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106-462: Like the other cinder cones in the area, Lava Butte only experienced a single eruption , dated by geologists in 1977 to 6,150 carbon-14 years, equivalent to about 7,000 years ago. The eruption began with a fissure spewing hot cinders to form the cone. In the next phase, a river of hot basalt flowed from the base of the small volcano to cover a large area to the west with a lava flow which remains largely free of vegetation. The lava flows reached

212-701: A magnitude of 4, but acoustic waves travel well in water and over long periods of time. A system in the North Pacific , maintained by the United States Navy and originally intended for the detection of submarines , has detected an event on average every 2 to 3 years. The most common underwater flow is pillow lava , a rounded lava flow named for its unusual shape. Less common are glassy , marginal sheet flows, indicative of larger-scale flows. Volcaniclastic sedimentary rocks are common in shallow-water environments. As plate movement starts to carry

318-886: 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

424-498: A Peléan eruption are very similar to that of a Vulcanian eruption, except that in Peléan eruptions the volcano's structure is able to withstand more pressure, hence the eruption occurs as one large explosion rather than several smaller ones. Volcanoes known to have Peléan activity include: Plinian eruptions (or Vesuvian eruptions) are a type of volcanic eruption named for the historical eruption of Mount Vesuvius in 79 AD that buried

530-420: A Plinian eruption, and reach up 2 to 45 km (1 to 28 mi) into the atmosphere . The densest part of the plume, directly above the volcano, is driven internally by gas expansion . As it reaches higher into the air the plume expands and becomes less dense, convection and thermal expansion of volcanic ash drive it even further up into the stratosphere . At the top of the plume, powerful winds may drive

636-406: A coming eruption is the growth of a so-called Peléan or lava spine , a bulge in the volcano's summit preempting its total collapse. The material collapses upon itself, forming a fast-moving pyroclastic flow (known as a block -and- ash flow) that moves down the side of the mountain at tremendous speeds, often over 150 km (93 mi) per hour. These landslides make Peléan eruptions one of

742-437: 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,

848-443: 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

954-401: A probable cause for higher levels of volcanism. The technology for studying seamount eruptions did not exist until advancements in hydrophone technology made it possible to "listen" to acoustic waves , known as T-waves, released by submarine earthquakes associated with submarine volcanic eruptions. The reason for this is that land-based seismometers cannot detect sea-based earthquakes below

1060-435: A single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either. Some volcanoes exhibit lateral and fissure eruptions . Notably, many Hawaiian eruptions start from rift zones . Scientists believed that pulses of magma mixed together in the magma chamber before climbing upward—a process estimated to take several thousands of years. Columbia University volcanologists found that

1166-410: A stable height of around 2,500 m (8,200 ft) for 18 minutes, briefly peaking at a height of 3,400 m (11,000 ft). Volcanoes known to have Hawaiian activity include: Strombolian eruptions are a type of volcanic eruption named after the volcano Stromboli , which has been erupting nearly continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within

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1272-508: A type of volcanic eruption characterized by interactions between lava and ice , often under a glacier . The nature of glaciovolcanism dictates that it occurs at areas of high latitude and high altitude . It has been suggested that subglacial volcanoes that are not actively erupting often dump heat into the ice covering them, producing meltwater . This meltwater mix means that subglacial eruptions often generate dangerous jökulhlaups ( floods ) and lahars . Volcano A volcano

1378-490: A type of volcanic eruption named after the volcano Mount Pelée in Martinique , the site of a Peléan eruption in 1902 that is one of the worst natural disasters in history. In Peléan eruptions, a large amount of gas, dust, ash, and lava fragments are blown out the volcano's central crater, driven by the collapse of rhyolite , dacite , and andesite lava domes that often creates large eruptive columns . An early sign of

1484-446: A volcanic cone on Kilauea , erupted continuously for over 35 years. Another Hawaiian volcanic feature is the formation of active lava lakes , self-maintaining pools of raw lava with a thin crust of semi-cooled rock. Flows from Hawaiian eruptions are basaltic, and can be divided into two types by their structural characteristics. Pahoehoe lava is a relatively smooth lava flow that can be billowy or ropey. They can move as one sheet, by

1590-632: 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

1696-555: 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

1802-465: 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

1908-739: 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

2014-445: 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,

2120-412: 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

2226-437: Is characterized by a series of short-lived explosions, lasting a few minutes to a few hours and typified by the ejection of volcanic bombs and blocks . These eruptions wear down the lava dome holding the magma down, and it disintegrates, leading to much more quiet and continuous eruptions. Thus an early sign of future Vulcanian activity is lava dome growth, and its collapse generates an outpouring of pyroclastic material down

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2332-565: 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

2438-663: Is expelled from a volcanic vent or fissure —have been distinguished by volcanologists . These are often named after famous volcanoes where that type of behavior has been observed. Some volcanoes may exhibit only one characteristic type of eruption during a period of activity, while others may display an entire sequence of types all in one eruptive series. There are three main types of volcanic eruption: Within these broad eruptive types are several subtypes. The weakest are Hawaiian and submarine , then Strombolian , followed by Vulcanian and Surtseyan . The stronger eruptive types are Pelean eruptions , followed by Plinian eruptions ;

2544-584: 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

2650-502: Is generally in the form of episodic explosive eruptions accompanied by the distinctive loud blasts. During eruptions, these blasts occur as often as every few minutes. The term "Strombolian" has been used indiscriminately to describe a wide variety of volcanic eruptions, varying from small volcanic blasts to large eruptive columns . In reality, true Strombolian eruptions are characterized by short-lived and explosive eruptions of lavas with intermediate viscosity , often ejected high into

2756-537: 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

2862-500: Is only moderately dispersed, and its abundance indicates a high degree of fragmentation , the result of high gas contents within the magma. In some cases these have been found to be the result of interaction with meteoric water , suggesting that Vulcanian eruptions are partially hydrovolcanic . Volcanoes that have exhibited Vulcanian activity include: Vulcanian eruptions are estimated to make up at least half of all known Holocene eruptions. Peléan eruptions (or nuée ardente ) are

2968-471: 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

3074-420: The 1886 eruption of Mount Tarawera . Littoral cones are another hydrovolcanic feature, generated by the explosive deposition of basaltic tephra (although they are not truly volcanic vents). They form when lava accumulates within cracks in lava, superheats and explodes in a steam explosion , breaking the rock apart and depositing it on the volcano's flank. Consecutive explosions of this type eventually generate

3180-617: 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

3286-477: The Deschutes River about 2.5 miles (4.0 km) to the west of the cone, burying its former channel under over 100 feet (30 m) of lava and damming the river to form a lake, known as Lake Benham. The river eventually overflowed the lava dam and eroded down into it, draining the lake and forming Benham Falls . Geologists estimate that 90% of the magma erupted as lava flows, 9% as scoria which forms

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3392-470: The Roman towns of Pompeii and Herculaneum and, specifically, for its chronicler Pliny the Younger . The process powering Plinian eruptions starts in the magma chamber , where dissolved volatile gases are stored in the magma. The gases vesiculate and accumulate as they rise through the magma conduit . These bubbles agglutinate and once they reach a certain size (about 75% of the total volume of

3498-804: 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,

3604-410: The effusive eruption of very fluid basalt -type lavas with low gaseous content . The volume of ejected material from Hawaiian eruptions is less than half of that found in other eruptive types. Steady production of small amounts of lava builds up the large, broad form of a shield volcano . Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around

3710-428: The eruption column . Base surges are caused by the gravitational collapse of a vaporous eruptive column, one that is denser overall than a regular volcanic column. The densest part of the cloud is nearest to the vent, resulting in a wedge shape. Associated with these laterally moving rings are dune -shaped depositions of rock left behind by the lateral movement. These are occasionally disrupted by bomb sags , rock that

3816-834: 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

3922-419: The magma . These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slugs . These grow large enough to rise through the lava column. Upon reaching the surface, the difference in air pressure causes the bubble to burst with a loud pop, throwing magma in the air in a way similar to a soap bubble . Because of the high gas pressures associated with the lavas, continued activity

4028-430: The magma chamber differentiates with upper portions rich in silicon dioxide , or if magma ascends rapidly. Plinian eruptions are similar to both Vulcanian and Strombolian eruptions, except that rather than creating discrete explosive events, Plinian eruptions form sustained eruptive columns. They are also similar to Hawaiian lava fountains in that both eruptive types produce sustained eruption columns maintained by

4134-417: The pyroclastic flows generated by material collapse, which move down the side of the mountain at extreme speeds of up to 700 km (435 mi) per hour and with the ability to extend the reach of the eruption hundreds of kilometers. The ejection of hot material from the volcano's summit melts snowbanks and ice deposits on the volcano, which mixes with tephra to form lahars , fast moving mudflows with

4240-503: The ʻAʻā lava flow of Lava Butte. The cinder cone was also exploited to some extent for its economic value. In June 1926, a quarry was developed in the fault scarp east of Lava Butte as a source for paving material for the first The Dalles - California Highway (later U.S. Route 97 ). In November 1929, cinders from Lava Butte were shipped to Longview, Washington , to be used in construction of Longview Bridge across Columbia River . A United States Forest Service fire lookout tower

4346-666: The Bend Chamber of Commerce simulated an eruption to surprise a visiting Portland group. In 1925, USGS geologist Harold Stearns studied the Newberry area and recognized the fissure system which extends from Lava Butte to East Lake within Newberry Caldera . Sometime after 1901, the Great Northern Railway was extended south through the area. The construction crew built the rail line directly through

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4452-568: The Hawaiian volcano deity). During especially high winds these chunks may even take the form of long drawn-out strands, known as Pele's hair . Sometimes basalt aerates into reticulite , the lowest density rock type on earth. Although Hawaiian eruptions are named after the volcanoes of Hawaii, they are not necessarily restricted to them; the highest lava fountain recorded was during the 23 November 2013 eruption of Mount Etna in Italy, which reached

4558-567: The Lava Butte Geological Area. From early May to mid October, a shuttle transports visitors up Red Cinder Road from the Lava Lands Visitor Center to the lookout on Lava Butte. Hiking up Red Cinder Road is a year-round option. A scenic rim trail around the top of Lava Butte is 0.35 miles (0.56 km) long. Volcanic eruption Several types of volcanic eruptions —during which material

4664-570: 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

4770-583: The U.S. Forest Service created the 8,983 acres (3,635 ha) Lava Butte Geological Area to protect the cinder cone, with plans for recreational and interpretive development. Construction of the Lava Lands Visitor Center located just south of the cone began in April 1969 and it was finally dedicated in September 1975. In November 1990, Newberry National Volcanic Monument was created encompassing Newberry Crater, Lava Cast Forest Geological Area, Lava River Cave, and

4876-613: 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

4982-468: The advancement of "toes", or as a snaking lava column. A'a lava flows are denser and more viscous than pahoehoe, and tend to move slower. Flows can measure 2 to 20 m (7 to 66 ft) thick. A'a flows are so thick that the outside layers cools into a rubble-like mass, insulating the still-hot interior and preventing it from cooling. A'a lava moves in a peculiar way—the front of the flow steepens due to pressure from behind until it breaks off, after which

5088-427: The air before hitting the ground, resulting in the accumulation of cindery scoria fragments; when the air is especially thick with clasts , they cannot cool off fast enough due to the surrounding heat, and hit the ground still hot, the accumulation of which forms spatter cones . If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived; Puʻu ʻŌʻō ,

5194-1087: The air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basaltic lava, and its end product is mostly scoria . The relative passivity of Strombolian eruptions, and its non-damaging nature to its source vent allow Strombolian eruptions to continue unabated for thousands of years, and also makes it one of the least dangerous eruptive types. Strombolian eruptions eject volcanic bombs and lapilli fragments that travel in parabolic paths before landing around their source vent. The steady accumulation of small fragments builds cinder cones composed completely of basaltic pyroclasts . This form of accumulation tends to result in well-ordered rings of tephra . Strombolian eruptions are similar to Hawaiian eruptions , but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive columns , do not produce some volcanic products associated with Hawaiian volcanism (specifically Pele's tears and Pele's hair ), and produce fewer molten lava flows (although

5300-510: 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

5406-606: The buildup of high gas pressure , eventually popping the cap holding the magma down and resulting in an explosive eruption. Unlike Strombolian eruptions, ejected lava fragments are not aerodynamic; this is due to the higher viscosity of Vulcanian magma and the greater incorporation of crystalline material broken off from the former cap. They are also more explosive than their Strombolian counterparts, with eruptive columns often reaching between 5 and 10 km (3 and 6 mi) high. Lastly, Vulcanian deposits are andesitic to dacitic rather than basaltic . Initial Vulcanian activity

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5512-402: 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

5618-563: The cone, and 1% as volcanic ash which forms a thin layer extending to the north. The early history of Lava Butte is not known, but it is assumed that Native Americans observed the eruptions and later ascended the prominent new landmark. White settlers arriving in the 1800s also noted the landmark. In 1903, I.C. Russell was the first geologist to study the butte and speculated that it erupted as recently as 150 years ago. Dr. Howel Williams estimated it to be much older, but incorrectly at 1,000 years old. In September 1914, Lava Butte "erupted" when

5724-434: The cone. Volcanoes known to have Surtseyan activity include: Submarine eruptions occur underwater. An estimated 75% of volcanic eruptive volume is generated by submarine eruptions near mid ocean ridges alone. Problems detecting deep sea volcanic eruptions meant their details were virtually unknown until advances in the 1990s made it possible to observe them. Submarine eruptions may produce seamounts , which may break

5830-422: The consistency of wet concrete that move at the speed of a river rapid . Major Plinian eruptive events include: Phreatomagmatic eruptions are eruptions that arise from interactions between water and magma . They are driven by thermal contraction of magma when it comes in contact with water (as distinguished from magmatic eruptions, which are driven by thermal expansion). This temperature difference between

5936-799: 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

6042-650: The eruption and formation of the island of Surtsey off the coast of Iceland in 1963. Surtseyan eruptions are the "wet" equivalent of ground-based Strombolian eruptions , but because they take place in water they are much more explosive. As water is heated by lava, it flashes into steam and expands violently, fragmenting the magma it contacts into fine-grained ash . Surtseyan eruptions are typical of shallow-water volcanic oceanic islands , but they are not confined to seamounts. They can happen on land as well, where rising magma that comes into contact with an aquifer (water-bearing rock formation) at shallow levels under

6148-441: The eruption of Costa Rica's Irazú Volcano in 1963 was likely triggered by magma that took a nonstop route from the mantle over just a few months. It is important when studying the products of explosive eruptions to distinguish between...: George P. L. Walker , Quoted The volcanic explosivity index (commonly shortened to VEI) is a scale, from 0 to 8, for measuring the strength of eruptions but does not capture all of

6254-466: The eruptive material does tend to form small rivulets). Volcanoes known to have Strombolian activity include: Vulcanian eruptions are a type of volcanic eruption named after the volcano Vulcano . It was named so following Giuseppe Mercalli 's observations of its 1888–1890 eruptions. In Vulcanian eruptions, intermediate viscous magma within the volcano make it difficult for vesiculate gases to escape. Similar to Strombolian eruptions, this leads to

6360-444: The explosive nature than thermal contraction. Fuel coolant reactions may fragment the volcanic material by propagating stress waves , widening cracks and increasing surface area that ultimately leads to rapid cooling and explosive contraction-driven eruptions. A Surtseyan (or hydrovolcanic) eruption is a type of volcanic eruption characterized by shallow-water interactions between water and lava, named after its most famous example,

6466-431: 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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6572-610: 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

6678-585: 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

6784-429: The general mass behind it moves forward. Pahoehoe lava can sometimes become A'a lava due to increasing viscosity or increasing rate of shear , but A'a lava never turns into pahoehoe flow. Hawaiian eruptions are responsible for several unique volcanological objects. Small volcanic particles are carried and formed by the wind, chilling quickly into teardrop-shaped glassy fragments known as Pele's tears (after Pele ,

6890-466: 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

6996-434: The growth of bubbles that move up at about the same speed as the magma surrounding them. Regions affected by Plinian eruptions are subjected to heavy pumice airfall affecting an area 0.5 to 50 km (0 to 12 cu mi) in size. The material in the ash plume eventually finds its way back to the ground, covering the landscape in a thick layer of many cubic kilometers of ash. The most dangerous eruptive feature are

7102-492: 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

7208-423: The magma conduit) they explode. The narrow confines of the conduit force the gases and associated magma up, forming an eruptive column . Eruption velocity is controlled by the gas contents of the column, and low-strength surface rocks commonly crack under the pressure of the eruption, forming a flared outgoing structure that pushes the gases even faster. These massive eruptive columns are the distinctive feature of

7314-419: 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

7420-551: 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

7526-424: The most dangerous in the world, capable of tearing through populated areas and causing serious loss of life. The 1902 eruption of Mount Pelée caused tremendous destruction, killing more than 30,000 people and completely destroying St. Pierre , the worst volcanic event in the 20th century . Peléan eruptions are characterized most prominently by the incandescent pyroclastic flows that they drive. The mechanics of

7632-415: 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

7738-438: 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

7844-452: 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

7950-876: 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

8056-549: 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

8162-420: 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

8268-471: 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

8374-403: The one extreme there are effusive Hawaiian eruptions, which are characterized by lava fountains and fluid lava flows , which are typically not very dangerous. On the other extreme, Plinian eruptions are large, violent, and highly dangerous explosive events. Volcanoes are not bound to one eruptive style, and frequently display many different types, both passive and explosive, even in the span of

8480-468: 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

8586-425: 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

8692-422: The plume away from the volcano . These highly explosive eruptions are usually associated with volatile-rich dacitic to rhyolitic lavas, and occur most typically at stratovolcanoes . Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic volcanoes. Although they are usually associated with felsic magma, Plinian eruptions can occur at basaltic volcanoes, if

8798-619: 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

8904-618: The properties that may be perceived to be important. It is used by the Smithsonian Institution 's Global Volcanism Program in assessing the impact of historic and prehistoric lava flows. It operates in a way similar to the Richter scale for earthquakes , in that each interval in value represents a tenfold increasing in magnitude (it is logarithmic ). The vast majority of volcanic eruptions are of VEIs between 0 and 2. Magmatic eruptions produce juvenile clasts during explosive decompression from gas release. They range in intensity from

9010-445: The relatively small lava fountains on Hawaii to catastrophic Ultra-Plinian eruption columns more than 30 km (19 mi) high, bigger than the eruption of Mount Vesuvius in 79 AD that buried Pompeii . Hawaiian eruptions are a type of volcanic eruption named after the Hawaiian volcanoes , such as Mauna Loa , with this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by

9116-504: The rising plate, lowering its melting point . Each process generates different rock; mid-ocean ridge volcanics are primarily basaltic , whereas subduction flows are mostly calc-alkaline , and more explosive and viscous . Spreading rates along mid-ocean ridges vary widely, from 2 cm (0.8 in) per year at the Mid-Atlantic Ridge , to up to 16 cm (6 in) along the East Pacific Rise . Higher spreading rates are

9222-435: 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

9328-492: 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

9434-622: 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

9540-732: The strongest eruptions are called Ultra-Plinian . Subglacial and phreatic eruptions are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is the Volcanic Explosivity Index an order-of-magnitude scale, ranging from 0 to 8, that often correlates to eruptive types. Volcanic eruptions arise through three main mechanisms: In terms of activity, there are explosive eruptions and effusive eruptions . The former are characterized by gas-driven explosions that propel magma and tephra. The latter pour out lava without significant explosion. Volcanic eruptions vary widely in strength. On

9646-471: The summit and from fissure vents radiating out of the center. Hawaiian eruptions often begin as a line of vent eruptions along a fissure vent , a so-called "curtain of fire." These die down as the lava begins to concentrate at a few of the vents. Central-vent eruptions, meanwhile, often take the form of large lava fountains (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in

9752-400: The surface and form volcanic islands. Submarine volcanism is driven by various processes. Volcanoes near plate boundaries and mid-ocean ridges are built by the decompression melting of mantle rock that rises on an upwelling portion of a convection cell to the crustal surface. Eruptions associated with subducting zones , meanwhile, are driven by subducting plates that add volatiles to

9858-406: 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

9964-434: 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

10070-444: 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

10176-424: The two causes violent water-lava interactions that make up the eruption. The products of phreatomagmatic eruptions are believed to be more regular in shape and finer grained than the products of magmatic eruptions because of the differences in eruptive mechanisms. There is debate about the exact nature of phreatomagmatic eruptions, and some scientists believe that fuel-coolant reactions may be more critical to

10282-431: 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

10388-429: The volcano can cause them. The products of Surtseyan eruptions are generally oxidized palagonite basalts (though andesitic eruptions do occur, albeit rarely), and like Strombolian eruptions Surtseyan eruptions are generally continuous or otherwise rhythmic. A defining feature of a Surtseyan eruption is the formation of a pyroclastic surge (or base surge ), a ground hugging radial cloud that develops along with

10494-467: The volcano's slope. Deposits near the source vent consist of large volcanic blocks and bombs , with so-called " bread-crust bombs " being especially common. These deeply cracked volcanic chunks form when the exterior of ejected lava cools quickly into a glassy or fine-grained shell, but the inside continues to cool and vesiculate . The center of the fragment expands, cracking the exterior. The bulk of Vulcanian deposits are fine grained ash . The ash

10600-492: 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

10706-463: The volcanoes away from their eruptive source, eruption rates start to die down, and water erosion grinds the volcano down. The final stages of eruption cap the seamount in alkalic flows. There are about 100,000 deepwater volcanoes in the world, although most are beyond the active stage of their life. Some exemplary seamounts are Kamaʻehuakanaloa (formerly Loihi), Bowie Seamount , Davidson Seamount , and Axial Seamount . Subglacial eruptions are

10812-424: 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

10918-494: Was built on the summit in 1931, and in early 1933 a steep, single-lane road was constructed spiraling up to the summit. In February of that year, the local Skyliners ski club proposed a ski jump on Lava Butte, but it was never built. In June 1946, widening of the road up Lava Butte to two lanes was completed, along with constructing two small parking lots at the summit. The road was later paved in July 1950. The original lookout

11024-421: 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

11130-605: Was flung out by the explosive eruption and followed a ballistic path to the ground. Accumulations of wet, spherical ash known as accretionary lapilli are another common surge indicator. Over time Surtseyan eruptions tend to form maars , broad low- relief volcanic craters dug into the ground, and tuff rings , circular structures built of rapidly quenched lava. These structures are associated with single vent eruptions. If eruptions arise along fracture zones , rift zones may be dug out. Such eruptions tend to be more violent than those which form tuff rings or maars, an example being

11236-483: Was replaced with a larger one in 1957, which was subsequently enlarged in 1962 to accommodate a small visitor center and museum on the first floor. In 1998 this was replaced with a new lookout built in the original L-4 style of 1931. In July 1966, twenty-two astronauts trained in Central Oregon for the upcoming Moon landings , at sites including Lava Butte, Lava River Cave , and Newberry Crater. In May 1967

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