zones. During their storage in the crust, magma compositions may be modified by fractional crystallization, contamination with crustal melts, magma mixing, and degassing. Following their ascent through the crust, magmas may feed a volcano or solidify underground to form an intrusion. While the study of magma has historically relied on observing magma in the form of lava flows, magma has been encountered in situ three times during geothermal drilling projects—twice in Iceland, and once in Hawaii.
Hotspots are volcanic areas believed to be formed by mantle plumes, which are hypothesized to be columns of hot material rising from the core-mantle boundary in a fixed space that causes large-volume melting. Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume. The Hawaiian Islands are said to have been formed in such a manner; so has the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate above the hot spot. This theory, however, has been doubted.
The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; however, this describes just one of the many types of volcano. The features of volcanoes are much more complicated and their structure and behavior depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus. Vents that issue volcanic material (including lava and ash) and gases (mainly steam and magmatic gases) can develop anywhere on the landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea. Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn, and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when the mud volcano is actually a vent of an igneous volcano.
Volcanic fissure vents are flat, linear fractures through which lava emerges.
Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent. They generally do not explode catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.
Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount Saint Helens, but can also form independently, as in the case of Lassen Peak. Like stratovolcanoes, they can produce violent, explosive eruptions, but their lava generally does not flow far from the originating vent.
Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example; lava beneath the surface of the mountain created an upward bulge which slid down the north side of the mountain.
Volcanic cones or cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico, Caja del Rio is a volcanic field of over 60 cinder cones.
Based on satellite images it was suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon.
Stratovolcanoes or composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that gives rise to the name. Stratovolcanoes are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Strato/composite volcanoes are made of cinders, ash, and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process repeats. Classic examples include Mount Fuji in Japan, Mayon Volcano in the Philippines, and Mount Vesuvius and Stromboli in Italy.
Throughout recorded history, ash produced by the explosive eruption of stratovolcanoes has posed the greatest volcanic hazard to civilizations. Not only do stratovolcanoes have greater pressure buildup from the underlying lava flow than shield volcanoes, but their fissure vents and monogenetic volcanic fields (volcanic cones) also have more powerful eruptions because they are often under extension. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars.Large pieces of tephra are called volcanic bombs. Big bombs can measure more than 4 feet(1.2 meters) across and weigh several tons.
A supervolcano usually has a large caldera and can produce devastation on an enormous, sometimes continental, scale. Such volcanoes are able to severely cool global temperatures for many years after the eruption due to the huge volumes of sulfur and ash released into the atmosphere. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States); Lake Taupo in New Zealand; Lake Toba in Sumatra, Indonesia; and Ngorongoro Crater in Tanzania. Because of the enormous area they may cover, supervolcanoes are hard to identify centuries after an eruption. Similarly, large igneous provinces are also considered supervolcanoes because of the vast amount of basalt lava erupted (even though the lava flow is non-explosive).
Submarine volcanoes are common features of the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above the ocean's surface. In the ocean's deep, the tremendous weight of the water above prevents the explosive release of steam and gases; however, they can be detected by hydrophones and discoloration of water because of volcanic gases. Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form under water. Even large submarine eruptions may not disturb the ocean surface due to the rapid cooling effect and increased buoyancy of water (as compared to air) which often causes volcanic vents to form steep pillars on the ocean floor. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break the ocean surface as new islands or floating pumice rafts.
Subglacial volcanoes develop underneath icecaps. They are made up of flat lava which flows at the top of extensive pillow lavas and palagonite. When the icecap melts, the lava on top collapses, leaving a flat-topped mountain. These volcanoes are also called table mountains, tuyas, or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland, however, there are also tuyas in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.
Mud volcanoes or mud domes are formations created by geo-excreted liquids and gases, although there are several processes which may cause such activity. The largest structures are 10 kilometers in diameter and reach 700 meters high.
Another way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into four different compositions:
Two types of lava are named according to the surface texture: ʻAʻa (pronounced [ˈʔaʔa] ) and pāhoehoe ( [paːˈho.eˈho.e] ), both Hawaiian words. ʻAʻa is characterized by a rough, clinkery surface and is the typical texture of viscous lava flows. However, even basaltic or mafic flows can be erupted as ʻaʻa flows, particularly if the eruption rate is high and the slope is steep.
Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow with greater fluidity.
A popular way of classifying magmatic volcanoes is by their frequency of eruption [ according to whom? ], with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant or inactive, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes.
There is no consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.
Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions. Most scientists consider a volcano active if it has erupted in the last 10,000 years (Holocene times)—the Smithsonian Global Volcanism Program uses this definition of active. Most volcanoes are situated on the Pacific Ring of Fire.An estimated 500 million people live near active volcanoes.
Historical time (or recorded history) is another timeframe for active.The Catalogue of the Active Volcanoes of the World, published by the International Association of Volcanology, uses this definition, by which there are more than 500 active volcanoes. However, the span of recorded history differs from region to region. In China and the Mediterranean, it reaches back nearly 3,000 years, but in the Pacific Northwest of the United States and Canada, it reaches back less than 300 years, and in Hawaii and New Zealand, only around 200 years.
As of 2013, the following are considered Earth's most active volcanoes:
As of August 2013 [update] , the longest ongoing (but not necessarily continuous) volcanic eruptive phases are:
Other very active volcanoes include:
Extinct volcanoes are those that scientists consider unlikely to erupt again because the volcano no longer has a magma supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian – Emperor seamount chain in the Pacific Ocean (although some volcanoes at the eastern end of the chain are active), Hohentwiel in Germany, Shiprock in New Mexico, Zuidwal volcano in the Netherlands and many volcanoes in Italy like Monte Vulture. Edinburgh Castle in Scotland is famously located atop an extinct volcano. Otherwise, whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. Some volcanologists refer to extinct volcanoes as inactive, though the term is now more commonly used for dormant volcanoes once thought to be extinct.
It is difficult to distinguish an extinct volcano from a dormant (inactive) one. Dormant volcanoes are those that have not erupted for thousands of years, but are likely to erupt again in the future.Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless, volcanoes may remain dormant for a long period of time. For example, Yellowstone has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. Vesuvius was described by Roman writers as having been covered with gardens and vineyards before its eruption of 79 CE, which destroyed the towns of Herculaneum and Pompeii. Before its catastrophic eruption of 1991, Pinatubo was an inconspicuous volcano, unknown to most people in the surrounding areas. Two other examples are the long-dormant Soufrière Hills volcano on the island of Montserrat, thought to be extinct before activity resumed in 1995, and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE and had long been thought to be extinct.
The three common popular classifications of volcanoes can be subjective and some volcanoes thought to have been extinct have erupted again. To help prevent people from falsely believing they are not at risk when living on or near a volcano, countries have adopted new classifications to describe the various levels and stages of volcanic activity.Some alert systems use different numbers or colors to designate the different stages. Other systems use colors and words. Some systems use a combination of both.
The United States Geological Survey (USGS) has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. The new volcano alert-level system classifies volcanoes now as being in a normal, advisory, watch or warning stage. Additionally, colors are used to denote the amount of ash produced.
The Decade Volcanoes are 16 volcanoes identified by the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. They are named Decade Volcanoes because the project was initiated as part of the United Nations-sponsored International Decade for Natural Disaster Reduction (the 1990s). The 16 current Decade Volcanoes are
The Deep Earth Carbon Degassing Project, an initiative of the Deep Carbon Observatory, monitors nine volcanoes, two of which are Decade volcanoes. The focus of the Deep Earth Carbon Degassing Project is to use Multi-Component Gas Analyzer System instruments to measure CO2/SO2 ratios in real-time and in high-resolution to allow detection of the pre-eruptive degassing of rising magmas, improving prediction of volcanic activity.
There are many different types of volcanic eruptions and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.
The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxideand sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.
Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The SO2 emissions alone of two different eruptions are sufficient to compare their potential climatic impact. The aerosols increase the Earth's albedo—its reflection of radiation from the Sun back into space—and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years; sulfur dioxide from the eruption of Huaynaputina probably caused the Russian famine of 1601–1603.
A volcanic winter is thought to have taken place around 70,000 years ago after the supereruption of Lake Toba on Sumatra island in Indonesia.According to the Toba catastrophe theory to which some anthropologists and archeologists subscribe, it had global consequences, killing most humans then alive and creating a population bottleneck that affected the genetic inheritance of all humans today.
It has been suggested that volcanic activity caused or contributed to the End-Ordovician, Permian-Triassic, Late Devonian mass extinctions, and possibly others. The massive eruptive event which formed the Siberian Traps, one of the largest known volcanic events of the last 500 million years of Earth's geological history, continued for a million years and is considered to be the likely cause of the "Great Dying" about 250 million years ago, which is estimated to have killed 90% of species existing at the time.
The 1815 eruption of Mount Tambora created global climate anomalies that became known as the "Year Without a Summer" because of the effect on North American and European weather.Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in one of the worst famines of the 19th century.
The freezing winter of 1740–41, which led to widespread famine in northern Europe, may also owe its origins to a volcanic eruption.
Sulfate aerosols promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth's radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.
Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year.Volcanic eruptions may inject aerosols into the Earth's atmosphere. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.
Ash thrown into the air by eruptions can present a hazard to aircraft, especially jet aircraft where the 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. Dangerous encounters in 1982 after the eruption of Galunggung in Indonesia, and 1989 after the eruption of Mount Redoubt in Alaska raised awareness of this phenomenon. Nine Volcanic Ash Advisory Centers were established by the International Civil Aviation Organization to monitor ash clouds and advise pilots accordingly. The 2010 eruptions of Eyjafjallajökull caused major disruptions to air travel in Europe.
The Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core.However, the Moon does have many volcanic features such as maria (the darker patches seen on the moon), rilles and domes.
The planet Venus has a surface that is 90% basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago,from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank.
There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years,but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.
Jupiter's moon Io is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io. Europa, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system.
In 1989 the Voyager 2 spacecraft observed cryovolcanoes (ice volcanoes) on Triton, a moon of Neptune, and in 2005 the Cassini–Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn.The ejecta may be composed of water, liquid nitrogen, ammonia, dust, or methane compounds. Cassini–Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere. It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.
A 2010 study of the exoplanet COROT-7b, which was detected by transit in 2009, suggested that tidal heating from the host star very close to the planet and neighboring planets could generate intense volcanic activity similar to that found on Io.
This section needs expansion. You can help by adding to it.(October 2016)
Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. To the ancient Greeks, volcanoes' capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth's tears.One early idea counter to this was proposed by Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.
Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.
Volcanism is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface.
A stratovolcano, also known as a composite volcano, is a conical volcano built up by many layers (strata) of hardened lava, tephra, pumice and ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile with a summit crater and periodic intervals of explosive eruptions and effusive eruptions, although some have collapsed summit craters called calderas. The lava flowing from stratovolcanoes typically cools and hardens before spreading far, due to high viscosity. The magma forming this lava is often felsic, having high-to-intermediate levels of silica, with lesser amounts of less-viscous mafic magma. Extensive felsic lava flows are uncommon, but have travelled as far as 15 km (9.3 mi).
The Ring of Fire is a major area in the basin of the Pacific Ocean where many earthquakes and volcanic eruptions occur. In a large 40,000 km (25,000 mi) horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and plate movements. It has 452 volcanoes. The Ring of Fire is sometimes called the circum-Pacific belt.
A shield volcano is a type of volcano usually composed almost entirely of fluid lava flows. It is named for its low profile, resembling a warrior's shield lying on the ground. This is caused by the highly fluid lava erupted, which travels farther than lava erupted from a stratovolcano, and results in the steady accumulation of broad sheets of lava, building up the shield volcano's distinctive form. It's name mainly comes from it's shape.
The geology of the Lassen volcanic area presents a record of sedimentation and volcanic activity in the area in and around Lassen Volcanic National Park in Northern California, U.S. The park is located in the southernmost part of the Cascade Mountain Range in the Pacific Northwest region of the United States. Pacific Oceanic tectonic plates have plunged below the North American Plate in this part of North America for hundreds of millions of years. Heat from these subducting plates has fed scores of volcanoes in California, Oregon, Washington and British Columbia over at least the past 30 million years and is also responsible for activities in the Lassen volcanic area.
The Garibaldi Volcanic Belt is a northwest-southeast trending volcanic chain in the Pacific Ranges of the Coast Mountains that extends from Watts Point in the south to the Ha-Iltzuk Icefield in the north. This chain of volcanoes is located in southwestern British Columbia, Canada. It forms the northernmost segment of the Cascade Volcanic Arc, which includes Mount St. Helens and Mount Baker. Most volcanoes of the Garibaldi chain are dormant stratovolcanoes and subglacial volcanoes that have been eroded by glacial ice. Less common volcanic landforms include cinder cones, volcanic plugs, lava domes and calderas. These diverse formations were created by different styles of volcanic activity, including Peléan and Plinian eruptions.
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relatively gentle, low level eruption; it is so named because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high temperature at the vent. Very small amounts of volcanic ash are produced. This type of eruption occurs most often at hotspot volcanoes such as Kīlauea on Hawaii's big island and in Iceland, though it can occur near subduction zones and rift zones. Another example of Hawaiian eruptions occurred on the island of Surtsey in Iceland from 1964 to 1967, when molten lava flowed from the crater to the sea.
Strombolian eruptions are relatively mild blasts with a volcanic explosivity index of about 1 to 3. They are named for the Italian volcano Stromboli. Strombolian eruptions consist of ejection of incandescent cinder, lapilli, and lava bombs, to altitudes of tens to a few hundreds of metres. The eruptions are small to medium in volume, with sporadic violence.
Hoodoo Mountain is a potentially active flat-topped stratovolcano in the Stikine Country of northwestern British Columbia, Canada, located 74 km (46 mi) northeast of Wrangell, Alaska, on the north side of the lower Iskut River and 30 km (19 mi) east of its junction with the Stikine River. It is situated in the Boundary Ranges of the Coast Mountains and existed since the Late Pleistocene stage of the Pleistocene epoch, which began 130,000 years ago and ended 10,000 years ago.
Several types of volcanic eruptions—during which lava, tephra, and assorted gases are expelled from a volcanic vent or fissure—have been distinguished by volcanologists. These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series.
Volcanology of Canada includes lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, submarine volcanoes, calderas, diatremes, and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds. It has a very complex volcanological history spanning from the Precambrian eon at least 3.11 billion years ago when this part of the North American continent began to form.
A cinder cone or scoria cone is a steep conical hill of loose pyroclastic fragments, such as either volcanic clinkers, volcanic ash, or cinder that has been built around a volcanic vent. The pyroclastic fragments are formed by explosive eruptions or lava fountains from a single, typically cylindrical, vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as either cinders, clinkers, or scoria around the vent to form a cone that often is symmetrical; with slopes between 30–40°; and a nearly circular ground plan. Most cinder cones have a bowl-shaped crater at the summit.
The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere.
The Silverthrone Caldera is a potentially active caldera complex in southwestern British Columbia, Canada, located over 350 kilometres (220 mi) northwest of the city of Vancouver and about 50 kilometres (31 mi) west of Mount Waddington in the Pacific Ranges of the Coast Mountains. The caldera is one of the largest of the few calderas in western Canada, measuring about 30 kilometres (19 mi) long (north-south) and 20 kilometres (12 mi) wide (east-west). Mount Silverthrone, an eroded lava dome on the caldera's northern flank that is 2,864 metres (9,396 ft) high may be the highest volcano in Canada.
The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia, Canada, located approximately 130 km (81 mi) north of Kamloops. It is situated in the Cariboo Mountains of the Columbia Mountains and on the Quesnel and Shuswap Highlands. As a monogenetic volcanic field, it is a place with numerous small basaltic volcanoes and extensive lava flows.
The Mount Edziza volcanic complex is a large and potentially active north-south trending complex volcano in Stikine Country, northwestern British Columbia, Canada, located 38 kilometres (24 mi) southeast of the small community of Telegraph Creek. It occupies the southeastern portion of the Tahltan Highland, an upland area of plateau and lower mountain ranges, lying east of the Boundary Ranges and south of the Inklin River, which is the east fork of the Taku River. As a volcanic complex, it consists of many types of volcanoes, including shield volcanoes, calderas, lava domes, stratovolcanoes, and cinder cones.
The Mess Lake Lava Field is a volcanic field associated with the Mount Edziza volcanic complex of the Northern Cordilleran Volcanic Province in northwestern British Columbia, Canada. It lies northwest of the Spectrum Range on the Kitsu Plateau and consists of young basaltic lava flows and tephra. The source for the basaltic lava and tephra was three cinder cones, including Mess Lake Cone and The Ash Pit, which may be the youngest volcanic feature of the Mount Edziza volcanic complex.
The Volcano, also known as Lava Fork volcano, is a small cinder cone in the Boundary Ranges of the Coast Mountains in northwestern British Columbia, Canada. It is located approximately 60 km (40 mi) northwest of the small community of Stewart near the head of Lava Fork. With a summit elevation of 1,656 m (5,433 ft) and a topographic prominence of 311 m (1,020 ft), it rises above the surrounding rugged landscape on a remote mountain ridge that represents the northern flank of a glaciated U-shaped valley.
The volcanic history of the Northern Cordilleran Volcanic Province presents a record of volcanic activity in northwestern British Columbia, central Yukon and the U.S. state of easternmost Alaska. The volcanic activity lies in the northern part of the Western Cordillera of the Pacific Northwest region of North America. Extensional cracking of the North American Plate in this part of North America has existed for millions of years. Continuation of this continental rifting has fed scores of volcanoes throughout the Northern Cordilleran Volcanic Province over at least the past 20 million years and occasionally continued into geologically recent times.
There are more than 500 active volcanoes (those that have erupted at least once within recorded history) in the world
|Wikimedia Commons has media related to Volcanoes .|
|Wikivoyage has a travel guide for Volcanoes .|
| Library resources about |