Types of volcanic eruptions
Encyclopedia
During a volcanic eruption, lava
, tephra
(ash
, lapilli
, volcanic bomb
s and blocks), and various gases are expelled from a volcanic vent or fissure
. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcano
es 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 different metatypes of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruption
s are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The last eruptive metatype is the Phreatic eruption
, which is driven by the superheating
of steam
via contact with magma
; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.
Within these wide-defining eruptive types are several subtypes. The weakest are Hawaiian
and submarine, then Strombolian
, followed by Vulcanian
and Surtseyan
. The stronger eruptive types are Pelean eruption
s, followed by Plinian eruption
s; the strongest eruptions are called "Ultra Plinian." Subglacial
and Phreatic eruption
s are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index
(VEI), a magnitudic
scale ranging from 0 to 8 that often correlates to eruptive types.
Volcanic eruptions arise through three main mechanisms:
There are two types of eruptions in terms of activity, explosive eruption
s and effusive eruption
s. Explosive eruptions are characterized by gas-driven explosions that propels magma
and tephra
. Effusive eruptions, meanwhile, are characterized by the outpouring of lava
without significant explosive eruption.
Volcanic eruptions vary widely in strength. On the one extreme there are effusive Hawaiian eruption
s, which are characterized by lava fountain
s and fluid
lava flow
s, which are typically not very dangerous. On the other extreme, Plinian eruption
s 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 the span of 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 eruption
s start from rift zone
s, and some of the strongest Surtseyan eruption
s develop along fracture zone
s.
(commonly shortened VEI) is a scale, from 0 to 8, for measuring the strength of eruptions. 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 earthquake
s, in that each interval in value represents a tenfold increasing in magnitude (it is logarithm
ic). The vast majority of volcanic eruptions are of VEIs between 0 and 2.
Volcanic eruptions by VEI index
produce juvenile
clasts during explosive
decompression from gas release. They range in intensity from the relatively small lava fountain
s on Hawaii
to catastrophic Ultra Plinian eruption column
s more than 30 km (19 mi) high, bigger than the AD 79 eruption that buried Pompeii
.
Hawaiian eruptions are a type of volcanic eruption, named after the Hawaiian volcanoes
with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption
eruption of very fluid
basalt
-type lava
s 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 the summit and from fissure vent
s 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 beings to concentrate at a few of the vents. Central-vent eruptions, meanwhile, often take the form of large lava fountain
s (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery scoria
fragments; however, 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 splatter cones. If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived; Pu'u O'o, a cinder cone
of Kilauea
, has been erupting continuously since 1983. Another Hawaiian volcanic feature is the formation of active lava lake
s, self-maintaining pools of raw lava with a thin crust of semi-cooled rock; there are currently only 5 such lakes in the world, and the one at Kīlauea
's Kupaianaha vent is one of them.
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 the advancement of "toes," or as a snaking lava column. A'a lava flows are denser and more viscous then pahoehoe, but tend to move slower. Flows can measure 2 to 20 m (6.6 to 65.6 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 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, the Hawaiian volcano deity). During especially high winds these chunks may even take the form of long drawn out rods, known as Pele's hair
. Sometimes basant 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 largest lava fountain ever recorded formed on the island of Izu Ōshima
(on Mount Mihara
) in 1986, a 1600 m (5,249 ft) gusher that was more than twice as high as the mountain itself (which stands at 764 m (2,507 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 continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within the magma
. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slug
s. 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 is generally in the form of episodic explosive eruption
s 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 the air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basalt
ic 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 bomb
s and lapilli
fragments that travel in parabolic paths before landing around their source vent. The steady accumulation of small fragments builds cinder cone
s composed completely of basaltic pyroclasts. This form of accumulation tends to result in well-ordered rings of tephra
.
Strombolian eruptions are similar to Hawaiian eruption
s, but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive column
s, 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 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
, which also gives its name to the word Volcano
. It was named so following Giuseppe Mercalli
's observations of its 1888-1890 eruptions. In Vulcanian eruptions, highly viscous
magma within the volcano make it difficult for vesiculate gases
to escape. Similar to Strombolian eruptions, this leads to the buildup of high gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. However, unlike Strombolian eruptions, ejected lava fragments are not aerodynamical; 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 column
s often reaching between 5 and 10 km (3.1 and 6.2 mi) high. Lastly, Vulcanian deposits are andesitic to dacitic rather than basalt
ic.
Initial Vulcanian activity is characterized by a series of short-lived explosions, lasting a few minutes to a few hours and typified by the ejection of volcanic bomb
s 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 the volcano's slope.
Deposits near the source vent consist of large volcanic blocks and bomb
s, 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. However the bulk of Vulcanian deposits are fine grained ash
. The ash 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:
Peléan eruptions (or nuée ardente
) are a type of volcanic eruption, named after the volcano Mount Pelée
in Martinique
, the site of a massive 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 fragmets are blown out the volcano's central crater, driven by the collapse of rhyolite
, dacite
, and andesite
lava dome
collapses that often create large eruptive column
s. An early sign of 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 massive landslide
s make Peléan eruptions one of the most dangerous in the world, capable of tearing through populated areas and causing massive loss of life. The 1902 eruption of Mount Pelée caused tremendous destruction, killing more than 30,000 people and competely destroying the town of 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 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) are a type of volcanic eruption, named for the historical AD 79 eruption of Mount Vesuvius
that buried 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
gas
es 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 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 a Plinian eruption, and reach up 2 to 45 km (1.2 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 prevailing winds drive the plume in a direction away from the volcano.
These highly explosive eruption
s are associated with volatile-rich dacitic to rhyolitic lavas, and occur most typically at stratovolcano
es. Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic
volcanoes. Although they are associated with felsic magma, Plinian eruptions can just as well occur at basalt
ic volcanoes, given that the magma chamber
differentiates
and has a structure rich in silicon dioxide
.
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 fountain
s in that both eruptive types produce sustained eruption columns maintained by 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 km³ (0.119956379302143 to 12 cumi) 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.
However the most dangerous eruptive feature are the pyroclastic flow
s 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 lahar
s, fast moving mudslides with the consistency of wet concrete that move at the speed of a river rapid
.
Major Plinian eruptive events include:
and magma
. They are driven from thermal contraction
(as opposed to magmatic eruptions, which are driven by thermal expansion) of magma when it comes in contact with water. This temperature difference between 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
grain
ed 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 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 ultimetly lead to rapid cooling and explosive contraction-driven eruptions.
A Surtseyan eruption (or hydrovolcanic) is a type of volcanic eruption caused by shallow-water interactions between water and lava, named so after its most famous example, 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 eruption
s, but because of where they are taking place they are much more explosive. This is because as water is heated by lava, it flashes
in steam
and expands violently, fragmenting the magma it is in contact with into fine-grained ash
. Surtseyan eruptions are the hallmark of shallow-water volcanic
oceanic islands, however they are not specifically confined to them. Surtseyan eruptions can happen on land as well, and are caused by rising magma
that comes into contact with an aquifer
(water-bearing rock formation) at shallow levels under the volcano. The products of Surtseyan eruptions are generally oxidized palagonite
basalt
s (though andesitic eruptions do occur, albeit rarely), and like Strombolian eruptions Surtseyan eruptions are generally continuous or otherwise rhythmic.
A distinct 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 the eruption column
. Base surges are caused by the gravitational collapse of a vaperous
eruptive column, one that is denser overall then a regular volcanic column. The densest part of the cloud is nearest to the vent, resulting 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 was flung out by the explosive eruption and followed a ballistic
path to the ground. Accumulations of wet, spherical ash known as accretionary lapilli is another common surge indicator.
Over time Surtseyan eruptions tend to form maar
s, broad low-relief
volcanic crater
s dug into the ground, and tuff rings, circular structures built of rapidly quenched lava. These structures are associated with a single vent eruption, however if eruptions arise along fracture zone
s a rift zone
may be dug out; these eruptions tend to be more violent then the ones forming a tuff ring or maars, an example being 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 the cone.
Volcanoes known to have Surtseyan activity include:
Submarine eruptions are a type of volcanic eruption that occurs underwater. An estimated 75% of the total volcanic eruptive volume is generated by submarine eruptions near mid ocean ridges alone, however because of the problems associated with detecting deep sea
volcanics, they remained virtually unknown until advances in the 1990s made it possible to observe them.
Submarine eruptions may produce seamount
s which may break the surface to form volcanic islands and island chains.
Submarine volcanism is driven by various processes. Volcanoes near plate boundaries
and mid-ocean ridge
s 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 plate
s that add volatiles
to the rising plate, lowering its melting point
. Each process generates different rock; mid-ocean ridge volcanics are primarily basalt
ic, whereas subduction flows are mostly calc-alkaline
, and more explosive and viscous.
Spreading rates along mid-ocean ridges vary widely, from 2 cm (0.78740157480315 in) per year at the Mid-Atlantic Ridge
, to up to 16 cm (6 in) along the East Pacific Rise
. Higher spreading rates are a probably 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 wave
s, known as T-waves, released by submarine earthquake
s associated with submarine volcanic eruptions. The reason for this is that land-based seismometer
s cannot detect sea-based earthquakes below a magnitude of 4, but acoustic waves travel well in water and long periods of time. A system in the North Pacific, maintained by the United States Navy
and originally intended for the detection of submarine
s, has detected an event on average every 2 to 3 years.
The most common underwater flow is pillow lava
, a circular lava flow named after its unusual shape. Less common are glassy
, marginal sheet flows, indicative of larger-scale flows. Volcaniclastic
sedimentary rock
s are common in shallow-water environments. As plate movement starts to carry 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 caps 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 exemplery seamounts are Loihi Seamount
, Bowie Seamount
, Cross Seamount
, and Denson Seamount
.
Subglacial eruptions are 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 jökulhlaup
s (flood
s) and lahar
s.
The study of glaciovolcanism is still a relatively new field. Early accounts described the unusual flat-topped steep-sided volcanoes (called tuya
s) in Iceland
that were suggested to have formed from eruptions below ice. The first English-language paper on the subject was published in 1947 by William Henry Mathews, describing the Tuya Butte
field in northwest British Columbia
, Canada
. The eruptive process that builds these structures, originally inferred in the paper, begins with volcanic growth below the glacier. At first the eruptions resemble those that occur in the deep sea, forming piles of pillow lava
at the base of the volcanic structure. Some of the lava shatters when it comes in contact with the cold ice, forming a glassy
breccia
called hyaloclastite
. After a while the ice finally melts into a lake, and the more explosive eruptions of Surtseyan activity
begins, building up flanks made up of mostly hyaloclastite. Eventually the lake boils off from continued volcanism, and the lava flows become more effusive
and thicken as the lava cools much more slowly, often forming columnar jointing. Well-preserved tuyas show all of these stages, for example Hjorleifshofdi in Iceland.
Products of volcano-ice interactions stand as various structures, whose shape is dependent on complex eruptive and environmental interactions. Glacial volcanism is a good indicator of past ice distribution, making it an important climatic marker. Since they are imbedded in ice, as ice retracts worldwide there are concerns that tuya
s and other structures may destabalize, resulting in mass landslide
s. Evidence of volcanic-glacial interactions are evident in Iceland
and parts of British Columbia
, and it's even possible that they play a role in deglaciation
.
Glaciovolcanic products have been identified in Iceland, the Canadian province of British Columbia, the U.S. states of Hawaii
and Alaska
, the Cascade Range
of western North America, South America
and even on the planet Mars
. Volcanoes known to have subglacial activity include:
Phreatic eruptions (or steam-blast eruptions) are a type of eruption driven by the expansion of steam
. When cold ground or surface water come into contact with hot rock or magma it superheat
s and explodes
, fracturing the surrounding rock and thrusting out a mixture of steam, water
, ash
, volcanic bomb
s, and volcanic blocks. The distinguishing feature of phreatic explosions is that they only blast out fragments of pre-existing solid rock from the volcanic conduit; no new magma is erupted. Because they are driven by the cracking of rock stata under pressure, phreatic activity does not always result in an eruption; if the rock face is strong enough to withstand the explosive force, outright eruptions may not occur, although cracks in the rock will probably develop and weaken it, furthering future eruptions.
Often a precursor of future volcanic activity, phreatic eruptions are generally weak, although there have been exceptions. Some phreatic events may be triggered by earthquake
activity, another volcanic precursor, and they may also travel along dike
lines. Phreatic eruptions form base surges, lahar
s, avalanche
s, and volcanic block "rain." They may also release deadly toxic gas able to suffocate anyone in range of the eruption.
Volcanoes known to exhibit phreatic activity include:
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
, tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
(ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
, lapilli
Lapilli
Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli means "little stones" in Latin. They are in some senses similar to ooids or pisoids in calcareous sediments.By definition lapilli range...
, volcanic bomb
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
s and blocks), and various gases are expelled from a volcanic vent or fissure
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
. Several types of volcanic eruptions have been distinguished by volcanologists. These are often named after famous volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es 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 different metatypes of eruptions. The most well-observed are magmatic eruptions, which involve the decompression of gas within magma that propels it forward. Phreatomagmatic eruption
Phreatomagmatic eruption
Phreatomagmatic eruptions are defined as juvenile forming eruptions as a result of interaction between water and magma. They are different from magmatic and phreatic eruptions. The products of phreatomagmatic eruptions contain juvenile clasts, unlike phreatic eruptions, and are the result of...
s are another type of volcanic eruption, driven by the compression of gas within magma, the direct opposite of the process powering magmatic activity. The last eruptive metatype is the Phreatic eruption
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...
, which is driven by the superheating
Superheating
In physics, superheating is the phenomenon in which a liquid is heated to a temperature higher than its boiling point, without boiling...
of steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
via contact with magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
; these eruptive types often exhibit no magmatic release, instead causing the granulation of existing rock.
Within these wide-defining eruptive types are several subtypes. The weakest are Hawaiian
Hawaiian eruption
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
and submarine, then Strombolian
Strombolian eruption
Strombolian eruptions are relatively low-level volcanic eruptions, named after the Italian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters...
, followed by Vulcanian
Vulcanian eruption
The term Vulcanian was first used by Giuseppe Mercalli, witnessing the 1888-1890 eruptions on the island of Vulcano. His description of the eruption style is now used all over the world for eruptions characterised by a dense cloud of ash-laden gas exploding from the crater and rising high above the...
and Surtseyan
Surtseyan eruption
A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland....
. The stronger eruptive types are Pelean eruption
Pelean eruption
Peléan eruptions are a type of volcanic eruption. They can occur when viscous magma, typically of rhyolitic or andesitic type, is involved, and share some similarities with Vulcanian eruptions. The most important characteristics of a Peléan eruption is the presence of a glowing avalanche of hot...
s, followed by Plinian eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....
s; the strongest eruptions are called "Ultra Plinian." Subglacial
Subglacial eruption
A subglacial eruption is a volcanic eruption that has occurred under ice, or under a glacier. Subglacial eruptions can cause dangerous floods, lahars and create hyaloclastite and pillow lava. Subglacial eruptions sometimes form a subglacial volcano called a tuya. Tuyas in Iceland are called table...
and Phreatic eruption
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...
s are defined by their eruptive mechanism, and vary in strength. An important measure of eruptive strength is Volcanic Explosivity Index
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
(VEI), a magnitudic
Order of magnitude
An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
scale ranging from 0 to 8 that often correlates to eruptive types.
Eruption mechanisms
- Gas release under decompression causing magmatic eruptions.
- Thermal contraction from chilling on contact with water causing phreatomagmatic eruptionPhreatomagmatic eruptionPhreatomagmatic eruptions are defined as juvenile forming eruptions as a result of interaction between water and magma. They are different from magmatic and phreatic eruptions. The products of phreatomagmatic eruptions contain juvenile clasts, unlike phreatic eruptions, and are the result of...
s. - Ejection of entrained particles during steam eruptions causing phreatic eruptionPhreatic eruptionA phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...
s.
There are two types of eruptions in terms of activity, explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s and effusive eruption
Effusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
s. Explosive eruptions are characterized by gas-driven explosions that propels magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
and tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
. Effusive eruptions, meanwhile, are characterized by the outpouring of lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
without significant explosive eruption.
Volcanic eruptions vary widely in strength. On the one extreme there are effusive Hawaiian eruption
Hawaiian eruption
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
s, which are characterized by lava fountain
Lava fountain
A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...
s and fluid
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
lava flow
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
s, which are typically not very dangerous. On the other extreme, Plinian eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....
s 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 the span of a single eruptive cycle. Volcanoes do not always erupt vertically from a single crater near their peak, either. Some volcanoes exhibit lateral
Lateral eruption
A lateral eruption, also called a flank eruption or lateral blast if explosive, is a volcanic eruption that takes place on the flanks of a volcano instead of at the summit. Lateral eruptions are typical at rift zones where a volcano is breaking apart...
and fissure
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
eruptions. Notably, many Hawaiian eruption
Hawaiian eruption
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
s start from rift zone
Rift zone
A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...
s, and some of the strongest Surtseyan eruption
Surtseyan eruption
A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland....
s develop along fracture zone
Fracture zone
A fracture zone is a linear oceanic feature--often hundreds, even thousands of kilometers long--resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on either side of an active transform fault move in opposite directions;...
s.
Volcano explosivity index
The Volcanic Explosivity IndexVolcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
(commonly shortened VEI) is a scale, from 0 to 8, for measuring the strength of eruptions. It is used by the Smithsonian Institution
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...
's Global Volcanism Program
Global Volcanism Program
The Smithsonian Institution's Global Volcanism Program documents Earth's volcanoes and their eruptive history over the past 10,000 years. The GVP reports on current eruptions from around the world as well as maintaining a database repository on active volcanoes and their eruptions. In this way, a...
in assessing the impact of historic and prehistoric lava flows. It operates in a way similar to the Richter scale for earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
s, in that each interval in value represents a tenfold increasing in magnitude (it is logarithm
Logarithm
The logarithm of a number is the exponent by which another fixed value, the base, has to be raised to produce that number. For example, the logarithm of 1000 to base 10 is 3, because 1000 is 10 to the power 3: More generally, if x = by, then y is the logarithm of x to base b, and is written...
ic). The vast majority of volcanic eruptions are of VEIs between 0 and 2.
Volcanic eruptions by VEI index
| VEI | Plume height | Eruptive volume * | Eruption type | Frequency ** | Example |
|---|---|---|---|---|---|
| 0 | <100 m (328.1 ft) | 1000 m³ (35,314.7 cu ft) | Hawaiian Hawaiian eruption A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high... |
Continuous | Kilauea Kilauea Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern... |
| 1 | 100–1000 m (328.1–3,280.8 ft) | 10000 m³ (353,146.7 cu ft) | Hawaiian/Strombolian Strombolian eruption Strombolian eruptions are relatively low-level volcanic eruptions, named after the Italian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters... |
Months | Stromboli Stromboli Stromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy. It is one of the eight Aeolian Islands, a volcanic arc north of Sicily. This name is a corruption of the Ancient Greek name Strongulē which was given to it... |
| 2 | 1–5 km (0.621372736649807–3.1 mi) | 1000000 m³ (35,314,666.2 cu ft) † | Strombolian/Vulcanian Vulcanian eruption The term Vulcanian was first used by Giuseppe Mercalli, witnessing the 1888-1890 eruptions on the island of Vulcano. His description of the eruption style is now used all over the world for eruptions characterised by a dense cloud of ash-laden gas exploding from the crater and rising high above the... |
Months | Galeras Galeras Galeras is an Andean stratovolcano in the Colombian department of Nariño, near the departmental capital Pasto. Its summit rises above sea level. It has erupted frequently since the Spanish conquest, with its first historical eruption being recorded on December 7, 1580... (1992) |
| 3 | 3–15 km (1.9–9.3 mi) | 10000000 m³ (353,146,662.1 cu ft) | Vulcanian | Yearly | Nevado del Ruiz Nevado del Ruiz The Nevado del Ruiz, also known as La Mesa de Herveo or Kumanday in the language of the local pre-Columbian indigenous people, is a volcano located on the border of the departments of Caldas and Tolima in Colombia, about west of the capital city Bogotá. It is a stratovolcano, composed of many... (1985) |
| 4 | 10–25 km (6.2–15.5 mi) | 100000000 m³ (0.0239912758604287 cu mi) | Vulcanian/Peléan Pelean eruption Peléan eruptions are a type of volcanic eruption. They can occur when viscous magma, typically of rhyolitic or andesitic type, is involved, and share some similarities with Vulcanian eruptions. The most important characteristics of a Peléan eruption is the presence of a glowing avalanche of hot... |
Few years | Eyjafjallajökull Eyjafjallajökull Eyjafjallajökull is one of the smaller ice caps of Iceland, situated to the north of Skógar and to the west of Mýrdalsjökull. The ice cap covers the caldera of a volcano with a summit elevation of . The volcano has erupted relatively frequently since the last glacial period, most recently in... (2010) |
| 5 | >25 km (16 mi) | 1 km³ (0.239912758604287 cu mi) | Plinian Plinian eruption Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 .... |
5–10 years | Mount St. Helens Mount St. Helens Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a... (1980 1980 eruption of Mount St. Helens The 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California... ) |
| 6 | >25 km (16 mi) | 10 km³ (2 cu mi) | Plinian/Ultra Plinian | 1,000 years | Krakatoa Krakatoa Krakatoa is a volcanic island made of a'a lava in the Sunda Strait between the islands of Java and Sumatra in Indonesia. The name is used for the island group, the main island , and the volcano as a whole. The island exploded in 1883, killing approximately 40,000 people, although some estimates... (1883 1883 eruption of Krakatoa The 1883 eruption of Krakatoa began in May 1883 and culminated with the destruction of Krakatoa on 27 August 1883. Minor seismic activity continued to be reported until February 1884, though reports after October 1883 were later dismissed by Rogier Verbeek's investigation.-Early phase:In the years... ) |
| 7 | >25 km (16 mi) | 100 km³ (24 cu mi) | Ultra Plinian | 10,000 years | Tambora Mount Tambora Mount Tambora is an active stratovolcano, also known as a composite volcano, on the island of Sumbawa, Indonesia. Sumbawa is flanked both to the north and south by oceanic crust, and Tambora was formed by the active subduction zone beneath it. This raised Mount Tambora as high as , making it... (1815) |
| 8 | >25 km (16 mi) | 1000 km³ (239.9 cu mi) | Ultra Plinian | 100,000 years | Lake Toba Lake Toba Lake Toba is a lake and supervolcano. The lake is 100 kilometres long and 30 kilometres wide, and 505 metres at its deepest point. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about , the lake stretches from to... (74 ka Toba catastrophe theory The Toba supereruption was a supervolcanic eruption that occurred some time between 69,000 and 77,000 years ago at Lake Toba . It is recognized as one of the Earth's largest known eruptions... ) |
| * This is the minimum eruptive volume necessary for the eruption to be considered within the category. ** Values are a rough estimate. Exceptions occur. † There is a discontinuity between the 2nd and 3rd VEI level; instead of increasing by a magnitude of 10, the value increases by a magnitude of 100 (from 10,000 to 1,000,000). |
|||||
Magmatic eruptions
Magmatic eruptionsMagma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
produce juvenile
Ejecta
Ejecta can mean:*In volcanology, particles that came out of a volcanic vent, traveled through the air or under water, and fell back on the ground surface or on the ocean floor...
clasts during explosive
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
decompression from gas release. They range in intensity from the relatively small lava fountain
Lava fountain
A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...
s on Hawaii
Hawaiian eruption
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
to catastrophic Ultra Plinian eruption column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
s more than 30 km (19 mi) high, bigger than the AD 79 eruption that buried Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...
.
Hawaiian
Hawaii hotspot
The Hawaii hotspot is the volcanic hotspot that created the Hawaiian Islands in the central Pacific Ocean, and is one of Earth's best-known and most heavily-studied hotspots....
with which this eruptive type is hallmark. Hawaiian eruptions are the calmest types of volcanic events, characterized by the effusive eruption
Effusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
eruption of very fluid
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
-type lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
s with low gaseous content
Volcanic gas
|250px|thumb|right|Image of the [[rhyolitic]] [[lava dome]] of [[Chaitén Volcano]] during its 2008-2010 eruption.Volcanic gases include a variety of substances given off by active volcanoes...
. 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
Shield volcano
A shield volcano is a type of volcano usually built almost entirely of fluid lava flows. They are named for their large size and low profile, resembling a warrior's shield. This is caused by the highly fluid lava they erupt, which travels farther than lava erupted from more explosive volcanoes...
. Eruptions are not centralized at the main summit as with other volcanic types, and often occur at vents around the summit and from fissure vent
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
s radiating out of the center.
Hawaiian eruptions often begin as a line of vent eruptions along a fissure vent
Fissure vent
A fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
, a so-called "curtain of fire." These die down as the lava beings to concentrate at a few of the vents. Central-vent eruptions, meanwhile, often take the form of large lava fountain
Lava fountain
A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...
s (both continuous and sporadic), which can reach heights of hundreds of meters or more. The particles from lava fountains usually cool in the air before hitting the ground, resulting in the accumulation of cindery scoria
Scoria
Scoria is a volcanic rock containing many holes or vesicles. It is most generally dark in color , and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity...
fragments; however, 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 splatter cones. If eruptive rates are high enough, they may even form splatter-fed lava flows. Hawaiian eruptions are often extremely long lived; Pu'u O'o, a cinder cone
Cinder cone
According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...
of Kilauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
, has been erupting continuously since 1983. Another Hawaiian volcanic feature is the formation of active lava lake
Lava lake
Lava lakes are large volumes of molten lava, usually basaltic, contained in a volcanic vent, crater, or broad depression. The term is used to describe both lava lakes that are wholly or partly molten and those that are solidified...
s, self-maintaining pools of raw lava with a thin crust of semi-cooled rock; there are currently only 5 such lakes in the world, and the one at Kīlauea
Kilauea
Kīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
's Kupaianaha vent is one of them.
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher 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
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
fragments known as Pele's tears
Pele's tears
Pele’s tears is a geological term for small pieces of solidified lava drops formed when airborne particles of molten material fuse into tearlike drops of volcanic glass. Pele’s tears are jet black in color and are often found on one end of a strand of Pele's hair...
(after Pele, the Hawaiian volcano deity). During especially high winds these chunks may even take the form of long drawn out rods, known as Pele's hair
Pele's hair
Pele's hair is a geological term for volcanic glass threads or fibers formed when small particles of molten material are thrown into the air and spun out by the wind into long hair-like strands. The diameter of the strands is less than 0.5 mm, and they can be as long as 2 meters. Pele’s...
. Sometimes basant 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 largest lava fountain ever recorded formed on the island of Izu Ōshima
Izu Oshima
is a volcanic island in the Izu Islands and administered by the Tokyo Metropolitan government, Japan, lies about 100 km south of Tokyo, 22 km east of the Izu Peninsula and 36 km southwest of Bōsō Peninsula. serves as the local government of the island...
(on Mount Mihara
Mount Mihara
is an active volcano on the Japanese isle of Izu Ōshima. Although the volcano is predominantly basaltic, major eruptions have occurred at intervals of 100–150 years....
) in 1986, a 1600 m (5,249 ft) gusher that was more than twice as high as the mountain itself (which stands at 764 m (2,507 ft)).
Volcanoes known to have Hawaiian activity include:
- Pu'u O'o, a parasitic cinder coneCinder coneAccording to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...
located on KilaueaKilaueaKīlauea is a volcano in the Hawaiian Islands, and one of five shield volcanoes that together form the island of Hawaii. Kīlauea means "spewing" or "much spreading" in the Hawaiian language, referring to its frequent outpouring of lava. The Puu Ōō cone has been continuously erupting in the eastern...
on the island of HawaiiHawaii (island)The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
which has been erupting continuously since 1983. The eruptions began with a 6 km (4 mi)-long fissure-basedFissure ventA fissure vent, also known as a volcanic fissure or simply fissure, is a linear volcanic vent through which lava erupts, usually without any explosive activity. The vent is usually a few meters wide and may be many kilometers long. Fissure vents can cause large flood basalts and lava channels...
"curtain of fire" on January 3. These gave way to centralized eruptions on the site of Kilauea's east rift, eventually building up the still active cone. - For a list of all of the volcanoes of HawaiiHawaiiHawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
, see List of volcanoes in the Hawaiian - Emperor seamount chain. - Mount EtnaMount EtnaMount Etna is an active stratovolcano on the east coast of Sicily, close to Messina and Catania. It is the tallest active volcano in Europe, currently standing high, though this varies with summit eruptions; the mountain is 21 m higher than it was in 1981.. It is the highest mountain in...
, ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. - Mount MiharaMount Miharais an active volcano on the Japanese isle of Izu Ōshima. Although the volcano is predominantly basaltic, major eruptions have occurred at intervals of 100–150 years....
in 1986 (see above paragraph)
Strombolian
Stromboli
Stromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy. It is one of the eight Aeolian Islands, a volcanic arc north of Sicily. This name is a corruption of the Ancient Greek name Strongulē which was given to it...
, which has been erupting continuously for centuries. Strombolian eruptions are driven by the bursting of gas bubbles within the magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
. These gas bubbles within the magma accumulate and coalesce into large bubbles, called gas slug
Gas slug
A gas slug is a conglomerate of high pressure gas bubbles that forms within certain volcanoes, the agittation of which is a key driving factor in Strombolian eruptions. They start out as small bubbles of gas inside of volcanic magma. These accumulate into one large bubble, which starts to rise...
s. 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
Soap bubble
A soap bubble is a thin film of soapy water enclosing air, that forms a hollow sphere with an iridescent surface. Soap bubbles usually last for only a few seconds before bursting, either on their own or on contact with another object. They are often used for children's enjoyment, but they are also...
. Because of the high gas pressures
Partial pressure
In a mixture of ideal gases, each gas has a partial pressure which is the pressure which the gas would have if it alone occupied the volume. The total pressure of a gas mixture is the sum of the partial pressures of each individual gas in the mixture....
associated with the lavas, continued activity is generally in the form of episodic explosive eruption
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s 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
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
. In reality, true Strombolian eruptions are characterized by short-lived and explosive eruptions of lavas with intermediate viscosity
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
, often ejected high into the air. Columns can measure hundreds of meters in height. The lavas formed by Strombolian eruptions are a form of relatively viscous basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic lava, and its end product is mostly scoria
Scoria
Scoria is a volcanic rock containing many holes or vesicles. It is most generally dark in color , and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity...
. 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.
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
s and lapilli
Lapilli
Lapilli is a size classification term for tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. Lapilli means "little stones" in Latin. They are in some senses similar to ooids or pisoids in calcareous sediments.By definition lapilli range...
fragments that travel in parabolic paths before landing around their source vent. The steady accumulation of small fragments builds cinder cone
Cinder cone
According to the , Cinder Cone is the proper name of 1 cinder cone in Canada and 7 cinder cones in the United States:In Canada: Cinder Cone In the United States:...
s composed completely of basaltic pyroclasts. This form of accumulation tends to result in well-ordered rings of tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
.
Strombolian eruptions are similar to Hawaiian eruption
Hawaiian eruption
A Hawaiian eruption is a type of volcanic eruption where lava flows from the vent in a relative gentle, low level eruption, so called because it is characteristic of Hawaiian volcanoes. Typically they are effusive eruptions, with basaltic magmas of low viscosity, low content of gases, and high...
s, but there are differences. Strombolian eruptions are noisier, produce no sustained eruptive column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
s, do not produce some volcanic products associated with Hawaiian volcanism (specifically Pele's tears
Pele's tears
Pele’s tears is a geological term for small pieces of solidified lava drops formed when airborne particles of molten material fuse into tearlike drops of volcanic glass. Pele’s tears are jet black in color and are often found on one end of a strand of Pele's hair...
and Pele's hair
Pele's hair
Pele's hair is a geological term for volcanic glass threads or fibers formed when small particles of molten material are thrown into the air and spun out by the wind into long hair-like strands. The diameter of the strands is less than 0.5 mm, and they can be as long as 2 meters. Pele’s...
), and produce fewer molten lava flows (although the eruptive material does tend to form small rivulets).
Volcanoes known to have Strombolian activity include:
- ParícutinParicutínParícutin is a cinder cone volcano in the Mexican state of Michoacán, close to a lava-covered village of the same name. It appears on many versions of the Seven Natural Wonders of the World...
, MexicoMexicoThe United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...
, which erupted from a fissure in a cornfield in 1943. Two years into its life, pyroclastic activity began to wane, and the outpouring of lava from its base became its primary mode of activity. Eruptions ceased in 1952, and the final height was 424 m (1,391 ft). This was the first time that scientists are able to observe the complete life cycle of a volcano. - Mount EtnaMount EtnaMount Etna is an active stratovolcano on the east coast of Sicily, close to Messina and Catania. It is the tallest active volcano in Europe, currently standing high, though this varies with summit eruptions; the mountain is 21 m higher than it was in 1981.. It is the highest mountain in...
, ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, which has displayed Strombolian activity in recent eruptions, for example in 1981, 1999, 2002-2003, and 2009. - Mount ErebusMount ErebusMount Erebus in Antarctica is the southernmost historically active volcano on Earth, the second highest volcano in Antarctica , and the 6th highest ultra mountain on an island. With a summit elevation of , it is located on Ross Island, which is also home to three inactive volcanoes, notably Mount...
in Antarctica, the southernmost active volcano in the world, having been observed erupting since 1972. Eruptive activity at Erebrus consists of frequent Strombolian activity. - StromboliStromboliStromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy. It is one of the eight Aeolian Islands, a volcanic arc north of Sicily. This name is a corruption of the Ancient Greek name Strongulē which was given to it...
itself. The namesake of the mild explosive activity that it possesses has been active throughout historical time; essentially continuous Strombolian eruptions, occasionally accompanied by lava flows, have been recorded at Stromboli for more than a millennium.
Vulcanian
Vulcano
thumb| The Gran Cratere. A sense of scale is provided by the tourist visible near the centre of the crater.thumb|right|250px|View of Vulcano from the island of Lipari. The green islet centre left is Vulcanello, which is connected to Vulcano by an isthmus...
, which also gives its name to the word Volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
. It was named so following Giuseppe Mercalli
Giuseppe Mercalli
Giuseppe Mercalli was an Italian volcanologist. He is best remembered today for his Mercalli scale for measuring earthquakes which is still used today.-Biography:...
's observations of its 1888-1890 eruptions. In Vulcanian eruptions, highly viscous
Viscosity
Viscosity is a measure of the resistance of a fluid which is being deformed by either shear or tensile stress. In everyday terms , viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity...
magma within the volcano make it difficult for vesiculate gases
Vesicular texture
Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...
to escape. Similar to Strombolian eruptions, this leads to the buildup of high gas pressure, eventually popping the cap holding the magma down and resulting in an explosive eruption. However, unlike Strombolian eruptions, ejected lava fragments are not aerodynamical; 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 column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
s often reaching between 5 and 10 km (3.1 and 6.2 mi) high. Lastly, Vulcanian deposits are andesitic to dacitic rather than basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic.
Initial Vulcanian activity is characterized by a series of short-lived explosions, lasting a few minutes to a few hours and typified by the ejection of volcanic bomb
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
s and blocks. These eruptions wear down the lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
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 the volcano's slope.
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
s, 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
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
or fine-grained
Particle size (grain size)
Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the...
shell, but the inside continues to cool and vesiculate
Vesicular texture
Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...
. The center of the fragment expands, cracking the exterior. However the bulk of Vulcanian deposits are fine grained ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
. The ash 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
Meteoric water
Meteoric water is a hydrologic term of long standing for water in the ground which originates from precipitation. This includes water from lakes, rivers, and icemelts, which all originate from precipitation indirectly.- Overview :...
, suggesting that Vulcanian eruptions are partially hydrovolcanic
Phreatomagmatic eruption
Phreatomagmatic eruptions are defined as juvenile forming eruptions as a result of interaction between water and magma. They are different from magmatic and phreatic eruptions. The products of phreatomagmatic eruptions contain juvenile clasts, unlike phreatic eruptions, and are the result of...
.
Volcanoes that have exhibited Vulcanian activity include:
- SakurajimaSakurajima, also romanized as Sakurashima or Sakura-jima, is an active composite volcano and a former island of the same name in Kagoshima Prefecture in Kyūshū, Japan...
, JapanJapanJapan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
has been the site of Vulcanian activity near-continuously since 1955. - TavurvurTavurvurTavurvur is an active volcano that lies near Rabaul in Papua New Guinea. It is a sub-vent of the Rabaul caldera and lies on the eastern rim of the larger feature...
, Papua New GuineaPapua New GuineaPapua New Guinea , officially the Independent State of Papua New Guinea, is a country in Oceania, occupying the eastern half of the island of New Guinea and numerous offshore islands...
, one of several volcanoes in the Rabaul CalderaRabaul calderaRabaul caldera is a large volcano situated in East New Britain, Papua New Guinea. It derives its name from the town of Rabaul situated inside the caldera. The highest of its multiple peaks is ....
. - Irazú VolcanoIrazú VolcanoThe Irazú Volcano is an active volcano in Costa Rica, situated in the Cordillera Central close to the city of Cartago.The name could come from either the combination of "ara" and "tzu" or a corruption of Iztarú, which was the name of an indigenous village on the flanks of the volcano...
in Costa RicaCosta RicaCosta Rica , officially the Republic of Costa Rica is a multilingual, multiethnic and multicultural country in Central America, bordered by Nicaragua to the north, Panama to the southeast, the Pacific Ocean to the west and the Caribbean Sea to the east....
exhibited Vulcanian activity in its 1965 eruption.
Peléan
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
) are a type of volcanic eruption, named after the volcano Mount Pelée
Mount Pelée
Mount Pelée is an active volcano at the northern end of the island and French overseas department of Martinique in the Lesser Antilles island arc of the Caribbean. Its volcanic cone is composed of layers of volcanic ash and hardened lava....
in Martinique
Martinique
Martinique is an island in the eastern Caribbean Sea, with a land area of . Like Guadeloupe, it is an overseas region of France, consisting of a single overseas department. To the northwest lies Dominica, to the south St Lucia, and to the southeast Barbados...
, the site of a massive 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 fragmets are blown out the volcano's central crater, driven by the collapse of rhyolite
Rhyolite
This page is about a volcanic rock. For the ghost town see Rhyolite, Nevada, and for the satellite system, see Rhyolite/Aquacade.Rhyolite is an igneous, volcanic rock, of felsic composition . It may have any texture from glassy to aphanitic to porphyritic...
, dacite
Dacite
Dacite is an igneous, volcanic rock. It has an aphanitic to porphyritic texture and is intermediate in composition between andesite and rhyolite. The relative proportions of feldspars and quartz in dacite, and in many other volcanic rocks, are illustrated in the QAPF diagram...
, and andesite
Andesite
Andesite is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and dacite. The mineral assemblage is typically dominated by plagioclase plus pyroxene and/or hornblende. Magnetite,...
lava dome
Lava dome
|250px|thumb|right|Image of the [[rhyolitic]] lava dome of [[Chaitén Volcano]] during its 2008–2009 eruption.In volcanology, a lava dome is a roughly circular mound-shaped protrusion resulting from the slow extrusion of viscous lava from a volcano...
collapses that often create large eruptive column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
s. An early sign of a coming eruption is the growth of a so-called Peléan or lava spine
Lava spine
A lava spine is a vertically growing monolith of viscous lava that is slowly forced from a volcanic vent, such as those growing on a lava dome . It may also be considered a kind of dome called a spiny dome . In February of 1983, the dome activity of Mount St...
, a bulge in the volcano's summit preempting its total collapse. The material collapses upon itself, forming a fast-moving pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
(known as a block-and-ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
flow) that moves down the side of the mountain at tremendous speeds, often over 150 km (93 mi) per hour. These massive landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s make Peléan eruptions one of the most dangerous in the world, capable of tearing through populated areas and causing massive loss of life. The 1902 eruption of Mount Pelée caused tremendous destruction, killing more than 30,000 people and competely destroying the town of St. Pierre
Saint-Pierre, Martinique
Saint-Pierre is a town and commune of France's Caribbean overseas department of Martinique, founded in 1635 by Pierre Belain d'Esnambuc. Before the total destruction of Saint-Pierre in 1902 by a volcanic eruption, it was the most important city of Martinique culturally and economically, being known...
, the worst volcanic event in the 20th century.
Peléan eruptions are characterized most prominently by the incandescent
Incandescence
Incandescence is the emission of light from a hot body as a result of its temperature. The term derives from the Latin verb incandescere, to glow white....
pyroclastic flows that they drive. The mechanics of 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:
- Mount PeléeMount PeléeMount Pelée is an active volcano at the northern end of the island and French overseas department of Martinique in the Lesser Antilles island arc of the Caribbean. Its volcanic cone is composed of layers of volcanic ash and hardened lava....
, MartiniqueMartiniqueMartinique is an island in the eastern Caribbean Sea, with a land area of . Like Guadeloupe, it is an overseas region of France, consisting of a single overseas department. To the northwest lies Dominica, to the south St Lucia, and to the southeast Barbados...
. The 1902 eruption of Mount Pelée completely devastated the island, destroying the town of St. PierreSaint-Pierre, MartiniqueSaint-Pierre is a town and commune of France's Caribbean overseas department of Martinique, founded in 1635 by Pierre Belain d'Esnambuc. Before the total destruction of Saint-Pierre in 1902 by a volcanic eruption, it was the most important city of Martinique culturally and economically, being known...
and leaving only 3 survivors. The eruption was directly preceded by lava dome growth. - Mayon VolcanoMayon VolcanoMayon Volcano, also known as Mount Mayon, is an active volcano in the province of Albay, on the island of Luzon in the Philippines. Renowned as the "perfect cone" because of its almost symmetric conical shape, Mayon forms the northern boundary of Legazpi City, the largest city in terms of...
, the PhilippinesPhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
most active volcano. It has been the site of many different types of eruptions, Peléan included. Approximarly 40 ravines radiate from the summit and provide pathways for frequent pyroclastic flowPyroclastic flowA pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s and mudslides to the lowlands below. Mayon's most violent eruption occurred in 1814 and was responsible for over 1200 deaths. - The 1951 Peléan eruption of Mount LamingtonMount LamingtonMount Lamington is an andesitic stratovolcano in the Oro Province of Papua New Guinea. The forested peak of the volcano had not been recognised as such until its devastating eruption in 1951 that caused about 3,000 deaths....
. Prior to this eruption the peak had not even been recognized as a volcano. Over 3,000 people were killed, and it has become a benchmark for studying large Peléan eruptions.
Plinian
Mount Vesuvius
Mount Vesuvius is a stratovolcano in the Gulf of Naples, Italy, about east of Naples and a short distance from the shore. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting...
that buried the Roman
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
towns of Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...
and Herculaneum
Herculaneum
Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...
, and specifically for its chronicler Pliny the Younger
Pliny the Younger
Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo , better known as Pliny the Younger, was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and educate him...
. The process powering Plinian eruptions starts in the magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...
, where dissolved
Dissolution (chemistry)
Dissolution is the process by which a solid, liquid or gas forms a solution in a solvent. In solids this can be explained as the breakdown of the crystal lattice into individual ions, atoms or molecules and their transport into the solvent. For liquids and gases, the molecules must be compatible...
volatile
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...
es are stored in the magma. The gases vesiculate
Vesicular texture
Vesicular texture is a volcanic rock texture characterised by a rock being pitted with many cavities at its surface and inside. The texture is often found in extrusive aphanitic, or glassy, igneous rock...
and accumulate as they rise through the magma conduit
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
. These bubbles agglutinate and once they reach a certain size (about 75% of the total volume of the magma conduit) they explode. The narrow confines of the conduit force the gases and associated magma up, forming an eruptive column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
. 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 a Plinian eruption, and reach up 2 to 45 km (1.2 to 28 mi) into the atmosphere
Atmosphere
An atmosphere is a layer of gases that may surround a material body of sufficient mass, and that is held in place by the gravity of the body. An atmosphere may be retained for a longer duration, if the gravity is high and the atmosphere's temperature is low...
. The densest part of the plume, directly above the volcano, is driven internally by gas expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
. As it reaches higher into the air the plume expands and becomes less dense, convection
Convection
Convection is the movement of molecules within fluids and rheids. It cannot take place in solids, since neither bulk current flows nor significant diffusion can take place in solids....
and thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
of volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
drive it even further up into the stratosphere
Stratosphere
The stratosphere is the second major layer of Earth's atmosphere, just above the troposphere, and below the mesosphere. It is stratified in temperature, with warmer layers higher up and cooler layers farther down. This is in contrast to the troposphere near the Earth's surface, which is cooler...
. At the top of the plume, powerful prevailing winds drive the plume in a direction away from the volcano.
Explosive eruption
An explosive eruption is a volcanic term to describe a violent, explosive type of eruption. Mount St. Helens in 1980 was an example. Such an eruption is driven by gas accumulating under great pressure. Driven by hot rising magma, it interacts with ground water until the pressure increases to the...
s are associated with volatile-rich dacitic to rhyolitic lavas, and occur most typically at stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...
es. Eruptions can last anywhere from hours to days, with longer eruptions being associated with more felsic
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....
volcanoes. Although they are associated with felsic magma, Plinian eruptions can just as well occur at basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic volcanoes, given that the magma chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...
differentiates
Igneous differentiation
In geology, igneous differentiation is an umbrella term for the various processes by which magmas undergo bulk chemical change during the partial melting process, cooling, emplacement or eruption.-Primary melts:...
and has a structure rich in silicon dioxide
Silicon dioxide
The chemical compound silicon dioxide, also known as silica , is an oxide of silicon with the chemical formula '. It has been known for its hardness since antiquity...
.
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 fountain
Lava fountain
A lava fountain is a volcanic phenomenon in which lava is forcefully but non-explosively ejected from a crater, vent, or fissure. Lava fountains may reach heights of up to . They may occur as a series of short pulses, or a continuous jet of lava. They are commonly seen in Hawaiian eruptions.-See...
s in that both eruptive types produce sustained eruption columns maintained by 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
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
airfall affecting an area 0.5 to 50 km³ (0.119956379302143 to 12 cumi) 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.
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...
s 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
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
to form lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s, fast moving mudslides with the consistency of wet concrete that move at the speed of a river rapid
Rapid
A rapid is a section of a river where the river bed has a relatively steep gradient causing an increase in water velocity and turbulence. A rapid is a hydrological feature between a run and a cascade. A rapid is characterised by the river becoming shallower and having some rocks exposed above the...
.
Major Plinian eruptive events include:
- The historical AD 79 eruption of Mount VesuviusMount VesuviusMount Vesuvius is a stratovolcano in the Gulf of Naples, Italy, about east of Naples and a short distance from the shore. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting...
buried the RomanRoman EmpireThe Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....
towns of PompeiiPompeiiThe city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...
and HerculaneumHerculaneumHerculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...
under a layer of ashVolcanic ashVolcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
and tephraTephra200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....
. It is the model Plinian eruption. Mount Vesuvius has erupted multiple times since then, for example in 1822. - The 1980 eruption1980 eruption of Mount St. HelensThe 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California...
of Mount St. HelensMount St. HelensMount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...
in Washington, which ripped apart the volcano's summit, was a Plinian eruption of Volcanic Explosivity IndexVolcanic Explosivity IndexThe Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....
(VEI) 5. - The strongest types of erupions, with a VEI of 8, are so-called "Ulta-Plinian" eruptions, such as the most recent one at Lake TobaLake TobaLake Toba is a lake and supervolcano. The lake is 100 kilometres long and 30 kilometres wide, and 505 metres at its deepest point. Located in the middle of the northern part of the Indonesian island of Sumatra with a surface elevation of about , the lake stretches from to...
74 thousand years ago, which put out 2800 times the material erupted by Mount St. Helens in 1980. - HeklaHeklaHekla is a stratovolcano located in the south of Iceland with a height of . Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since 874. During the Middle Ages, Icelanders called the volcano the "Gateway to Hell."Hekla is part of a volcanic...
in IcelandIcelandIceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, an example of basaltBasaltBasalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic Pilian volcanism being its 1947-48 eruption. The past 800 years have been a pattern of violent initial eruptions of pumicePumicePumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...
followed by prolonged extrusionExtrusionExtrusion is a process used to create objects of a fixed cross-sectional profile. A material is pushed or drawn through a die of the desired cross-section...
of basaltic lava from the lower part of the volcano. - Pinatubo in the PhilippinesPhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
on 15 June 1991, which produced 5 km³ (1 cu mi) of dacitic magma, a 40 km (25 mi) high eruption column, and released 17 megatonsTonneThe tonne, known as the metric ton in the US , often put pleonastically as "metric tonne" to avoid confusion with ton, is a metric system unit of mass equal to 1000 kilograms. The tonne is not an International System of Units unit, but is accepted for use with the SI...
of sulfur dioxideSulfur dioxideSulfur dioxide is the chemical compound with the formula . It is released by volcanoes and in various industrial processes. Since coal and petroleum often contain sulfur compounds, their combustion generates sulfur dioxide unless the sulfur compounds are removed before burning the fuel...
.
Phreatomagmatic eruptions
Phreatomagmatic eruptions are eruptions that arise from interactions between waterWater
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
and magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
. They are driven from thermal contraction
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
(as opposed to magmatic eruptions, which are driven by thermal expansion) of magma when it comes in contact with water. This temperature difference between 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
Granularity
Granularity is the extent to which a system is broken down into small parts, either the system itself or its description or observation. It is the "extent to which a larger entity is subdivided...
grain
Particle size (grain size)
Particle size, also called grain size, refers to the diameter of individual grains of sediment, or the lithified particles in clastic rocks. The term may also be applied to other granular materials. This is different from the crystallite size, which is the size of a single crystal inside the...
ed 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 the explosive nature than thermal contraction. Fuel coolant reactions may fragment the volcanic material by propagating stress waves, widening cracks and increasing surface area
Surface area
Surface area is the measure of how much exposed area a solid object has, expressed in square units. Mathematical description of the surface area is considerably more involved than the definition of arc length of a curve. For polyhedra the surface area is the sum of the areas of its faces...
that ultimetly lead to rapid cooling and explosive contraction-driven eruptions.
Surtseyan
Surtsey
Surtsey is a volcanic island off the southern coast of Iceland. At it is also the southernmost point of Iceland. It was formed in a volcanic eruption which began 130 metres below sea level, and reached the surface on 15 November 1963. The eruption lasted until 5 June 1967, when the island...
off the coast of Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
in 1963. Surtseyan eruptions are the "wet" equivalent of ground-based Strombolian eruption
Strombolian eruption
Strombolian eruptions are relatively low-level volcanic eruptions, named after the Italian volcano Stromboli, where such eruptions consist of ejection of incandescent cinder, lapilli and lava bombs to altitudes of tens to hundreds of meters...
s, but because of where they are taking place they are much more explosive. This is because as water is heated by lava, it flashes
Superheated water
Superheated water is liquid water under pressure at temperatures between the usual boiling point and the critical temperature . It is also known as subcritical water and pressurized hot water...
in steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
and expands violently, fragmenting the magma it is in contact with into fine-grained ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
. Surtseyan eruptions are the hallmark of shallow-water volcanic
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
oceanic islands, however they are not specifically confined to them. Surtseyan eruptions can happen on land as well, and are caused by rising magma
Magma
Magma is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and is expected to exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and dissolved gas and sometimes also gas bubbles. Magma often collects in...
that comes into contact with an aquifer
Aquifer
An aquifer is a wet underground layer of water-bearing permeable rock or unconsolidated materials from which groundwater can be usefully extracted using a water well. The study of water flow in aquifers and the characterization of aquifers is called hydrogeology...
(water-bearing rock formation) at shallow levels under the volcano. The products of Surtseyan eruptions are generally oxidized palagonite
Palagonite
Palagonite is an alteration product from the interaction of water with volcanic glass of chemical composition similar to basalt. Palagonite can also result from the interaction between water and basalt melt...
basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
s (though andesitic eruptions do occur, albeit rarely), and like Strombolian eruptions Surtseyan eruptions are generally continuous or otherwise rhythmic.
A distinct defining feature of a Surtseyan eruption is the formation of a pyroclastic surge
Pyroclastic surge
A pyroclastic surge is a fluidized mass of turbulent gas and rock fragments which is ejected during some volcanic eruptions. It is similar to a pyroclastic flow but it has a lower density or contains a much higher proportion of gas to rock ratio, which makes it more turbulent and allows it to rise...
(or base surge), a ground hugging radial cloud that develops along with the eruption column
Eruption column
An eruption column consists of hot volcanic ash emitted during an explosive volcanic eruption. The ash forms a column rising many kilometres into the air above the peak of the volcano. In the most explosive eruptions, the eruption column may rise over 40 km, penetrating the stratosphere...
. Base surges are caused by the gravitational collapse of a vaperous
Water vapor
Water vapor or water vapour , also aqueous vapor, is the gas phase of water. It is one state of water within the hydrosphere. Water vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. Under typical atmospheric conditions, water vapor is continuously...
eruptive column, one that is denser overall then a regular volcanic column. The densest part of the cloud is nearest to the vent, resulting 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 was flung out by the explosive eruption and followed a ballistic
Ballistics
Ballistics is the science of mechanics that deals with the flight, behavior, and effects of projectiles, especially bullets, gravity bombs, rockets, or the like; the science or art of designing and accelerating projectiles so as to achieve a desired performance.A ballistic body is a body which is...
path to the ground. Accumulations of wet, spherical ash known as accretionary lapilli is another common surge indicator.
Over time Surtseyan eruptions tend to form maar
Maar
A maar is a broad, low-relief volcanic crater that is caused by a phreatomagmatic eruption, an explosion caused by groundwater coming into contact with hot lava or magma. A maar characteristically fills with water to form a relatively shallow crater lake. The name comes from the local Moselle...
s, broad low-relief
Relief
Relief is a sculptural technique. The term relief is from the Latin verb levo, to raise. To create a sculpture in relief is thus to give the impression that the sculpted material has been raised above the background plane...
volcanic crater
Volcanic crater
A volcanic crater is a circular depression in the ground caused by volcanic activity. It is typically a basin, circular in form within which occurs a vent from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of great depth...
s dug into the ground, and tuff rings, circular structures built of rapidly quenched lava. These structures are associated with a single vent eruption, however if eruptions arise along fracture zone
Fracture zone
A fracture zone is a linear oceanic feature--often hundreds, even thousands of kilometers long--resulting from the action of offset mid-ocean ridge axis segments. They are a consequence of plate tectonics. Lithospheric plates on either side of an active transform fault move in opposite directions;...
s a rift zone
Rift zone
A rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...
may be dug out; these eruptions tend to be more violent then the ones forming a tuff ring or maars, an example being 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
Steam explosion
A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...
, breaking the rock apart and depositing it on the volcano's flank. Consecutive explosions of this type eventually generate the cone.
Volcanoes known to have Surtseyan activity include:
- SurtseySurtseySurtsey is a volcanic island off the southern coast of Iceland. At it is also the southernmost point of Iceland. It was formed in a volcanic eruption which began 130 metres below sea level, and reached the surface on 15 November 1963. The eruption lasted until 5 June 1967, when the island...
, IcelandIcelandIceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
. The volcano built itself up from depth and emerged above the Atlantic OceanAtlantic OceanThe Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
off the coast of Iceland in 1963. Initial hydrovolcanics were highly explosive, but as the volcano grew out rising lava started to interact less with the water and more with the air, until finally Surtseyan activity waned and became more Strombolian in character. - Ukinrek MaarsUkinrek MaarsFrom Miller and others : "Ukinrek Maars are a pair ofphreatomagmatic explosion vents that formed on a low , 4-km-long, ridge in the Bering Sea Lowland 1.5 km south of Becharof Lake and 12 km northwest of Peulik Volcano...
in AlaskaAlaskaAlaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, 1977, and CapelinhosCapelinhosThe Capelinhos is a monogenetic volcano located on the western coast of the island of Faial in the Azores. It is part of the larger Volcanic Complex of Capelo, that includes 20 escoria cones and lava fields that are aligned west-northwest to east-southeast from the Cabeço Gordo caldera...
in the AzoresAzoresThe Archipelago of the Azores is composed of nine volcanic islands situated in the middle of the North Atlantic Ocean, and is located about west from Lisbon and about east from the east coast of North America. The islands, and their economic exclusion zone, form the Autonomous Region of the...
, 1957, both examples of above-water Surtseyan activity. - Mount TaraweraMount TaraweraMount Tarawera is the volcano responsible for New Zealand's largest historic eruption. Located 24 kilometres southeast of Rotorua in the North Island, it consists of a series of rhyolitic lava domes that were fissured down the middle by an explosive basaltic eruption in 1886, which killed over...
in New ZealandNew ZealandNew Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
erupted along a rift zoneRift zoneA rift zone is a feature of some volcanoes, especially the shield volcanoes of Hawaii, in which a linear series of fissures in the volcanic edifice allows lava to be erupted from the volcano's flank instead of from its summit...
in 1886, killing 150 people. - FerdinandeaFerdinandeaFerdinandea is a submerged volcanic island which forms part of the underwater volcano Empedocles, south of Sicily, and which is one of a number of submarine volcanoes known as the Campi Flegrei del Mar di Sicilia. Currently a seamount, eruptions have raised it above sea level several times...
, a seamountSeamountA seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
in the Mediterranean SeaMediterranean SeaThe Mediterranean Sea is a sea connected to the Atlantic Ocean surrounded by the Mediterranean region and almost completely enclosed by land: on the north by Anatolia and Europe, on the south by North Africa, and on the east by the Levant...
, breached sea level in July 1831 and was the source of a dispute over sovereigntySovereigntySovereignty is the quality of having supreme, independent authority over a geographic area, such as a territory. It can be found in a power to rule and make law that rests on a political fact for which no purely legal explanation can be provided...
between ItalyItalyItaly , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
, FranceFranceThe French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, and Great BritainGreat BritainGreat Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
. The volcano did not build tuff cones strongly enough to withstand erosion, and disappeared back below the waves soon after it appeared. - The underwater volcano Hunga TongaHunga TongaHunga Tonga-Hunga Haapai is a volcano located about 30 km south-southeast of Fonuafoou , part of Tonga.The volcano is part of the highly active Tonga-Kermadec Islands volcanic arc, a subduction zone extending from New Zealand north-northeast to Fiji. The volcano lies about above a very active...
in TongaTongaTonga, officially the Kingdom of Tonga , is a state and an archipelago in the South Pacific Ocean, comprising 176 islands scattered over of ocean in the South Pacific...
breached sea level in 20092009 Tonga undersea volcanic eruptionThe 2009 Tonga undersea volcanic eruption refers to ongoing volcanic activity that began on March 16, 2009, near the island of Hunga Tonga, approximately from the Tongan capital of Tongatapu. The volcano is in a highly active volcanic region that represents a portion of the Pacific Ring of Fire...
. Both of its vents exhibited Surtseyan activity for much of the time. It was also the site of an earlier eruption in May 1988.
Submarine
Deep sea
The deep sea, or deep layer, is the lowest layer in the ocean, existing below the thermocline and above the seabed, at a depth of 1000 fathoms or more. Little or no light penetrates this part of the ocean and most of the organisms that live there rely for subsistence on falling organic matter...
volcanics, they remained virtually unknown until advances in the 1990s made it possible to observe them.
Submarine eruptions may produce seamount
Seamount
A seamount is a mountain rising from the ocean seafloor that does not reach to the water's surface , and thus is not an island. These are typically formed from extinct volcanoes, that rise abruptly and are usually found rising from a seafloor of depth. They are defined by oceanographers as...
s which may break the surface to form volcanic islands and island chains.
Submarine volcanism is driven by various processes. Volcanoes near plate boundaries
Divergent boundary
In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. Divergent boundaries within continents initially produce rifts which produce rift valleys...
and mid-ocean ridge
Mid-ocean ridge
A mid-ocean ridge is a general term for an underwater mountain system that consists of various mountain ranges , typically having a valley known as a rift running along its spine, formed by plate tectonics. This type of oceanic ridge is characteristic of what is known as an oceanic spreading...
s 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
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
, meanwhile, are driven by subducting plate
Plate tectonics
Plate tectonics is a scientific theory that describes the large scale motions of Earth's lithosphere...
s that add volatiles
Volatiles
In planetary science, volatiles are that group of chemical elements and chemical compounds with low boiling points that are associated with a planet's or moon's crust and/or atmosphere. Examples include nitrogen, water, carbon dioxide, ammonia, hydrogen, and methane, all compounds of C, H, O...
to the rising plate, lowering its melting point
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...
. Each process generates different rock; mid-ocean ridge volcanics are primarily basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic, whereas subduction flows are mostly calc-alkaline
Calc-alkaline
The calc-alkaline magma series is one of two main magma series in igneous rocks, the other magma series being the tholeiitic. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
, and more explosive and viscous.
Spreading rates along mid-ocean ridges vary widely, from 2 cm (0.78740157480315 in) per year at the Mid-Atlantic Ridge
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South...
, to up to 16 cm (6 in) along the East Pacific Rise
East Pacific Rise
The East Pacific Rise is a mid-oceanic ridge, a divergent tectonic plate boundary located along the floor of the Pacific Ocean. It separates the Pacific Plate to the west from the North American Plate, the Rivera Plate, the Cocos Plate, the Nazca Plate, and the Antarctic Plate...
. Higher spreading rates are a probably cause for higher levels of volcanism. The technology for studying seamount eruptions did not exist until advancements in hydrophone
Hydrophone
A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...
technology made it possible to "listen" to acoustic wave
Acoustic wave
Acoustic waves are a type of longitudinal waves that propagate by means of adiabatic compression and decompression. Longitudinal waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle...
s, known as T-waves, released by submarine earthquake
Submarine earthquake
A submarine, undersea, or underwater earthquake is an earthquake that occurs underwater at the bottom of a body of water, especially an ocean. They are the leading cause of tsunamis...
s associated with submarine volcanic eruptions. The reason for this is that land-based seismometer
Seismometer
Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, volcanic eruptions, and other seismic sources...
s cannot detect sea-based earthquakes below a magnitude of 4, but acoustic waves travel well in water and long periods of time. A system in the North Pacific, maintained by the United States Navy
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. The U.S. Navy is the largest in the world; its battle fleet tonnage is greater than that of the next 13 largest navies combined. The U.S...
and originally intended for the detection of submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s, has detected an event on average every 2 to 3 years.
The most common underwater flow is pillow lava
Pillow lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...
, a circular lava flow named after its unusual shape. Less common are glassy
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
, marginal sheet flows, indicative of larger-scale flows. Volcaniclastic
Pyroclastic rock
Pyroclastic rocks or pyroclastics are clastic rocks composed solely or primarily of volcanic materials. Where the volcanic material has been transported and reworked through mechanical action, such as by wind or water, these rocks are termed volcaniclastic...
sedimentary rock
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
s are common in shallow-water environments. As plate movement starts to carry 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 caps 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 exemplery seamounts are Loihi Seamount
Loihi Seamount
Lōihi Seamount is an active undersea volcano located around off the southeast coast of the island of Hawaii about below sea level. It lies on the flank of Mauna Loa, the largest shield volcano on Earth...
, Bowie Seamount
Bowie Seamount
Bowie Seamount is a large submarine volcano in the northeastern Pacific Ocean, located west of Haida Gwaii, British Columbia, Canada.The seamount is named after William Bowie of the Coast & Geodetic Survey....
, Cross Seamount
Cross Seamount
Cross Seamount is a seamount far southwest of the Hawaii archipelago, about equidistant from the cities of Honolulu and Kona. It is one of the numerous seamounts surrounding Hawaii, although unrelated to the Hawaiian hotspot...
, and Denson Seamount
Denson Seamount
Denson Seamount is a submarine volcano in the Kodiak-Bowie Seamount chain, with an estimated age of 18 million years. It lies at the southern end of the chain near the Canada-United States border. It was one of the underground volcanic extrusions investigated by the 2004 Gulf of Alaska Seamount...
.
Subglacial
Ice
Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...
, often under a glacier
Glacier
A glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
. The nature of glaciovolcanism dictates that it occurs at areas of high latitude
Latitude
In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...
and high altitude
Altitude
Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...
. It has been suggested that subglacial volcanoes that are not actively erupting often dump heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...
into the ice covering them, producing meltwater
Meltwater
Meltwater is the water released by the melting of snow or ice, including glacial ice and ice shelfs over oceans. Meltwater is often found in the ablation zone of glaciers, where the rate of snow cover is reducing...
. This meltwater mix means that subglacial eruptions often generate dangerous jökulhlaup
Jökulhlaup
A jökulhlaup is a glacial outburst flood. It is an Icelandic term that has been adopted by the English language. It originally referred to the well-known subglacial outburst floods from Vatnajökull, Iceland which are triggered by geothermal heating and occasionally by a volcanic subglacial...
s (flood
Flood
A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water...
s) and lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s.
The study of glaciovolcanism is still a relatively new field. Early accounts described the unusual flat-topped steep-sided volcanoes (called tuya
Tuya
A tuya is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are somewhat rare worldwide, being confined to regions which were covered by glaciers and also had active volcanism during the same time period.-Formation:Tuyas are...
s) in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
that were suggested to have formed from eruptions below ice. The first English-language paper on the subject was published in 1947 by William Henry Mathews, describing the Tuya Butte
Tuya Butte
Tuya Butte is a tuya in the Tuya Range of north-central British Columbia, Canada. It is a bit less isolated from other ranges than neighbouring Mount Josephine...
field in northwest British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
. The eruptive process that builds these structures, originally inferred in the paper, begins with volcanic growth below the glacier. At first the eruptions resemble those that occur in the deep sea, forming piles of pillow lava
Pillow lava
Pillow lavas are lavas that contain characteristic pillow-shaped structures that are attributed to the extrusion of the lava under water, or subaqueous extrusion. Pillow lavas in volcanic rock are characterized by thick sequences of discontinuous pillow-shaped masses, commonly up to one metre in...
at the base of the volcanic structure. Some of the lava shatters when it comes in contact with the cold ice, forming a glassy
Volcanic glass
Volcanic glass is the amorphous product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas...
breccia
Breccia
Breccia is a rock composed of broken fragments of minerals or rock cemented together by a fine-grained matrix, that can be either similar to or different from the composition of the fragments....
called hyaloclastite
Hyaloclastite
Hyaloclastite is a hydrated tuff-like breccia rich in black volcanic glass, formed during volcanic eruptions under water, under ice or where subaerial flows reach the sea or other bodies of water. It has the appearance of angular flat fragments sized between a millimeter to few centimeters...
. After a while the ice finally melts into a lake, and the more explosive eruptions of Surtseyan activity
Surtseyan eruption
A Surtseyan eruption is a type of volcanic eruption that takes place in shallow seas or lakes. It is named after the island of Surtsey off the southern coast of Iceland....
begins, building up flanks made up of mostly hyaloclastite. Eventually the lake boils off from continued volcanism, and the lava flows become more effusive
Effusive eruption
An effusive eruption is a volcanic eruption characterized by the outpouring of lava onto the ground...
and thicken as the lava cools much more slowly, often forming columnar jointing. Well-preserved tuyas show all of these stages, for example Hjorleifshofdi in Iceland.
Products of volcano-ice interactions stand as various structures, whose shape is dependent on complex eruptive and environmental interactions. Glacial volcanism is a good indicator of past ice distribution, making it an important climatic marker. Since they are imbedded in ice, as ice retracts worldwide there are concerns that tuya
Tuya
A tuya is a type of distinctive, flat-topped, steep-sided volcano formed when lava erupts through a thick glacier or ice sheet. They are somewhat rare worldwide, being confined to regions which were covered by glaciers and also had active volcanism during the same time period.-Formation:Tuyas are...
s and other structures may destabalize, resulting in mass landslide
Landslide
A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...
s. Evidence of volcanic-glacial interactions are evident in Iceland
Iceland
Iceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
and parts of British Columbia
British Columbia
British Columbia is the westernmost of Canada's provinces and is known for its natural beauty, as reflected in its Latin motto, Splendor sine occasu . Its name was chosen by Queen Victoria in 1858...
, and it's even possible that they play a role in deglaciation
Ice age
An ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
.
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
and Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
, the Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
of western North America, South America
South America
South America is a continent situated in the Western Hemisphere, mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere. The continent is also considered a subcontinent of the Americas. It is bordered on the west by the Pacific Ocean and on the north and east...
and even on the planet Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
. Volcanoes known to have subglacial activity include:
- Mauna KeaMauna KeaMauna Kea is a volcano on the island of Hawaii. Standing above sea level, its peak is the highest point in the state of Hawaii. However, much of the mountain is under water; when measured from its oceanic base, Mauna Kea is over tall—significantly taller than Mount Everest...
in tropical HawaiiHawaii (island)The Island of Hawaii, also called the Big Island or Hawaii Island , is a volcanic island in the North Pacific Ocean...
. There is evidence of past subglacial eruptive activity on the volcano in the form of a subglacial deposit on its summit. The eruptions originated about 10,000 years ago, during the last ice ageIce ageAn ice age or, more precisely, glacial age, is a generic geological period of long-term reduction in the temperature of the Earth's surface and atmosphere, resulting in the presence or expansion of continental ice sheets, polar ice sheets and alpine glaciers...
, when the summit of Mauna Kea was covered in ice. - In 2008, the British Antarctic SurveyBritish Antarctic SurveyThe British Antarctic Survey is the United Kingdom's national Antarctic operation and has an active role in Antarctic affairs. BAS is part of the Natural Environment Research Council and has over 400 staff. It operates five research stations, two ships and five aircraft in and around Antarctica....
reported a volcanic eruption under the Antarctica ice sheetIce sheetAn ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...
2,200 years ago. It is believed to be that this was the biggest eruption in Antarctica in the last 10,000 years. Volcanic ash deposits from the volcano were identified through an airborne radar surveyAerial surveyAerial survey is a geomatics method of collecting information by using aerial photography, LiDAR or from remote sensing imagery using other bands of the electromagnetic spectrum, such as infrared, gamma, or ultraviolet. It can also refer to the chart or map made by analysing a region from the air...
, buried under later snowfalls in the Hudson MountainsHudson MountainsThe Hudson Mountains is a group of parasitic cones forming nunataks just above the Antarctic ice sheet in west Ellsworth Land. They lie just east of Cranton Bay and Pine Island Bay at the eastern extremity of Amundsen Sea, and are bounded on the north by Cosgrove Ice Shelf and on the south by Pine...
, close to Pine Island GlacierPine Island Glacier- Ice sheet drainage :The Antarctic ice sheet is the largest mass of ice on earth, containing a volume of water equivalent to of global sea level. The ice sheet forms from snow which falls onto the continent and compacts under its own weight. The ice then moves under its own weight toward the...
. - IcelandIcelandIceland , described as the Republic of Iceland, is a Nordic and European island country in the North Atlantic Ocean, on the Mid-Atlantic Ridge. Iceland also refers to the main island of the country, which contains almost all the population and almost all the land area. The country has a population...
, well known for both glacierGlacierA glacier is a large persistent body of ice that forms where the accumulation of snow exceeds its ablation over many years, often centuries. At least 0.1 km² in area and 50 m thick, but often much larger, a glacier slowly deforms and flows due to stresses induced by its weight...
s and volcanoVolcano2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...
es, is often a site of subglacial eruptions. An example an eruption under the VatnajökullVatnajökullVatnajökull is the largest glacier in Iceland. It is located in the south-east of the island, covering more than 8% of the country.-Size:With an area of 8,100 km², Vatnajökull is the largest ice cap in Europe by volume and the second largest in area Vatnajökull is the largest glacier in...
ice capIce capAn ice cap is an ice mass that covers less than 50 000 km² of land area . Masses of ice covering more than 50 000 km² are termed an ice sheet....
in 1996, which occurred under an estimated 2500 ft (762 m) of ice. - As part of the search for life on MarsLife on MarsScientists have long speculated about the possibility of life on Mars owing to the planet's proximity and similarity to Earth. Fictional Martians have been a recurring feature of popular entertainment of the 20th and 21st centuries, but it remains an open question whether life currently exists on...
, scientists have suggested that there may be subglacial volcanoes on the red planet. Several potential sites of such volcanism have been reviewed, and compared extensively with similar features in Iceland:
Phreatic eruptions
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...
. When cold ground or surface water come into contact with hot rock or magma it superheat
Superheat
Superheat is a live album by Dutch alternative rock band The Gathering, released on 25 January 2000 by Century Media. The album was recorded at Paradiso, Amsterdam, Netherlands on 16 April 1999, with the exception of "Rescue Me" & "Strange Machines", which were recorded at 013, Tilburg, Netherlands...
s and explodes
Steam explosion
A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...
, fracturing the surrounding rock and thrusting out a mixture of steam, water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
, ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...
, volcanic bomb
Volcanic bomb
A volcanic bomb is a mass of molten rock larger than 65 mm in diameter, formed when a volcano ejects viscous fragments of lava during an eruption. They cool into solid fragments before they reach the ground. Because volcanic bombs cool after they leave the volcano, they do not have grains...
s, and volcanic blocks. The distinguishing feature of phreatic explosions is that they only blast out fragments of pre-existing solid rock from the volcanic conduit; no new magma is erupted. Because they are driven by the cracking of rock stata under pressure, phreatic activity does not always result in an eruption; if the rock face is strong enough to withstand the explosive force, outright eruptions may not occur, although cracks in the rock will probably develop and weaken it, furthering future eruptions.
Often a precursor of future volcanic activity, phreatic eruptions are generally weak, although there have been exceptions. Some phreatic events may be triggered by earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...
activity, another volcanic precursor, and they may also travel along dike
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
lines. Phreatic eruptions form base surges, lahar
Lahar
A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley. The term is a shortened version of "berlahar" which originated in the Javanese language of...
s, avalanche
Avalanche
An avalanche is a sudden rapid flow of snow down a slope, occurring when either natural triggers or human activity causes a critical escalating transition from the slow equilibrium evolution of the snow pack. Typically occurring in mountainous terrain, an avalanche can mix air and water with the...
s, and volcanic block "rain." They may also release deadly toxic gas able to suffocate anyone in range of the eruption.
Volcanoes known to exhibit phreatic activity include:
- Mount St. HelensMount St. HelensMount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is south of Seattle, Washington and northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a...
, which exhibited Phreatic activity just prior to its catastrophic 1980 eruption1980 eruption of Mount St. HelensThe 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California...
(which was itself PlinianPlinian eruptionPlinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....
). - Taal VolcanoTaal VolcanoTaal Volcano is a complex volcano located on the island of Luzon in the Philippines. Historical eruptions are concentrated on Volcano Island, an island near the middle of Lake Taal. The lake partially fills Taal Caldera, which was formed by powerful prehistoric eruptions between 140,000 to 5,380 BP...
, PhilippinesPhilippinesThe Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, 1965. - La SoufrièreLa Grande SoufrièreLa Grande Soufrière, , is an active stratovolcano located on the French island of Basse-Terre, in Guadeloupe. It is the tallest mountain in the Lesser Antilles, and rises 1,467 m high....
of GuadeloupeGuadeloupeGuadeloupe is an archipelago located in the Leeward Islands, in the Lesser Antilles, with a land area of 1,628 square kilometres and a population of 400,000. It is the first overseas region of France, consisting of a single overseas department. As with the other overseas departments, Guadeloupe...
(Lesser AntillesLesser AntillesThe Lesser Antilles are a long, partly volcanic island arc in the Western Hemisphere. Most of its islands form the eastern boundary of the Caribbean Sea with the Atlantic Ocean, with the remainder located in the southern Caribbean just north of South America...
), 1975-1976 activity.
See also
- Timetable of major worldwide volcanic eruptionsTimetable of major worldwide volcanic eruptionsThis article is a list of volcanic eruptions of approximately at least magnitude 6 on the Volcanic Explosivity Index or equivalent sulfur dioxide emission around the Quaternary period. Some cooled the global climate; the extent of this effect depends on the amount of sulfur dioxide emitted...
- List of currently erupting volcanoes
- List of Quaternary volcanic eruptions
External links
- USGS Hawaiian Volcano Observatory (HVO) homepage. USGS.
- Distinguishing eruptive types.
- How Volcanoes Work. San Diego State UniversitySan Diego State UniversitySan Diego State University , founded in 1897 as San Diego Normal School, is the largest and oldest higher education facility in the greater San Diego area , and is part of the California State University system...
.