1.
Mount Vesuvius
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Mount Vesuvius is a somma-stratovolcano located on the Gulf of Naples in Campania, Italy, about 9 km east of Naples and a short distance from the shore. It is one of several volcanoes which form the Campanian volcanic arc, Vesuvius consists of a large cone partially encircled by the steep rim of a summit caldera caused by the collapse of an earlier and originally much higher structure. Mount Vesuvius is best known for its eruption in AD79 that led to the burying and destruction of the Roman cities of Pompeii and Herculaneum, more than 1,000 people died in the eruption, but exact numbers are unknown. The only surviving account of the event consists of two letters by Pliny the Younger to the historian Tacitus. Vesuvius has erupted many times since and is the volcano on the European mainland to have erupted within the last hundred years. Vesuvius has a historic and literary tradition. An inscription from Capua to IOVI VESVVIO indicates that he was worshipped as a power of Jupiter and it was inhabited by bandits, the sons of the Earth, who were giants. With the assistance of the gods he pacified the region and went on, the facts behind the tradition, if any, remain unknown, as does whether Herculaneum was named after it. An epigram by the poet Martial in 88 AD suggests that both Venus, patroness of Pompeii, and Hercules were worshipped in the devastated by the eruption of 79. Mount Vesuvius was regarded by the Romans as being devoted to the hero, Vesuvius was a name of the volcano in frequent use by the authors of the late Roman Republic and the early Roman Empire. Its collateral forms were Vesaevus, Vesevus, Vesbius and Vesvius, writers in ancient Greek used Οὐεσούιον or Οὐεσούιος. Many scholars since then have offered an etymology, as peoples of varying ethnicity and language occupied Campania in the Roman Iron Age, the etymology depends to a large degree on the presumption of what language was spoken there at the time. Naples was settled by Greeks, as the name Nea-polis, New City, the Oscans, a native Italic people, lived in the countryside. The Latins also competed for the occupation of Campania, etruscan settlements were in the vicinity. Other peoples of unknown provenance are said to have been there at some time by various ancient authors. Some theories about its origin are, From Greek οὔ = not prefixed to a root from or related to the Greek word σβέννυμι = I quench, from Greek ἕω = I hurl and βίη violence, hurling violence, *vesbia, taking advantage of the collateral form. From an Indo-European root, *eus- < *ewes- < *wes-, shine sense the one who lightens, the Gran Cono was produced during the A. D.79 eruption. For this reason, the volcano is also called Somma-Vesuvius or Somma-Vesuvio, the caldera started forming during an eruption around 17,000 years ago and was enlarged by later paroxysmal eruptions, ending in the one of AD79
2.
Eruption of Mount Vesuvius in 79
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The 79 AD eruption of Mount Vesuvius was one of the most catastrophic volcanic eruptions in European history. Historians have learned about the eruption from the account of Pliny the Younger. It is the namesake for Vesuvian eruptions, several Roman settlements were obliterated and buried underneath massive pyroclastic surges and ashfall deposits, the most well known being Pompeii and Herculaneum. The remains of about 1,500 people have found at Pompeii and Herculaneum. The 79 AD eruption was preceded by a powerful earthquake seventeen years before on February 5,62 AD, which caused widespread destruction around the Bay of Naples, some of the damage had still not been repaired when the volcano erupted. Suetonius recorded that the emperor continued singing through the earthquake until he had finished his song, the Romans grew accustomed to minor earth tremors in the region, the writer Pliny the Younger wrote that they were not particularly alarming because they are frequent in Campania. Small earthquakes started taking place on 20 August 79, becoming more frequent over the four days. Reconstructions of the eruption and its effects vary considerably in the details but have the same overall features, the eruption lasted for two days. Mount Vesuvius violently erupted, spewing up a column from which ash and pumice began to fall. Rescues and escapes occurred during this time, at some time in the night or early the next day, August 25, pyroclastic flows in the close vicinity of the volcano began. Lights seen on the mountain were interpreted as fires, people as far away as Misenum fled for their lives. These were accompanied by additional light tremors and a tsunami in the Bay of Naples. By evening of the day, the eruption was over. Pliny the Younger wrote an account of the eruption, Broad sheets of flame were lighting up many parts of Vesuvius, their light, two pyroclastic surges engulfed Pompeii, burning and asphyxiating the stragglers who had remained behind. Oplontis and Herculaneum received the brunt of the surges and were buried in ash, pumice, lava fragments. In an article published in 2002, Sigurdsson and Casey elaborate on the evidence based on excavations. Subsequently, the cloud collapsed as the gases densified and lost their capability to support their solid contents, releasing it as a pyroclastic surge, the eruption alternated between Vesuvian and Peléan six times. Surges 4 and 5 are believed by the authors to have destroyed and buried Pompeii, surges are identified in the deposits by dune and cross-bedding formations, which are not produced by fallout
3.
Volcanic cone
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Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature, types of volcanic cones include stratocones, spatter cones, tuff cones, and cinder cones. Stratocones are large cone-shaped volcanoes made up of lava flows, explosively erupted pyroclastic rocks, unlike shield volcanoes, they are characterized by a steep profile and periodic, often alternating, explosive eruptions and effusive eruptions. Some have collapsed craters called calderas, the central core of a stratocone is commonly dominated by a central core of intrusive rocks that range from around 500 meters to over several kilometers in diameter. This central core is surrounded by generations of lava flows, many of which are brecciated. The typical stratocone is an andesitic to dacitic volcano that is associated with subduction zones and they are also known as either stratified volcano, composite cone, bedded volcano, cone of mixed type or Vesuvian-type volcano. A spatter cone is a low, steep-sided hill or mound that consists of welded lava fragments, called spatter, typically, spatter cones are about 3–5 meters high. In case of a fissure, lava fountaining will create broad embankments of spatter, called spatter ramparts. Spatter cones are circular and cone shaped, while spatter ramparts are linear wall-like features. Spatter cones and spatter ramparts are typically formed by lava fountaining associated with mafic, highly fluid lavas, as blobs of molten lava, spatter, are erupted into the air by a lava fountain, they can lack the time needed to cool completely before hitting the ground. Consequently, the spatter are not fully solid, like taffy, as they land, as a result, the spatter builds up a cone that is composed of spatter either agglutinated or welded to each other. They are characterized by rims that have a maximum relief of 100–800 meters above the crater floor. They typically have a rim to rim diameter of 300–5,000 meters, a tuff cone consists typically of thick-bedded pyroclastic flow and surge deposits created by eruption-fed density currents and bomb-scoria beds derived from fallout from its eruption column. The tuffs composing a tuff cone have commonly been altered, palagonitized, by either its interaction with groundwater or when it was deposited warm and wet. The pyroclastic deposits of tuff cones differ from the deposits of spatter cones by their lack or paucity of lava spatter, smaller grain-size. Typically, but not always, tuff cones lack associated lava flows and they are characterized by rims that have a low, broad topograhic profiles and gentle topographic slopes that are 25 degrees or less. The maximum thickness of the pyroclastic debris comprising the rim of a tuff ring is generally thin
4.
Volcano
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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. Earths volcanoes occur because its crust is broken into 17 major, therefore, on Earth, volcanoes are generally found where tectonic plates are diverging or converging. 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 boundary,3,000 km deep in the Earth. Volcanoes are usually not created where two plates slide past one another. Erupting volcanoes can pose hazards, not only in the immediate vicinity of the eruption. Historically, so-called volcanic winters have caused catastrophic famines, 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, 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. Most divergent plate boundaries are at the bottom of the oceans, therefore, most volcanic activity is submarine, black smokers are evidence of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the 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 temperature of the overlying mantle wedge. This magma tends to be very viscous due to its high content, so it often does not reach the surface. When it does reach the surface, a volcano is formed, typical examples of this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire. Because tectonic plates move across them, each volcano becomes dormant and is eventually re-formed as the plate advances over the postulated plume and this theory is currently under criticism, however. The most common perception of a volcano is of a mountain, spewing lava and poisonous gases from a crater at its summit, however. The features of volcanoes are more complicated and their structure. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have features such as massive plateaus
5.
Lava
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Lava is the molten rock expelled by a volcano during an eruption. The resulting rock after solidification and cooling is called lava. The molten rock is formed in the interior of planets, including Earth. The source of the heat melts the rock within the earth is geothermal energy. When first erupted from a vent, lava is a liquid usually at temperatures from 700 to 1,200 °C. A lava flow is an outpouring of lava, which is created during a non-explosive effusive eruption. When it has stopped moving, lava solidifies to form igneous rock, the term lava flow is commonly shortened to lava. Although lava can be up to 100,000 times more viscous than water, lava can flow great distances before cooling and solidifying because of its thixotropic, explosive eruptions produce a mixture of volcanic ash and other fragments called tephra, rather than lava flows. The word lava comes from Italian, and is derived from the Latin word labes which means a fall or slide. The first use in connection with extruded magma was apparently in an account written by Francesco Serao on the eruption of Vesuvius between May 14 and June 4,1737. Serao described a flow of lava as an analogy to the flow of water. The composition of almost all lava of the Earths crust is dominated by silicate minerals, mostly feldspars, olivine, pyroxenes, amphiboles, micas, igneous rocks, which form lava flows when erupted, can be classified into three chemical types, felsic, intermediate, and mafic. These classes are primarily chemical, however, the chemistry of lava also tends to correlate with the temperature, its viscosity. Felsic or silicic lavas such as rhyolite and dacite typically form lava spines, most silicic lava flows are extremely viscous, and typically fragment as they extrude, producing blocky autobreccias. Felsic magmas can erupt at temperatures as low as 650 to 750 °C, unusually hot rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in the Snake River Plain of the northwestern United States. Intermediate or andesitic lavas are lower in aluminium and silica, and usually somewhat richer in magnesium, intermediate lavas form andesite domes and block lavas, and may occur on steep composite volcanoes, such as in the Andes. Poorer in aluminium and silica than felsic lavas, and also commonly hotter, greater temperatures tend to destroy polymerized bonds within the magma, promoting more fluid behaviour and also a greater tendency to form phenocrysts. Higher iron and magnesium tends to manifest as a darker groundmass, mafic or basaltic lavas are typified by their high ferromagnesian content, and generally erupt at temperatures in excess of 950 °C
6.
Tephra
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Tephra is fragmental material produced by a volcanic eruption regardless of composition, fragment size or emplacement mechanism. Volcanologists also refer to airborne fragments as pyroclasts, once clasts have fallen to the ground they remain as tephra unless hot enough to fuse together into pyroclastic rock or tuff. Tephra mixed in with precipitation can also be acidic and cause acid rain, the use of tephra layers, which bear their own unique chemistry and character, as temporal marker horizons in archaeological and geological sites is known as tephrochronology. The word tephra and pyroclast both derive from Greek, τέφρα tephra means ash, while the word pyroclast is derived from the Greek πῦρ, meaning fire, media related to Tephra at Wikimedia Commons How Volcanoes Work Volcanic Materials Identification
7.
Pumice
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Pumice, called pumicite in its powdered or dust form, is a volcanic rock that consists of highly vesicular rough textured volcanic glass, which may or may not contain crystals. Scoria is another vesicular volcanic rock that differs from pumice in having larger vesicles, thicker walls and being dark colored. Pumice is created when super-heated, highly pressurized rock is violently ejected from a volcano, the unusual foamy configuration of pumice happens because of simultaneous rapid cooling and rapid depressurization. The depressurization creates bubbles by lowering the solubility of gases that are dissolved in the lava, the simultaneous cooling and depressurization freezes the bubbles in a matrix. Eruptions under water are cooled and the large volume of pumice created can be a shipping hazard for cargo ships. Pumice is composed of highly microvesicular glass pyroclastic with very thin and it is commonly, but not exclusively of silicic or felsic to intermediate in composition, but basaltic and other compositions are known. Pumice is commonly pale in color, ranging from white, cream, blue or grey and it forms when volcanic gases exsolving from viscous magma form bubbles that remain within the viscous magma as it cools to glass. Pumice is a product of explosive eruptions and commonly forms zones in upper parts of silicic lavas. Pumice has a porosity of 90%, and initially floats on water. Scoria differs from pumice in being denser, with larger vesicles and thicker vesicle walls, it sinks rapidly. The difference is the result of the viscosity of the magma that forms scoria. When larger amounts of gas are present, the result is a variety of pumice known as pumicite. Pumice is considered a glass because it has no crystal structure, pumice varies in density according to the thickness of the solid material between the bubbles, many samples float in water. After the explosion of Krakatoa, rafts of pumice drifted through the Pacific Ocean for up to 20 years, in fact, pumice rafts disperse and support several marine species. In 1979,1984 and 2006, underwater volcanic eruptions near Tonga created large pumice rafts, there are two main forms of vesicles. Most pumice contains tubular microvesicles that can impart a silky or fibrous fabric, the elongation of the microvesicles occurs due to ductile elongation in the volcanic conduit or, in the case of pumiceous lavas, during flow. The other form of vesicles are subspherical to spherical and result from high pressure during eruption. Pumice is widely used to make concrete or insulative low-density cinder blocks
8.
Volcanic ash
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Volcanic ash consists of fragments of pulverized rock, minerals and volcanic glass, created during volcanic eruptions and measuring less than 2 mm in diameter. The term volcanic ash is often loosely used to refer to all explosive eruption products. Volcanic ash is formed during volcanic eruptions when dissolved gases in magma expand. The force of the escaping gas shatters the magma and propels it into the atmosphere where it solidifies into fragments of volcanic rock and glass. Ash is also produced when magma comes into contact with water during phreatomagmatic eruptions, once in the air, ash is transported by wind up to thousands of kilometers away. Volcanic ash is formed during volcanic eruptions, phreatomagmatic eruptions. Explosive eruptions occur when magma decompresses as it rises, allowing dissolved volatiles to exsolve into gas bubbles, as more bubbles nucleate a foam is produced, which decreases the density of the magma, accelerating it up the conduit. Fragmentation occurs when bubbles occupy ~70-80 vol% of the erupting mixture, when fragmentation occurs, violently expanding bubbles tear the magma apart into fragments which are ejected into the atmosphere where they solidify into ash particles. Fragmentation is an efficient process of ash formation and is capable of generating very fine ash even without the addition of water. Volcanic ash is produced during phreatomagmatic eruptions. During these eruptions fragmentation occurs when magma comes into contact with bodies of water groundwater, as the magma, which is significantly hotter than the boiling point of water, comes into contact with water an insulating vapor film forms. Eventually this vapor film will collapse leading to direct coupling of the cold water and this increases the heat transfer which leads to the rapid expansion of water and fragmentation of the magma into small particles which are subsequently ejected from the volcanic vent. Fragmentation causes an increase in area between magma and water creating a feedback mechanism, leading to further fragmentation and production of fine ash particles. Pyroclastic density currents can also produce ash particles and these are typically produced by lava dome collapse or collapse of the eruption column. Within pyroclastic density currents particle abrasion occurs as particles interact with each resulting in a reduction in grain size. In addition, ash can be produced during secondary fragmentation of pumice fragments and these processes produce large quantities of very fine grained ash which is removed from pyroclastic density currents in co-ignimbrite ash plumes. Physical and chemical characteristics of volcanic ash are primarily controlled by the style of volcanic eruption, another parameter controlling the amount of ash produced is the duration of the eruption, the longer the eruption is sustained, the more ash will be produced. The types of minerals present in volcanic ash are dependent on the chemistry of the magma from which it erupted, low energy eruptions of basalt produce a characteristically dark coloured ash containing ~45 - 55% silica that is generally rich in iron and magnesium
9.
Shield volcano
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A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their low profile, resembling a warriors shield lying on the ground and this is caused by the highly fluid lava they erupt, which travels farther than lava erupted from stratovolcanoes. This results in the accumulation of broad sheets of lava. The shape of shield volcanoes is due to the low viscosity of their mafic lava, Shield volcanoes are built by effusive eruptions, which flow out in all directions to create a shield like that of a warrior. Shield volcano itself is taken from the German term Schildvulkan, examples of pyroclastic shields include Billy Mitchell volcano in Papua New Guinea and the Purico Complex in Chile, an example of a felsic shield is the Big Obsidian Flow in Oregon. Active shield volcanoes experience near-continuous eruptive activity over long periods of time. Mount Everest, by comparison, is 8,848 m in height, the research has not yet been confirmed. Shield volcanoes feature a slope that gradually steepens with elevation before eventually flattening near the summit. In height they are typically about one twentieth their width, although the general form of a typical shield volcano varies little worldwide regional differences exist in their size and morphological characteristics. 4° and an average volume of 1.7 km3. Rift zones are a prevalent feature on shield volcanoes that is rare on other volcanic types, the large, decentralized shape of Hawaiian volcanoes as compared to their smaller, symmetrical Icelandic cousins can be attributed to rift eruptions. Fissure venting is common in Hawaiʻi, most Hawaiian eruptions begin with a wall of fire along a major fissure line before centralizing to a small number of points. These eruptions, the calmest of volcanic events, are characterized by the emission of highly fluid basaltic lavas with low gaseous content. These lavas travel a far greater distance than those of other types before solidifying, forming extremely wide. Low volumes of such lavas layered over long periods of time are what slowly constructs the characteristically low, central-vent eruptions, meanwhile, often take the form of large lava fountains, which can reach heights of hundreds of meters or more. If eruptive rates are enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived, Puʻu ʻŌʻō, a cone of Kilauea, has been erupting continuously since 1983. These lava flows can be anywhere between 2 and 20 m thick, pāhoehoe flows, in contrast, move in more conventional sheets, or by the advancement of lava toes in snaking lava columns. Increasing viscosity on the part of the lava or shear stress on the part of local topography can morph a pāhoehoe flow into an aa one, although most shield volcanoes are by volume almost entirely Hawaiian and basaltic in origin, they are rarely exclusively so
10.
Explosive eruption
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An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example, such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, Explosive eruptions can send rocks, dust, gas and pyroclastic material up to 20 km into the atmosphere at rate of up to 100,000 tonnes per second, traveling at several hundred meters per second. This cloud will collapse, creating a pyroclastic flow of hot volcanic matter. An explosive eruption always begins with some form of blockage in the crater of a volcano that prevents the release of trapped in highly viscous andesitic or rhyolitic magma. The high viscosity of these forms of magma prevents the release of trapped gases, when this type of magma flows towards the surface pressure builds, eventually causing the blockage to be blasted out in an explosive eruption. The pressure from the magma and gases are released through the weakest point in the cone, however, in the case of the eruption of Mount St. Helens, pressure was released through the side of the volcano, rather than the crater. The size and duration of the column depends on the volume of magma being released, the eruption column of ash is supported by pressure from the gases being released, and as the gases are depleted, pressure falls and the eruption column begins to collapse. When the column collapses in on itself, ash and rock fall back down to the ground and these flows can travel at up to 80 km per hour, and reach temperatures of 200° to 700° Celsius. The high temperatures can cause combustion of any flammable materials in its path, including wood, vegetation, when snow and ice melt as a part of an eruption, large amounts of water mixed in with the flow can create lahars. The risk of lahars is particularly high on volcanoes such as Mount Rainier near Seattle and Tacoma, the eruption of supervolcanoes is the rarest of volcanic eruptions but also the most destructive. The timescale between these eruptions is generally marked by hundreds or thousands of years and this type of eruption generally causes destruction on a continental scale, and can also result in the lowering of temperatures worldwide. Effusive eruption Volcanic explosivity index Recent Developments in Explosive Volcanism
11.
Effusive eruption
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An effusive eruption is a type of volcanic eruption in which lava steadily flows out of a volcano onto the ground. Effusive eruption differs from explosive eruption, wherein magma is violently fragmented when expelled from a volcano, the shape of the lava flows created by effusive eruptions is governed by the type of lava, rate and duration of eruption, and slope of the surrounding areas. A volcanic eruption is effusive when low-viscosity magma, usually basaltic in composition, is released from the Earths crust, in an effusive eruption, gas escapes the magma as it erupts and forms lava that flows downhill continuously. This type of flow can build shield volcanoes, which are numerous in Hawaii. Eruptions of basaltic magma often transition between effusive and explosive eruption patterns, the behavior of these eruptions is largely dependent on the permeability of the magma and the magma ascent rate. For an effusive eruption to occur, magma must be enough to allow the expulsion of gas bubbles contained within it. If the magma is not above a certain permeability threshold, it cannot degas, additionally, at a certain threshold, fragmentation within the magma can cause an explosive eruption. This threshold is governed by the Reynolds Number, a number in fluid dynamics that is directly proportional to fluid velocity. Eruptions will be if the magma has a low ascent velocity. At higher magma ascent rates, the fragmentation within the magma passes a threshold, silicic magma also exhibits this transition between effusive and explosive eruptions, but the fragmentation mechanism differs. The 1912 Novarupta eruption and the 2003 Stromboli eruption both exhibited a transition between explosive and effusive eruption patterns, effusive basalt lava flows cool to either of two forms, ʻaʻā or pāhoehoe. Andesite lava typically forms blocky lava flows, dacite lava flows often form steep-sided mounds, called lava domes, due to their greater viscosity
12.
Caldera
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A caldera is a large cauldron-like depression that forms following the evacuation of a magma chamber/reservoir. When large volumes of magma are erupted over a time period. The ground surface then collapses downward into the emptied magma chamber. Although sometimes described as a crater, the feature is actually a type of sinkhole, as it is formed through subsidence, only seven known caldera-forming collapses have occurred since the start of the 20th century, most recently at Bárðarbunga volcano in Iceland. The word comes from Spanish caldera, and this from Latin caldaria, in some texts the English term cauldron is also used. If enough magma is ejected, the chamber is unable to support the weight of the volcanic edifice above it. A roughly circular fracture, the fault, develops around the edge of the chamber. Ring fractures serve as feeders for fault intrusions which are known as ring dykes. Secondary volcanic vents may form above the ring fracture, as the magma chamber empties, the center of the volcano within the ring fracture begins to collapse. The collapse may occur as the result of a cataclysmic eruption. The total area that collapses may be hundreds or thousands of square kilometers, some calderas are known to host rich ore deposits. One of the worlds best-preserved mineralized calderas is the Sturgeon Lake Caldera in northwestern Ontario, Canada, if the magma is rich in silica, the caldera is often filled in with ignimbrite, tuff, rhyolite, and other igneous rocks. Silica-rich magma has a high viscosity, and therefore does not flow easily like basalt, as a result, gases tend to become trapped at high pressure within the magma. Further lava flows may be erupted, if volcanic activity continues, the center of the caldera may be uplifted in the form of a resurgent dome such as is seen at Cerro Galán, Lake Toba, Yellowstone, etc. by subsequent intrusion of magma. A silicic or rhyolitic caldera may erupt hundreds or even thousands of kilometers of material in a single event. Even small caldera-forming eruptions, such as Krakatoa in 1883 or Mount Pinatubo in 1991, may result in significant local destruction, large calderas may have even greater effects. When Yellowstone Caldera last erupted some 650,000 years ago, it released about 1,000 km3 of material, by comparison, when Mount St. Helens erupted in 1980, it released ~1.2 km3 of ejecta. The ecological effects of the eruption of a large caldera can be seen in the record of the Lake Toba eruption in Indonesia, more recently several geneticists, including Lynn Jorde and Henry Harpending have proposed that the human species was reduced to approximately five to ten thousand people
13.
Felsic
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In geology, felsic refers to igneous rocks that are relatively rich in elements that form feldspar and quartz. It is contrasted with mafic rocks, which are richer in magnesium. It refers to those rocks rich in minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium. They are usually light in color and have specific gravities less than 3, the most common felsic rock is granite. Common felsic minerals include quartz, muscovite, orthoclase, and the sodium-rich plagioclase feldspars, in terms of chemistry, felsic minerals and rocks are at the other end of the elemental spectrum from the mafic minerals and rocks. In modern usage, the acid rock, although sometimes used as a synonym, refers to a high-silica-content volcanic rock. The term was used broadly in older geologic literature. It is considered archaic now, as the acidic and basic rock were based on an incorrect idea, dating from the 19th century. The term felsic combines the words feldspar and silica, in order for a rock to be classified as felsic, it generally needs to contain more than 75% felsic minerals, namely quartz, orthoclase and plagioclase. Rocks with greater than 90% felsic minerals can also be called leucocratic, the chemical name of a felsic rock is given according to the TAS classification of Le Maitre. However, this applies to volcanic rocks. If the rock is analyzed and found to be felsic but is metamorphic and has no definite volcanic protolith, there are examples known of highly sheared granites which can be mistaken for rhyolites. For phaneritic felsic rocks, the QAPF diagram should be used, the rock texture thus determines the basic name of a felsic rock. QAPF diagram List of minerals List of rock types Le Maitre, igneous Rocks, A Classification and Glossary of Terms 2nd edition, Cambridge
14.
Rhyolite
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Rhyolite is an igneous, volcanic rock, of felsic composition. It may have any texture from glassy to aphanitic to porphyritic, the mineral assemblage is usually quartz, sanidine and plagioclase. Biotite and hornblende are common accessory minerals and it is the extrusive equivalent to granite. Rhyolite can be considered as the equivalent to the plutonic granite rock. Due to their content of silica and low iron and magnesium contents, rhyolite melts are highly polymerized. They also occur as breccias or in volcanic plugs and dikes, rhyolites that cool too quickly to grow crystals form a natural glass or vitrophyre, also called obsidian. Slower cooling forms microscopic crystals in the lava and results in such as flow foliations, spherulitic, nodular. Some rhyolite is highly vesicular pumice, many eruptions of rhyolite are highly explosive and the deposits may consist of fallout tephra/tuff or of ignimbrites. Eruptions of rhyolite are relatively rare compared to eruptions of less felsic lavas, etsch Valley Vulcanite Group near Bolzano and the surrounding area Gréixer rhyolitic complex at Moixeró range Vosges Iceland, all active and extinct central volcanoes, e. g. g. Wichita Mountains within the Southern Oklahoma Aulacogen St, in North American pre-historic times, rhyolite was quarried extensively in eastern Pennsylvania in the United States. Among the leading quarries was the Carbaugh Run Rhyolite Quarry Site in Adams County, comendite List of rock types Pantellerite Thunderegg University of North Dakota description of rhyolite Information from rocks-rock. com
15.
Dacite
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Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite, the word dacite comes from Dacia, a province of the Roman Empire which lay between the Danube River and Carpathian Mountains where the rock was first described. Dacite consists mostly of feldspar with biotite, hornblende. It has quartz as rounded, corroded phenocrysts, or as an element of the ground-mass, the relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram. The TAS classification, based on silica and alkali contents, puts dacite in the O3 sector, the plagioclase ranges from oligoclase to andesine and labradorite. Sanidine occurs, although in small proportions, in some dacites, the groundmass of these rocks is composed of plagioclase and quartz. In the hand specimen many of the hornblende and biotite dacites are grey or pale brown and yellow rocks with white feldspars, other dacites, especially pyroxene bearing dacites, are darker colored. In thin section, dacites may have an aphanitic to porphyritic texture, porphyritic dacites contain blocky highly zoned plagioclase phenocrysts and/or rounded corroded quartz phenocrysts. Subhedral hornblende and elongated biotite grains are present, sanidine phenocrysts and augite are found in some samples. Dacite usually forms as a rock such as a dike or sill. Examples of this type of dacite outcrop are found in northwestern Montana, nevertheless, because of the moderate silica content, dacitic magma is quite viscous and therefore prone to explosive eruption. A notorious example of this is Mount St. Helens in which dacite domes formed from previous eruptions, pyroclastic flows may also be of dacitic composition as is the case with the Fish Canyon Tuff of La Garita Caldera. Dacitic magma is formed by the subduction of oceanic crust under a thick felsic continental plate. Oceanic crust is hydrothermally altered causing addition of quartz and sodium, as the young, hot oceanic plate is subducted under continental crust, the subducted slab partially melts and interacts with the upper mantle through convection and dehydration reactions. The process of subduction creates metamorphism in the subducting slab, when this slab reaches the mantle and initiates the dehydration reactions, minerals such as talc, serpentine, mica and amphiboles break down generating a more sodic melt. The magma then continues to migrate upwards causing differentiation and becomes even more sodic and silicic as it rises, once at the cold surface, the sodium rich magma crystallizes plagioclase, quartz and hornblende. Accessory minerals like pyroxenes provide insight to the history of the magma, the formation of dacite provides a great deal of information about the connection between oceanic crust and continental crust. It provides a model for the generation of felsic, buoyant, perennial rock from a mafic, dense, the process by which dacite forms has been used to explain the generation of continental crust during the Archean eon
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Andesite
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For the extinct cephalopod genus, see Andesites. Andesite is an igneous, volcanic rock, of intermediate composition. In a general sense, it is the type between basalt and dacite, and ranges from 57 to 63% silicon dioxide as illustrated in TAS diagrams. The mineral assemblage is dominated by plagioclase plus pyroxene or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals, alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other rocks are illustrated in QAPF diagrams. Classification of andesites may be refined according to the most abundant phenocryst, example, hornblende-phyric andesite, if hornblende is the principal accessory mineral. Andesite can be considered as the equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs, the average composition of the continental crust is andesitic. Along with basalts they are a component of the Martian crust. The name andesite is derived from the Andes mountain range, magmatism in island arc regions comes from the interplay of the subducting plate and the mantle wedge, the wedge-shaped region between the subducting and overriding plates. During subduction, the oceanic crust is submitted to increasing pressure and temperature. Hydrous minerals such as amphibole, zeolites, chlorite etc. dehydrate as they change to more stable, anhydrous forms, releasing water, fluxing water into the wedge lowers the solidus of the mantle material and causes partial melting. Due to the density of the partially molten material, it rises through the wedge until it reaches the lower boundary of the overriding plate. Basalt thus formed can contribute to the formation of andesite through fractional crystallization, partial melting of crust, or magma mixing, andesite is typically formed at convergent plate margins but may occur in other tectonic settings. Intermediate volcanic rocks are created via several processes, Fractional crystallization of a mafic parent magma and this removal can take place in a variety of ways, but most commonly this occurs by crystal settling. The first minerals to crystallize and be removed from a parent are olivines and amphiboles. These mafic minerals settle out of the magma, forming mafic cumulates, there is geophysical evidence from several arcs that large layers of mafic cumulates lie at the base of the crust
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Igneous rock
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Igneous rock, or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or lava, the magma can be derived from partial melts of existing rocks in either a planets mantle or crust. Typically, the melting is caused by one or more of three processes, an increase in temperature, a decrease in pressure, or a change in composition, solidification into rock occurs either below the surface as intrusive rocks or on the surface as extrusive rocks. Igneous rock may form with crystallization to form granular, crystalline rocks, Igneous and metamorphic rocks make up 90–95% of the top 16 km of the Earths crust by volume. Igneous rocks form about 15% of the Earths current land surface, most of the Earths oceanic crust is made of igneous rock. In terms of modes of occurrence, igneous rocks can be either intrusive or extrusive, the mineral grains in such rocks can generally be identified with the naked eye. Intrusive rocks can also be classified according to the shape and size of the intrusive body, typical intrusive formations are batholiths, stocks, laccoliths, sills and dikes. When the magma solidifies within the earths crust, it cools slowly forming coarse textured rocks, such as granite, gabbro, the central cores of major mountain ranges consist of intrusive igneous rocks, usually granite. When exposed by erosion, these cores may occupy huge areas of the Earths surface, intrusive igneous rocks that form at depth within the crust are termed plutonic rocks and are usually coarse-grained. Intrusive igneous rocks that form near the surface are termed subvolcanic or hypabyssal rocks, hypabyssal rocks are less common than plutonic or volcanic rocks and often form dikes, sills, laccoliths, lopoliths, or phacoliths. Extrusive igneous rocks, also known as rocks, are formed at the crusts surface as a result of the partial melting of rocks within the mantle. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks and they are formed by the cooling of molten magma on the earths surface. The magma, which is brought to the surface through fissures or volcanic eruptions, hence such rocks are smooth, crystalline and fine-grained. Basalt is an extrusive igneous rock and forms lava flows, lava sheets. Some kinds of basalt solidify to form long polygonal columns, the Giants Causeway in Antrim, Northern Ireland is an example. The molten rock, with or without suspended crystals and gas bubbles, is called magma and it rises because it is less dense than the rock from which it was created. When magma reaches the surface from beneath water or air, it is called lava, eruptions of volcanoes into air are termed subaerial, whereas those occurring underneath the ocean are termed submarine. Black smokers and mid-ocean ridge basalt are examples of volcanic activity
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Krakatoa
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Krakatoa, or Krakatau, is a volcanic island situated in the Sunda Strait between the islands of Java and Sumatra in the Indonesian province of Lampung. The explosion is considered to be the loudest sound heard in modern history. The shock waves from the explosion were recorded on barographs worldwide for days afterward, in 1927 a new island, Anak Krakatau, or Child of Krakatoa, emerged from the caldera formed in 1883 and is the current location of eruptive activity. The most notable eruptions of Krakatoa culminated in a series of explosions over August 26–27,1883. The 1883 eruption ejected approximately 25 km3 of rock, the cataclysmic explosion was heard 4,800 km away in Alice Springs, as well as on the island of Rodrigues near Mauritius,4,653 km to the west. According to the records of the Dutch East Indies colony,165 villages and towns were destroyed near Krakatoa. At least 36,417 people died, and many thousands were injured. The eruption destroyed two-thirds of the island of Krakatoa, eruptions in the area since 1927 have built a new island at the same location, named Anak Krakatau. Periodic eruptions have continued since, with recent eruptions in 2009,2010,2011, as of late 2011, this island has a radius of roughly 2 kilometres, and a high point of about 324 metres above sea level, growing 5 metres each year. About two dozen variants have found, including Crackatouw, Cracatoa, and Krakatao. The first known appearance of the spelling Krakatau was by Wouter Schouten, the origin of the Indonesian name Krakatau is uncertain. The Smithsonian Institutions Global Volcanism Program cites the Indonesian name, Krakatau, as the correct name, while Krakatoa is more common in the English-speaking world, the Indonesian Krakatau tends to be favored by others, including geologists. Indonesia has over 130 active volcanoes, the most of any nation and they make up the axis of the Indonesian island arc system, which was produced by northeastward subduction of the Indo-Australian Plate. A majority of volcanoes lie along Indonesias two largest islands, Java and Sumatra. These two islands are separated by the Sunda Strait, which is located at a bend in the axis of the island arc. At some point in prehistory, an earlier caldera-forming eruption had occurred, leaving as remnants Verlaten, Lang, Poolsche Hoed, later, at least two more cones formed and eventually joined with Rakata, forming the main island of Krakatoa. At the time of the 1883 eruption, the Krakatoa group comprised Lang, Verlaten, and Krakatoa itself, there were also the tree-covered islet near Lang and several small rocky islets or banks between Krakatoa and Verlaten. There were three volcanic cones on Krakatoa island, Rakata, to the south, Danan, near the center, and Perboewatan, to the north
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1883 eruption of Krakatoa
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The 1883 eruption was one of the deadliest and most destructive volcanic events in recorded history. At least 36,417 deaths are attributed to the eruption, significant additional effects were also felt around the world in the days and weeks after the volcanos destruction. In the years before the 1883 eruption, seismic activity around the Krakatoa volcano was intense, beginning May 20,1883, steam venting began to occur regularly from Perboewatan, the northernmost of the islands three cones. Eruptions of ash reached an altitude of 6 km and explosions could be heard in New Batavia 160 km away. Activity died down by the end of May, and there was no recorded activity for several weeks. Eruptions at Krakatoa started again around June 16, with loud explosions, on June 24, a prevailing east wind cleared the cloud, and two ash columns could be seen issuing from Krakatoa. The seat of the eruption is believed to have been a new vent or vents that formed between Perboewatan and Danan, the violence of the ongoing eruptions caused tides in the vicinity to be unusually high, and ships at anchor had to be moored with chains. Earthquakes were felt at Anyer, Banten, and ships began to report large pumice masses to the west in the Indian Ocean, on August 11, a Dutch topographical engineer, Captain H. J. G. Ferzenaar, investigated the Krakatoa islands. He noted three major ash columns, which obscured the western part of the island, and steam plumes from at least eleven other vents, mostly between Danan and Rakata. When he landed, he noted an ash layer about 0.5 m thick, and he advised against any further landings. The next day, a passing to the north reported a new vent only a few meters above sea level. By August 25, the Krakatoa eruptions intensified, at about 13,00 on August 26, the volcano went into its paroxysmal phase. By 14,00, a cloud of ash could be seen 27 km high. At this point, the eruption was virtually continuous and explosions could be heard every ten minutes or so, ships within 20 km of the volcano reported heavy ash fall, with pieces of hot pumice up to 10 cm in diameter landing on their decks. Between 18,00 and 19,00 hours, a tsunami hit the shores of Java and Sumatra. On August 27, four enormous explosions occurred, at 5,30 am, the first explosion was at Perboewatan, triggering a tsunami heading straight to Telok Betong, now known as Bandar Lampung. At 6,44 am, Krakatoa exploded again at Danan, the third explosion has been reported as the loudest sound heard in historic times. The loudness of the blast heard 160 km from the volcano has been calculated to have been 180 dB, each explosion was accompanied by tsunamis estimated to have been over 30 meters high in places
20.
Mount St. Helens
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Mount St. Helens or Louwala-Clough is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 96 miles south of Seattle, Washington, and 50 miles northeast of Portland, Mount St. Helens takes its English name from the British diplomat Lord St Helens, a friend of explorer George Vancouver who made a survey of the area in the late 18th century. The volcano is located in the Cascade Range and is part of the Cascade Volcanic Arc and this volcano is well known for its ash explosions and pyroclastic flows. Mount St. Helens is most notorious for its major 1980 eruption, fifty-seven people were killed,250 homes,47 bridges,15 miles of railways, and 185 miles of highway were destroyed. The debris avalanche was up to 0.7 cubic miles in volume, the Mount St. Helens National Volcanic Monument was created to preserve the volcano and allow for its aftermath to be scientifically studied. As with most other volcanoes in the Cascade Range, Mount St. Helens is a large eruptive cone consisting of lava rock interlayered with ash, pumice, the mountain includes layers of basalt and andesite through which several domes of dacite lava have erupted. The largest of the domes formed the previous summit. Both were destroyed in the 1980 eruption, Mount St. Helens is 34 miles west of Mount Adams, in the western part of the Cascade Range. These sister and brother volcanic mountains are approximately 50 miles from Mount Rainier, Mount Hood, the nearest major volcanic peak in Oregon, is 60 miles southeast of Mount St. Helens. Mount St. Helens is geologically young compared with the other major Cascade volcanoes and it formed only within the past 40,000 years, and the pre-1980 summit cone began rising about 2,200 years ago. The volcano is considered the most active in the Cascades within the Holocene epoch, prior to the 1980 eruption, Mount St. Helens was the fifth-highest peak in Washington. It stood out prominently from surrounding hills because of the symmetry and extensive snow and ice cover of the summit cone. The peak rose more than 5,000 feet above its base, the mountain is 6 miles across at its base, which is at an elevation of 4,400 feet on the northeastern side and 4,000 feet elsewhere. At the pre-eruption tree line, the width of the cone was 4 miles. Streams that originate on the volcano enter three main systems, the Toutle River on the north and northwest, the Kalama River on the west. The streams are fed by abundant rain and snow, the average annual rainfall is 140 inches, and the snow pack on the mountains upper slopes can reach 16 feet. The Lewis River is impounded by three dams for power generation. The southern and eastern sides of the drain into an upstream impoundment, the Swift Reservoir
21.
Mount Pinatubo
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Its eruptive history was unknown to most before the pre-eruption volcanic activities of 1991, just before June. Pinatubo was heavily eroded, inconspicuous and obscured from view and it was covered with dense forests which supported a population of several thousand indigenous Aetas. The volcanos Ultra Plinian eruption on June 15,1991 produced the second-largest terrestrial eruption of the 20th century after the 1912 eruption of Novarupta in the Alaska Peninsula. Complicating the eruption was the arrival of Typhoon Yunya, bringing a lethal mix of ash and rain to towns. Predictions at the onset of the eruption led to the evacuation of tens of thousands of people from the surrounding areas. Surrounding areas were damaged by pyroclastic surges, ash falls. This caused extensive destruction to infrastructure and changed river systems for years after the eruption, the effects of the eruption were felt worldwide. It ejected roughly 10,000,000,000 tonnes or 10 km3 of magma and it injected more particulate into the stratosphere than any eruption since Krakatoa in 1883. Over the following months, the aerosols formed a layer of sulfuric acid haze. Global temperatures dropped by about 0.5 °C in the years 1991–93, the volcano is 87 km northwest of Manila, the capital of the Philippines. Near Mount Pinatubo, the United States maintained two military bases in the region. The U. S. Naval Base Subic Bay was 37 km south of Pinatubo, the volcano is near to about 6 million people. It is part of a chain of volcanoes lie along the western side of the edge of the island of Luzon called the Zambales Mountains. Pinatubo belongs to the Cabusilan sub-range of the Zambales Mountains, which consists of Mt. Cuadrado, Mt. Negron, Mt. Mataba and they are subduction volcanoes, formed by the Eurasian Plate sliding under the Philippine Mobile Belt along the Manila Trench to the west. Mount Pinatubo and the volcanoes on this volcanic belt arise due to magmatic occlusion from this subduction plate boundary. Pinatubo is flanked on the west by the Zambales Ophiolite Complex, the Tarlac Formation north, east and southeast of Pinatubo consists of marine, nonmarine and volcanoclastic sediments formed in the late Miocene and Pliocene. He recognized two life histories of the mountain, which he classified as ancestral and modern Pinatubo, activity of Ancestral Pinatubo seems to have begun about 1.1 million years ago and probably ended tens of thousands of years or more before the birth of Modern Pinatubo. Much of the land around the present volcano consists of remnants of ancestral Pinatubo
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Solar System
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The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly. Of those objects that orbit the Sun directly, the largest eight are the planets, with the remainder being significantly smaller objects, such as dwarf planets, of the objects that orbit the Sun indirectly, the moons, two are larger than the smallest planet, Mercury. The Solar System formed 4.6 billion years ago from the collapse of a giant interstellar molecular cloud. The vast majority of the mass is in the Sun. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being composed of rock. The four outer planets are giant planets, being more massive than the terrestrials. All planets have almost circular orbits that lie within a flat disc called the ecliptic. The Solar System also contains smaller objects, the asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptunes orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets, identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. In addition to two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds. Six of the planets, at least four of the dwarf planets, each of the outer planets is encircled by planetary rings of dust and other small objects. The solar wind, a stream of charged particles flowing outwards from the Sun, the heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium, it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, the Solar System is located in the Orion Arm,26,000 light-years from the center of the Milky Way. For most of history, humanity did not recognize or understand the concept of the Solar System, the invention of the telescope led to the discovery of further planets and moons. The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99. 86% of the known mass. The Suns four largest orbiting bodies, the giant planets, account for 99% of the mass, with Jupiter. The remaining objects of the Solar System together comprise less than 0. 002% of the Solar Systems total mass, most large objects in orbit around the Sun lie near the plane of Earths orbit, known as the ecliptic
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Subduction
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Subduction is a geological process that takes place at convergent boundaries of tectonic plates where one plate moves under another and is forced or sinks due to gravity into the mantle. Regions where this occurs are known as subduction zones. Rates of subduction are typically in centimeters per year, with the rate of convergence being approximately two to eight centimeters per year along most plate boundaries. Plates include both oceanic crust and continental crust, stable subduction zones involve the oceanic lithosphere of one plate sliding beneath the continental or oceanic lithosphere of another plate due to the higher density of the oceanic lithosphere. That is, the lithosphere is always oceanic while the overriding lithosphere may or may not be oceanic. Subduction zones are sites that have a rate of volcanism, earthquakes. Subduction zones are sites of convective downwelling of Earths lithosphere, subduction zones exist at convergent plate boundaries where one plate of oceanic lithosphere converges with another plate. The descending slab, the plate, is over-ridden by the leading edge of the other plate. The slab sinks at an angle of approximately twenty-five to forty-five degrees to Earths surface and this sinking is driven by the temperature difference between the subducting oceanic lithosphere and the surrounding mantle asthenosphere, as the colder oceanic lithosphere is, on average, denser. At a depth of approximately 80–120 kilometers, the basalt of the oceanic crust is converted to a rock called eclogite. At that point, the density of the oceanic crust increases and provides additional negative buoyancy and it is at subduction zones that Earths lithosphere, oceanic crust, sedimentary layers and some trapped water are recycled into the deep mantle. Earth is so far the only planet where subduction is known to occur, subduction is the driving force behind plate tectonics, and without it, plate tectonics could not occur. Subduction zones dive down into the mantle beneath 55,000 kilometers of convergent plate margins, subduction zones burrow deeply but are imperfectly camouflaged, and geophysics and geochemistry can be used to study them. Not surprisingly, the shallowest portions of subduction zones are known best, subduction zones are strongly asymmetric for the first several hundred kilometers of their descent. They start to go down at oceanic trenches and their descents are marked by inclined zones of earthquakes that dip away from the trench beneath the volcanoes and extend down to the 660-kilometer discontinuity. Subduction zones are defined by the array of earthquakes known as the Wadati–Benioff zone after the two scientists who first identified this distinctive aspect. Subduction zone earthquakes occur at greater depths than elsewhere on Earth, such deep earthquakes may be driven by deep phase transformations, thermal runaway, the subducting basalt and sediment are normally rich in hydrous minerals and clays. Additionally, large quantities of water are introduced into cracks and fractures created as the slab bends downward
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Oceanic crust
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Oceanic crust is the uppermost layer of the oceanic portion of a tectonic plate. The crust overlies the solidified and uppermost layer of the mantle, the crust and the solid mantle layer together constitute oceanic lithosphere. Oceanic crust is the result of erupted mantle material originating from below the plate, cooled and in most instances and this occurs mostly at mid-ocean ridges, but also at scattered hotspots, and also in rare but powerful occurrences known as flood basalt eruptions. It is primarily composed of rocks, or sima, which is rich in iron. Although a complete section of oceanic crust has not yet been drilled, Oceanic crust is significantly simpler than continental crust and generally can be divided in three layers. Layer 1 is on an average 0.4 km thick and it consists of unconsolidated or semiconsolidated sediments, usually thin or even not present near the mid-ocean ridges but thickens farther away from the ridge. Layer 3 is formed by slow cooling of magma beneath the surface and consists of coarse grained gabbros and it constitutes over two-thirds of oceanic crust volume with almost 5 km thickness. The most voluminous volcanic rocks of the floor are the mid-oceanic ridge basalts. These rocks have low concentrations of large ion lithophile elements, light rare earth elements, volatile elements, there can be found basalts enriched with incompatible elements, but they are rare and associated with mid-ocean ridge hot spots such as surroundings of Galapagos Islands, the Azores and Iceland. Oceanic crust is continuously being created at mid-ocean ridges, as plates diverge at these ridges, magma rises into the upper mantle and crust. As it moves away from the ridge, the lithosphere becomes cooler and denser, the youngest oceanic lithosphere is at the oceanic ridges, and it gets progressively older away from the ridges. As the mantle rises it cools and melts, as the pressure decreases, the amount of melt produced depends only on the temperature of the mantle as it rises. Hence most oceanic crust is the same thickness, an example of this is the Gakkel Ridge under the Arctic Ocean. Thicker than average crust is found above plumes as the mantle is hotter and hence it crosses the solidus and melts at a depth, creating more melt. An example of this is Iceland which has crust of thickness ~20 km, the oceanic lithosphere subducts at what are known as convergent boundaries. These boundaries can exist between oceanic lithosphere on one plate and oceanic lithosphere on another, or between oceanic lithosphere on one plate and continental lithosphere on another, in the second situation, the oceanic lithosphere always subducts because the continental lithosphere is less dense. The subduction process consumes older oceanic lithosphere, so oceanic crust is more than 200 million years old. The process of super-continent formation and destruction via repeated cycles of creation and destruction of oceanic crust is known as the Wilson cycle, the oldest large scale oceanic crust is in the west Pacific and north-west Atlantic - both are about up to 180-200 million years old
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Continental crust
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The continental crust is the layer of igneous, sedimentary, and metamorphic rocks that forms the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial because its composition is more felsic compared to the oceanic crust. The continental crust consists of layers, with a bulk composition that is intermediate to felsic. The average density of continental crust is about 2.7 g/cm3, less dense than the material that makes up the mantle. Continental crust is less dense than oceanic crust, whose density is about 2.9 g/cm3. At 25 to 70 km, continental crust is thicker than oceanic crust. About 40% of Earths surface is occupied by continental crust. It makes up about 70% of the volume of Earths crust, because the surface of continental crust mainly lies above sea level, its existence allowed land life to evolve from marine life. There is little evidence of continental crust prior to 3.5 Ga, all continental crust ultimately derives from the fractional differentiation of oceanic crust over many eons. This process has been and continues today primarily as a result of the associated with subduction. In contrast to the persistence of continental crust, the size, shape, different tracts rift apart, collide and recoalesce as part of a grand supercontinent cycle. There are currently about 7 billion cubic kilometers of continental crust, the relative permanence of continental crust contrasts with the short life of oceanic crust. Because continental crust is less dense oceanic crust, when active margins of the two meet in subduction zones, the oceanic crust is typically subducted back into the mantle. Continental crust is rarely subducted.01 Ga, whereas the oldest oceanic crust is from the Jurassic, Continental crust and the rock layers that lie on and within it are thus the best archive of Earths history. The height of mountain ranges is usually related to the thickness of crust and this results from the isostasy associated with orogeny. The crust is thickened by the compressive forces related to subduction or continental collision, the buoyancy of the crust forces it upwards, the forces of the collisional stress balanced by gravity and erosion. This forms a keel or mountain root beneath the mountain range, the thinnest continental crust is found in rift zones, where the crust is thinned by detachment faulting and eventually severed, replaced by oceanic crust. The edges of continental fragments formed this way are termed passive margins, igneous rock may also be underplated to the underside of the crust, i. e. adding to the crust by forming a layer immediately beneath it
26.
Cascade Range
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The Cascade Range or Cascades is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades, the small part of the range in British Columbia is referred to as the Canadian Cascades or, locally, as the Cascade Mountains. The highest peak in the range is Mount Rainier in Washington at 14,411 feet, the Cascades are part of the Pacific Oceans Ring of Fire, the ring of volcanoes and associated mountains around the Pacific Ocean. All of the eruptions in the contiguous United States over the last 200 years have been from Cascade volcanoes, the two most recent were Lassen Peak from 1914 to 1921 and a major eruption of Mount St. Helens in 1980. Minor eruptions of Mount St. Helens have also occurred since, the Cascade Range is a part of the American Cordillera, a nearly continuous chain of mountain ranges that form the western backbone of North America, Central America, and South America. The Cascades extend northward from Lassen Peak in northern California to the confluence of the Nicola, the Fraser River separates the Cascades from the Coast Mountains. The highest volcanoes of the Cascades, known as the High Cascades, dominate their surroundings and they often have a visual height of one mile or more. The highest peaks, such as the 14, 411-foot Mount Rainier, Mount Baker in Washington recorded a world-record single-season snowfall in the winter of 1998–99 with 1,140 inches. Prior to that year, Mount Rainier held the record for snow accumulation at Paradise in 1978. It is not uncommon for some places in the Cascades to have over 500 inches of snow accumulation, such as at Lake Helen. Most of the High Cascades are therefore white with snow and ice year-round, annual rainfall is as low as 9 inches on the eastern foothills due to a rain shadow effect. Beyond the eastern foothills is a plateau that was largely created 17 to 14 million years ago by the many flows of the Columbia River Basalt Group. Together, these sequences of fluid volcanic rock form the 200, 000-square-mile Columbia Plateau in eastern Washington, Oregon, the Columbia River Gorge is the only major break of the range in the United States. When the Cascades began to rise 7 million years ago in the Pliocene, as the range grew, erosion from the Columbia River was able to keep pace, creating the gorge and major pass seen today. The gorge also exposes uplifted and warped layers of basalt from the plateau, in early 1792, British navigator George Vancouver explored Puget Sound and gave English names to the high mountains he saw. Mount Baker was named for Vancouvers third lieutenant, Joseph Baker, although the first European to see it was Manuel Quimper, Mount Rainier was named after Admiral Peter Rainier. Later in 1792, Vancouver had his lieutenant William Robert Broughton explore the lower Columbia River and he named Mount Hood after Lord Samuel Hood, an admiral of the Royal Navy. Mount St. Helens was sighted by Vancouver in May 1792 and it was named for Alleyne FitzHerbert, 1st Baron St Helens, a British diplomat
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Andes
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The Andes or Andean Mountains are the longest continental mountain range in the world. They are a range of highlands along the western edge of South America. This range is about 7,000 km long, about 200 to 700 km wide, the Andes extend from north to south through seven South American countries, Venezuela, Colombia, Ecuador, Peru, Bolivia, Argentina and Chile. Along their length, the Andes are split into several ranges, the Andes are the location of several high plateaus – some of which host major cities, such as Quito, Bogotá, Arequipa, Medellín, Sucre, Mérida and La Paz. The Altiplano plateau is the worlds second-highest after the Tibetan plateau and these ranges are in turn grouped into three major divisions based on climate, the Tropical Andes, the Dry Andes, and the Wet Andes. The Andes are the worlds highest mountain range outside of Asia, the highest mountain outside Asia, Mount Aconcagua, rises to an elevation of about 6,961 m above sea level. The peak of Chimborazo in the Ecuadorean Andes is farther from the Earths center than any other location on the Earths surface, the worlds highest volcanoes are in the Andes, including Ojos del Salado on the Chile-Argentina border, which rises to 6,893 m. The etymology of the word Andes has been debated, the majority consensus is that it derives from the Quechua word anti, which means east as in Antisuyu, one of the four regions of the Inca Empire. In the northern part of the Andes, the isolated Sierra Nevada de Santa Marta range is considered to be part of the Andes. The term cordillera comes from the Spanish word cordel, meaning rope, the Andes range is about 200 km wide throughout its length, except in the Bolivian flexure where it is about 640 kilometres wide. The Andes are the result of plate tectonics processes, caused by the subduction of oceanic crust beneath the South American plate. The main cause of the rise of the Andes is the compression of the rim of the South American Plate due to the subduction of the Nazca Plate. In the south, the Andes share a boundary with the former Patagonia Terrane. To the west, the Andes end at the Pacific Ocean, from a geographical approach, the Andes are considered to have their western boundaries marked by the appearance of coastal lowlands and a less rugged topography. The Andes Mountains also contain large quantities of iron ore located in mountains within the range. The Andean orogen has a series of bends or oroclines, the Bolivian Orocline is a seaward concave bending in the coast of South America and the Andes Mountains at about 18° S. At this point the orientation of the Andes turns from Northwest in Peru to South in Chile, the Andean segment north and south of the orocline have been rotated 15° to 20° counter clockwise and clockwise respectively. The Bolivian Orocline area overlaps with the area of maximum width of the Altiplano Plateau, the specific point at 18° S where the coastline bends is known as the Arica Elbow
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Campanian volcanic arc
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The Campanian volcanic arc is a volcanic arc that consists of a number of active, dormant, and extinct volcanoes in the Campania region of Italy. The Campanian volcanic arc centers on the bay of Naples and includes, Mount Vesuvius, Campi Flegrei, a huge, ancient caldera containing the western area of Naples. Mount Epomeo,20 kilometres west of Naples on the island of Ischia, palinuro, Vavilev, Marsili, and Magnaghi, undersea extinct or dormant volcanoes south of Vesuvius. The last three were discovered in the 1950s and bear the names of the geologists who discovered them. At present, there is concern about the state of dormancy of Marsili. Satellite cones of recent origin have been detected on Marsili, volcanology of Italy Milia A. et al. Volcanism in the Campania Plain, Vesuvius, Campi Flegrei and Ignimbrites
29.
Island arc
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An island arc is a type of archipelago, often composed of a chain of volcanoes, with arc-shaped alignment, situated parallel and close to a boundary between two converging tectonic plates. Most of these island arcs are formed as one oceanic plate subducts another one and. For example, large parts of the Andes/Central American/Canadian mountain chain may be known as a volcanic arc, on the other hand, the Aegean or Hellenic arc in the Mediterranean area, composed of numerous islands such as Crete, is an island arc, but is not volcanic. Parallel to it is the South Aegean Volcanic Arc, which is the island arc of the same tectonic system. There is some debate about the usefulness of the distinction between island arcs and volcanic arcs, the term volcanic island arc is merely a sub-classification of island arc. Island arcs are tectonically created arc-shaped mountain belts that are partly below sea level, essentially, they represent a specific geographic-topographic situation in which a mountain belt is partly submerged in ocean. Many of these are composed of volcanoes, and can thus be classified as volcanic island arcs. This process, called flux melting, generates low-density calc-alkaline magma that rises to intrude. The resulting volcano chain has the shape of an arc parallel to the convergent plate boundary, on the subducting side of the island arc is a deep and narrow oceanic trench, which is the trace at the Earth’s surface of the boundary between the downgoing and overriding plates. This trench is created by the pull of the relatively dense subducting plate pulling the leading edge of the plate downward. Multiple earthquakes occur along this boundary with the seismic hypocenters located at increasing depth under the island arc. Ocean basins that are being reduced by subduction are called remnant oceans as they will slowly be shrunken out of existence and this process has happened repeatedly in the geological history of the Earth. Insular Islands Intermontane Islands Back-arc basin High island Volcanic arc
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Japan
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Japan is a sovereign island nation in Eastern Asia. Located in the Pacific Ocean, it lies off the eastern coast of the Asia Mainland and stretches from the Sea of Okhotsk in the north to the East China Sea, the kanji that make up Japans name mean sun origin. 日 can be read as ni and means sun while 本 can be read as hon, or pon, Japan is often referred to by the famous epithet Land of the Rising Sun in reference to its Japanese name. Japan is an archipelago consisting of about 6,852 islands. The four largest are Honshu, Hokkaido, Kyushu and Shikoku, the country is divided into 47 prefectures in eight regions. Hokkaido being the northernmost prefecture and Okinawa being the southernmost one, the population of 127 million is the worlds tenth largest. Japanese people make up 98. 5% of Japans total population, approximately 9.1 million people live in the city of Tokyo, the capital of Japan. Archaeological research indicates that Japan was inhabited as early as the Upper Paleolithic period, the first written mention of Japan is in Chinese history texts from the 1st century AD. Influence from other regions, mainly China, followed by periods of isolation, from the 12th century until 1868, Japan was ruled by successive feudal military shoguns who ruled in the name of the Emperor. Japan entered into a period of isolation in the early 17th century. The Second Sino-Japanese War of 1937 expanded into part of World War II in 1941, which came to an end in 1945 following the bombings of Hiroshima and Nagasaki. Japan is a member of the UN, the OECD, the G7, the G8, the country has the worlds third-largest economy by nominal GDP and the worlds fourth-largest economy by purchasing power parity. It is also the worlds fourth-largest exporter and fourth-largest importer, although Japan has officially renounced its right to declare war, it maintains a modern military with the worlds eighth-largest military budget, used for self-defense and peacekeeping roles. Japan is a country with a very high standard of living. Its population enjoys the highest life expectancy and the third lowest infant mortality rate in the world, in ancient China, Japan was called Wo 倭. It was mentioned in the third century Chinese historical text Records of the Three Kingdoms in the section for the Wei kingdom, Wa became disliked because it has the connotation of the character 矮, meaning dwarf. The 倭 kanji has been replaced with the homophone Wa, meaning harmony, the Japanese word for Japan is 日本, which is pronounced Nippon or Nihon and literally means the origin of the sun. The earliest record of the name Nihon appears in the Chinese historical records of the Tang dynasty, at the start of the seventh century, a delegation from Japan introduced their country as Nihon
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Philippines
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The Philippines, officially the Republic of the Philippines, is a sovereign island country in Southeast Asia situated in the western Pacific Ocean. It consists of about 7,641 islands that are categorized broadly under three main geographical divisions from north to south, Luzon, Visayas, and Mindanao, the capital city of the Philippines is Manila and the most populous city is Quezon City, both part of Metro Manila. The Philippines has an area of 300,000 square kilometers, and it is the eighth-most populated country in Asia and the 12th most populated country in the world. As of 2013, approximately 10 million additional Filipinos lived overseas, multiple ethnicities and cultures are found throughout the islands. In prehistoric times, Negritos were some of the archipelagos earliest inhabitants and they were followed by successive waves of Austronesian peoples. Exchanges with Chinese, Malay, Indian, and Islamic nations occurred, then, various competing maritime states were established under the rule of Datus, Rajahs, Sultans or Lakans. The arrival of Ferdinand Magellan in Homonhon, Eastern Samar in 1521 marked the beginning of Hispanic colonization, in 1543, Spanish explorer Ruy López de Villalobos named the archipelago Las Islas Filipinas in honor of Philip II of Spain. With the arrival of Miguel López de Legazpi from Mexico City, in 1565, the Philippines became part of the Spanish Empire for more than 300 years. This resulted in Roman Catholicism becoming the dominant religion, during this time, Manila became the western hub of the trans-Pacific trade connecting Asia with Acapulco in the Americas using Manila galleons. Aside from the period of Japanese occupation, the United States retained sovereignty over the islands until after World War II, since then, the Philippines has often had a tumultuous experience with democracy, which included the overthrow of a dictatorship by a non-violent revolution. It is a member of the United Nations, World Trade Organization, Association of Southeast Asian Nations, the Asia-Pacific Economic Cooperation forum. It also hosts the headquarters of the Asian Development Bank, the Philippines was named in honor of King Philip II of Spain. Spanish explorer Ruy López de Villalobos, during his expedition in 1542, named the islands of Leyte, eventually the name Las Islas Filipinas would be used to cover all the islands of the archipelago. Before that became commonplace, other such as Islas del Poniente. The official name of the Philippines has changed several times in the course of its history, during the Philippine Revolution, the Malolos Congress proclaimed the establishment of the República Filipina or the Philippine Republic. From the 1898 Treaty of Paris, the name Philippines began to appear, since the end of World War II, the official name of the country has been the Republic of the Philippines. The metatarsal of the Callao Man, reliably dated by uranium-series dating to 67,000 years ago is the oldest human remnant found in the archipelago to date and this distinction previously belonged to the Tabon Man of Palawan, carbon-dated to around 26,500 years ago. Negritos were also among the archipelagos earliest inhabitants, but their first settlement in the Philippines has not been reliably dated, there are several opposing theories regarding the origins of ancient Filipinos
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Aleutian Islands
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The Aleutian Islands are a chain of 14 large volcanic islands and 55 smaller ones belonging to both the United States and Russia. Crossing longitude 180°, at which point east and west longitude end, the westernmost U. S. island in real terms, however, is Attu Island, west of which runs the International Date Line. The islands, with their 57 volcanoes, are in the part of the Pacific Ring of Fire. Physiographically, they are a section of the larger Pacific Border province. These Islands are most known for the battles and skirmishes occurred there during the Aleutian Islands Campaign of World War II. It was one of two attacks on the United States during that war. The largest islands in the Aleutians are Attu, and Unalaska, Umnak, and Unimak in the Fox Islands. The largest of those is Unimak Island, with an area of 1,571.41 mi², followed by Unalaska Island, the axis of the archipelago near the mainland of Alaska has a southwest trend, but near 179° its direction changes to the northwest. This change of direction corresponds to a curve in the line of fissures that have contributed their products to the building of the islands. Such curved chains are repeated about the Pacific Ocean in the Kuril Islands, the Japanese chain, and in the Philippines. All these island arcs are at the edge of the Pacific Plate and experience much seismic activity, but are still habitable, the general elevation is greatest in the eastern islands and least in the western. The island chain is a continuation of the Aleutian Range on the mainland. The coasts are rocky and surf-worn, and the approaches are exceedingly dangerous and these volcanic islands reach heights of 6,200 feet. Makushin Volcano located on Unalaska Island, is not quite visible from within the town of Unalaska, though the steam rising from its cone is visible on a clear day. Residents of Unalaska need only to one of the smaller hills in the area, such as Pyramid Peak or Mt. Newhall. The volcanic Bogoslof and Fire Islands, which rose from the sea in 1796 and 1883 respectively, in 1906 a new volcanic cone rose between the islets of Bogoslof and Grewingk, near Unalaska, followed by another in 1907. These cones were demolished by an explosive eruption on September 1,1907. Newly found information in 2017, the volcanic cone erupted sending ash, the Aleutians seen from space The climate of the islands is oceanic, with moderate and fairly uniform temperatures and heavy rainfall
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Basalt
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Basalt is a common extrusive igneous rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of a planet or moon. Flood basalt describes the formation in a series of basalt flows. By definition, basalt is an igneous rock with generally 45-55% silica and less than 10% feldspathoid by volume. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains, the average density is 3.0 gm/cm3. Basalt is defined by its content and texture, and physical descriptions without mineralogical context may be unreliable in some circumstances. Basalt is usually grey to black in colour, but rapidly weathers to brown or rust-red due to oxidation of its mafic minerals into hematite, although usually characterized as dark, basaltic rocks exhibit a wide range of shading due to regional geochemical processes. Due to weathering or high concentrations of plagioclase, some basalts can be quite light-coloured and these phenocrysts usually are of olivine or a calcium-rich plagioclase, which have the highest melting temperatures of the typical minerals that can crystallize from the melt. Basalt with a texture is called vesicular basalt, when the bulk of the rock is mostly solid. Gabbro is often marketed commercially as black granite and these ultramafic volcanic rocks, with silica contents below 45% are usually classified as komatiites. Agricola applied basalt to the black rock of the Schloßberg at Stolpen. Tholeiitic basalt is relatively rich in silica and poor in sodium, included in this category are most basalts of the ocean floor, most large oceanic islands, and continental flood basalts such as the Columbia River Plateau. Basalt rocks are in some cases classified after their content in High-Ti and Low-Ti varieties. High-Ti and Low-Ti basalts have been distinguished in the Paraná and Etendeka traps and it has greater than 17% alumina and is intermediate in composition between tholeiite and alkali basalt, the relatively alumina-rich composition is based on rocks without phenocrysts of plagioclase. Alkali basalt is relatively poor in silica and rich in sodium and it is silica-undersaturated and may contain feldspathoids, alkali feldspar and phlogopite. Boninite is a form of basalt that is erupted generally in back-arc basins. Ocean island basalt Lunar basalt On Earth, most basalt magmas have formed by melting of the mantle. Basalt commonly erupts on Io, the third largest moon of Jupiter, and has formed on the Moon, Mars, Venus. The crustal portions of oceanic tectonic plates are composed predominantly of basalt, produced from upwelling mantle below, the mineralogy of basalt is characterized by a preponderance of calcic plagioclase feldspar and pyroxene
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Mantle (geology)
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The mantle is a layer inside a terrestrial planet and some other rocky planetary bodies. For a mantle to form, the body must be large enough to have undergone the process of planetary differentiation by density. The mantle surrounds the planetary core, the mantle is surrounded by the crust. The terrestrial planets, the Moon, two of Jupiters moons and the asteroid Vesta each have a made of silicate rock. Interpretation of spacecraft data suggests that at least two moons of Jupiter, as well as Titan and Triton each have a mantle made of ice or other solid volatile substances. The interior of Earth, similar to the terrestrial planets, is divided into layers of different composition. The mantle is a layer between the crust and the outer core, Earths mantle is a silicate rocky shell with an average thickness of 2,886 kilometres. The mantle makes up about 84% of Earths volume and it is predominantly solid but in geological time it behaves as a very viscous fluid. The mantle encloses the hot core rich in iron and nickel, past episodes of melting and volcanism at the shallower levels of the mantle have produced a thin crust of crystallized melt products near the surface. A thin crust, the part of the lithosphere, surrounds the mantle and is about 5 to 75 km thick. In some places under the ocean the mantle is exposed on the surface of Earth. The mantle is divided into sections which are based upon results from seismology and these layers are the following, the upper mantle, the transition zone, the lower mantle, and anomalous core–mantle boundary with a variable thickness. The uppermost mantle plus overlying crust are relatively rigid and form the lithosphere, below the lithosphere the upper mantle becomes notably more plastic. In some regions below the lithosphere, the shear velocity is reduced. Inge Lehmann discovered a seismic discontinuity at about 220 km depth, although this discontinuity has been found in other studies, the transition zone is an area of great complexity, it physically separates the upper and lower mantle. Very little is known about the lower mantle apart from that it appears to be relatively seismically homogeneous, the D layer at the core–mantle boundary separates the mantle from the core. A principal source of the heat that drives plate tectonics is the decay of uranium, thorium. The mantle differs substantially from the crust in its properties as the direct consequence of the difference in composition
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Asthenosphere
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The asthenosphere is the highly viscous, mechanically weak and ductilely deforming region of the upper mantle of the Earth. It lies below the lithosphere, at depths between approximately 80 and 200 km below the surface, the Lithosphere-Asthenosphere boundary is usually referred to as LAB. The asthenosphere is generally solid, although some of its regions could be melted, the lower boundary of the asthenosphere is not well defined. The thickness of the asthenosphere depends mainly on the temperature, in some regions the asthenosphere could extend as deep as 700 km. It is considered the region of mid-ocean ridge basalt. The asthenosphere is a part of the mantle just below the lithosphere that is involved in plate tectonic movement. The lithosphere-asthenosphere boundary is taken at the 1300 °C isotherm, above which the mantle behaves in a rigid fashion. Seismic waves pass relatively slowly through the asthenosphere compared to the lithospheric mantle, thus it has been called the low-velocity zone. This decreasing in seismic waves velocity from lithosphere to asthenosphere could be caused by the presence of a small percentage of melt in the asthenosphere. The lower boundary of the LVZ lies at a depth of 180–220 km, in the old oceanic mantle the transition from the lithosphere to the asthenosphere, the so-called lithosphere-asthenosphere boundary is shallow with a sharp and large velocity drop. At the mid-ocean ridges the LAB rises to within a few kilometers of the ocean floor, the upper part of the asthenosphere is believed to be the zone upon which the great rigid and brittle lithospheric plates of the Earths crust move about. In this way, it flows like a current, radiating heat outward from the Earths interior. Above the asthenosphere, at the rate of deformation, rock behaves elastically and, being brittle, can break. The rigid lithosphere is thought to float or move about on the slowly flowing asthenosphere, an Introduction to the Solar System. San Diego State University, The Earths internal heat energy and interior structure
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Melting point
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The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phase exist in equilibrium, the melting point of a substance depends on pressure and is usually specified at standard pressure. When considered as the temperature of the change from liquid to solid. Because of the ability of some substances to supercool, the point is not considered as a characteristic property of a substance. For most substances, melting and freezing points are approximately equal, for example, the melting point and freezing point of mercury is 234.32 kelvins. However, certain substances possess differing solid-liquid transition temperatures, for example, agar melts at 85 °C and solidifies from 31 °C to 40 °C, such direction dependence is known as hysteresis. The melting point of ice at 1 atmosphere of pressure is close to 0 °C. In the presence of nucleating substances the freezing point of water is the same as the melting point, the chemical element with the highest melting point is tungsten, at 3687 K, this property makes tungsten excellent for use as filaments in light bulbs. Many laboratory techniques exist for the determination of melting points, a Kofler bench is a metal strip with a temperature gradient. Any substance can be placed on a section of the strip revealing its thermal behaviour at the temperature at that point, differential scanning calorimetry gives information on melting point together with its enthalpy of fusion. A basic melting point apparatus for the analysis of crystalline solids consists of an oil bath with a transparent window, the several grains of a solid are placed in a thin glass tube and partially immersed in the oil bath. The oil bath is heated and with the aid of the melting of the individual crystals at a certain temperature can be observed. In large/small devices, the sample is placed in a heating block, the measurement can also be made continuously with an operating process. For instance, oil refineries measure the point of diesel fuel online, meaning that the sample is taken from the process. This allows for more frequent measurements as the sample does not have to be manually collected, for refractory materials the extremely high melting point may be determined by heating the material in a black body furnace and measuring the black-body temperature with an optical pyrometer. For the highest melting materials, this may require extrapolation by several hundred degrees, the spectral radiance from an incandescent body is known to be a function of its temperature. An optical pyrometer matches the radiance of a body under study to the radiance of a source that has been previously calibrated as a function of temperature, in this way, the measurement of the absolute magnitude of the intensity of radiation is unnecessary. However, known temperatures must be used to determine the calibration of the pyrometer, for temperatures above the calibration range of the source, an extrapolation technique must be employed
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Lithosphere
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A lithosphere is the rigid, outermost shell of a terrestrial-type planet or natural satellite that is defined by its rigid mechanical properties. On Earth, it is composed of the crust and the portion of the mantle that behaves elastically on time scales of thousands of years or greater. The outermost shell of a planet, the crust, is defined on the basis of its chemistry. Earths lithosphere includes the crust and the uppermost mantle, which constitute the hard, the lithosphere is subdivided into tectonic plates. The uppermost part of the lithosphere that chemically reacts to the atmosphere, hydrosphere and biosphere through the forming process is called the pedosphere. The lithosphere is underlain by the asthenosphere which is the weaker, hotter, the study of past and current formations of landscapes is called geomorphology. The concept of the lithosphere as Earth’s strong outer layer was described by A. E. H, love in his 1911 monograph Some problems of Geodynamics and further developed by Joseph Barrell, who wrote a series of papers about the concept and introduced the term lithosphere. The concept was based on the presence of significant gravity anomalies over continental crust and these ideas were expanded by Reginald Aldworth Daly in 1940 with his seminal work Strength and Structure of the Earth and have been broadly accepted by geologists and geophysicists. The temperature at which olivine begins to deform viscously is often used to set this isotherm because olivine is generally the weakest mineral in the upper mantle, the mantle part of the lithosphere consists largely of peridotite. The crust is distinguished from the mantle by the change in chemical composition that takes place at the Moho discontinuity. Oceanic lithosphere consists mainly of mafic crust and ultramafic mantle and is denser than continental lithosphere, oceanic lithosphere thickens as it ages and moves away from the mid-ocean ridge. This thickening occurs by conductive cooling, which converts hot asthenosphere into lithospheric mantle and causes the oceanic lithosphere to become increasingly thick, the thickness of the mantle part of the oceanic lithosphere can be approximated as a thermal boundary layer that thickens as the square root of time. H ∼2 κ t Here, h is the thickness of the mantle lithosphere, κ is the thermal diffusivity for silicate rocks. The age is equal to L/V, where L is the distance from the spreading centre of mid-oceanic ridge. Oceanic lithosphere is less dense than asthenosphere for a few tens of millions of years and this is because the chemically differentiated oceanic crust is lighter than asthenosphere, but thermal contraction of the mantle lithosphere makes it more dense than the asthenosphere. New oceanic lithosphere is constantly being produced at mid-ocean ridges and is recycled back to the mantle at subduction zones, geoscientists can directly study the nature of the subcontinental mantle by examining mantle xenoliths brought up in kimberlite, lamproite, and other volcanic pipes. The histories of these xenoliths have been investigated by many methods, such studies have confirmed that mantle lithospheres below some cratons have persisted for periods in excess of 3 billion years, despite the mantle flow that accompanies plate tectonics. Cryosphere Geosphere Kola Superdeep Borehole Plate tectonics Solid Earth Chernicoff, Stanley, Whitney, earths Crust, Lithosphere and Asthenosphere Crust and Lithosphere
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Crust (geology)
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In geology, the crust is the outermost solid shell of a rocky planet or natural satellite, which is chemically distinct from the underlying mantle. The crust of the Earth is composed of a variety of igneous, metamorphic. The crust is underlain by the mantle, the upper part of the mantle is composed mostly of peridotite, a rock denser than rocks common in the overlying crust. The boundary between the crust and mantle is conventionally placed at the Mohorovičić discontinuity, a boundary defined by a contrast in seismic velocity, the crust occupies less than 1% of Earths volume. The crust of the Earth is of two types, oceanic and continental. The oceanic crust is 5 km to 10 km thick and is composed primarily of basalt, diabase, the continental crust is typically from 30 km to 50 km thick and is mostly composed of slightly less dense rocks than those of the oceanic crust. Some of these less dense rocks, such as granite, are common in the continental crust, both the continental and oceanic crust float on the mantle. Because the continental crust is thicker, it both to greater elevations and greater depth than the oceanic crust. The slightly lower density of continental rock compared to basaltic oceanic rock contributes to the higher relative elevation of the top of the continental crust. As the top of the continental crust reaches elevations higher than that of the oceanic, the temperature of the crust increases with depth, reaching values typically in the range from about 200 °C to 400 °C at the boundary with the underlying mantle. The crust and underlying relatively rigid uppermost mantle make up the lithosphere, because of convection in the underlying plastic upper mantle and asthenosphere, the lithosphere is broken into tectonic plates that move. The temperature increases by as much as 30 °C for every kilometer locally in the part of the crust. Earth has probably always had some form of basaltic crust, in contrast, the bulk of the continental crust is much older. The oldest continental crustal rocks on Earth have ages in the range from about 3.7 to 4, some zircon with age as great as 4.3 billion years has been found in the Narryer Gneiss Terrane. The average age of the current Earths continental crust has been estimated to be about 2.0 billion years, most crustal rocks formed before 2.5 billion years ago are located in cratons. Such old continental crust and the underlying mantle asthenosphere are less dense than elsewhere in Earth, formation of new continental crust is linked to periods of intense orogeny, these periods coincide with the formation of the supercontinents such as Rodinia, Pangaea and Gondwana. The continental crust has a composition similar to that of andesite. The most abundant minerals in Earths continental crust are feldspars, which make up about 41% of the crust by weight, followed by quartz at 12%, Continental crust is enriched in incompatible elements compared to the basaltic ocean crust and much enriched compared to the underlying mantle
39.
Magma chamber
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A magma chamber is a large underground pool of liquid rock found beneath the surface of the Earth. The molten rock in such a chamber is under pressure, and given enough time. If it finds a way to the surface, then the result will be a volcanic eruption, magma chambers are hard to detect, and most of the known ones are therefore close to the surface of the Earth, commonly between 1 km and 10 km under the surface. In geological terms, this is close to the surface, although in human terms. Magma rises through cracks from beneath and across the crust because it is less dense than the surrounding rock, when the magma cannot find a path upwards it pools into a magma chamber. Magma chambers are built up incrementally, by successive horizontal or vertical magma injections. Influx of new magma causes reaction of pre-existing crystals and the pressure in the chamber to increase, upon cooling, new mineral phases saturate and the rock type changes, typically forming gabbro, diorite, tonalite and granite or gabbro, diorite, syenite and granite. If magma resides in a chamber for a period, then it can become stratified with lower density components rising to the top. Rocks accumulate in layers, forming a layered intrusion, additionally, the removal of the lower melting point components will tend to make the magma more viscous. If the magma is not vented to the surface in an eruption, it will slowly cool. Often, a volcano may have a deep magma chamber many kilometers down, as a volcano erupts, emptying the magma chamber, the surrounding rock will collapse into it. If a large amount of magma is erupted, causing the chamber to reduce considerably in volume, then this can result in a depression at the surface called a caldera
40.
Volatility (chemistry)
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In chemistry and physics, volatility is quantified by the tendency of a substance to vaporize. Volatility is directly related to a vapor pressure. At a given temperature, a substance with higher vapor pressure vaporizes more readily than a substance with a vapor pressure. The vapor pressure of a substance is the pressure at which its gas phase is in equilibrium with its condensed phases and it is a measure of the tendency of molecules and atoms to escape from a liquid or a solid. The higher the pressure of a liquid at a given temperature, the higher the volatility. The vapor pressure chart displays the vapor pressures dependency for a variety of liquids as a function of temperature, for example, at any given temperature, chloromethane has the highest vapor pressure of any of the liquids in the chart. It also has the lowest normal boiling point, which is where the pressure curve intersects the horizontal pressure line of one atmosphere of absolute vapor pressure
41.
Carbonated water
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Carbonated water is water into which carbon dioxide gas under pressure has been dissolved. Some of these have additives, such as chloride, sodium bicarbonate or similar. This process, known as carbonation, is a process that causes the water to become effervescent, most carbonated water is sold in ready to drink bottles as carbonated beverages such as soft drinks. However, it is easy to prepare at home with soda makers. These additives are included to emulate the slightly salty taste soda water developed years ago from first using them as preservatives. By itself, carbonated water appears to have impact on health. While carbonated water is acidic, this acidity is quickly neutralized by saliva. Carbonated water may increase irritable bowel syndrome symptoms of bloating and gas due to the release of carbon dioxide in the digestive tract and it does not appear to have an effect on gastro-oesophageal reflux disease. There is tentative evidence that water may help with constipation among people who have had a stroke. Some carbonated waters have added sodium, so they may be an issue for those on low-sodium diets, typical carbonated soft drinks such as colas do have health risks. Carbonated colas have a correlation with slightly decreased bone density in older women, soft drinks are about 100 times more erosive to teeth than plain carbonated water. Carbon dioxide gas dissolved in water at a low concentration creates carbonic acid according to the following reaction, the pH level between 3 and 4 is approximately in between apple juice and orange juice in acidity, but much less acidic than the acid in the stomach. The human body robustly maintains pH equilibrium via acid–base homeostasis and will not be affected by consumption of plain carbonated water, if an alkaline salt, such as sodium bicarbonate, potassium bicarbonate, or potassium citrate is added to the water, its acidity is reduced. The amount of a gas like carbon dioxide that can be dissolved in water is described by Henrys Law, Water is chilled, optimally to just above freezing, in order to permit the maximum amount of carbon dioxide to dissolve in it. Higher gas pressure and lower temperature cause more gas to dissolve in the liquid, when the temperature is raised or the pressure is reduced, carbon dioxide escapes from the solution, in the form of bubbles. Many alcoholic drinks, such as beer, wine and champagne, were carbonated through the process for centuries. In 1662 Christopher Merret was creating sparkling wine, in 1750 the Frenchman Gabriel François Venel produced artificial carbonated water for the first time. It is thought that William Brownrigg and Henry Cavendish also infused water with carbon dioxide around this time
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Sicily
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Sicily is the largest island in the Mediterranean Sea. It is an autonomous Region of Italy, along with surrounding minor islands, Sicily is located in the central Mediterranean Sea, south of the Italian Peninsula, from which it is separated by the narrow Strait of Messina. Its most prominent landmark is Mount Etna, the tallest active volcano in Europe, the island has a typical Mediterranean climate. The earliest archaeological evidence of activity on the island dates from as early as 12,000 BC. It became part of Italy in 1860 following the Expedition of the Thousand, a revolt led by Giuseppe Garibaldi during the Italian unification, Sicily was given special status as an autonomous region after the Italian constitutional referendum of 1946. Sicily has a rich and unique culture, especially regard to the arts, music, literature, cuisine. It is also home to important archaeological and ancient sites, such as the Necropolis of Pantalica, the Valley of the Temples, Sicily has a roughly triangular shape, earning it the name Trinacria. To the east, it is separated from the Italian mainland by the Strait of Messina, about 3 km wide in the north, and about 16 km wide in the southern part. The northern and southern coasts are each about 280 km long measured as a line, while the eastern coast measures around 180 km. The total area of the island is 25,711 km2, the terrain of inland Sicily is mostly hilly and is intensively cultivated wherever possible. Along the northern coast, the ranges of Madonie,2,000 m, Nebrodi,1,800 m. The cone of Mount Etna dominates the eastern coast, in the southeast lie the lower Hyblaean Mountains,1,000 m. The mines of the Enna and Caltanissetta districts were part of a leading sulphur-producing area throughout the 19th century, Sicily and its surrounding small islands have some highly active volcanoes. Mount Etna is the largest active volcano in Europe and still casts black ash over the island with its ever-present eruptions and it currently stands 3,329 metres high, though this varies with summit eruptions, the mountain is 21 m lower now than it was in 1981. It is the highest mountain in Italy south of the Alps, Etna covers an area of 1,190 km2 with a basal circumference of 140 km. This makes it by far the largest of the three volcanoes in Italy, being about two and a half times the height of the next largest, Mount Vesuvius. In Greek Mythology, the deadly monster Typhon was trapped under the mountain by Zeus, Mount Etna is widely regarded as a cultural symbol and icon of Sicily. The Aeolian Islands in the Tyrrhenian Sea, to the northeast of mainland Sicily form a volcanic complex, the three volcanoes of Vulcano, Vulcanello and Lipari are also currently active, although the latter is usually dormant
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Mount Fuji
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Mount Fuji, located on Honshu Island, is the highest mountain in Japan at 3,776.24 m. An active stratovolcano that last erupted in 1707–08, Mount Fuji lies about 100 kilometres south-west of Tokyo, Mount Fuji is one of Japans Three Holy Mountains along with Mount Tate and Mount Haku. It is also a Special Place of Scenic Beauty and one of Japans Historic Sites and it was added to the World Heritage List as a Cultural Site on June 22,2013. Per UNESCO, Mount Fuji has inspired artists and poets and been the object of pilgrimage for centuries, UNESCO recognizes 25 sites of cultural interest within the Mt. Fuji locality. These 25 locations include the mountain itself, Fujisan, in Shinto mythology, Kuninotokotachi is one of the two gods born from something like a reed that arose from the soil when the earth was chaotic. He is known by mythology to reside on top of Mount Fuji, Kuninotokotachi is described as a hitorigami and genderless in Kojiki, while as a male god in Nihon Shoki. Yoshida Kanetomo, the founder of the Yoshida Shintō sect, identified Kuninotokotachi with Amenominakanushi, the current kanji for Mount Fuji, 富 and 士, mean wealth or abundant and a man with a certain status respectively. The origin of the name Fuji is unclear, having no recording of it being first called by this name. A text of the 10th century, Tale of the Bamboo Cutter, says that the name came from immortal, an early folk etymology claims that Fuji came from 不二, meaning without equal or nonpareil. Another claims that it came from 不尽, meaning neverending, a Japanese classical scholar in the Edo era, Hirata Atsutane, speculated that the name is from a word meaning, a mountain standing up shapely as an ear of a rice plant. It is also pointed that huchi means an old woman and ape is the word for fire, research on the distribution of place names that include fuji as a part also suggest the origin of the word fuji is in the Yamato language rather than Ainu. A Japanese toponymist Kanji Kagami argued that the name has the root as wisteria and rainbow. In English, the mountain is known as Mount Fuji, some sources refer to it as Fuji-san, Fujiyama or, redundantly, Mt. Fujiyama. Japanese speakers refer to the mountain as Fuji-san and this san is not the honorific suffix used with peoples names, such as Watanabe-san, but the Sino-Japanese reading of the character yama used in Sino-Japanese compounds. In Nihon-shiki and Kunrei-shiki romanization, the name is transliterated as Huzi, among the most renowned works are Hokusais 36 Views of Mount Fuji and his One Hundred Views of Mount Fuji, as well as Utagawa Hiroshiges similarly-titled 36 Views of Mount Fuji. The mountain is mentioned in Japanese literature throughout the ages and is the subject of many poems and it is thought that the first recorded ascent was in 663 by an anonymous monk. The summit has been thought of as sacred since ancient times and was forbidden to women until the Meiji Era, ancient samurai used the base of the mountain as a remote training area, near the present-day town of Gotemba. The shogun Minamoto no Yoritomo held yabusame in the area in the early Kamakura period, the first ascent by a foreigner was by Sir Rutherford Alcock in September 1868, from the foot of the mountain to the top in eight hours and three hours for the descent
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Honshu
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Honshu is the largest and most populous island of Japan, located south of Hokkaido across the Tsugaru Strait, north of Shikoku across the Inland Sea, and northeast of Kyushu across the Kanmon Straits. The island separates the Sea of Japan, which lies to its north and west, from the North Pacific Ocean to its south and it is the seventh-largest island in the world, and the second-most populous after the Indonesian island of Java. Honshu had a population of 103 million as of 2005, mostly concentrated in the coastal lowlands, as the historical center of Japanese culture and political power, the island includes several past Japanese capitals, including Kyoto, Nara, and Kamakura. Much of the southern shore forms part of the Taiheiyō Belt. The island is linked to the three major Japanese islands by a number of bridges and tunnels. Its climate is humid and mild, the island is roughly 1,300 km long and ranges from 50 to 230 km wide, and its total area is 225,800 km2, 60% of the total area of Japan, making it slightly larger than Great Britain. Its land area has been increasing with land reclamation and coastal uplift in the north, Honshu has 5,450 kilometres of coastline. Mountainous and volcanic, Honshu experiences frequent earthquakes, the highest peak is the active volcano Mount Fuji at 3,776 m, which makes Honshu the worlds 7th highest island. There are many rivers, including the Shinano River, Japans longest, the northernmost point on Honshu is the tip of the Shimokita Peninsula in Ōma, Aomori, Cape Kure lies at the southern extreme in Kushimoto, Wakayama. The islands eastern extremity is Todogasaki in Miyako, Iwate, and its western one is Bishanohana in Shimonoseki, Honshu spans more than eight degrees of latitude and 11 degrees of longitude. Honshu is connected to the islands of Hokkaido, Kyushu and Shikoku by tunnels or bridges, the island is divided into five nominal regions and contains 34 prefectures, including metropolitan Tokyo. Administratively, some islands are included within these prefectures, notably including the Ogasawara Islands, Sado Island, Izu Ōshima. Fruits, vegetables, grains, rice and cotton are grown in Honshu, niigata is noted as an important producer of rice. The Kantō and Nōbi plains produce rice and vegetables, yamanashi is a major fruit-growing area, and Aomori is famous for its apples. Rare species of the lichen genus Menegazzia are found only in Honshu, yields of zinc, copper, and oil have been found on Honshu
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Mount Unzen
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Mount Unzen is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki Prefecture, on the island of Kyūshū, Japans southernmost main island. In 1792, the collapse of one of its several lava domes triggered a megatsunami that killed 14,524 people in Japans worst-ever volcanic-related disaster. The volcano was most recently active from 1990 to 1995, currently its highest peaks are Fugen-dake at 1,359 metres and Heisei-shinzan at 1,486 metres. The latter emerged during the eruptions of the early, eponymous Heisei era, Mount Unzen is part of Shimabara Peninsula, which has seen extensive volcanism over millions of years. The oldest volcanic deposits in the date from over 6 million years ago. The origins of the Unzen complex are traced to the formation of a graben through crustal faulting and this caused parts of the peninsula to subside by up to 1,000 metres below sea level and may have caused eruptive activity to localize at one site inside the graben. Eruptions of dacitic lava began from a site slightly to the south of todays Mount Unzen, the volcano rapidly grew during its first 200,000 years, forming a large cone. Later eruptions over the following 150,000 years filled in much of the graben, initially, activity was dominated by blocky andesitic lava and ash flows, changing to dacitic pumice flows and airfall deposits from 500,000 to 400,000 years ago. The period from 400,000 to 300,000 years ago saw the emplacement of large areas of flow and lahar deposits. Beginning 300,000 to 150,000 years ago, thick phreatomagmatic deposits were laid down, Fugen-dake has been the site of most eruptions during the past 20,000 years and lies about 6 kilometres from the center of Shimabara. Unzens deadliest eruption occurred in 1792, with a large lava flow coming from Fugen-dake. The east flank of the Mayu-yama dome collapsed unexpectedly following a post-eruption earthquake and this caused a megatsunami that reached a height of 100 metres, and killed an estimated 15,000 people. As of 2011 it is the worst volcanic related eruption in Japan, after 1792, the volcano remained dormant until November 1989 when an earthquake swarm began about 20 kilometres underneath and 10 kilometres west of Fugendake. Over the following year, earthquakes continued, their hypocentres gradually migrating towards the summit, the first phreatic eruptions began in November 1990, and after inflation of the summit area, fresh lava began to emerge on May 20,1991. The threat of further disastrous events prompted authorities to evacuate 12,000 local residents from their homes, on June 3,1991, the volcano erupted violently, possibly as a result of depressurisation of the magma column after a landslide in the crater. Between 1991 and 1994 the volcano generated at least 10,000 small pyroclastic flows, from 1993 onward, the rate of lava effusion gradually decreased, and eruptions came to an end in 1995. Since then heavy rains have frequently remobilised pyroclastic material, generating lahars, dikes have been constructed in several river valleys to channel lahar flows away from vulnerable areas, and warning systems and evacuation plans have been developed and deployed. In 1999, a project began at Mount Unzen to drill deep inside the volcano
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Kyushu
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Kyushu is the third biggest island of Japan and most southwesterly of its four main islands. Its alternative ancient names include Kyūkoku, Chinzei, and Tsukushi-no-shima, the historical regional name Saikaidō referred to Kyushu and its surrounding islands. In the 8th century Taihō Code reforms, Dazaifu was established as an administrative term for the region. As of 2016, Kyushu has a population of 12,970,479, the island is mountainous, and Japans most active volcano, Mt Aso at 1,591 metres, is on Kyushu. There are many signs of tectonic activity, including numerous areas of hot springs. The most famous of these are in Beppu, on the east shore, the island is separated from Honshu by the Kanmon Straits. The name Kyūshū comes from the nine ancient provinces of Saikaidō situated on the island, Chikuzen, Chikugo, Hizen, Higo, Buzen, Bungo, Hyūga, Osumi, excepting Oita and Miyazaki cities, the eastern seaboard shows a general decline in population. Designated cities Fukuoka Kitakyushu Kumamoto Core cities Kagoshima Ōita Nagasaki Miyazaki Naha Kurume Parts of Kyushu have a climate, particularly Miyazaki. Major agricultural products are rice, tea, tobacco, sweet potatoes, the island is noted for various types of porcelain, including Arita, Imari, Satsuma, and Karatsu. Heavy industry is concentrated in the north around Fukuoka, Kitakyushu, Nagasaki, and Oita and includes chemicals, automobiles, semiconductors, in 2010, the graduate employment rate in the region was the lowest nationwide, at 88. 9%. Besides the volcanic area of the south, there are significant mud hot springs in the part of the island, around Beppu. These springs are the site of occurrence of certain extremophile micro-organisms, the Kanmon Bridge also connects the island with Honshu. Railways on the island are operated by the Kyushu Railway Company, and Nishitetsu Railway
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Mount Etna
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Mount Etna is an active stratovolcano on the east coast of Sicily, Italy, in the Metropolitan City of Catania, between the cities of Messina and Catania. It lies above the convergent plate margin between the African Plate and the Eurasian Plate and it is the tallest active volcano in Europe, currently 3,329 m high, though this varies with summit eruptions. It is the highest peak in Italy south of the Alps, Etna covers an area of 1,190 km2 with a basal circumference of 140 km. This makes it by far the largest of the three volcanoes in Italy, being about two and a half times the height of the next largest, Mount Vesuvius. Only Mount Teide in Tenerife surpasses it in the whole of the European–North-African region, Mount Etna is one of the most active volcanoes in the world and is in an almost constant state of activity. The fertile volcanic soils support extensive agriculture, with vineyards and orchards spread across the slopes of the mountain. Due to its history of recent activity and nearby population, Mount Etna has been designated a Decade Volcano by the United Nations, in June 2013, it was added to the list of UNESCO World Heritage Sites. According to Adrian Room’s book Place-names of the World, the name Etna originated from the Phoenician word attuna meaning furnace or chimney and he dismisses the hypothesis that Etna is from the Greek αἴθω, meaning I burn, through an iotacist pronunciation. In Classical Greek, it is called Αἴτνη, a name also to Catania and the city originally known as Inessa. In Arabic, it was called جبل النار Jabal al-Nār and it is also known as Mungibeddu in Sicilian and Mongibello or Montebello in Italian. The term is not in use today, although some older people still call it this. According to another hypothesis the term Mongibello comes from the Latin Mulciber, the people of the Etna sometimes use the jargon term a muntagna, simply the mountain par excellence. Nowadays, the term Mongibello indicates the top area of the two central craters encompassing also the craters in the southeast and the northeast of the volcanic cone. Volcanic activity first took place at Etna about 500,000 years ago, about 300,000 years ago, volcanism began occurring to the southwest of the summit then, before activity moved towards the present centre 170,000 years ago. Eruptions at this time built up the first major volcanic edifice, the growth of the mountain was occasionally interrupted by major eruptions, leading to the collapse of the summit to form calderas. From about 35,000 to 15,000 years ago, Etna experienced some highly explosive eruptions, generating pyroclastic flows. Ash from these eruptions has been found as far away as south of Romes border,800 km to the north, the landslide left a large depression in the side of the volcano, known as Valle del Bove. Research published in 2006 suggested this occurred around 8000 years ago, and caused a huge tsunami and it may have been the reason the settlement of Atlit Yam, now below sea level, was suddenly abandoned around that time
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Pyroclastic flow
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A pyroclastic flow is a fast-moving current of hot gas and volcanic matter, which reaches speeds moving away from a volcano of up to 700 km/h. The gases can reach temperatures of about 1,000 °C, Pyroclastic flows normally touch the ground and hurtle downhill, or spread laterally under gravity. Their speed depends upon the density of the current, the output rate. They are a common and devastating result of explosive eruptions. The word pyroclast is derived from the Greek πῦρ, meaning fire, a name for some pyroclastic flows is nuée ardente, this was first used to describe the disastrous 1902 eruption of Mount Pelée on Martinique. In the dark, these pyroclastic flows glowed red, Pyroclastic flows that contain a much higher proportion of gas to rock are known as fully dilute pyroclastic density currents or pyroclastic surges. The lower density sometimes allows them to flow over higher topographic features or water such as ridges, hills, rivers and seas. They may also contain steam, water and rock at less than 250 °C, cold pyroclastic surges can occur when the eruption is from a vent under a shallow lake or the sea. A pyroclastic flow is a type of gravity current, in literature they are sometimes abbreviated to PDC. There are several mechanisms that can produce a flow, Fountain collapse of an eruption column from a Plinian eruption. In such an eruption, the forcefully ejected from the vent heats the surrounding air. If the erupted jet is unable to heat the air sufficiently, convection currents will not be strong enough to carry the plume upwards and it falls. Fountain collapse of an eruption column associated with a Vulcanian eruption The gas and projectiles create a cloud that is denser than the surrounding air, frothing at the mouth of the vent during degassing of the erupted lava. This can lead to the production of a rock called ignimbrite and this occurred during the eruption of Novarupta in 1912. Gravitational collapse of a dome or spine, with subsequent avalanches. The directional blast when part of a volcano collapses or explodes, as distance from the volcano increases, this rapidly transforms into a gravity-driven current. The volumes range from a few hundred meters to more than a thousand cubic kilometres. The larger ones can travel for hundreds of kilometres, although none on that scale have occurred for several hundred thousand years, most pyroclastic flows are around one to ten cubic kilometres and travel for several kilometres
This article incorporates public domain material from the United States Geological Survey document: "Principal Types of Volcanoes". Retrieved 2009-01-19.
This article incorporates 
