A volcano is a rupture in the crust of a planetary-mass object, such
as Earth, that allows hot lava, volcanic ash, and gases to escape from
a magma chamber below the surface.
Earth's volcanoes occur because its crust is broken into 17 major,
rigid tectonic plates that float on a hotter, softer layer in its
mantle. Therefore, on Earth, volcanoes are generally found where
tectonic plates are diverging or converging, and most are found
underwater. For example, a mid-oceanic ridge, such as the Mid-Atlantic
Ridge, has volcanoes caused by divergent tectonic plates whereas the
Pacific Ring of Fire
Pacific Ring of Fire has volcanoes caused by convergent tectonic
plates. Volcanoes can also form where there is stretching and thinning
of the crust's plates, e.g., in the
East African Rift
East African Rift and the Wells
Gray-Clearwater volcanic field and
Rio Grande Rift
Rio Grande Rift in North America.
This type of volcanism falls under the umbrella of "plate hypothesis"
Volcanism away from plate boundaries has also been
explained as mantle plumes. These so-called "hotspots", for example
Hawaii, are postulated to arise from upwelling diapirs with magma from
the core–mantle boundary, 3,000 km deep in the Earth. Volcanoes
are usually not created where two tectonic plates slide past one
Erupting volcanoes can pose many hazards, not only in the immediate
vicinity of the eruption. One such hazard is that volcanic ash can be
a threat to aircraft, in particular those with jet engines where ash
particles can be melted by the high operating temperature; the melted
particles then adhere to the turbine blades and alter their shape,
disrupting the operation of the turbine. Large eruptions can affect
temperature as ash and droplets of sulfuric acid obscure the sun and
cool the Earth's lower atmosphere (or troposphere); however, they also
absorb heat radiated from the Earth, thereby warming the upper
atmosphere (or stratosphere). Historically, volcanic winters have
caused catastrophic famines.
2 Plate tectonics
2.1 Divergent plate boundaries
2.2 Convergent plate boundaries
3 Volcanic features
3.1 Fissure vents
3.2 Shield volcanoes
3.5 Volcanic cones (cinder cones)
3.6 Stratovolcanoes (composite volcanoes)
3.8 Underwater volcanoes
3.9 Subglacial volcanoes
3.10 Mud volcanoes
4 Erupted material
5 Volcanic activity
5.1 Popular classification of volcanoes
5.1.3 Dormant and reactivated
5.2 Technical classification of volcanoes
5.2.1 Volcanic-alert level
Volcano warning schemes of the United States
6 Decade volcanoes
7 Effects of volcanoes
7.1 Volcanic gases
7.2 Significant consequences
7.3 Acid rain
8 Volcanoes on other celestial bodies
9 Traditional beliefs about volcanoes
10 See also
12 Further reading
13 External links
The word volcano is derived from the name of Vulcano, a volcanic
island in the
Aeolian Islands of Italy whose name in turn comes from
Vulcan, the god of fire in Roman mythology. The study of volcanoes
is called volcanology, sometimes spelled vulcanology.
Map showing the divergent plate boundaries (oceanic spreading ridges)
and recent sub-aerial volcanoes
Main article: Plate tectonics
Divergent plate boundaries
Main article: Divergent boundary
At the mid-oceanic ridges, two tectonic plates diverge from one
another as new oceanic crust is formed by the cooling and solidifying
of hot molten rock. Because the crust is very thin at these ridges due
to the pull of the tectonic plates, the release of pressure leads to
adiabatic expansion (without transfer of heat or matter) 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 on the
submarine, forming new seafloor. Black smokers (also known as deep sea
vents) are evidence of this kind of volcanic activity. Where the
mid-oceanic ridge is above sea-level, volcanic islands are formed; for
Convergent plate boundaries
Main article: Convergent boundary
Subduction 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. In a process called flux melting, water
released from the subducting plate lowers the melting temperature of
the overlying mantle wedge, thus creating magma. This magma tends to
be extremely viscous because of its high silica content, so it often
does not attain the surface but cools and solidifies at depth. When it
does reach the surface, however, a volcano is formed. Typical examples
Mount Etna and the volcanoes in the Pacific Ring of Fire.
Main article: Hotspot (geology)
Hotspots are volcanic areas believed to be formed by mantle plumes,
which are hypothesized to be columns of hot material rising from the
core-mantle boundary in a fixed space that causes large-volume
melting. Because tectonic plates move across them, each volcano
becomes dormant and is eventually re-formed as the plate advances over
the postulated plume. The
Hawaiian Islands are said to have been
formed in such a manner; so has the Snake River Plain, with the
Yellowstone Caldera being the part of the North American plate above
the hot spot. This theory, however, has been doubted.
Lakagigar fissure vent in Iceland, source of the major world climate
alteration of 1783–84
Skjaldbreiður, a shield volcano whose name means "broad shield"
The most common perception of a volcano is of a conical mountain,
spewing lava and poisonous gases from a crater at its summit; however,
this describes just one of the many types of volcano. The features of
volcanoes are much more complicated and their structure and behavior
depends on a number of factors. Some volcanoes have rugged peaks
formed by lava domes rather than a summit crater while others have
landscape features such as massive plateaus. Vents that issue volcanic
material (including lava and ash) and gases (mainly steam and magmatic
gases) can develop anywhere on the landform and may give rise to
smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea.
Other types of volcano include cryovolcanoes (or ice volcanoes),
particularly on some moons of Jupiter, Saturn, and Neptune; and mud
volcanoes, 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 the mud volcano
is actually a vent of an igneous volcano.
Main article: Fissure vent
Volcanic fissure vents are flat, linear fractures through which lava
Main article: Shield volcano
Shield volcanoes, so named for their broad, shield-like profiles, are
formed by the eruption of low-viscosity lava that can flow a great
distance from a vent. They generally do not explode catastrophically.
Since low-viscosity magma is typically low in silica, shield volcanoes
are more common in oceanic than continental settings. The Hawaiian
volcanic chain is a series of shield cones, and they are common in
Iceland, as well.
Lava domes are built by slow eruptions of highly viscous lava. They
are sometimes formed within the crater of a previous volcanic
eruption, as in the case of Mount Saint Helens, but can also form
independently, as in the case of Lassen Peak. Like stratovolcanoes,
they can produce violent, explosive eruptions, but their lava
generally does not flow far from the originating vent.
Cryptodomes are formed when viscous lava is forced upward causing the
surface to bulge. The
1980 eruption of Mount St. Helens
1980 eruption of Mount St. Helens was an
example; lava beneath the surface of the mountain created an upward
bulge which slid down the north side of the mountain.
Volcanic cones (cinder cones)
Main articles: volcanic cone and Cinder cone
Izalco (volcano), located in the
Cordillera de Apaneca
Cordillera de Apaneca volcanic range
complex in El Salvador. Only a few generations old, Izalco is the
youngest and best known cone volcano. Izalco erupted almost
continuously from 1770 (when it formed) to 1958, earning it the
nickname of "Lighthouse of the Pacific".
Volcanic cones or cinder cones result from eruptions of mostly small
pieces of scoria and pyroclastics (both resemble cinders, hence the
name of this volcano type) that build up around the vent. These can be
relatively short-lived eruptions that produce a cone-shaped hill
perhaps 30 to 400 meters high. Most cinder cones erupt only once.
Cinder cones may form as flank vents on larger volcanoes, or occur on
Parícutin in Mexico and
Sunset Crater in
examples of cinder cones. In New Mexico,
Caja del Rio
Caja del Rio is a volcanic
field of over 60 cinder cones.
Based on satellite images it was suggested that cinder cones might
occur on other terrestrial bodies in the
Solar system too; on the
Mars and the Moon.
Stratovolcanoes (composite volcanoes)
Cross-section through a stratovolcano (vertical scale is exaggerated):
Large magma chamber
Layers of ash emitted by the volcano
Layers of lava emitted by the volcano
Main article: Stratovolcano
Stratovolcanoes or composite volcanoes are tall conical mountains
composed of lava flows and other ejecta in alternate layers, the
strata that gives rise to the name. Stratovolcanoes are also known as
composite volcanoes because they are created from multiple 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 repeats. Classic examples include
Mount Fuji in
Mayon Volcano in the Philippines, and
Mount Vesuvius and
Stromboli in Italy.
Throughout recorded history, ash produced by the explosive eruption of
stratovolcanoes has posed the greatest volcanic hazard to
civilizations. Not only do stratovolcanoes have greater pressure build
up from the underlying lava flow than shield volcanoes, but their
fissure vents and monogenetic volcanic fields (volcanic cones) have
more powerful eruptions, as they are many times under extension. They
are also steeper than shield volcanoes, with slopes of 30–35°
compared to slopes of generally 5–10°, and their loose tephra are
material for dangerous lahars. Large pieces of tephra are called
volcanic bombs. Big bombs can measure more than 4 feet(1.2 meters)
across and weigh several tons.
Main article: Supervolcano
See also: List of largest volcanic eruptions
A supervolcano usually has a large caldera and can produce devastation
on an enormous, sometimes continental, scale. Such volcanoes are able
to severely cool global temperatures for many years after the eruption
due to the huge volumes of sulfur and ash released into the
atmosphere. They are the most dangerous type of volcano. Examples
Yellowstone Caldera in
Yellowstone National Park
Yellowstone National Park and Valles
New Mexico (both western United States);
Lake Taupo in New
Lake Toba in Sumatra, Indonesia; and
Ngorongoro Crater in
Tanzania. Because of the enormous area they may cover, supervolcanoes
are hard to identify centuries after an eruption. Similarly, large
igneous provinces are also considered supervolcanoes because of the
vast amount of basalt lava erupted (even though the lava flow is
Main article: Submarine volcano
See also: Subaqueous volcano
Submarine volcanoes are common features of the ocean floor. In shallow
water, active volcanoes disclose their presence by blasting steam and
rocky debris high above the ocean's surface. In the ocean's deep, the
tremendous weight of the water above prevents the explosive release of
steam and gases; however, they can be detected by hydrophones and
discoloration of water because of volcanic gases.
Pillow lava is a
common eruptive product of submarine volcanoes and is characterized by
thick sequences of discontinuous pillow-shaped masses which form under
water. Even large submarine eruptions may not disturb the ocean
surface due to the rapid cooling effect and increased buoyancy of
water (as compared to air) which often causes volcanic vents to form
steep pillars on the ocean floor. Hydrothermal vents are common near
these volcanoes, and some support peculiar ecosystems based on
dissolved minerals. Over time, the formations created by submarine
volcanoes may become so large that they break the ocean surface as new
islands or floating pumice rafts.
Main article: Subglacial volcano
Subglacial 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 lava on top collapses, leaving
a flat-topped mountain. These volcanoes are also called table
mountains, tuyas, 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
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
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.
Main article: Mud volcano
Mud 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.
Pāhoehoe lava flow on Hawaii. The picture shows overflows of a main
Stromboli stratovolcano off the coast of
Sicily has erupted
continuously for thousands of years, giving rise to the term
San Miguel (volcano), El Salvador. On December 29, 2013, San Miguel
volcano, also known as "Chaparrastique", erupted at 10:30 local time,
spewing a large column of ash and smoke into the sky; the eruption,
the first in 11 years, was seen from space and prompted the
evacuation of thousands of people living in a 3 km radius around
Ash plume from
San Miguel (volcano)
San Miguel (volcano) "Chaparrastique", seen from a
satellite, as it heads towards the Pacific Ocean from the El Salvador
Central America coast, December 29, 2013
Another way of classifying volcanoes is by the composition of material
erupted (lava), since this affects the shape of the volcano.
be broadly classified into four different compositions:
If the erupted magma contains a high percentage (>63%) of silica,
the lava is called felsic.
Felsic lavas (dacites or rhyolites) tend to be highly viscous (not
very fluid) and are erupted as domes or short, stubby flows. Viscous
lavas tend to form stratovolcanoes or lava domes.
Lassen Peak in
California 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 volatiles
(gases) that are present, which cause the magma to erupt
catastrophically, eventually forming stratovolcanoes. Pyroclastic
flows (ignimbrites) 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 flows, 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. Alaska's Valley of Ten Thousand Smokes, formed by the eruption
Novarupta near Katmai in 1912, is an example of a thick pyroclastic
flow or ignimbrite deposit.
Volcanic ash that is light enough to be
erupted high into the
Earth's atmosphere may travel many kilometres
before it falls back to ground as a tuff.
If the erupted magma contains 52–63% silica, the lava is of
These "andesitic" volcanoes generally only occur above subduction
Mount Merapi in Indonesia).
Andesitic lava is typically formed at convergent boundary margins of
tectonic plates, by several processes:
Hydration melting of peridotite and fractional crystallization
Sarychev Peak eruption, Matua Island, oblique satellite view
Melting of subducted slab containing sediments
Magma mixing between felsic rhyolitic and mafic basaltic magmas in an
intermediate reservoir prior to emplacement or lava flow.
If the erupted magma contains <52% and >45% silica, the lava is
called mafic (because it contains higher percentages of magnesium (Mg)
and iron (Fe)) or basaltic. These lavas are usually much less viscous
than rhyolitic lavas, depending on their eruption temperature; they
also tend to be hotter than felsic lavas.
Mafic lavas occur in a wide
range of settings:
At mid-ocean ridges, where two oceanic plates are pulling apart,
basaltic lava erupts as pillows to fill the gap;
Shield volcanoes (e.g. the Hawaiian Islands, including
Mauna Loa and
Kilauea), on both oceanic and continental crust;
As continental flood basalts.
Some erupted magmas contain <=45% silica and produce ultramafic
Ultramafic flows, also known as komatiites, are very rare;
indeed, very few have been erupted at the Earth's surface since the
Proterozoic, when the planet's heat flow was higher. They are (or
were) the hottest lavas, and probably more fluid than common mafic
Two types of lava are named according to the surface texture: ʻAʻa
(pronounced [ˈʔaʔa]) and pāhoehoe ([paːˈho.eˈho.e]), both
Hawaiian words. ʻAʻa 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 ʻaʻa 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.
Mount Vesuvius behind
Bacchus and Agathodaemon, as seen in
Pompeii's House of the Centenary
Popular classification of volcanoes
A popular way of classifying magmatic volcanoes is by their frequency
of eruption[according to whom?], with those that erupt regularly
called active, those that have erupted in historical times but are now
quiet called dormant or inactive, 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.
See also: Category:Active volcanoes, Category:Potentially active
volcanoes, and List of currently erupting volcanoes
There is no 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 the last
10,000 years (
Holocene times) – the Smithsonian Global Volcanism
Program uses this definition of active. Most volcanoes are situated on
the Pacific Ring of Fire. An estimated 500 million people live
near active volcanoes.
Historical time (or recorded history) is another timeframe for
active. The Catalogue of the Active Volcanoes of the World,
published by the International Association of Volcanology, uses this
definition, by which there are more than 500 active volcanoes.
However, the span of recorded history differs from region to region.
In China and the Mediterranean, it reaches back nearly 3,000 years,
but in the Pacific Northwest of the United States and Canada, it
reaches back less than 300 years, and in
Hawaii and New Zealand, only
around 200 years.
Kīlauea lava entering the sea.
Lava flows at Holuhraun, Iceland, September 2014
As of 2013, the following are considered Earth's most active
Kīlauea, the famous Hawaiian volcano, has been in continuous,
effusive eruption (in which lava steadily flows onto the ground) since
1983 and has the longest-observed lava lake.
Mount Etna and nearby Stromboli, two
Mediterranean volcanoes in
"almost continuous eruption"[vague] since antiquity.[clarification
Mount Yasur, in Vanuatu, has been erupting "nearly continuously" for
over 800 years.
As of August 2013[update], the longest ongoing (but not
necessarily continuous) volcanic eruptive phases are:
Mount Yasur, 111 years
Mount Etna, 109 years
Stromboli, 108 years
Santa María, 101 years
Sangay, 94 years
Other very active volcanoes include:
Mount Nyiragongo and its neighbor, Nyamuragira, are Africa's most
Nyiragongo's lava lake
Piton de la Fournaise, in Réunion, erupts frequently enough to be a
Erta Ale, in the Afar Triangle, has maintained a lava lake since at
Mount Erebus, in Antarctica, has maintained a lava lake since at least
Whakaari / White Island, has been in a continuous state of releasing
volcanic gas since its discovery in 1769.
Ol Doinyo Lengai
"Extinct volcano" redirects here. For the category of extinct
volcanoes, see Category:Extinct volcanoes.
Fourpeaked volcano, Alaska, in September 2006 after being thought
extinct for over 10,000 years
Rinjani eruption in 1994, in Lombok, Indonesia
Extinct volcanoes are those that scientists consider unlikely to erupt
again because the volcano no longer has a magma supply. Examples of
extinct volcanoes are many volcanoes on the Hawaiian – Emperor
seamount chain in the Pacific Ocean (although some volcanoes at the
eastern end of the chain are active),
Hohentwiel in Germany, Shiprock
in New Mexico, and
Zuidwal volcano in the Netherlands. Edinburgh
Castle in Scotland is famously located atop an extinct volcano.
Otherwise, whether a volcano is truly extinct is often difficult to
determine. Since "supervolcano" calderas 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. Some volcanologists refer to
extinct volcanoes as inactive, though the term is now more commonly
used for dormant volcanoes once thought to be extinct.
Dormant and reactivated
See also: Category:Dormant volcanoes and Category:Inactive volcanoes
Narcondam Island, India, is classified as a dormant volcano by the
Geological Survey of India
It is difficult to distinguish an extinct volcano from a dormant
(inactive) 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 700,000 years, and Toba of around
Vesuvius was described by Roman writers as having
been covered with gardens and vineyards before its eruption of 79 CE,
which destroyed the towns of Herculaneum and Pompeii. 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 in Alaska, which, before its September 2006
eruption, had not erupted since before 8000 BCE and had long been
thought to be extinct.
Climate change can reportedly trigger volcanic
activity in sensitive areas by changing pressure of ice or seawater
and extreme weather.
Technical classification of volcanoes
The three common popular classifications of volcanoes can be
subjective and some volcanoes thought to have been extinct have
erupted again. To help prevent people 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 States
The 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 U.S. system can be found at
Volcano warning schemes of
the United States.
Koryaksky volcano towering over
Petropavlovsk-Kamchatsky on Kamchatka
Peninsula, Far Eastern Russia
Lists of volcanoes
Lists of volcanoes and Decade Volcanoes
Decade Volcanoes are 17 volcanoes identified by the International
Volcanology and Chemistry of the Earth's Interior
(IAVCEI) as being worthy of particular study in light of their history
of large, destructive eruptions and proximity to populated areas. They
Decade Volcanoes because the project was initiated as part
of the United Nations-sponsored International Decade for Natural
Disaster Reduction. The 17 current
Decade Volcanoes are
Koryaksky (grouped together), Kamchatka, Russia
Nevado de Colima,
Jalisco and Colima, Mexico
Mount Etna, Sicily, Italy
Galeras, Nariño, Colombia
Mauna Loa, Hawaii, USA
Mount Merapi, Central Java, Indonesia
Mount Nyiragongo, Democratic Republic of the Congo
Mount Rainier, Washington, USA
Sakurajima, Kagoshima Prefecture, Japan
Santa Maria/Santiaguito, Guatemala
Santorini, Cyclades, Greece
Taal Volcano, Luzon, Philippines
Teide, Canary Islands, Spain
Ulawun, New Britain, Papua New Guinea
Mount Unzen, Nagasaki Prefecture, Japan
Vesuvius, Naples, Italy
Carbon Degassing Project, an initiative of the Deep
Carbon Observatory, monitors nine volcanoes, two of which are Decade
volcanoes. The focus of the Deep
Carbon Degassing Project is to
Multi-Component Gas Analyzer System instruments to measure CO2/SO2
ratios in real-time and in high-resolution to allow detection of the
pre-eruptive degassing of rising magmas, improving prediction of
Effects of volcanoes
Schematic of volcano injection of aerosols and gases
Solar radiation graph 1958–2008, showing how the radiation is
reduced after major volcanic eruptions
Sulfur dioxide concentration over the Sierra Negra Volcano, Galapagos
Islands, during an eruption in October 2005
There are many different types of volcanic eruptions 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 flows, lahars (debris
flow) and carbon dioxide emission. All of these activities can pose a
hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and
geysers often accompany volcanic activity.
The concentrations of different volcanic gases 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, halocarbons, 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 SO2 emissions alone of two different eruptions
are sufficient to compare their potential climatic impact. The
aerosols increase the Earth's albedo—its reflection of radiation
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
Huaynaputina probably caused the Russian famine of
A volcanic winter is said to have taken place around 70,000 years ago
after the supereruption of
Lake Toba on
Sumatra island in
Indonesia. According to the
Toba catastrophe theory
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
It has been suggested that volcanic activity caused or contributed to
the End-Ordovician, Permian-Triassic, 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 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.
Ash plume rising from
Eyjafjallajökull on April 17, 2010
Sulfate aerosols 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 clouds 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
Gas emissions from volcanoes are a natural contributor to acid rain.
Volcanic activity releases about 130 to 230 teragrams (145 million to
255 million short tons) 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
Main article: Volcanic hazards
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; the melted particles then adhere to the turbine
blades and alter their shape, disrupting the operation of the turbine.
Dangerous encounters in 1982 after the eruption of
Indonesia, and 1989 after the eruption of
Mount Redoubt in Alaska
raised awareness of this phenomenon. Nine Volcanic Ash Advisory
Centers 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 celestial bodies
See also: List of extraterrestrial volcanoes, Geology of the Moon,
Volcanology of Mars,
Volcanology of Io, and
Volcanology of Venus
The Tvashtar volcano erupts a plume 330 km (205 mi) above
the surface of Jupiter's moon Io.
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), rilles
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.
Olympus Mons (Latin, "Mount Olympus"), located on the planet Mars, is
the tallest known mountain in the Solar System.
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
Mars Express spacecraft has found evidence that volcanic
activity may have occurred on
Mars in the recent past as well.
Jupiter's moon Io 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 and silicate 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 cryovolcanoes (ice
volcanoes) on Triton, a moon of Neptune, 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, ammonia, dust, or methane
Cassini–Huygens also found evidence of a methane-spewing
cryovolcano on the Saturnian 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
A 2010 study of the exoplanet COROT-7b, which was detected by transit
in 2009, suggested that tidal heating from the host star very close to
the planet and neighboring planets could generate intense volcanic
activity similar to that found on Io.
Traditional beliefs about volcanoes
This section needs expansion. You can help by adding to it. (October
See also: Popocatepetl and Iztaccihuatl
Many ancient accounts ascribe volcanic eruptions to supernatural
causes, such as the actions of gods or demigods. 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 Athanasius Kircher
(1602–1680), who witnessed eruptions of
Mount Etna and Stromboli,
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 eruptions
Prediction of volcanic activity
Timeline of volcanism on Earth
Volcanic Explosivity Index
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Wikimedia Commons has media related to Volcanoes.
Wikivoyage has a travel guide for Volcanoes.
Library resources about
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Volcanoes at Curlie (based on DMOZ)
Federal Emergency Management Agency
Federal Emergency Management Agency FEMA
Volcanos (Worsley School)
List and volcanoes groups
Lists of volcanoes
Fast radio burst
Cosmic rays (Ultra-high-energy cosmic ray)
Solar proton event
Coronal mass ejection
Tidal disruption event
Heat death of the universe
False vacuum metastability event
Prediction of volcanic activity
Volcanic Explosivity Index
Volcanic Seven Summits
Currently erupting volcanoes
Large volume volcanic eruptions in the Basin and Range Province
Largest volcanic eruptions
Quaternary volcanic eruptions
Volcanic eruption deaths