96-744: The Virunga Mountains (also known as Mufumbiro ) are a chain of volcanoes in East Africa , in the area where Rwanda , the Democratic Republic of the Congo (DRC), and Uganda meet. The mountain range is a branch of the Albertine Rift Mountains , which border the western branch of the East African Rift . They are located between Lake Edward and Lake Kivu . The name "Virunga" is an English version of
192-489: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Cryovolcanism A cryovolcano (sometimes informally referred to as an ice volcano ) is a type of volcano that erupts gases and volatile material such as liquid water , ammonia , and hydrocarbons . The erupted material is collectively referred to as cryolava ; it originates from
288-819: 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
384-481: A body's surface. A variety of hypotheses have been proposed by planetary scientists to explain how cryomagma erupts onto the surface: In addition to overcoming the density barrier, cryomagma also requires a way to reach the surface in order to erupt. Fractures in particular, either the result of global or localized stress in the icy crust, providing potential eruptive conduits for cryomagma to exploit. Such stresses may come from tidal forces as an object orbits around
480-420: A cryovolcanic origin of these structures remains elusive in imagery. Saturn 's moon Enceladus is host to the most dramatic example of cryovolcanism yet observed, with a series of vents erupting 250 kilograms (550 lb) of material per second that feeds Saturn's E ring . These eruptions take place across Enceladus's south polar region, sourced from four major ridges which form a region informally known as
576-437: A feature that is formally classified as an impact crater, is actually a cryovolcanic caldera complex. Although Sputnik Planitia represents the youngest surface on Pluto, it is not a cryovolcanic structure; Sputnik Planitia continuously resurfaces itself with the convective overturning of glacial nitrogen ice, fuelled by Pluto's internal heat and sublimation into Pluto's atmosphere. Charon 's surface dichotomy indicates that
672-536: A few million years old, Triton is one of the most geologically active worlds in the Solar System. Large-scale cryovolcanic landforms have been identified on Triton's young surface, with nearly all of Triton's observed surface features likely related to cryovolcanism. One of Triton's major cryovolcanic features, Leviathan Patera , the apparent primary vent of the Cipango Planum cryovolcanic plateau which
768-437: 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,
864-539: A large section of its surface may have been flooded in large, effusive eruptions, similar to the Lunar maria . These floodplains form Vulcan Planitia and may have erupted as Charon's internal ocean froze. In 2022, low-resolution near-infrared (0.7–5 μm) spectroscopic observations by the James Webb Space Telescope (JWST) detected light hydrocarbons and complex organic molecules on the surfaces of
960-454: A lens-shaped region of melting. Other proposed methods of producing localized melts include the buildup of stress within strike-slip faults , where friction may be able to generate enough heat to melt ice; and impact events that violently heat the impact site. Intrusive models, meanwhile, propose that a deeper subsurface ocean directly injects cryomagma through fractures in the ice shell, much like volcanic dike and sill systems. Water
1056-685: A manner similar to Earth's mid-ocean ridges . In addition to this, Europa may experience a form of subduction , with one block of its icy crust sliding underneath another. Despite its young surface age, few, if any, distinct cryovolcanoes have been definitively identified on the Europan surface in the past. Nevertheless, observations of Europa from the Hubble Space Telescope (HST) in December 2012 detected columns of excess water vapor up to 200 kilometres (120 miles) high, hinting at
SECTION 10
#17327658330821152-540: A massive ~11 km (6.8 mi) high mountain that was observed on its limb at the time of Voyager 2 ' s flyby; the precise origins of the mountain is unclear, but it may be of cryovolcanic origin. Neptune and its largest moon Triton were explored by the Voyager 2 spacecraft on 25 August 1989, revealing Triton's surface features up close for the first time. With an estimated average surface age of 10–100 million years old, with some regions possibly being only
1248-623: A mountain reminiscent of a shield or dome edifice; and the neighoring Sotra Patera , an ovular depression that resembles a caldera. Several round lakes and depressions in Titan's polar regions show structural evidence of an explosive origin, including overlapping depressions, raised rims (or "ramparts"), and islands or mountains within depression rim. These characteristics led to a 2020 hypothesis by planetary scientists Charles A. Wood and Jani Radebaugh that they form from either maar -like eruptions—forming by explosions of boiling subsurface liquid as it
1344-443: 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
1440-442: A parent planet, especially if the object is on an eccentric orbit or if its orbit changes. True polar wander , where the object's surface shifts relative to its rotational axis, can introduce deformities in the ice shell. Impact events also provide an additional source of fracturing by violently disrupting and weakening the crust. An alternative model for cryovolcanic eruptions invokes solid-state convection and diapirism . If
1536-521: A portion of an object's ice shell is warm and ductile enough, it could begin to convect, much as the Earth's mantle does. As the ice convects, warmer ice becomes buoyant relative to surrounding colder ice, rising towards the surface. The convection can be aided by local density differences in the ice due to an uneven distribution of impurities in the ice shell. If the warm ice intrudes on particularly impure ice (such as ice containing large amounts of salts),
1632-406: A reservoir of subsurface cryomagma . Cryovolcanic eruptions can take many forms, such as fissure and curtain eruptions, effusive cryolava flows, and large-scale resurfacing, and can vary greatly in output volumes. Immediately after an eruption, cryolava quickly freezes, constructing geological features and altering the surface. Although rare in the inner Solar System , past and recent cryovolcanism
1728-400: A reservoir, the cryomagma must have a force driving ascent, and conduits need to be formed to the surface where cryomagma is able to ascend. A major challenge in models of cryovolcanic mechanisms is that liquid water is substantially denser than water ice, in contrast to silicates where liquid magma is less dense than solid rock. As such, cryomagma must overcome this in order to erupt onto
1824-498: A sort of solid greenhouse effect ; however, more recent analysis in 2022 disfavors the solid greenhouse effect model. An alternative cryovolcanic model, first proposed by R. L. Kirk and collaborators in 1995, instead suggests that the plumes represent explosive cryovolcanic eruption columns—an interpretation supported by the estimated observed output rate of ~200 kg/s, comparable to the output of Enceladus's plumes. The dwarf planet Pluto and its system of five moons were explored by
1920-400: A team of planetary scientists interpreted these depressions as diapirs, caldera collapse structures, or impact craters filled in by cryolava flows. To the south of Tuonela Planitia, isolated conical hills with central depressions have been noted as resembling terrestrial cinder cones, possibly pointing to cryovolcanic activity beyond Tuonela Planitia's plains. Triton's southern polar ice cap
2016-806: A team of researchers as the site of very shallow cryomagma lakes. As these subsurface lakes melt and refreeze, they fracture Europa's crust into small blocks, creating the chaos terrain. Later, in 2023, a field of cryovolcanic cones was tentatively identified near the western edge of Argadnel Regio , a region in Europa's southern hemisphere. Ganymede 's surface, like Europa's, is heavily tectonized yet appears to have few cryovolcanic features. By 2009, at least 30 irregularly-shaped depressions (termed paterae ) were identified on Ganymede's surface from Voyager and Galileo imagery. The paterae have been hypothesized by several teams of planetary scientists as caldera-like cryovolcanic vents. However, conclusive evidence for
SECTION 20
#17327658330822112-632: 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
2208-555: 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
2304-465: 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
2400-642: Is Mount Sabyinyo , which rises 3,634 metres (11,923 ft) above sea level. The Virunga Mountains are home of the endangered mountain gorilla , listed on the IUCN Red List of Endangered Species due to habitat loss , poaching , disease, and war (Butynski et al. 2003). The Karisoke Research Center , founded by Dian Fossey to observe gorillas in their native habitat, is located between Mount Karisimbi and Mount Bisoke . 01°25′45″S 29°32′54″E / 1.42917°S 29.54833°E / -1.42917; 29.54833 Volcano A volcano
2496-739: 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
2592-445: 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,
2688-412: 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
2784-437: Is common on planetary objects in the outer Solar System, especially on the icy moons of the giant planets and potentially amongst the dwarf planets as well. As such, cryovolcanism is important to the geological histories of these worlds, constructing landforms or even resurfacing entire regions. Despite this, only a few eruptions have ever been observed in the Solar System. The sporadic nature of direct observations means that
2880-565: 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
2976-449: Is expected to be the dominant component of cryomagmas. Besides water, cryomagma may contain additional impurities, drastically changing its properties. Certain compounds can lower the density of cryomagma. Ammonia ( NH 3 ) in particular may be a common component of cryomagmas, and has been detected in the plumes of Saturn 's moon Enceladus . A partially frozen ammonia-water eutectic mixture can be positively buoyant with respect to
Virunga Mountains - Misplaced Pages Continue
3072-584: 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
3168-552: Is marked by a multitude of dark streaks, likely composed of organic tholins deposited by wind-blown plumes. At least two plumes, the Mahilani Plume and the Hili Plume, have been observed, with the two plumes reaching 8 kilometres (5.0 miles) in altitude. These plumes have been hypothesized by numerous teams of researchers in the early 1990s to be driven by the buildup of nitrogen gas underneath solid nitrogen ice through
3264-663: Is one of the largest volcanic or cryovolcanic edifices in the Solar System. Triton hosts four walled plains: Ruach Planitia and Tuonela Planitia form a northern pair, and Sipapu Planitia and Ryugu Planitia form a southern pair. The walled plains are characterized by crenulated, irregularly-shaped cliffs that enclose a flat, young plain with a single group of pits and mounds. The walled plains are likely young cryovolcanic lakes and may represent Triton's youngest cryovolcanic features. The regions around Ruach and Tuonela feature additional smaller subcircular depressions, some of which are partially bordered by walls and scarps. In 2014,
3360-537: 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
3456-441: Is pulverized in violent explosions much like volcanic ash and tephra , producing cryoclastic material. Effusive cryovolcanism takes place with little to no explosive activity and is instead characterized by widespread cryolava flows which cover the pre-existing landscape. In contrast to explosive cryovolcanism, no instances of active effusive cryovolcanism have been observed. Structures constructed by effusive eruptions depend on
3552-456: Is rapidly heated by magma (in this case, cryomagma) —or the flooding of collapse calderas. On 24 January 1986, Uranus and its system of moons were explored for the first time by the Voyager 2 spacecraft. Of Uranus's five major satellites, Miranda and Ariel appear to have unusually youthful surfaces indicative of relatively recent activity. Miranda in particular has extraordinarily varied terrain, with striking angular features known as
3648-722: Is the innermost object in the Solar System known to be cryovolcanically active. Upon the arrival of the Dawn orbiter in March 2015, the dwarf planet was discovered to have numerous bright spots (designated as faculae ) located within several major impact basins, most prominently in the center of Occator Crater . These bright spots are composed primarily of various salts, and are hypothesized to have formed from impact-induced upwelling of subsurface material that erupt brine to Ceres's surface. The distribution of hydrated sodium chloride on one particular bright spot, Cerealia Facula , indicates that
3744-471: 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
3840-617: The New Horizons spacecraft in a flyby on 14 July 2015, observing their surface features in detail for the first time. The surface of Pluto varies dramatically in age, and several regions appear to display relatively recent cryovolcanic activity. The most reliably identified cryovolcanic structures are Wright Mons and Piccard Mons , two large mountains with central depressions which have led to hypotheses that they may be cryovolcanoes with peak calderas. The two mountains are surrounded by an unusual region of hilly "hummocky terrain", and
3936-536: The Tiger Stripes . Enceladus's cryovolcanic activity is sustained by a global subsurface ocean. Other regions centered on Enceladus's leading and trailing hemispheres—the hemispheres that "face" towards or against the direction of Enceladus's orbit—exhibit similar terrain to that of the Tiger Stripes, possibly indicating that Enceladus has experienced discrete periods of heightened cryovolcanism in
Virunga Mountains - Misplaced Pages Continue
4032-411: The coronae cutting across older terrain. Inverness Corona is located near Miranda's south pole and is estimated to be less than 1 billion years old, and broad similarities between Miranda's coronae and Enceladus's south polar region have been noted. These characteristics have led to several teams of researchers to propose a cryovolcanic origin of the coronae, where eruptions of viscous cryomagma form
4128-617: 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
4224-527: The Kinyarwanda word ibirunga , which means "volcanoes". The mountain range consists of eight major volcanoes. Most of them are dormant, except Mount Nyiragongo 3,462 metres (11,358 ft) and Mount Nyamuragira 3,063 metres (10,049 ft), both in the DRC. Recent eruptions occurred in 2006, 2010 and May 2021. Mount Karisimbi is the highest volcano at 4,507 metres (14,787 ft). The oldest mountain
4320-804: 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,
4416-834: 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
4512-622: 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
4608-613: 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
4704-510: 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
4800-402: 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
4896-423: The decay of radioactive isotopes in their rocky cores. Reservoirs of cryomagma can hypothetically form within the shell of an icy world as well, either from direct localized melting or the injection of cryomagma from a deeper subsurface ocean. A convective layer in the ice shell can generate warm plumes that spread laterally at the base of the brittle icy crust. The intruding warm ice can melt impure ice, forming
SECTION 50
#17327658330824992-485: The dwarf planets Quaoar , Gonggong , and Sedna . The detection indicated that all three have experienced internal melting and planetary differentiation in their pasts. The presence of volatiles on their surfaces indicates that cryovolcanism may be resupplying methane. JWST spectral observations of Eris and Makemake revealed that hydrogen-deuterium and carbon isotopic ratios indicated that both dwarf planets are actively replenishing surface methane as well, possibly with
5088-799: 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
5184-463: The existence of weak, possibly cryovolcanic plumes. The plumes were observed again by the HST in 2014. However, as these are distant observations, the plumes have yet to be definitively confirmed as eruptions. Recent analyses of some Europan surface features have proposed cryovolcanic origins for them as well. In 2011, Europa's chaos terrain , where the crust appears especially disrupted, was interpreted by
5280-431: 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
5376-610: 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
5472-585: 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
5568-466: 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
5664-587: The icy crust, enabling its eruption. Methanol ( CH 3 OH ) can lower cryomagma density even further, whilst significantly increasing viscosity. Conversely, some impurities can increase the density of cryomagma. Salts, such as magnesium sulfate ( MgSO 4 ) and sodium sulfate ( Na 2 SO 4 ) significantly increases density with comparatively minor changes in viscosity. Salty or briny cryomagma compositions may be important cryovolcanism on Jupiter 's icy moons, where salt-dominated impurities are likely more common. Besides affecting density and viscosity,
5760-567: The inclusions of impurities—particularly salts and especially ammonia—can encourage melting by significantly lowering the melting point of cryomagma. Although there are broad parallels between cryovolcanism and terrestrial (or "silicate") volcanism, such as the construction of domes and shields, the definitive identification of cryovolcanic structures is difficult. The unusual properties of water-dominated cryolava, for example, means that cryovolcanic features are difficult to interpret using criteria applied to terrestrial volcanic features. Ceres
5856-492: 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
SECTION 60
#17327658330825952-491: The lack of distinct flow features have led to an alternative proposal in 2022 by a team of researchers that the structures may instead be formed by sequential dome-forming eruptions, with nearby Coleman Mons being a smaller independent dome. Virgil Fossae, a large fault within Belton Regio , may also represent another site of cryovolcanism on Pluto. An estimated 300 kilometres (190 miles) of Virgil Fossae's western section
6048-419: 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
6144-551: 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
6240-452: The moon's slightly eccentric orbit allows the rocky core to dissipate energy and generate heat. Evidence for subsurface oceans also exist for the dwarf planets Pluto and, to a lesser extent, Ceres , Eris , Makemake , Sedna , Gonggong , and Quaoar . In the case of Pluto and the other dwarf planets, there is comparatively little, if any, long-term tidal heating. Thus, heating must largely be self-generated, primarily coming from
6336-415: 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
6432-400: The most prominent construct on Ceres, despite its geologically young age. Europa receives enough tidal heating from Jupiter to sustain a global liquid water ocean. Its surface is exceedingly young, at roughly 60 to 90 million years old. Its most striking features, a dense web of linear cracks and faults termed lineae , appear to be the sites of active resurfacing on Europa, proceeding in
6528-438: 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
6624-452: 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
6720-876: 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
6816-549: 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
6912-420: 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
7008-471: 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
7104-468: 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
7200-425: 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
7296-442: The past. Saturn's moon Titan has a dense atmospheric haze layer which permanently obscures visible observations of its surface features, making the definitive identification of cryovolcanic structures especially difficult. Titan has an extensive subsurface ocean, encouraging searches for evidence of cryovolcanism. From Cassini radar data, several features have been proposed as candidate cryovolcanoes, most notably Doom Mons ,
7392-619: 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
7488-649: The presence of a subsurface ocean. These observations, combined with the discoveries in the Pluto system by the New Horizons spacecraft, indicate that icy worlds are capable of sustaining enough heat on their own to drive cryovolcanic activity. In contrast to the icy satellites of the giant planets, where many benefit from extensive tidal heating from their parent planets, the dwarf planets must rely on heat generated primarily or almost entirely by themselves. Leftover primordial heat from formation and radiogenic heat from
7584-435: 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
7680-492: 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
7776-622: 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
7872-502: The structures with some tectonic involvement. Ariel also exhibits widespread resurfacing, with large polygonal crustal blocks divided by large canyons ( chasmata ) with floors as young as ~0.8 ± 0.5 billion years old, while relatively flat plains may have been the site of large flood eruptions. Evidence for relatively recent cryovolcanism on the other three round moons of Uranus is less clear. Titania hosts large chasms but does not show any clear evidence of cryovolcanism. Oberon has
7968-406: 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
8064-600: The term ice volcano is sometimes used colloquially. Explosive cryovolcanism, or cryoclastic eruptions , is expected to be driven by the exsolvation of dissolved volatile gasses as pressure drops whilst cryomagma ascends, much like the mechanisms of explosive volcanism on terrestrial planets. Whereas terrestrial explosive volcanism is primarily driven by dissolved water ( H 2 O ), carbon dioxide ( CO 2 ), and sulfur dioxide ( SO 2 ), explosive cryovolcanism may instead be driven by methane ( CH 4 ) and carbon monoxide ( CO ). Upon eruption, cryovolcanic material
8160-434: 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
8256-444: 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
8352-582: The true number of extant cryovolcanoes is contentious. Like volcanism on the terrestrial planets , cryovolcanism is driven by escaping internal heat from within a celestial object, often supplied by extensive tidal heating in the case of the moons of the giant planets. However, isolated dwarf planets are capable of retaining enough internal heat from formation and radioactive decay to drive cryovolcanism on their own, an observation which has been supported by both in situ observations by spacecraft and distant observations by telescopes. The term cryovolcano
8448-431: 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
8544-591: The upwelling occurred recently or is currently ongoing. That brine exists in Ceres's interior implies that salts played a role in keeping Ceres's subsurface ocean liquid, potentially even to the present day. Dawn also discovered Ahuna Mons and Yamor Mons (formerly Ysolos Mons), two prominent isolated mountains which are likely young cryovolcanic domes. It is expected that cryovolcanic domes eventually subside after becoming extinct due to viscous relaxation, flattening them. This would explain why Ahuna Mons appears to be
8640-478: The viscosity of the erupted material. Eruptions of less viscous cryolava can resurface large regions and form expansive, relatively flat plains, similar to shield volcanoes and flood basalt eruptions on terrestrial planets. More viscous erupted material does not travel as far, and instead can construct localized high-relief features such as cryovolcanic domes. For cryovolcanism to occur, three conditions must be met: an ample supply of cryomagma must be produced in
8736-492: 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
8832-424: 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
8928-437: The warm ice can lead to the melting of the impure ice. The melting may then go on to erupt or uplift terrain to form surface diapirs. Cryovolcanism implies the generation of large volumes of molten fluid in the interiors of icy worlds. A primary reservoir of such fluid are subsurface oceans. Subsurface oceans are widespread amongst the icy satellites of the giant planets and are largely maintained by tidal heating , where
9024-536: Was coined by Steven K. Croft in a 1987 conference abstract at the Geological Society of America (GSA) Abstract with Programs. The term is ultimately a combination of cryo-, from the Ancient Greek κρῠ́ος ( krúos , meaning cold or frost), and volcano. In general, terminology used to describe cryovolcanism is analogous to volcanic terminology: As cryovolcanism largely takes place on icy worlds,
9120-421: 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
9216-402: Was likely the site of a fountaining eruption, spewing and dispersing material that covered surrounding terrain up to 200 kilometres (120 miles) away. More recently, in 2021 Hekla Cavus was hypothesized to have formed from a cryovolcanic collapse by a team of two researchers, C. J. Ahrens and V. F. Chevrier. Similarly, in 2021 a team of planetary scientists led by A. Emran proposed that Kiladze,
#81918