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86-433: They are made up of four larger islands, each a few kilometres across, named, from west to east, Mancarroncito , Mancarrón , San Fernando and La Venada , along with some 32 smaller islands with rocky headlands which afford shelter to numerous aquatic birds. The islands’ origins are volcanic . The highest point in the islands is found on Mancarrón; it is 257 m (843 ft) above sea level . The Solentiname Islands are

172-886: A mid-ocean ridge , such as the Mid-Atlantic Ridge , has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift , the Wells Gray-Clearwater volcanic field , and the Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from

258-721: A National Monument. They constitute one of the 78 protected areas of Nicaragua . There is some confusion over what the archipelago's name means. Some hold that it is from a Nahuatl word that means "covey of quail", and others say that it comes from the Nahuatl word Celentinametl , which means "place of many guests". The latter opinion is found in the majority of sources. The Solentiname Islands are tropical in every sense. They are covered in tropical tree species, transitional between wet and dry tropical, and are home to various colourful bird species, including various kinds of parrot and toucans ; there are 76 species in all. The waters about

344-483: A character, as well as the community's small art gallery. 11°12′N 85°2′W  /  11.200°N 85.033°W  / 11.200; -85.033 Vulcanology Volcanology (also spelled vulcanology ) is the study of volcanoes , lava , magma and related geological , geophysical and geochemical phenomena ( volcanism ). The term volcanology is derived from the Latin word vulcan . Vulcan

430-414: A depiction of an erupting volcano, with a cluster of houses below shows a twin peaked volcano in eruption, with a town at its base (though archaeologists now question this interpretation). The volcano may be either Hasan Dağ , or its smaller neighbour, Melendiz Dağ. The classical world of Greece and the early Roman Empire explained volcanoes as sites of various gods. Greeks considered that Hephaestus ,

516-542: A detailed chronology and description of Vesuvius' eruptions. Volcano 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. The process that forms volcanoes is called volcanism . On Earth, volcanoes are most often found where tectonic plates are diverging or converging , and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example,

602-437: A graduated spectrum, with much overlap between categories, and does not always fit neatly into only one of these three separate categories. The USGS defines a volcano as "erupting" whenever the ejection of magma from any point on the volcano is visible, including visible magma still contained within the walls of the summit crater. While there is no international consensus among volcanologists on how to define an active volcano,

688-466: A key role in volcano explanations until the 16th century after Anaxagoras , in the fifth century BC, had proposed eruptions were caused by a great wind. Lucretius , a Roman philosopher, claimed Etna was completely hollow and the fires of the underground driven by a fierce wind circulating near sea level. Ovid believed that the flame was fed from "fatty foods" and eruptions stopped when the food ran out. Vitruvius contended that sulfur, alum and bitumen fed

774-820: A large area to be monitored easily. They can measure the spread of an ash plume, such as the one from Eyjafjallajökull 's 2010 eruption, as well as SO 2 emissions. InSAR and thermal imaging can monitor large, scarcely populated areas where it would be too expensive to maintain instruments on the ground. Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns that may indicate volcano-induced faulting and magma upwelling. Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions. Compositional analysis has been very successful in

860-443: A paper was published suggesting a new definition for the word 'volcano' that includes processes such as cryovolcanism . It suggested that a volcano be defined as 'an opening on a planet or moon's surface from which magma , as defined for that body, and/or magmatic gas is erupted.' This article mainly covers volcanoes on Earth. See § Volcanoes on other celestial bodies and cryovolcano for more information. The word volcano

946-512: A spiteful jealous fight ensued. Some Māori will not to this day live on the direct line between Tongariro and Taranaki for fear of the dispute flaring up again. In the Hawaiian religion , Pele ( / ˈ p eɪ l eɪ / Pel-a; [ˈpɛlɛ] ) is the goddess of volcanoes and a popular figure in Hawaiian mythology . Pele was used for various scientific terms as for Pele's hair , Pele's tears , and Limu o Pele (Pele's seaweed). A volcano on

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1032-468: A variety of all-embracing systems. Volcanic eruptions and earthquakes were generally linked in these systems to the existence of great open caverns under the Earth where inflammable vapours could accumulate until they were ignited. According to Thomas Burnet , much of the Earth itself was inflammable, with pitch, coal and brimstone all ready to burn. In William Whiston 's theory the presence of underground air

1118-632: A volcano is largely determined by the composition of the lava it erupts. The viscosity (how fluid the lava is) and the amount of dissolved gas are the most important characteristics of magma, and both are largely determined by the amount of silica in the magma. Magma rich in silica is much more viscous than silica-poor magma, and silica-rich magma also tends to contain more dissolved gases. Lava can be broadly classified into four different compositions: Mafic lava flows show two varieties of surface texture: ʻAʻa (pronounced [ˈʔaʔa] ) and pāhoehoe ( [paːˈho.eˈho.e] ), both Hawaiian words. ʻAʻa

1204-555: A volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit; however, this describes just one of the many types of volcano. The features of volcanoes are varied. The structure and behaviour of volcanoes depend on several factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater while others have landscape features such as massive plateaus . Vents that issue volcanic material (including lava and ash ) and gases (mainly steam and magmatic gases) can develop anywhere on

1290-465: A volcano that has experienced one or more eruptions that produced over 1,000 cubic kilometres (240 cu mi) of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic caldera -forming eruption. Ash flow tuffs emplaced by such eruptions are the only volcanic product with volumes rivalling those of flood basalts . Supervolcano eruptions, while

1376-410: Is 26 °C (79 °F). The islands’ tranquility and colourfulness are likely what has attracted artists to their shores. Painters and woodcarvers share the islands with farmers and fishermen. The archipelago's population is less than 1000, and its land area is about 38 km (15 sq mi). Modern amenities, including electricity and running water, are quite rare in the islands. Mancarrón

1462-436: Is Solentiname's largest island. It is here that the priest and poet Ernesto Cardenal ’s historical parish is to be found. Father Cardenal arrived in the islands in 1966 and is known for establishing a communal society for artists in the early 1970s which persists to this day. The community developed its own naïve art movement based on existing folk forms, and with some help from painter Róger Pérez de la Rocha . There

1548-739: Is a volcanic field of over 60 cinder cones. Based on satellite images, it has been suggested that cinder cones might occur on other terrestrial bodies in the Solar system too; on the surface of Mars and the Moon. Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and tephra in alternate layers, the strata that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include Mount Fuji in Japan, Mayon Volcano in

1634-488: Is a small art gallery where the craftsmen and painters display their works: birds, mobiles featuring the local fauna carved out of balsawood , as well as much sought-after colourful primitivist Solentiname paintings, largely inspired by the islands’ rich wildlife and plant species. Painters resident at the art colony included Asilia Guillén . For these very things, the Solentiname Islands have also been

1720-412: Is characterized by a rough, clinkery surface and is the typical texture of cooler basalt lava flows. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Pāhoehoe flows are sometimes observed to transition to ʻaʻa flows as they move away from the vent, but never the reverse. More silicic lava flows take the form of block lava, where

1806-565: 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 . According to the theory of plate tectonics, Earth's lithosphere , its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to convection in

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1892-584: Is expressed using the volcanic explosivity index (VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions. As of December 2022 , the Smithsonian Institution 's Global Volcanism Program database of volcanic eruptions in the Holocene Epoch (the last 11,700 years) lists 9,901 confirmed eruptions from 859 volcanoes. The database also lists 1,113 uncertain eruptions and 168 discredited eruptions for

1978-537: Is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analysed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near

2064-587: Is the prediction of eruptions; there is currently no accurate way to do this, but predicting or forecasting eruptions, like predicting earthquakes, could save many lives. In 1841, the first volcanological observatory, the Vesuvius Observatory , was founded in the Kingdom of the Two Sicilies . Volcanology advances have required more than just structured observation, and the science relies upon

2150-471: Is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland , as well. Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of Mount St. Helens , but can also form independently, as in

2236-455: The 1631 eruption of Mount Vesuvius (1632 and later editions) and Francesco Serao 's account of the eruption of Vesuvius in 1737 (1737, with editions in French and English). The Jesuit Athanasius Kircher (1602–1680) witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by

2322-617: The Cascade Volcanoes or the Japanese Archipelago , or the eastern islands of Indonesia . Hotspots are volcanic areas thought to be formed by mantle plumes , which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off

2408-525: The Jovian moon Io is also named Pele . Saint Agatha is patron saint of Catania , close to mount Etna, and an important highly venerated (till today ) example of virgin martyrs of Christian antiquity. In 253 CE, one year after her violent death, the stilling of an eruption of Mt. Etna was attributed to her intercession. Catania was however nearly completely destroyed by the eruption of Mt. Etna in 1169, and over 15,000 of its inhabitants died. Nevertheless,

2494-697: The core–mantle boundary , 3,000 kilometres (1,900 mi) deep within Earth. This results in hotspot volcanism , of which the Hawaiian hotspot is an example. Volcanoes are usually not created where two tectonic plates slide past one another. Large eruptions can affect atmospheric temperature as ash and droplets of sulfuric acid obscure the Sun and cool Earth's troposphere . Historically, large volcanic eruptions have been followed by volcanic winters which have caused catastrophic famines. Other planets besides Earth have volcanoes. For example, volcanoes are very numerous on Venus. Mars has significant volcanoes. In 2009,

2580-834: The landform and may give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Kīlauea in Hawaii. Volcanic craters are not always at the top of a mountain or hill and may be filled with lakes such as with Lake Taupō in New Zealand. Some volcanoes can be low-relief landform features, with the potential to be hard to recognize as such and be obscured by geological processes. Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter , Saturn , and Neptune ; and mud volcanoes , which are structures often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes except when

2666-400: The Earth was an animal, and that its internal heat, earthquakes and eruptions were all signs of life. This animistic philosophy was waning by the end of the seventeenth century, but traces continued well into the eighteenth. Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water ( Neptunism ). Of

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2752-622: The Philippines, and Mount Vesuvius and Stromboli in Italy. Ash produced by the explosive eruption of stratovolcanoes has historically posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as pyroclastic surges like

2838-613: The USGS defines a volcano as active whenever subterranean indicators, such as earthquake swarms , ground inflation, or unusually high levels of carbon dioxide or sulfur dioxide are present. The USGS defines a dormant volcano as any volcano that is not showing any signs of unrest such as earthquake swarms, ground swelling, or excessive noxious gas emissions, but which shows signs that it could yet become active again. Many dormant volcanoes have not erupted for thousands of years, but have still shown signs that they may be likely to erupt again in

2924-510: The boundary with the Yukon Territory . Mud volcanoes (mud domes) are formations created by geo-excreted liquids and gases, although several processes may cause such activity. The largest structures are 10 kilometres in diameter and reach 700 meters high. The material that is expelled in a volcanic eruption can be classified into three types: The concentrations of different volcanic gases can vary considerably from one volcano to

3010-530: The burning of sulfur, bitumen and coal. He published his view of this in Mundus Subterraneus with volcanoes acting as a type of safety valve. The causes of these phenomena were discussed in the large number of theories of the Earth that were published in the hundred years after 1650. The authors of these theories were not themselves observers, but combined the observations of others with Newtonian, Cartesian, Biblical or animistic science to produce

3096-402: The case of Lassen Peak . Like stratovolcanoes, they can produce violent, explosive eruptions, but the lava generally does not flow far from the originating vent. Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example; lava beneath the surface of the mountain created an upward bulge, which later collapsed down

3182-509: The deep fires. Observations by Pliny the Elder noted the presence of earthquakes preceded an eruption; he died in the eruption of Vesuvius in 79 CE while investigating it at Stabiae . His nephew, Pliny the Younger , gave detailed descriptions of the eruption in which his uncle died, attributing his death to the effects of toxic gases. Such eruptions have been named Plinian in honour of

3268-799: The enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful geologic mapping . Known examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States); Lake Taupō in New Zealand; Lake Toba in Sumatra , Indonesia; and Ngorongoro Crater in Tanzania. Volcanoes that, though large, are not large enough to be called supervolcanoes, may also form calderas in

3354-464: The eruption of Vesuvius rained twinned pyroxene crystals and ash upon the nearby villages. The crystals resembled the crucifix and this was interpreted as the work of Saint Januarius . In Naples , the relics of St Januarius are paraded through town at every major eruption of Vesuvius. The register of these processions and the 1779 and 1794 diary of Father Antonio Piaggio allowed British diplomat and amateur naturalist Sir William Hamilton to provide

3440-495: The flames his breath and the tremors his railing against the bars of his prison. Enceladus' brother Mimas was buried beneath Vesuvius by Hephaestus, and the blood of other defeated giants welled up in the Phlegrean Fields surrounding Vesuvius. The Greek philosopher Empedocles (c. 490-430 BCE) saw the world divided into four elemental forces, of Earth, Air, Fire and Water. Volcanoes, Empedocles maintained, were

3526-431: The flow is covered with angular, vesicle-poor blocks. Rhyolitic flows typically consist largely of obsidian . Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases when it flows to the surface . These violent explosions produce particles of material that can then fly from

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3612-610: The formation of a submarine volcano off the coast of Mayotte . Subglacial volcanoes develop underneath ice caps . They are made up of lava plateaus capping extensive pillow lavas and palagonite . These volcanoes are also called table mountains, tuyas , or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in British Columbia . The origin of the term comes from Tuya Butte , which

3698-585: The future. In an article justifying the re-classification of Alaska's Mount Edgecumbe volcano from "dormant" to "active", volcanologists at the Alaska Volcano Observatory pointed out that the term "dormant" in reference to volcanoes has been deprecated over the past few decades and that "[t]he term "dormant volcano" is so little used and undefined in modern volcanology that the Encyclopedia of Volcanoes (2000) does not contain it in

3784-466: The glossaries or index", however the USGS still widely employs the term. Previously a volcano was often considered to be extinct if there were no written records of its activity. Such a generalization is inconsistent with observation and deeper study, as has occurred recently with the unexpected eruption of the Chaitén volcano in 2008. Modern volcanic activity monitoring techniques, and improvements in

3870-464: The god of fire, sat below the volcano Etna , forging the weapons of Zeus . The Greek word used to describe volcanoes was etna , or hiera , after Heracles , the son of Zeus. The Roman poet Virgil , in interpreting the Greek mythos, held that the giant Enceladus was buried beneath Etna by the goddess Athena as punishment for rebellion against the gods; the mountain's rumblings were his tormented cries,

3956-426: The grouping of volcanoes by type, origin of magma, including matching of volcanoes to a mantle plume of a particular hotspot , mantle plume melting depths, the history of recycled subducted crust, matching of tephra deposits to each other and to volcanoes of origin, and the understanding the formation and evolution of magma reservoirs, an approach which has now been validated by real time sampling. Some of

4042-492: The interior of a continent and lead to rifting. Early stages of rifting are characterized by flood basalts and may progress to the point where a tectonic plate is completely split. A divergent plate boundary then develops between the two halves of the split plate. However, rifting often fails to completely split the continental lithosphere (such as in an aulacogen ), and failed rifts are characterized by volcanoes that erupt unusual alkali lava or carbonatites . Examples include

4128-436: The islands contain plentiful fish. There are about 46 species , including tarpon , freshwater sharks , sawfish , and swordfish . The island of La Venada is known for its deer , and also named for them ( La Venada is Spanish for "The Doe"). The yearly rainfall in the islands measures between 1,400 and 1,800 mm (55 and 71 in), with most of it falling between May and December. Solentiname's mean yearly temperature

4214-505: The lakeshore, home to both monkeys and alligators , and the Solentiname National Monument, which consists of the islands themselves and the lakeshores around them. Solentiname's agricultural products include avocado , cotton , sesame , corn , coffee and cacao . Parts of the story "Apocalipsis de Solentiname" by Julio Cortázar are set on the Solentiname Islands. The story features Ernesto Cardenal as

4300-468: The manifestation of Elemental Fire. Plato contended that channels of hot and cold waters flow in inexhaustible quantities through subterranean rivers. In the depths of the earth snakes a vast river of fire, the Pyriphlegethon , which feeds all the world's volcanoes. Aristotle considered underground fire as the result of "the...friction of the wind when it plunges into narrow passages." Wind played

4386-419: The mid-oceanic ridge is above sea level, volcanic islands are formed, such as Iceland . Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore. In a process called flux melting , water released from the subducting plate lowers the melting temperature of

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4472-479: The miniDOAS), which analyzes the presence of volcanic gases such as sulfur dioxide ; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption. Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents, which may indicate upcoming activity. Satellites are widely used to monitor volcanoes, as they allow

4558-551: The modelling of the factors that produce eruptions, have helped the understanding of why volcanoes may remain dormant for a long time, and then become unexpectedly active again. The potential for eruptions, and their style, depend mainly upon the state of the magma storage system under the volcano, the eruption trigger mechanism and its timescale. For example, the Yellowstone volcano has a repose/recharge period of around 700,000 years, and Toba of around 380,000 years. Vesuvius

4644-415: The most dangerous type, are very rare; four are known from the last million years , and about 60 historical VEI 8 eruptions have been identified in the geologic record over millions of years. A supervolcano can produce devastation on a continental scale, and severely cool global temperatures for many years after the eruption due to the huge volumes of sulfur and ash released into the atmosphere. Because of

4730-438: The mud volcano is actually a vent of an igneous volcano. Volcanic fissure vents are flat, linear fractures through which lava emerges. Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent. They generally do not explode catastrophically but are characterized by relatively gentle effusive eruptions . Since low-viscosity magma

4816-520: The next initial onset time of an eruption, as it might also address the size of a future eruption, and evolution of an eruption once it has begun. Volcanology has an extensive history. The earliest known recording of a volcanic eruption may be on a wall painting dated to about 7,000 BCE found at the Neolithic site at Çatal Höyük in Anatolia , Turkey . This painting has been interpreted as

4902-452: The next. Water vapour is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide . Other principal volcanic gases include hydrogen sulfide , hydrogen chloride , and hydrogen fluoride . A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen , carbon monoxide , halocarbons , organic compounds, and volatile metal chlorides. The form and style of an eruption of

4988-876: The north side of the mountain. Cinder cones result from eruptions of mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 metres (100 to 1,300 ft) high. Most cinder cones erupt only once and some may be found in monogenetic volcanic fields that may include other features that form when magma comes into contact with water such as maar explosion craters and tuff rings . Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico , Caja del Rio

5074-504: The object of ecotourism in recent years, although currently, they are still a somewhat obscure destination. However, there are now three hotels in the islands, two of which are quite new. There are also important archaeological sites (including petroglyphs on San Fernando featuring images of parrots, monkeys, and people), the Los Guatuzos Wildlife Refuge , a 400 km (150 sq mi) marsh parallel to

5160-549: The ocean surface as new islands or floating pumice rafts . In May and June 2018, a multitude of seismic signals were detected by earthquake monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An oceanographic research campaign in May 2019 showed that the previously mysterious humming noises were caused by

5246-420: The ocean surface, due to the rapid cooling effect and increased buoyancy in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor. Hydrothermal vents are common near these volcanoes, and some support peculiar ecosystems based on chemotrophs feeding on dissolved minerals. Over time, the formations created by submarine volcanoes may become so large that they break

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5332-471: The ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases; however, submarine eruptions can be detected by hydrophones and by the discoloration of water because of volcanic gases . Pillow lava is a common eruptive product of submarine volcanoes and is characterized by thick sequences of discontinuous pillow-shaped masses which form underwater. Even large submarine eruptions may not disturb

5418-468: The one that destroyed the city of Saint-Pierre in Martinique in 1902. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose tephra are material for dangerous lahars . Large pieces of tephra are called volcanic bombs . Big bombs can measure more than 1.2 metres (4 ft) across and weigh several tons. A supervolcano is defined as

5504-425: The overlying mantle wedge, thus creating magma . This magma tends to be extremely viscous because of its high silica content, so it often does not reach the surface but cools and solidifies at depth . When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called volcanic arcs . Typical examples are the volcanoes in the Pacific Ring of Fire , such as

5590-619: The plume, and new volcanoes are created where the plate advances over the plume. The Hawaiian Islands are thought to have been formed in such a manner, as has the Snake River Plain , with the Yellowstone Caldera being part of the North American plate currently above the Yellowstone hotspot . However, the mantle plume hypothesis has been questioned. Sustained upwelling of hot mantle rock can develop under

5676-466: The rediscovery of Classical descriptions of them by wtiters like Lucretius and Strabo . Vesuvius, Stromboli and Vulcano provided an opportunity to study the nature of volcanic phenomena. Italian natural philosophers living within reach of these volcanoes wrote long and learned books on the subject: Giovanni Alfonso Borelli 's account of the eruption of Mount Etna in 1669 became a standard source of information, as did Giulio Cesare Recupito's account of

5762-665: The rise of molten rock to the surface. During the Renaissance, observers as Bernard Palissy , Conrad Gessner , and Johannes Kentmann (1518–1568) showed a deep intense interest in the nature, behavior, origin and history of the terrestrial globe. Many theories of volcanic action were framed during the late sixteenth mid-seventeenth centuries. Georgius Agricola argued the rays of the sun, as later proposed by Descartes had nothing to do with volcanoes. Agricola believed vapor under pressure caused eruptions of 'mointain oil' and basalt. Johannes Kepler considered volcanoes as conduits for

5848-475: The saint was invoked again for the 1669 Etna eruption and, for an outbreak that was endangering the town of Nicolosi in 1886. The way the saint is invoked and dealt with in Italian folk religion , in a quid pro quo manner, or bargaining approach which is sometimes used in prayerful interactions with saints, has been related (in the tradition of James Frazer ) to earlier pagan beliefs and practices. In 1660

5934-435: The same time interval. Volcanoes vary greatly in their level of activity, with individual volcanic systems having an eruption recurrence ranging from several times a year to once in tens of thousands of years. Volcanoes are informally described as erupting , active , dormant , or extinct , but the definitions of these terms are not entirely uniform among volcanologists. The level of activity of most volcanoes falls upon

6020-492: The same way; they are often described as "caldera volcanoes". Submarine volcanoes are common features of the ocean floor. Volcanic activity during the Holocene Epoch has been documented at only 119 submarine volcanoes, but there may be more than one million geologically young submarine volcanoes on the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above

6106-622: The solidified erupted material that makes up the mantle of a volcano may be stripped away that its inner anatomy becomes apparent. Using the metaphor of biological anatomy , such a process is called "dissection". Cinder Hill , a feature of Mount Bird on Ross Island , Antarctica , is a prominent example of a dissected volcano. Volcanoes that were, on a geological timescale, recently active, such as for example Mount Kaimon in southern Kyūshū , Japan , tend to be undissected. Eruption styles are broadly divided into magmatic, phreatomagmatic, and phreatic eruptions. The intensity of explosive volcanism

6192-406: The surrounding areas, and initially not seismically monitored before its unanticipated and catastrophic eruption of 1991. Two other examples of volcanoes that were once thought to be extinct, before springing back into eruptive activity were the long-dormant Soufrière Hills volcano on the island of Montserrat , thought to be extinct until activity resumed in 1995 (turning its capital Plymouth into

6278-399: The tears and excrement of the Earth, voiding bitumen, tar and sulfur. Descartes, pronouncing that God had created the Earth in an instant, declared he had done so in three layers; the fiery depths, a layer of water, and the air. Volcanoes, he said, were formed where the rays of the sun pierced the earth. The volcanoes of southern Italy attracted naturalists ever since the Renaissance led to

6364-464: The techniques mentioned above, combined with modelling, have proved useful and successful in the forecasting of some eruptions, such as the evacuation of the locality around Mount Pinatubo in 1991 that may have saved 20,000 lives. Short-term forecasts tend to use seismic or multiple monitoring data with long term forecasting involving the study of the previous history of local volcanism. However, volcanology forecasting does not just involve predicting

6450-434: The theory of plate tectonics. For example, some volcanoes are polygenetic with more than one period of activity during their history; other volcanoes that become extinct after erupting exactly once are monogenetic (meaning "one life") and such volcanoes are often grouped together in a geographical region. At the mid-ocean ridges , two tectonic plates diverge from one another as hot mantle rock creeps upwards beneath

6536-444: The thinned oceanic crust . The decrease of pressure in the rising mantle rock leads to adiabatic expansion and the partial melting of the rock, causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, and so most volcanic activity on Earth is submarine, forming new seafloor . Black smokers (also known as deep sea vents) are evidence of this kind of volcanic activity. Where

6622-423: The two authors. Thirteenth century Dominican scholar Restoro d'Arezzo devoted two entire chapters (11.6.4.6 and 11.6.4.7) of his seminal treatise La composizione del mondo colle sue cascioni to the origin of the endogenous energy of the Earth. Restoro maintained that the interior of the Earth was very hot and insisted, following Empedocles , that the Earth had a molten center and that volcanoes erupted through

6708-431: The underlying ductile mantle , and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created). During the development of geological theory, certain concepts that allowed the grouping of volcanoes in time, place, structure and composition have developed that ultimately have had to be explained in

6794-930: The understanding and integration of knowledge in many fields including geology , tectonics , physics , chemistry and mathematics , with many advances only being able to occur after the advance had occurred in another field of science. For example, the study of radioactivity only commenced in 1896, and its application to the theory of plate tectonics and radiometric dating took about 50 years after this. Many other developments in fluid dynamics , experimental physics and chemistry, techniques of mathematical modelling , instrumentation and in other sciences have been applied to volcanology since 1841. Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long period harmonic tremors, which signal magma movement through volcanic conduits. Surface deformation monitoring includes

6880-433: The use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR. Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface. Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by

6966-492: The volcano. Solid particles smaller than 2 mm in diameter ( sand-sized or smaller) are called volcanic ash. Tephra and other volcaniclastics (shattered volcanic material) make up more of the volume of many volcanoes than do lava flows. Volcaniclastics may have contributed as much as a third of all sedimentation in the geologic record. The production of large volumes of tephra is characteristic of explosive volcanism. Through natural processes, mainly erosion , so much of

7052-424: The volcanoes of the East African Rift . A volcano needs a reservoir of molten magma (e.g. a magma chamber), a conduit to allow magma to rise through the crust, and a vent to allow the magma to escape above the surface as lava. The erupted volcanic material (lava and tephra) that is deposited around the vent is known as a volcanic edifice , typically a volcanic cone or mountain. The most common perception of

7138-487: The volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism . Tribal legends of volcanoes abound from the Pacific Ring of Fire and the Americas, usually invoking the forces of the supernatural or the divine to explain the violent outbursts of volcanoes. Taranaki and Tongariro , according to Māori mythology, were lovers who fell in love with Pihanga , and

7224-421: Was described by Roman writers as having been covered with gardens and vineyards before its unexpected eruption of 79 CE , which destroyed the towns of Herculaneum and Pompeii . Accordingly, it can sometimes be difficult to distinguish between an extinct volcano and a dormant (inactive) one. Long volcano dormancy is known to decrease awareness. Pinatubo was an inconspicuous volcano, unknown to most people in

7310-466: Was necessary if ignition were to take place, while John Woodward stressed that water was essential. Athanasius Kircher maintained that the caverns and sources of the heat were deep, and reached down towards the centre of the Earth, while other writers, notably Georges Buffon , believed they were relatively superficial, and that volcanic fires were seated well up within the volcanic cone itself. A number of writers, most notably Thomas Robinson, believed that

7396-404: Was the ancient Roman god of fire. A volcanologist is a geologist who studies the eruptive activity and formation of volcanoes and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions , collect eruptive products including tephra (such as ash or pumice ), rock and lava samples. One major focus of enquiry

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