7. Layers of ash emitted by the volcano
| 9. Layers of lava emitted by the volcano
11. Parasitic cone
12. Lava flow
15. Ash cloud
A volcano is an opening, or rupture, in a planet's surface or crust
, which allows hot magma
, volcanic ash
and gases to escape from below the surface.
Volcanoes are generally found where tectonic plates
1783 The volcano Laki, in Iceland, begins an eight-month eruption which kills over 9,000 people and starts a seven-year famine.
1883 Krakatoa begins to erupt. The volcano's final and most notable explosion occurs on August 26.
1973 A volcanic eruption devastates Heimaey in the Vestmannaeyjar chain of islands off the south coast of Iceland.
1986 Carbon dioxide gas erupts from volcanic Lake Nyos in Cameroon, killing up to 1,800 people within a 20-kilometer range.
7. Layers of ash emitted by the volcano
| 9. Layers of lava emitted by the volcano
11. Parasitic cone
12. Lava flow
15. Ash cloud
A volcano is an opening, or rupture, in a planet's surface or crust
, which allows hot magma
, volcanic ash
and gases to escape from below the surface.
Volcanoes are generally found where tectonic plates
. A mid-oceanic ridge, for example the Mid-Atlantic Ridge
, has examples of volcanoes caused by divergent tectonic plates
pulling apart; the Pacific Ring of Fire
has examples of volcanoes caused by convergent tectonic plates
coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust
in the interiors of plates, e.g., in the East African Rift
, the Wells Gray-Clearwater volcanic field
and the Rio Grande Rift
in North America. This type of volcanism falls under the umbrella of "Plate hypothesis" volcanism.
Intraplate volcanism has also been postulated to be caused by mantle plume
s. These so-called "hotspots
", for example Hawaii
, are postulated to arise from upwelling diapir
s from the core-mantle boundary
, 3,000 km deep in the Earth.
EtymologyThe word volcano is derived from the name of Vulcano
, a volcanic island in the Aeolian Islands
of Italy whose name in turn originates from Vulcan
, the name of a god of fire
in Roman mythology
. The study of volcanoes is called volcanology
, sometimes spelled vulcanology.
Divergent plate boundariesAt the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust
is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic
expansion, and the partial melting of the mantle
causing volcanism and creating new oceanic crust. Most divergent plate boundaries
are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland
Convergent plate boundariesSubduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma
. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna
and the volcanoes in the Pacific Ring of Fire
" is the name given to volcanic provinces postulated to be formed by mantle plume
s. These are postulated to comprise columns of hot material that rise from the core-mantle boundary. They are suggested to be hot, causing large-volume melting, and to be fixed in space. Because the tectonic plates move across them, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the postulated plume. The Hawaiian Islands
have been suggested to have been formed in such a manner, as well as the Snake River Plain
, with the Yellowstone Caldera
being the part of the North American plate currently above the hot spot. This theory is currently under criticism, however.
mountain, spewing lava
and poisonous gases
from a crater
at its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava dome
s rather than a summit crater, whereas others present landscape
features such as massive plateau
s. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash
) and gases (mainly steam and magmatic gases) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as Puu Ōō
on a flank of Hawaii
Other types of volcano include cryovolcano
es (or ice volcanoes), particularly on some moons of Jupiter
; and mud volcano
es, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.
Fissure ventsVolcanic fissure vents are flat, linear cracks through which lava
Shield volcanoesShield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent, but not generally explode catastrophically. Since low-viscosity magma is typically low in silica, shield volcanoes are more common in oceanic than continental settings. The Hawaii
an volcanic chain is a series of shield cones, and they are common in Iceland
, as well.
Lava domesLava domes are built by slow eruptions of highly viscous lavas. They are sometimes formed within the crater of a previous volcanic eruption (as in Mount Saint Helens), but can also form independently, as in the case of Lassen Peak
. Like stratovolcanoes, they can produce violent, explosive eruptions, but their lavas generally do not flow far from the originating vent.
CryptodomesCryptodomes are formed when viscous lava forces its way up and causes a bulge. The 1980 eruption of Mount St. Helens
was an example. Lava was under great pressure and forced a bulge in the mountain, which was unstable and slid down the north side.
Volcanic cones (cinder cones)
and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Most cinder cones erupt only once
. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin
and Sunset Crater
are examples of cinder cones. In New Mexico
, Caja del Rio is a volcanic field
of over 60 cinder cones.
Stratovolcanoes (composite volcanoes)Stratovolcanoes or composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata
that give rise to the name. Stratovolcanoes are also known as composite volcanoes, created from several structures during different kinds of eruptions. Strato/composite volcanoes are made of cinders, ash and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process begins again. Classic examples include Mt. Fuji in Japan, Mayon Volcano
in the Philippines, and Mount Vesuvius
In recorded history, explosive eruptions by stratovolcanoes have posed the greatest hazard to civilizations, as ash
is produced by an explosive eruption
. No supervolcano erupted in recorded history. Shield volcanoes have not an enormous pressure build up from the lava flow. Fissure vents and monogenetic volcanic field
s (volcanic cones) have not powerful explosive eruptions, as they are many times under extension. Stratovolcanoes (30–35°) are steeper than shield volcanoes (generally 5–10°), their loose tephra
are material for dangerous lahar
SupervolcanoesA supervolcano is a large volcano that usually has a large caldera
and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur
and ash erupted. They are the most dangerous type of volcano. Examples include Yellowstone Caldera
in Yellowstone National Park
and Valles Caldera in New Mexico
(both western United States), Lake Taupo
in New Zealand
, Lake Toba
and Ngorogoro Crater in Tanzania
. Supervolcanoes are hard to identify centuries later, given the enormous areas they cover. Large igneous province
s are also considered supervolcanoes because of the vast amount of basalt
lava erupted, but are non-explosive
Submarine volcanoesSubmarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by hydrophone
s and discoloration of water because of volcanic gas
es. Pumice raft
s may also appear. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanoes. They may become so large that they break the ocean surface as new islands. Pillow lava
is a common eruptive product of submarine volcanoes. Hydrothermal vent
s are common near these volcanoes, and some support peculiar ecosystems based on dissolved minerals.
Subglacial volcanoesSubglacial volcanoes develop underneath icecaps
. They are made up of flat lava which flows at the top of extensive pillow lavas and palagonite
. When the icecap melts, the lavas on the top collapse, leaving a flat-topped mountain. These volcanoes are also called table mountains
s or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland, however, there are also tuyas in British Columbia
. The origin of the term comes from Tuya Butte
, which is one of the several tuyas in the area of the Tuya River
and Tuya Range
in northern British Columbia. Tuya Butte was the first such landform
analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park
was recently established to protect this unusual landscape, which lies north of Tuya Lake
and south of the Jennings River
near the boundary with the Yukon Territory.
Mud volcanoesMud volcanoes or mud domes are formations created by geo-excreted liquids and gases, although there are several processes which may cause such activity. The largest structures are 10 kilometers in diameter and reach 700 meters high.
Lava compositionAnother way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions (Cas & Wright, 1987):
- If the erupted magmaMagmaMagma 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...
contains a high percentage (>63%) of silica, the lava is called felsicFelsicThe 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....
- Felsic lavas (daciteDaciteDacite 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...
s or rhyoliteRhyoliteThis 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...
s) tend to be highly viscous (not very fluid) and are erupted as domes or short, stubby flows. Viscous lavas tend to form stratovolcanoStratovolcanoA 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 or lava domes. Lassen PeakLassen PeakLassen Peak is the southernmost active volcano in the Cascade Range. It is part of the Cascade Volcanic Arc which is an arc that stretches from northern California to southwestern British Columbia...
in CaliforniaCaliforniaCalifornia is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
is an example of a volcano formed from felsic lava and is actually a large lava dome.
- Because siliceous magmas are so viscous, they tend to trap volatilesVolatilesIn 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...
(gases) that are present, which cause the magma to erupt catastrophically, eventually forming stratovolcanoStratovolcanoA 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. 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 (ignimbriteIgnimbriteAn ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....
s) are highly hazardous products of such volcanoes, since they are composed of molten volcanic ash too heavy to go up into the atmosphere, so they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 1,200 °C are known to occur in 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, which will incinerate everything flammable in their path and thick layers of hot pyroclastic flow deposits can be laid down, often up to many meters thick. 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...
's Valley of Ten Thousand SmokesValley of Ten Thousand SmokesThe Valley of Ten Thousand Smokes is a valley within Katmai National Park and Preserve in Alaska which is filled with ash flow from the eruption of Novarupta on June 6–8, 1912. Following the eruption, thousands of fumaroles vented steam from the ash. Robert F...
, formed by the eruption of NovaruptaNovaruptaNovarupta, meaning "new eruption", is a volcano located on the Alaska Peninsula in Katmai National Park and Preserve, about southwest of Anchorage. Formed in 1912 during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma as the 1980 eruption of...
near KatmaiMount KatmaiMount Katmai is a large stratovolcano on the Alaska Peninsula in southern Alaska, located within Katmai National Park and Preserve. It is about in diameter with a central lake-filled caldera about 3 by 2 mi in area, formed during the Novarupta eruption of 1912. The caldera rim reaches a...
in 1912, is an example of a thick 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...
or ignimbriteIgnimbriteAn ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....
deposit. Volcanic ash that is light enough to be erupted high into the Earth's atmosphereEarth's atmosphereThe atmosphere of Earth is a layer of gases surrounding the planet Earth that is retained by Earth's gravity. The atmosphere protects life on Earth by absorbing ultraviolet solar radiation, warming the surface through heat retention , and reducing temperature extremes between day and night...
may travel many kilometres before it falls back to ground as a tuffTuffTuff is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered...
- Felsic lavas (dacite
- If the erupted magma contains 52–63% silica, the lava is of intermediate composition.
- These "andesiticAndesiteAndesite 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,...
" volcanoes generally only occur above subduction zones (e.g. Mount MerapiMount MerapiMount Merapi, Gunung Merapi , is an active stratovolcano located on the border between Central Java and Yogyakarta, Indonesia. It is the most active volcano in Indonesia and has erupted regularly since 1548...
in IndonesiaIndonesiaIndonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
- Andesitic lava is typically formed at convergent boundaryConvergent boundaryIn plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
margins of tectonic plates, by several processes:
- Hydration melting of peridotite and fractional crystallization
- Melting of subducted slabSlab (geology)In geology, a slab is the portion of a tectonic plate that is being subducted.Slabs constitute an important part of the global plate tectonic system. They drive plate tectonics both by pulling along the lithosphere to which they are attached in a processes known as slab pull and by inciting...
- Magma mixing between felsic rhyolitic and mafic basaltic magmas in an intermediate reservoir prior to emplacement or lava flow.
- These "andesitic
- If the erupted magma contains <52% and >45% silica, the lava is called maficMaficMafic is an adjective describing a silicate mineral or rock that is rich in magnesium and iron; the term is a portmanteau of the words "magnesium" and "ferric". Most mafic minerals are dark in color and the relative density is greater than 3. Common rock-forming mafic minerals include olivine,...
(because it contains higher percentages of magnesiumMagnesiumMagnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...
(Mg) and ironIronIron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
(Fe)) or 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. These lavas are usually much less viscous than rhyolitic lavas, depending on their eruption temperatureTemperatureTemperature is a physical property of matter that quantitatively expresses the common notions of hot and cold. Objects of low temperature are cold, while various degrees of higher temperatures are referred to as warm or hot...
; they also tend to be hotter than felsic lavas. Mafic lavas occur in a wide range of settings:
- At mid-ocean ridgeMid-ocean ridgeA 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, where two oceanic plates are pulling apart, basaltic lava erupts as pillows to fill the gap;
- Shield volcanoes (e.g. the Hawaiian IslandsHawaiian IslandsThe Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, including Mauna LoaMauna LoaMauna Loa is one of five volcanoes that form the Island of Hawaii in the U.S. state of Hawaii in the Pacific Ocean, and the largest on Earth in terms of volume and area covered. It is an active shield volcano, with a volume estimated at approximately , although its peak is about lower than that...
and 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 both oceanicOceanic crustOceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium...
and continental crustContinental crustThe continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in...
- As continental flood basaltsFlood basaltA flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges...
- At mid-ocean ridge
- Some erupted magmas contain <=45% silica and produce ultramafic lava. Ultramafic flows, also known as komatiiteKomatiiteKomatiite is a type of ultramafic mantle-derived volcanic rock. Komatiites have low silicon, potassium and aluminium, and high to extremely high magnesium content...
s, are very rare; indeed, very few have been erupted at the Earth's surface since the ProterozoicProterozoicThe Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
, when the planet's heat flow was higher. They are (or were) the hottest lavas, and probably more fluid than common mafic lavas.
Lava textureTwo types of lava are named according to the surface
texture: Aa and pāhoehoe (paːˈho.eˈho.e), both Hawaiian
words. Aa is characterized by a rough, clinkery surface and is the typical texture of viscous lava flows. However, even basaltic or mafic flows can be erupted as aa flows, particularly if the eruption rate is high and the slope is steep.
Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow with greater fluidity.
ActiveA popular way of classifying magmatic volcanoes is by their frequency of eruption
, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes, which was explained above.
There is no real consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.
Scientists usually consider a volcano to be erupting or likely to erupt if it is currently erupting, or showing signs of unrest such as unusual earthquake activity or significant new gas emissions. Most scientists consider a volcano active if it has erupted in holocene
times. Historic times is another timeframe for active. But it is important to note that the span of recorded history differs from region to region. In China
and the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States
, it reaches back less than 300 years, and in Hawaii
and New Zealand
, only around 200 years. The Smithsonian Global Volcanism Program's definition of active is having erupted within the last 10,000 years (the 'holocene' period).
Presently there are about 500 active volcanoes in the world – the majority following along the Pacific 'Ring of Fire
' – and around 50 of these erupt each year. The United States is home to 50 active volcanoes. There are more than 1,500 potentially active volcanoes. An estimated 500 million people live near active volcanoes.
Extinct volcanoes are those that scientists consider unlikely to erupt again, because the volcano no longer has a lava supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian – Emperor seamount chain in the Pacific Ocean
and the Zuidwal volcano
in the Netherlands
. Edinburgh Castle
is famously located atop an extinct volcano. Otherwise, whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" caldera
s can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct.
DormantIt is difficult to distinguish an extinct volcano from a dormant one. Volcanoes are often considered to be extinct if there are no written records of its activity. Nevertheless, volcanoes may remain dormant for a long period of time. For example, Yellowstone
has a repose/recharge period of around 700 ka, and Toba of around 380 ka. Vesuvius was described by Roman writers as having been covered with gardens and vineyards before its famous eruption of AD 79, which destroyed the towns of Herculaneum
. Before its catastrophic eruption of 1991, Pinatubo was an inconspicuous volcano, unknown to most people in the surrounding areas. Two other examples are the long-dormant Soufrière Hills
volcano on the island of Montserrat
, thought to be extinct before activity resumed in 1995 and Fourpeaked Mountain
, which, before its September 2006 eruption, had not erupted since before 8000 BC and had long been thought to be extinct.
Volcanic-alert levelThe three common popular classifications of volcanoes can be subjective and some volcanoes thought to have been extinct have announced to the world they were just pretending. To help prevent citizens from falsely believing they are not at risk when living on or near a volcano, countries have adopted new classifications to describe the various levels and stages of volcanic activity. Some alert systems use different numbers or colors to designate the different stages. Other systems use colors and words. Some systems use a combination of both.
Volcano warning schemes of the United StatesThe United States Geological Survey (USGS) has adopted a common system nationwide for characterizing the level of unrest and eruptive activity at volcanoes. The new volcano alert-level system classifies volcanoes now as being in a normal, advisory, watch or warning stage. Additionally, colors are used to denote the amount of ash produced. Details of the US system can be found at Volcano warning schemes of the United States.
Notable volcanoesThe 16 current Decade Volcanoes are:
, 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...
, Kagoshima Prefecture
is a prefecture of Japan located on the island of Kyushu. The capital is the city of Kagoshima.- Geography :Kagoshima Prefecture is located at the southwest tip of Kyushu and includes a chain of islands stretching further to the southwest for a few hundred kilometers...
Guatemala is a country in Central America bordered by Mexico to the north and west, the Pacific Ocean to the southwest, Belize to the northeast, the Caribbean to the east, and Honduras and El Salvador to the southeast...
Santorini , officially Thira , is an island located in the southern Aegean Sea, about southeast from Greece's mainland. It is the largest island of a small, circular archipelago which bears the same name and is the remnant of a volcanic caldera...
The Cyclades is a Greek island group in the Aegean Sea, south-east of the mainland of Greece; and a former administrative prefecture of Greece. They are one of the island groups which constitute the Aegean archipelago. The name refers to the islands around the sacred island of Delos...
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
Taal 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...
Luzon is the largest island in the Philippines. It is located in the northernmost region of the archipelago, and is also the name for one of the three primary island groups in the country centered on the Island of Luzon...
The 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...
Mount Teide , is a volcano on Tenerife, Canary Islands. Its summit is the highest point in Spain, the highest point above sea level in the islands of the Atlantic, and it is the third highest volcano in the world measured from its base on the ocean floor, after Mauna Loa and Mauna Kea located in...
, Canary Islands
The Canary Islands , also known as the Canaries , is a Spanish archipelago located just off the northwest coast of mainland Africa, 100 km west of the border between Morocco and the Western Sahara. The Canaries are a Spanish autonomous community and an outermost region of the European Union...
Spain , officially the Kingdom of Spain languages]] under the European Charter for Regional or Minority Languages. In each of these, Spain's official name is as follows:;;;;;;), is a country and member state of the European Union located in southwestern Europe on the Iberian Peninsula...
Ulawun is a basaltic and andesitic stratovolcano situated on the island of New Britain, Papua New Guinea, about 130 km southwest of Rabaul. It is the highest mountain in the Bismarck Archipelago at , and one of the most active volcanoes in Papua New Guinea. The first recorded eruption of...
, New Britain
New Britain, or Niu Briten, is the largest island in the Bismarck Archipelago of Papua New Guinea. It is separated from the island of New Guinea by the Dampier and Vitiaz Straits and from New Ireland by St. George's Channel...
, Papua New Guinea
Papua New Guinea
Papua 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...
is an active volcanic group of several overlapping stratovolcanoes, near the city of Shimabara, Nagasaki Prefecture, on the island of Kyūshū, Japan’s southernmost main island....
, Nagasaki Prefecture
is a prefecture of Japan located on the island of Kyūshū. The capital is the city of Nagasaki.- History :Nagasaki Prefecture was created by merging of the western half of the former province of Hizen with the island provinces of Tsushima and Iki...
Province of Naples
The Province of Naples is a province in the Campania region of Italy. Its capital city is Naples, within the province there are 92 Comuni of the Province of Naples.-Demographics:...
Effects of volcanoes
and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite
), effusive eruption of low-silica lava (e.g., basalt
), pyroclastic flow
s (debris flow) and carbon dioxide
emission. All of these activities can pose a hazard to humans. Earthquake
s, hot spring
s, mud pots and geyser
s often accompany volcanic activity.
The concentrations of different volcanic gas
es can vary considerably from one volcano to the next. Water vapor
is typically the most abundant volcanic gas, followed by carbon dioxide
and sulfur dioxide
. Other principal volcanic gases include hydrogen sulfide
, hydrogen chloride
, and hydrogen fluoride
. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen
, carbon monoxide
s, organic compounds, and volatile metal chlorides.
Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice
) into the stratosphere
to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid
(H2SO4), which condenses rapidly in the stratosphere to form fine sulfate
aerosols. The aerosols increase the Earth's albedo
—its reflection of radiation from the Sun
back into space – and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere
. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years — sulfur dioxide from the eruption of Huaynaputina
probably caused the Russian famine of 1601–1603
One proposed volcanic winter
happened c. 70,000 years ago following the supereruption
of Lake Toba
on Sumatra island in Indonesia. According to the Toba catastrophe theory
to which some anthropologists and archeologists subscribe, it had global consequences, killing most humans then alive and creating a population bottleneck
that affected the genetic inheritance of all humans today. The 1815 eruption of Mount Tambora
created global climate anomalies that became known as the "Year Without a Summer
" because of the effect on North American and European weather. Agricultural crops failed and livestock died in much of the Northern Hemisphere, resulting in one of the worst famines of the 19th century. The freezing winter of 1740–41, which led to widespread famine in northern Europe, may also owe its origins to a volcanic eruption.
It has been suggested that volcanic activity caused or contributed to the End-Ordovician
, Late Devonian
mass extinctions, and possibly others. The massive eruptive event which formed the Siberian Traps
, one of the largest known volcanic events of the last 500 million years of Earth's geological history, continued for a million years and is considered to be the likely cause of the "Great Dying" about 250 million years ago, which is estimated to have killed 90% of species existing at the time.
The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen
chemical species in the stratosphere. This effect, together with increased stratospheric chlorine
levels from chlorofluorocarbon
pollution, generates chlorine monoxide (ClO), which destroys ozone
(O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus cloud
s and further modify the Earth's radiation
balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain
. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon
for biogeochemical cycles.
s) of carbon dioxide
each year. Volcanic eruptions may inject aerosols into the Earth's atmosphere
. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate
mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil
through the weathering
process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.
Ash thrown into the air by eruptions can present a hazard to aircraft
, especially jet aircraft
where the particles can be melted by the high operating temperature. Dangerous encounters in 1982 after the eruption of Galunggung
in Indonesia, and 1989 after the eruption of Mount Redoubt
in Alaska raised awareness of this phenomenon. Nine Volcanic Ash Advisory Center
s were established by the International Civil Aviation Organization
to monitor ash clouds and advise pilots accordingly. The 2010 eruptions of Eyjafjallajökull
caused major disruptions to air travel in Europe.
Volcanoes on other planetary bodies
The Earth's Moon
has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core. However, the Moon does have many volcanic features such as maria
(the darker patches seen on the moon), rille
s and domes
The planet Venus
has a surface that is 90% basalt
, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons
, in the form of ash flows near the summit and on the northern flank.
There are several extinct volcanoes on Mars
, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons
, Ascraeus Mons
, Hecates Tholus
, Olympus Mons
, and Pavonis Mons
. These volcanoes have been extinct for many millions of years, but the European Mars Express
spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.
is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur
, sulfur dioxide
rock, and as a result, Io
is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io. Europa
, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system
In 1989 the Voyager 2
spacecraft observed cryovolcano
es (ice volcanoes) on Triton
, a moon
, and in 2005 the Cassini–Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn
. The ejecta may be composed of water
, liquid nitrogen
, dust, or methane
compounds. Cassini–Huygens also found evidence of a methane-spewing cryovolcano on the Saturn
ian moon Titan
, which is believed to be a significant source of the methane found in its atmosphere. It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar
A 2010 study of the exoplanet COROT-7b, which was detected by transit in 2009, studied that tidal heating
from the host star very close to the planet and neighboring planets could generate intense volcanic activity similar to Io.
Traditional beliefs about volcanoesMany ancient accounts ascribe volcanic eruptions to supernatural
causes, such as the actions of god
s or demigod
s. To the ancient Greeks, volcanoes' capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth's tears. One early idea counter to this was proposed by Jesuit
(1602–1680), who witnessed eruptions of Mount Etna
, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur
, bitumen and coal
Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle
structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.
- List of extraterrestrial volcanoes
- Maritime impacts of volcanic eruptionsMaritime impacts of volcanic eruptionsLess commonly publicized than the effects on aviation—and with less potential for catastrophe—maritime Impacts of volcanic eruptions are also dangerous...
- Prediction of volcanic activity
- 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...
- 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....
- Volcano NumberVolcano NumberThe Volcano Number is a hierarchical geographical systematic system to uniquely identify and tag volcanoes and volcanic features on Earth....
- Volcano observatoryVolcano observatoryA volcano observatory is an institution that conducts research and monitoring of a volcano.Each observatory provides continuous and periodic monitoring of the seismicity, other geophysical changes, ground movements, volcanic gas chemistry, and hydrologic conditions and activity between and during...
- Cas, R.A.F. and J.V. Wright, 1987. Volcanic Successions. Unwin Hyman Inc. 528p. ISBN 0-04-552022-4
- Macdonald, Gordon and Agatin T. Abbott. (1970). Volcanoes in the Sea. University of Hawaii Press, Honolulu. 441 p.
- Ollier, Cliff. (1988). Volcanoes. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).
- Sigurðsson, Haraldur, ed. (1999) Encyclopedia of Volcanoes. Academic Press. ISBN 0-12-643140-X. This is a reference aimed at geologists, but many articles are accessible to non-professionals.
- Volcano Eruptions, Ancient & Modern slideshow by Life magazine
- Volcano, U.S. Federal Emergency Management AgencyFederal Emergency Management AgencyThe Federal Emergency Management Agency is an agency of the United States Department of Homeland Security, initially created by Presidential Reorganization Plan No. 1 of 1978 and implemented by two Executive Orders...
- Volcano World