Misplaced Pages

#248751

67-434: Garibaldi Lake lies in a deep subalpine basin, with its surface at nearly 1,500 m (4,900 ft) above sea level and a depth exceeding 250 m (820 ft). It is almost entirely surrounded by mountains except at its northwestern tip, with volcanoes along the north, west, and south sides and non-volcanic peaks along the northeast and eastern shores. Lava flows from the volcanoes of Mount Price and Clinker Peak to

134-493: A ghost town ) and Fourpeaked Mountain in Alaska, which, before its September 2006 eruption, had not erupted since before 8000 BCE. Planetary-mass object A planetary-mass object ( PMO ), planemo , or planetary body (sometimes referred to as a world ) is, by geophysical definition of celestial objects , any celestial object massive enough to achieve hydrostatic equilibrium , but not enough to sustain core fusion like

201-842: 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

268-421: A star . The purpose of this term is to classify together a broader range of celestial objects than ' planet ', since many objects similar in geophysical terms do not conform to conventional expectations for a planet. Planetary-mass objects can be quite diverse in origin and location. They include planets , dwarf planets , planetary-mass satellites and free-floating planets , which may have been ejected from

335-437: 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,

402-472: A large boulder field which gives Rubble Creek its name. Concerns about the Barrier's instability due to volcanic, tectonic, or heavy rainfall activity prompted the provincial government to declare the area immediately below it unsafe for human habitation in 1981. This led to the evacuation of the nearby village of Garibaldi, British Columbia , and the relocation of residents to new recreational subdivisions away from

469-542: A larger object such as 2MASS J04414489+2301513 . Binary systems of sub-brown dwarfs are theoretically possible; Oph 162225-240515 was initially thought to be a binary system of a brown dwarf of 14 Jupiter masses and a sub-brown dwarf of 7 Jupiter masses, but further observations revised the estimated masses upwards to greater than 13 Jupiter masses, making them brown dwarfs according to the IAU working definitions. Rogue planets in stellar clusters have similar velocities to

536-443: 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

603-408: A subtype of planet. The International Astronomical Union (IAU) accepted the term (rather than the more neutral 'planetoid') but decided to classify dwarf planets as a separate category of object. In close binary star systems, one of the stars can lose mass to a heavier companion. Accretion-powered pulsars may drive mass loss. The shrinking star can then become a planetary-mass object. An example

670-416: A system ( rogue planets ) or formed through cloud-collapse rather than accretion ( sub-brown dwarfs ). While the term technically includes exoplanets and other objects, it is often used for objects with an uncertain nature or objects that do not fit in one specific class. Cases in which the term is often used: The three largest satellites Ganymede , Titan , and Callisto are of similar size or larger than

737-632: 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

SECTION 10

#1732845594249

804-555: 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

871-465: 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

938-727: 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

1005-427: Is a Jupiter-mass object orbiting the pulsar PSR J1719−1438 . These shrunken white dwarfs may become a helium planet or carbon planet . Stars form via the gravitational collapse of gas clouds, but smaller objects can also form via cloud collapse . Planetary-mass objects formed this way are sometimes called sub-brown dwarfs. Sub-brown dwarfs may be free-floating such as Cha 110913−773444 and OTS 44 , or orbiting

1072-412: 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

1139-554: 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

1206-567: 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

1273-477: Is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibrious shape (usually a spheroid), but has not cleared the neighborhood of other material around its orbit. Planetary scientist and New Horizons principal investigator Alan Stern , who proposed the term 'dwarf planet', has argued that location should not matter and that only geophysical attributes should be taken into account, and that dwarf planets are thus

1340-524: 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

1407-466: 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

SECTION 20

#1732845594249

1474-600: 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

1541-792: 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,

1608-824: 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

1675-612: 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

1742-595: The Squamish River. However, the "District of Squamish Integrated Flood Hazard Management Plan - Final Report" (PDF) . notes that a large collapse of the Barrier could potentially block the Cheakamus River increasing the possibility of a debris flood that could affect the Paradise Valley. All recreational activities in the area are governed by the regulations of Garibaldi Provincial Park . Primary access to

1809-609: 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

1876-409: The base of The Barrier. During spring snowmelt, outflow is sufficient for surface drainage to occur via a shallow channel across the lava flow, into Lesser Garibaldi Lake and Barrier Lake about 1.6 km (0.99 mi) west of the main lake's shore. The unstable lava formation of The Barrier has in the past unleashed several debris flows in the area below the lake, most recently in 1855-56 forming

1943-503: 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

2010-402: 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

2077-465: The eastern end of the lake is severely limited, since no trails have been constructed along the steep and unstable slopes which plunge directly into the lake. During winter, the lake is typically frozen from late December to late April, allowing backcountry skiers and snowshoers to easily reach the far shore. A pair of small alpine huts are located in Sphinx Bay on the eastern shore and Sentinel Bay at

Garibaldi Lake - Misplaced Pages Continue

2144-772: 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

2211-431: 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

2278-592: 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

2345-568: 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

2412-461: 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

2479-508: The hazard zone. Collapse of the barrier has been speculated upon, and there have been suggestions of potential catastrophic downstream consequences, however, the "District of Squamish, Integrated Flood Hazard Management Plan Background Report" (PDF) . concludes that there has never been any suggestion in any scientific evidence that the Barrier will eventually collapse to the point of creating an uncontrolled release of Garibaldi Lake or cause extreme flooding in downstream neighbourhoods along

2546-492: 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

2613-464: The lake is via the 9 km (5.6 mi) long Garibaldi Lake Trail, which gains approximately 920 m (3,020 ft) of elevation from the Rubble Creek Trailhead. There are campgrounds and day-use shelters on the west shore of Garibaldi Lake, and also farther northwest at Taylor Meadows. Nearly all sites have tent platforms to protect the surrounding ecosystem. During the summer, access to

2680-409: The liquid is methane rather than water). Proponents of the geophysical definition of planets argue that location should not matter and that only geophysical attributes should be taken into account in the definition of a planet. The term satellite planet is sometimes used for planet-sized satellites. A dwarf planet is a planetary-mass object that is neither a true planet nor a natural satellite; it

2747-419: 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

Garibaldi Lake - Misplaced Pages Continue

2814-545: 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

2881-415: 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

2948-438: 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

3015-452: 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

3082-867: 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

3149-541: 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

3216-420: 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

3283-471: 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

3350-462: 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

3417-425: 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

SECTION 50

#1732845594249

3484-479: The planet Mercury ; these and four more – Io , the Moon , Europa , and Triton – are larger and more massive than the largest and most massive dwarf planets, Pluto and Eris . Another dozen smaller satellites are large enough to have become round at some point in their history through their own gravity, tidal heating from their parent planets, or both. In particular, Titan has a thick atmosphere and stable bodies of liquid on its surface, like Earth (though for Titan

3551-595: 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

3618-435: 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

3685-485: 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

3752-501: The shore by simple man-made stone causeways . The turquoise colour of the lake's water is due to glacial flour suspended in the meltwater from its two primary inflows, the large Sphinx Glacier to the east and the Sentinel Glacier to the south on the flanks of Mount Garibaldi . Throughout most of the year, outflow from Garibaldi Lake occurs only via seepage through cracks in the lava dam, with Rubble Creek appearing from springs at

3819-622: 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

3886-399: The south blocked the ancestral valley, damming the waters of the lake behind the lava formation known as The Barrier . This lava dam is over 300 m (980 ft) in thickness and about 2 km (1.2 mi) wide where it impounds the lake. A series of lava outcrops along the northwestern shore of the lake form the numerous tiny Battleship Islands, several of which have been connected to

3953-516: The southeastern tip of the lake. Volcanoes A volcano is a rupture in the crust of a planetary-mass object , such as Earth , that allows hot lava , volcanic ash , and gases to escape from a magma chamber below the surface. The process that forms volcanoes is called volcanism . On Earth, volcanoes are most often found where tectonic plates are diverging or converging , and because most of Earth's plate boundaries are underwater, most volcanoes are found underwater. For example,

4020-403: The stars and so can be recaptured. They are typically captured into wide orbits between 100 and 10 AU. The capture efficiency decreases with increasing cluster volume, and for a given cluster size it increases with the host/primary mass. It is almost independent of the planetary mass. Single and multiple planets could be captured into arbitrary unaligned orbits, non-coplanar with each other or with

4087-406: 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

SECTION 60

#1732845594249

4154-434: 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

4221-444: 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

4288-431: 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

4355-492: 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

4422-424: 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

4489-421: 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

#248751