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77-589: The archipelago is volcanic and has been inhabited for thousands of years. Neolithic artefacts and Bronze Age obsidians have been excavated on the islands. The islands were used by the Etruscans who carved the "Blue Grottos". The earliest recorded history of the islands occurs with the Roman victory over the Volsci at 338 BC. According to a local legend, this was once the lost Kingdom of Tyrrhenia which sank with

154-573: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Volcanic winter A volcanic winter is a reduction in global temperatures caused by droplets of sulfuric acid obscuring the Sun and raising Earth 's albedo (increasing the reflection of solar radiation) after a large, sulfur-rich, particularly explosive volcanic eruption . Climate effects are primarily dependent upon

231-886: 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

308-452: A 1,500-year cooling period. GS-20 is considered the most isotopically extreme and coldest stadial, as well as having the weakest Asian monsoon , in the last 100,000 years. This timing has led some to speculate on the relation between YTT and GS-20. The stratigraphic position of YTT in relation to the GS-20 transition suggests that the stadial would have occurred without YTT, as the cooling

385-568: A cluster of closely spaced, large volcanic eruptions triggered or amplified the Little Ice Age , Late Antique Little Ice Age , stadials , Younger Dryas , Heinrich events , and Dansgaard-Oeschger events through the atmosphere-ice-ocean positive feedbacks. The weathering of a sufficiently large volume of rapidly erupted volcanic materials has been proposed as an important factor in Earth's silicate weathering cycle, which operates on

462-437: 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,

539-431: A massive flux of weathered freshly erupted materials entering the ocean, coinciding with the eruptions of large igneous provinces. Simulations demonstrate that the increased weatherability led to drop in atmospheric CO 2 of the order of 1,320 ppm and an 8 K cooling of global temperatures, triggering the most extraordinary episode of climate change in the geologic record. The causes of the population bottleneck  –

616-539: A narrow strip connected to mainland Italy. During the reign of Augustus , residential expansion on the islands was encouraged and people spread from Ponza to Ventotene. Rome used the two islands as a retreat and a place to exile politically troubling citizens. Some two thousand years later the islands were used for the same reason by the Fascist regime . Agrippina the Younger , mother to the future Roman emperor, Nero ,

693-443: 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

770-623: A popular tourist destination. 40°53′5″N 13°9′15″E  /  40.88472°N 13.15417°E  / 40.88472; 13.15417 Volcanic 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,

847-521: A sharp decrease in a species ' population, immediately followed by a period of great genetic divergence ( differentiation ) among survivors – is attributed to volcanic winters by some researchers. Such events may diminish populations to "levels low enough for evolutionary changes, which occur much faster in small populations, to produce rapid population differentiation". With the Lake Toba bottleneck, many species showed massive effects of narrowing of

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924-548: A timescale of tens of millions of years. During this process, weathered silicate minerals react with carbon dioxide and water, resulting in the formation of magnesium carbonate and calcium carbonate . These carbonates are then removed from the atmosphere and sequestrated on the ocean floor. The eruption of a large volume of volcanic materials can enhance weathering processes, thereby lowering atmospheric CO 2 levels and contributing to global temperature reduction. The rapid emplacement of mafic large igneous provinces has

1001-584: A volcanic winter within a few years after the eruption of YTT, but the resolution of the sediments is questioned due to sediment mixing. Directly above the YTT layer in Lake Malawi, there is evidence of a 2,000-year-long megadrought and cooling period. Greenland ice cores identify a 110-year period of accelerated cooling immediately following what is likely the YTT aerosol event. The enhanced weathering of continental flood basalts, which erupted just prior to

1078-632: 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

1155-555: 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

1232-465: 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

1309-437: A widespread lowering of snowline , enabling the rapid expansion of sea ice , ice caps and continental glacier . As a result, ocean temperatures decrease, and surface albedo increases, further reinforcing the expansion of sea ice, ice caps, and glacier. These processes create a strong positive feedback loop, allowing the cooling trend to persist over centennial-scale or even longer periods of time. It has been proposed that

1386-470: Is 1 to 3 times greater than that of the Samalas eruption in 1257 CE. Global climate models simulate peak global mean cooling of 2.3 to 4.1 K for this amount of erupted sulfate aerosols, and complete temperature recovery does not occur within 10 years. Empirical evidence for cooling induced by YTT, however, is mixed. YTT coincides with the onset of Greenland Stadial 20 (GS-20), which is characterized by

1463-739: 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

1540-412: 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

1617-514: 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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1694-584: 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

1771-537: 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

1848-598: Is regarded as the largest known Quaternary eruption and two orders of magnitude greater than the magma volume of the largest historical eruption, Tambora. The exceptional magnitude of this eruption has prompted sustained debate as to its global and regional impact on climate. Sulfate concentration and isotope measurements from polar ice cores taken around the time of 74,000 years BP have identified four atmospheric aerosol events that could potentially be attributed to YTT. The calculated stratospheric sulfate loadings for these four events range from 219 to 535 million tonnes, which

1925-423: Is shorter compared to those from tropical eruptions, due to a longer transport path from the tropics to removal across the mid- or high-latitude tropopause , but extratropical eruptions strengthens the hemispheric climate impact by confining the aerosol to a single hemisphere. Injections in the winter are also much less radiatively efficient than injections during the summer for high-latitude volcanic eruptions, when

2002-471: 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

2079-617: 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

2156-508: The Common Era . Surface temperature observations following historic eruptions show that there is no correlation between eruption size, as represented by the VEI or eruption volume, and the severity of the climate cooling. This is because eruption size does not correlate with the amount of SO 2 emitted. It has been proposed that the cooling effects of volcanic eruptions can extend beyond

2233-648: The Last Glacial Period is made possible by annually resolved δ O records. This is a non-exhaustive compilation of notable and consequential coolings that have been definitively attributed to volcanic aerosols, although the source volcanos of the aerosols are rarely identified. During the Last Glacial Period, volcanic coolings comparable to the largest volcanic coolings during the Common Era (e.g. Tambora, Samalas) are inferred based on

2310-752: 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,

2387-834: 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

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2464-622: 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

2541-613: 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

2618-412: The amount of injection of SO 2 and H 2 S into the stratosphere where they react with OH and H 2 O to form H 2 SO 4 on a timescale of a week, and the resulting H 2 SO 4 aerosols produce the dominant radiative effect. Volcanic stratospheric aerosols cool the surface by reflecting solar radiation and warm the stratosphere by absorbing terrestrial radiation for several years. Moreover,

2695-510: 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

2772-402: 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

2849-575: The coldest years during the last five millennia were directly caused by massive volcanic injections of SO 2 . Hemispheric temperature anomalies resulting from volcanic eruptions have primarily been reconstructed based on tree-ring data for the past two millennia . For earlier periods in the Holocene , the identification of frost rings that coincide with large ice core sulfate spikes serves as an indicator of severe volcanic winters. The quantification of volcanic coolings further back in time during

2926-415: The cooling trend can be further extended by atmosphere–ice–ocean feedback mechanisms. These feedbacks can continue to maintain the cool climate long after the volcanic aerosols have dissipated. An explosive volcanic eruption releases magma materials in the form of volcanic ash and gases into the atmosphere. While most volcanic ash settles to the ground within a few weeks after the eruption, impacting only

3003-799: 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

3080-431: 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

3157-610: 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

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3234-585: 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

3311-466: 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

3388-416: The initial several years, lasting for decades to possibly even millennia. This prolonged impact is hypothesized to be a result of positive feedback mechanisms involving ice and ocean dynamics, even after the H 2 SO 4 aerosols have dissipated. During the first few years following a volcanic eruption, the presence of H 2 SO 4 aerosols can induce a significant cooling effect. This cooling can lead to

3465-492: 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

3542-526: The islands, and they later became part of the Kingdom of Italy . Ponza and Ventotene are populated, but the smaller islands are not, with the total population of the archipelago at 4,066 inhabitants as of 2009. Ventotene and Santo Stefano are land and sea conservation areas supervised by the Italian State. Currently, tiny vineyards, wild herbs and flowers, and secluded beaches and grottos make them

3619-404: The local area for a short duration, the emitted SO 2 can lead to the formation of H 2 SO 4 aerosols in the stratosphere. These aerosols can circle the hemisphere of the eruption source in a matter of weeks and persist with an e -folding decay time of about a year. As a result, they have a radiative impact that can last for several years. The subsequent dispersal of a volcanic cloud in

3696-518: The magnitudes of δ O anomalies. In particular, in the period 12,000–32,000 years ago, the peak δ O cooling anomaly of the eruptions exceeds the anomaly after the largest eruptions in the Common Era. One Last Glacial Period eruption that have gained significant attention is the eruption of the Youngest Toba Tuff (YTT), which has sparked vigorous debates regarding its climate effects. The eruption of YTT from Toba Caldera , 74,000 years ago,

3773-419: 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

3850-551: 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

3927-415: 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

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4004-438: 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

4081-452: 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

4158-876: 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

4235-549: 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

4312-420: 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

4389-471: 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

4466-468: 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

4543-506: The onset of the Sturtian glaciation at 717 million years ago, is recognized as the trigger for the most severe glaciation in Earth's history. During this period, Earth's surface temperatures dropped below the freezing point of water everywhere, and ice rapidly advanced from low latitudes to the equator , covering a worldwide extent. This glaciation lasted almost 60 million years, from 717 to 659 million years ago. Geochronology dates

4620-425: 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

4697-619: 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

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4774-593: The potential to cause a swift decline in atmospheric CO 2 content, leading to a multi-million-year-long icehouse climate. A notable example is the Sturtian glaciation , which is considered the most severe and widespread known glacial event in Earth's history. This glaciation is believed to have been caused by the weathering of erupted Franklin Large Igneous Province . Tree-ring-based temperature reconstructions , historical records of dust veils, and ice cores studies have confirmed that some of

4851-494: The rapid emplacement of 5,000,000 km (1,900,000 sq mi) Franklin large igneous province just 1 million year before the onset of Sturtian glaciation. Multiple large igneous provinces on the scale of 1,000,000 km (390,000 sq mi) were also emplaced on Rodinia between 850 and 720 million years ago. Weathering of massive amount of fresh mafic materials initiated runaway cooling and ice-albedo feedback after 1 million year. Chemical isotopic compositions show

4928-501: The removal of stratospheric aerosols in polar regions is enhanced. The sulfate aerosol interacts strongly with solar radiation through scattering , giving rise to remarkable atmospheric optical phenomena in the stratosphere. These phenomena include solar dimming , coronae or Bishop's rings , peculiar twilight coloration, and dark total lunar eclipses . Historical records that documented these atmospheric events are indications of volcanic winters and date back to periods preceding

5005-435: 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

5082-492: 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

5159-622: 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

5236-513: The stratosphere and its impact on climate are strongly influenced by several factors, including the season of the eruption, the latitude of the source volcano, and the injection height. If the SO 2 injection height remains confined to the troposphere, the resulting H 2 SO 4 aerosols have a residence time of only a few days due to efficient removal through precipitation. The lifetime of H 2 SO 4 aerosols resulting from extratropical eruptions

5313-406: 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

5390-434: 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

5467-444: 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

5544-431: 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

5621-492: 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

5698-424: 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

5775-619: Was already underway. There is the possibility that YTT contributed to the extremity of GS-20. The South China Sea shows a 1 K cooling over 1,000 years following the deposition of YTT, while the Arabian Sea shows no discernible impact. In India and the Bay of Bengal , initial cooling and prolonged desiccation are observed above the YTT ash layer, but it is argued that these environmental changes were already occurring prior to YTT. Lake Malawi sediments do not provide evidence supporting

5852-421: 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

5929-538: Was exiled to the Pontine Islands by her brother, the then Roman emperor, Caligula , in 39 AD, before having the exile lifted by her uncle, the emperor Claudius upon his succession. Deposed Pope Silverius was exiled there in 537 shortly before his death. The Pontine were abandoned during the Middle Ages after raids by Saracens and pirates. During the 18th century, the Kingdom of Naples re-colonized

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