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A volcano is a rupture in the crust of a
planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, object, such as the trajectory of a planet around a star or a natural satellite around a planet. Normally, orbit r ...
, such as
Earth Earth is the third planet from the Sun and the only astronomical object known to harbour and support life. 29.2% of Earth's surface is land consisting of continents and islands. The remaining 70.8% is Water distribution on Earth, covered wi ...

Earth
, that allows hot
lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fracture in the Crust (geology), crust, ...

lava
,
volcanic ash Volcanic ash consists of fragments of rock, mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure ...
, and
gases Gas is one of the four fundamental states of matter (the others being solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a su ...
to escape from a
magma chamber A magma chamber is a large pool of liquid rock Rock most often refers to: * Rock (geology) A rock is any naturally occurring solid mass or aggregate of minerals or mineraloid matter. It is categorized by the minerals included, its Chemica ...

magma chamber
below the surface. On Earth, volcanoes are most often found where
tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is ...
are diverging or converging, and most are found underwater. For example, a
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
, such as the
Mid-Atlantic Ridge The Mid-Atlantic Ridge is a (a or constructive ) located along the floor of the , and part of the . In the North Atlantic, the ridge separates the from the and the , north and south of the respectively. In the South Atlantic, it separates the ...
, has volcanoes caused by divergent tectonic plates whereas the
Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many Types of volcanic eruptions, volcanic eruptions and e ...

Pacific Ring of Fire
has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the
East African Rift File:East Africa Rift System GPS and stresses.png, Main rift faults, plates, plate boundaries, GPS plate velocities between adjacent blocks and minimum horizontal stress directions The East African Rift (EAR) or East African Rift System (EARS) is ...
and the
Wells Gray-Clearwater volcanic field The Wells Gray-Clearwater volcanic field, also called the Clearwater Cone Group, is a potentially active monogenetic volcanic field in east-central British Columbia ( en, Splendour without diminishment) , image_map = British Colum ...
and Rio Grande Rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling
diapir A diapir (; , ) is a type of geologic intrusion in which a more mobile and ductily deformable material is forced into brittle overlying rocks. Depending on the tectonic environment, diapirs can range from idealized mushroom-shaped Rayleigh–T ...
s from the
core–mantle boundary The core–mantle boundary (CMB) of Earth lies between the planet's silicate In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and io ...
, deep in the Earth. This results in hotspot volcanism, of which the
Hawaiian hotspot The Hawai’i hotspot is a volcanic hotspot located near the namesake Hawaiian Islands The Hawaiian Islands ( haw, Mokupuni o Hawai‘i) are an archipelago of eight major islands, several atolls, numerous smaller islets, and seamounts i ...
is an example. Volcanoes are usually not created where two tectonic plates slide past one another. Large eruptions can affect atmospheric temperature as ash and droplets of
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthogra ...

sulfuric acid
obscure the Sun and cool the Earth's
troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere Planetary means relating to a planet A planet is an astronomical body orbiting a star or Stellar evo ...
. Historically, large volcanic eruptions have been followed by
volcanic winter A volcanic winter is a reduction in global temperatures caused by volcanic ash , Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a continent A continent is ...
s which have caused catastrophic famines.


Etymology

The word ''volcano'' is derived from the name of
Vulcano Vulcano ( scn, Vurcanu) or Vulcan is a small volcanic island Geologically, a high island or volcanic island is an island of volcano, volcanic origin. The term can be used to distinguish such islands from low islands, which are formed fr ...

Vulcano
, a volcanic island in the
Aeolian Islands The Aeolian Islands ( ; it, Isole Eolie ; scn, Ìsuli Eoli; el, Αιολίδες Νήσοι, Aiolídes Nísoi), sometimes referred to as the Lipari Islands or Lipari group ( , ) after their largest island, are a volcanic A volcano is a ru ...

Aeolian Islands
of Italy whose name in turn comes from
Vulcan Vulcan may refer to: Mythology * Vulcan (mythology), the god of fire, volcanoes, metalworking, and the forge in Roman mythology Arts, entertainment and media Film and television * Vulcan (Star Trek), Vulcan (''Star Trek''), name of a fictional rac ...
, the god of fire in
Roman mythology Roman mythology is the body of myths of ancient Rome as represented in the Latin literature, literature and Roman art, visual arts of the Romans. One of a wide variety of genres of Roman folklore, ''Roman mythology'' may also refer to the moder ...
. The study of volcanoes is called
volcanology Volcanology (also spelled vulcanology) is the study of volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajecto ...

volcanology
, sometimes spelled ''vulcanology''.


Plate tectonics

According to the theory of plate tectonics, Earth's
lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. On Earth, it is composed of the crust (geology), crust and the portion o ...
, its rigid outer shell, is broken into sixteen larger and several smaller plates. These are in slow motion, due to
convection Convection is single or multiphase fluid flow that occurs Spontaneous process, spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When t ...

convection
in the underlying ductile
mantle Mantle may refer to: *Mantle (geology) A mantle is a layer inside a planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a n ...
, and most volcanic activity on Earth takes place along plate boundaries, where plates are converging (and lithosphere is being destroyed) or are diverging (and new lithosphere is being created).


Divergent plate boundaries

At the
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
s, two
tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust is a thin shell on the outside of Earth, accounting for less than 1% of Earth's volume. It is ...
diverge from one another as hot mantle rock creeps upwards beneath the thinned
oceanic crust The oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates This is a list of tectonic plates on Earth's surface. Tectonic plates are pieces of Earth's crust 350px, Plates in the crust of Earth Earth's crust i ...
. The decrease of pressure in the rising mantle rock leads to
adiabatic
adiabatic
expansion and the
partial melting Partial melting occurs when only a portion of a solid is melted. For mixed substances, such as a rock containing several different mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound ...
of the rock, causing volcanism and creating new oceanic crust. Most
divergent plate boundaries In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two List of tectonic plates, tectonic plates that are moving away from ...
are at the bottom of the oceans, and so most volcanic activity on the Earth is submarine, forming new
seafloor The seabed (also known as the seafloor, sea floor, or ocean floor) is the bottom of the ocean, no matter how deep. All floors of the ocean are known as 'seabeds'. Structure Most of the oceans have a common structure, created by common ph ...

seafloor
.
Black smoker A hydrothermal vent is a fissure vent, fissure on the seafloor from which Geothermal (geology), geothermally heated water discharges. Hydrothermal vents are commonly found near volcano, volcanically active places, areas where tectonic plates are m ...
s (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, such as
Iceland Iceland ( is, Ísland; ) is a Nordic Nordic most commonly refers to: * Nordic countries, written in plural as Nordics, the northwestern European countries, including Scandinavia, Fennoscandia and the List of islands in the Atlantic Ocean#N ...

Iceland
.


Convergent plate boundaries

Subduction Subduction is a geological process in which the oceanic lithosphere A lithosphere ( grc, λίθος [] for "rocky", and [] for "sphere") is the rigid, outermost shell of a terrestrial planet, terrestrial-type planet or natural satellite. O ...

Subduction
zones are places where two plates, usually an oceanic plate and a continental plate, collide. The oceanic plate subducts (dives beneath the continental plate), forming a deep ocean trench just offshore. In a process called
flux melting In igneous petrology and volcanology, flux melting occurs when water and other volatile components are introduced to hot solid rock, depressing the Solidus (chemistry), solidus enough. In engineering and metallurgy, Flux (metallurgy), flux is a subs ...
, water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, thus creating
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
. This magma tends to be extremely
viscous The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...
because of its high
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
content, so it often does not reach the surface but cools and solidifies at depth. When it does reach the surface, however, a volcano is formed. Thus subduction zones are bordered by chains of volcanoes called
volcanic arc A volcanic arc is a chain of volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory of an physical body, obj ...
s. Typical examples are the volcanoes in the
Pacific Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a region around much of the rim of the Pacific Ocean where many Types of volcanic eruptions, volcanic eruptions and e ...

Pacific Ring of Fire
, such as the
Cascade Volcanoes :''This article is for the volcanic arc. For the namesake mountain range see Cascade Range The Cascade Range or Cascades is a major mountain range of western North America North America is a continent entirely within the Northern Hemis ...
or the
Japanese Archipelago The Japanese archipelago (Japanese: 日本列島, ''Nihon rettō'') is a group of 6,852 islands that form the country of Japan Japan ( ja, 日本, or , and formally ) is an island country An island country or an island nation is a ...
, or the
Sunda ArcSunda may refer to: Europe * Sunda, Faroe Islands India * Sunda (asura), an asura brother of Upasunda * Sunda (clan), a clan (gotra) of Jats in Haryana and Rajasthan, India Southeast Asia * Sundanese (disambiguation) ** Sundanese people ...
of
Indonesia Indonesia ( ), officially the Republic of Indonesia ( id, Republik Indonesia, links=yes ), is a country in Southeast Asia Southeast Asia, also spelled South East Asia and South-East Asia, and also known as Southeastern Asia or SEA, is t ...

Indonesia
.


Hotspots

Hotspots are volcanic areas thought to be formed by
mantle plume A mantle plume is a proposed mechanism of convection Convection is single or multiphase fluid flow that occurs Spontaneous process, spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, ...

mantle plume
s, which are hypothesized to be columns of hot material rising from the core-mantle boundary. As with mid-ocean ridges, the rising mantle rock experiences decompression melting which generates large volumes of magma. Because tectonic plates move across mantle plumes, each volcano becomes inactive as it drifts off the plume, and new volcanoes are created where the plate advances over the plume. The
Hawaiian Islands The Hawaiian Islands ( haw, Mokupuni o Hawai‘i) are an archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island An island (or isle) is an isolated pie ...
are thought to have been formed in such a manner, as has the
Snake River Plain The Snake River cutting through the plain leaves many canyons and Canyon#List of gorges">gorges, such as this one near Twin Falls, Idaho , 2008 The Snake River Plain is a geology, geologic feature located primarily within the U.S. state of Id ...

Snake River Plain
, with the
Yellowstone Caldera The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcano, volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northw ...

Yellowstone Caldera
being the part of the North American plate currently above the
Yellowstone hotspot The Yellowstone hotspot is a volcanic hotspot in the United States responsible for large scale volcanism in Idaho Idaho () is a U.S. state, state in the Pacific Northwest region of the United States. It borders the state of Montana to the ...
. However, the mantle plume hypothesis has been questioned.


Continental rifting

Sustained upwelling of hot mantle rock can develop under the interior of a continent and lead to rifting. Early stages of rifting are characterized by
flood basalt A flood basalt is the result of a giant volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, ...
s and may progress to the point where a tectonic plate is completely split. A divergent plate boundary then develops between the two halves of the split plate. However, rifting often fails to completely split the continental lithosphere (such as in an
aulacogen An aulacogen is a failed arm of a triple junction. Aulacogens are a part of plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to sc ...
), and failed rifts are characterized by volcanoes that erupt unusual alkali lava or
carbonatite Carbonatite lava at Ol Doinyo Lengai volcano, Tanzania Carbonatite () is a type of Intrusive rock, intrusive or extrusive igneous Rock (geology), rock defined by mineralogic composition consisting of greater than 50% carbonate minerals. Carbon ...

carbonatite
s. Examples include the volcanoes of the
East African Rift File:East Africa Rift System GPS and stresses.png, Main rift faults, plates, plate boundaries, GPS plate velocities between adjacent blocks and minimum horizontal stress directions The East African Rift (EAR) or East African Rift System (EARS) is ...
.


Volcanic features

The most common perception of a volcano is of a
conical A cone is a three-dimensional Three-dimensional space (also: 3-space or, rarely, tri-dimensional space) is a geometric setting in which three values (called parameter A parameter (from the Ancient Greek language, Ancient Greek wikt:π ...

conical
mountain, spewing
lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fracture in the Crust (geology), crust, ...

lava
and poisonous
gases Gas is one of the four fundamental states of matter (the others being solid Solid is one of the four fundamental states of matter (the others being liquid A liquid is a nearly incompressible fluid In physics, a fluid is a su ...
from a
crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surface ...
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 dome In volcanology Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma and related geology, geological, geophysical and geochemistry, geochemical phenomena (volcanism). The term ''volcanology'' is derived from the La ...
s rather than a summit crater while others have
landscape A landscape is the visible features of an area of land Land is the solid surface of Earth that is not permanently submerged in water. Most but not all land is situated at elevations above sea level (variable over geologic time frames) an ...

landscape
features such as massive
plateau In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the proces ...

plateau
s. Vents that issue volcanic material (including
lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fracture in the Crust (geology), crust, ...

lava
and
ash Ash or ashes are the solid remnants of fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because th ...
) and gases (mainly steam and magmatic gases) can develop anywhere on the
landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws ...

landform
and may give rise to smaller cones such as Puu Ōō on a flank of Hawaii's
Kīlauea Kīlauea ( , ) is an active shield volcano A shield volcano is a type of volcano A volcano is a rupture in the of a , such as , that allows hot , , and to escape from a below the surface. On Earth, volcanoes are most often found wh ...
. Other types of volcano include
cryovolcano , one of the most reliably identified cryovolcanoes on Saturn's moon Titan (moon), Titan A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane, instead of lava, molte ...
es (or ice volcanoes), particularly on some moons of
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

Jupiter
,
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It only has one-eighth the average density of Earth; how ...

Saturn
, and
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mo ...

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 Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others being Sedimentary rock, sedimentary and metamorphic rock, metamorphic. Igneous rock i ...
volcanoes except when the mud volcano is actually a vent of an igneous volcano.


Fissure vents

Volcanic fissure vents are flat, linear fractures through which
lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fracture in the Crust (geology), crust, ...

lava
emerges.


Shield volcanoes

Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lava that can flow a great distance from a vent. They generally do not explode catastrophically, but are characterized by relatively gentle
effusive eruption An effusive eruption is a type of volcanic eruption in which lava of pāhoehoe lava, Hawaii, United States , Iceland in 1984 Lava is molten Rock (geology), rock (magma) that has been expelled from the interior of a terrestrial planet (such as ...
s. 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 Iceland ( is, Ísland; ) is a Nordic Nordic most commonly refers to: * Nordic countries, written in plural as Nordics, the northwestern European countries, including Scandinavia, Fennoscandia and the List of islands in the Atlantic Ocean#N ...

Iceland
, as well.


Lava domes

Lava domes are built by slow eruptions of highly viscous lava. They are sometimes formed within the crater of a previous volcanic eruption, as in the case of
Mount St. Helens Mount St. Helens (known as Lawetlat'la to the Indigenous Cowlitz people The term Cowlitz people covers two culturally and linguistically distinct indigenous peoples of the Pacific Northwest; the Lower Cowlitz or Cowlitz proper, and th ...

Mount St. Helens
, but can also form independently, as in the case of
Lassen Peak Lassen Peak, commonly referred to as Mount Lassen, is the southernmost Volcano#Active, active volcano in the Cascade Range of the Western United States. Located in the Shasta Cascade region of Northern California, it is part of the Cascade Volca ...
. Like stratovolcanoes, they can produce violent, explosive eruptions, but the lava generally does not flow far from the originating vent.


Cryptodomes

Cryptodomes are formed when viscous lava is forced upward causing the surface to bulge. The 1980 eruption of Mount St. Helens was an example; lava beneath the surface of the mountain created an upward bulge, which later collapsed down the north side of the mountain.


Cinder cones

Cinder cones result from eruptions of mostly small pieces of
scoria Scoria is a highly , dark-colored that may or may not contain crystals (s). It is typically dark in color (generally dark brown, black or purplish-red), and ic or in composition. Scoria is relatively low in as a result of its numerous macros ...
and
pyroclastics 300px, USGS scientist examines Mount_St._Helens.html"_;"title="pumice_blocks_at_the_edge_of_a_pyroclastic_flow_from_Mount_St._Helens">pumice_blocks_at_the_edge_of_a_pyroclastic_flow_from_Mount_St._Helens_ File:Volcanic_Stone_3D.ogg.html" ;"titl ...
(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 high. Most cinder cones erupt only once. Cinder cones may form as
flank vents
flank vents
on larger volcanoes, or occur on their own.
Parícutin Parícutin (or Volcán de Parícutin, also accented Paricutín) is a cinder cone A cinder cone is a steep conical hill of loose pyroclastic 300px, USGS scientist examines Mount_St._Helens.html"_;"title="pumice_blocks_at_the_edge_of_a_pyro ...
in Mexico and
Sunset Crater Sunset Crater is a cinder cone A cinder cone is a steep conical hill of loose pyroclastic 300px, USGS scientist examines Mount_St._Helens.html"_;"title="pumice_blocks_at_the_edge_of_a_pyroclastic_flow_from_Mount_St._Helens">pumice_bloc ...

Sunset Crater
in
Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak) is a U.S. state, state in the Southwestern United States, Southwestern region of the United States. It is also usually considered part of the Mountain States, Mountain states. It is th ...

Arizona
are examples of cinder cones. In
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Greater Albuquerque , OfficialLang = None , Languages = English English usually refer ...

New Mexico
,
Caja del Rio Caja del Rio (Spanish language, Spanish: "canyon#Box_canyon, box of the river") is a dissected plateau, of volcanic origin, which covers approximately 84,000 acres of land in northern Santa Fe County, New Mexico, United States. The region is also k ...
is a
volcanic field A volcanic field is an area of the Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. About 29% of Earth's surface is land consisting of continent A continent is one of several la ...
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 surface of Mars and the Moon.


Stratovolcanoes (composite volcanoes)

Stratovolcanoes (composite volcanoes) are tall conical mountains composed of lava flows and
tephra Tephra is fragmental material produced by a volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural sa ...

tephra
in alternate layers, the
strata In geology and related fields, a stratum (plural: strata) is a layer of sedimentary rock or soil, or igneous rock that was formed at the Earth's surface, with internally consistent characteristics that distinguish it from other layers. The "str ...
that gives rise to the name. They are also known as composite volcanoes because they are created from multiple structures during different kinds of eruptions. Classic examples include
Mount Fuji , located on the island of Honshū , historically called , is the largest and most populous main island of Japan , image_flag = Flag of Japan.svg , alt_flag = Centered deep red circle on a white r ...

Mount Fuji
in Japan,
Mayon Volcano Mayon ( bcl, Bulkan Mayon; tl, Bulkang Mayon, ), also known as Mount Mayon and Mayon Volcano ( es, Monte Mayón, Volcán Mayón), is an active stratovolcano A stratovolcano, also known as a composite volcano, is a conical A cone is a t ...

Mayon Volcano
in the Philippines, and
Mount Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma A somma volcano (also known as a sommian) is a volcano, volcanic caldera that has been partially filled by a new central volcanic cone, ...
and
Stromboli Stromboli ( , ; scn, Struògnuli ; grc, Στρογγύλη, Strongýlē) is an island in the Tyrrhenian Sea The Tyrrhenian Sea (; it, Mar Tirreno , french: Mer Tyrrhénienne , sc, Mare Tirrenu, co, Mari Tirrenu, scn, Mari Tirrenu, nap, ...

Stromboli
in Italy.
Ash Ash or ashes are the solid remnants of fire BBQ. Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction Product (chemistry), products. Fire is hot because th ...
produced by the explosive eruption of stratovolcanoes has
historically History (from Ancient Greek, Greek , ''historia'', meaning "inquiry; knowledge acquired by investigation") is the study of the past. Events occurring before the History of writing#Inventions of writing, invention of writing systems are considered ...
posed the greatest volcanic hazard to civilizations. The lavas of stratovolcanoes are higher in silica, and therefore much more viscous, than lavas from shield volcanoes. High-silica lavas also tend to contain more dissolved gas. The combination is deadly, promoting explosive eruptions that produce great quantities of ash, as well as
pyroclastic surge 300px, USGS scientist examines Mount_St._Helens.html"_;"title="pumice_blocks_at_the_edge_of_a_pyroclastic_flow_from_Mount_St._Helens">pumice_blocks_at_the_edge_of_a_pyroclastic_flow_from_Mount_St._Helens_ File:Volcanic_Stone_3D.ogg.html" ;"titl ...
s like the one that destroyed the city of Saint-Pierre in Martinique in 1902. They are also steeper than shield volcanoes, with slopes of 30–35° compared to slopes of generally 5–10°, and their loose
tephra Tephra is fragmental material produced by a volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural sa ...

tephra
are material for dangerous
lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow" of debris that has become partially or fully liquified by the addition ...
s. Large pieces of tephra are called
volcanic bomb A volcanic bomb or lava bomb is a mass of molten rock (tephra Tephra is fragmental material produced by a volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from ...
s. Big bombs can measure more than 4 feet(1.2 meters) across and weigh several tons.


Supervolcanoes

A supervolcano is a volcano that has experienced one or more eruptions that produced over of volcanic deposits in a single explosive event. Such eruptions occur when a very large magma chamber full of gas-rich, silicic magma is emptied in a catastrophic
caldera A caldera is a large cauldron A cauldron (or caldron) is a large cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy cons ...

caldera
-forming eruption. Ash flow
tuff Tuff is a type of Rock (geology), rock made of volcanic ash ejected from a Volcano, vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is consider ...

tuff
s emplaced by such eruptions are the only volcanic product with volumes rivaling those of
flood basalt A flood basalt is the result of a giant volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, ...
s. A supervolcano can produce devastation on a continental scale. Such volcanoes are able to severely cool global temperatures for many years after the eruption due to the huge volumes of
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
and ash released into the atmosphere. They are the most dangerous type of volcano. Examples include
Yellowstone Caldera The Yellowstone Caldera, sometimes referred to as the Yellowstone Supervolcano, is a volcano, volcanic caldera and supervolcano in Yellowstone National Park in the Western United States. The caldera and most of the park are located in the northw ...

Yellowstone Caldera
in
Yellowstone National Park Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the U.S. Congress and signed into law by ...

Yellowstone National Park
and
Valles Caldera Valles Caldera (or Jemez Caldera) is a wide volcanic caldera in the Jemez Mountains of northern New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albu ...
in
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Greater Albuquerque , OfficialLang = None , Languages = English English usually refer ...

New Mexico
(both western United States);
Lake Taupō Lake Taupō (also spelled Taupo; mi, Taupō-nui-a-Tia or ) is a lake in the North Island of New Zealand. It is in the caldera of the Taupō Volcano. The lake is the namesake of the town of Taupō, which sits on a bay in the lake's north-easter ...

Lake Taupō
in New Zealand;
Lake Toba Lake Toba ( id, Danau Toba) is a large natural lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing watercourse, usually freshwater, flowing towards ...

Lake Toba
in
Sumatra Sumatra is one of the Sunda Islands The Sunda Islands are a group of islands in the Malay Archipelago. They consist of the Greater Sunda Islands The Greater Sunda Islands are four tropical islands situated within Southeast Asia S ...

Sumatra
, Indonesia; and
Ngorongoro Crater The Ngorongoro Conservation Area (, ) is a protected area Protected areas or conservation areas are locations which receive protection because of their recognized natural, ecological or cultural values. There are several kinds of protected a ...

Ngorongoro Crater
in Tanzania. Fortunately, supervolcano eruptions are very rare events, though because of the enormous area they cover, and subsequent concealment under vegetation and glacial deposits, supervolcanoes can be difficult to identify in the geologic record without careful
geologic map A geologic map or geological map is a special-purpose map A map is a symbol A symbol is a mark, sign, or that indicates, signifies, or is understood as representing an , , or . Symbols allow people to go beyond what is n or seen by ...
ping.


Submarine volcanoes

Submarine volcanoes are common features of the ocean floor. Volcanic activity during the
Holocene The Holocene ( ) is the current geological epoch In geochronology, an epoch is a subdivision of the geologic timescale that is longer than an age (geology), age but shorter than a period (geology), period. The current epoch is the Holocene E ...
Epoch has been documented at only 119 submarine volcanoes. but there may be more than one million geologically young submarine volcanoes on the ocean floor. In shallow water, active volcanoes disclose their presence by blasting steam and rocky debris high above the ocean's surface. In the deep ocean basins, the tremendous weight of the water prevents the explosive release of steam and gases; however, submarine eruptions can be detected by
hydrophone A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) is a microphone A microphone, colloquially called a mic or mike (), is a device – a transducer – that converts sound In physics Physics (from grc, φυσική ( ...

hydrophone
s and by the discoloration of water because of
volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities ( vesicles) in volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geo ...
es.
Pillow lava Pillow lavas are lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or through a Fissure vent, fracture in ...

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 in water (as compared to air), which often causes volcanic vents to form steep pillars on the ocean floor.
Hydrothermal vent A hydrothermal vent is a fissure A fissure is a long, narrow crack opening along the surface of the Earth. It is derived from the Latin word , which means 'cleft' or 'crack'. Fissures emerge in the Earth's crust, on ice sheets and glaciers, and ...
s are common near these volcanoes, and some support peculiar ecosystems based on
chemotroph Chemotrophs are organisms that obtain energy by the oxidation of electron donors in their environments. These molecules can be organic molecule, organic (chemoorganotrophs) or inorganic compound, inorganic (chemolithotrophs). The chemotroph design ...
s feeding 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 raft A pumice raft is a floating raft of pumice Pumice (), called pumicite in its powdered or dust form, is a volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a formed from erupted from a . In other words ...

pumice raft
s. In May and June 2018, a multitude of
seismic Seismology (; from Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following perio ...
signals were detected by
earthquake An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth resulting from a sudden release of energy in the Earth Earth is the third planet from the Sun and the only astronomical object known ...

earthquake
monitoring agencies all over the world. They took the form of unusual humming sounds, and some of the signals detected in November of that year had a duration of up to 20 minutes. An
oceanographic Oceanography (compound of the Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxim ...
research campaign in May 2019 showed that the previously mysterious humming noises were caused by the formation of a submarine volcano off the coast of
Mayotte Mayotte (french: Mayotte, ; Shimaore language, Shimaore: ''Maore'', ; mg, Maiôty) is an overseas department and region, overseas department/region and single territorial collectivity of France officially named the Department of Mayotte (Frenc ...

Mayotte
.


Subglacial volcanoes

Subglacial volcanoes develop underneath icecaps. They are made up of lava plateaus capping extensive pillow lavas and palagonite. These volcanoes are also called table mountains,
tuya , a tuya in Iceland A tuya is a flat-topped, steep-sided volcano A volcano is a rupture in the crust of a planetary-mass object A planet is an astronomical body orbit In physics, an orbit is the gravitationally curved trajectory ...
s, or (in Iceland) mobergs. Very good examples of this type of volcano can be seen in Iceland and in
British Columbia ( en, Splendour without diminishment) , image_map = British Columbia in Canada 2.svg , Label_map = yes , coordinates = , official_lang = None , Slogan = Beautiful British C ...

British Columbia
. The origin of the term comes from
Tuya Butte Tuya Butte is a tuya , a tuya in Iceland A tuya is a type of distinctive, flat-topped, steep-sided volcano A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and Volcanic ga ...
, which is one of the several tuyas in the area of the
Tuya River The Tuya River is a major tributary A tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem ri ...
and
Tuya Range The Tuya Range is a mountain range A mountain range is a series of mountains ranged in a line and connected by high ground. A mountain system or mountain belt is a group of mountain ranges with similarity in form, structure, and alignment tha ...
in northern British Columbia. Tuya Butte was the first such
landform A landform is a natural or artificial feature of the solid surface of the Earth or other planetary body A planet is an astronomical body Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws ...

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 Tuya Lake, located in northwestern British Columbia, Canada, presumably derives its name from the presence of nearby steep-sided, flat-topped volcanoes, known as tuyas. The lake is situated just south of Tuya Butte at a latitude of about 59th parall ...
and south of the
Jennings RiverThe Jennings River is a river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases a river flows into the ground and becomes dry at the end of its course without reach ...
near the boundary with the
Yukon Territory Yukon (; ; also called Yukon Territory and referred to by some as the Yukon) is the smallest and westernmost of Canada's three territories. It also is the least populated province or territory in Canada, with a population of 35,874 people as of ...
.


Mud volcanoes

Mud volcanoes (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.


Erupted material

The material that is expelled in a
volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or ...
can be classified into three types: #
Volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities ( vesicles) in volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geo ...
es, a mixture made mostly of
steam Steam is water Water (chemical formula H2O) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fl ...

steam
,
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
, and a sulfur compound (either
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
, SO2, or
hydrogen sulfide Hydrogen sulfide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...

hydrogen sulfide
, H2S, depending on the temperature) #
Lava Lava is magma Magma () is the molten or semi-molten natural material from which all s are formed. Magma is found beneath the surface of the , and evidence of has also been discovered on other and some s. Besides molten rock, magma may al ...

Lava
, the name of magma when it emerges and flows over the surface #
Tephra Tephra is fragmental material produced by a volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural sa ...

Tephra
, particles of solid material of all shapes and sizes ejected and thrown through the air


Volcanic gases

The concentrations of different
volcanic gas Volcanic gases are gases given off by active (or, at times, by dormant) volcanoes. These include gases trapped in cavities ( vesicles) in volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geo ...
es can vary considerably from one volcano to the next.
Water vapor (99.9839 °C) , - , Boiling point The boiling point of a substance is the temperature at which the vapor pressure 280px, The ''pistol test tube'' experiment. The tube contains alcohol and is closed with a piece of cork. By heating th ...
is typically the most abundant volcanic gas, followed by
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
. Other principal volcanic gases include
hydrogen sulfide Hydrogen sulfide is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by havi ...

hydrogen sulfide
,
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with ...

hydrogen chloride
, and
hydrogen fluoride Hydrogen fluoride is a chemical compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock in the preparation ...

hydrogen fluoride
. A large number of minor and trace gases are also found in volcanic emissions, for example
hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. Hydrogen is the lightest element. At standard temperature and pressure, standard conditions hydrogen is a gas of diatomic molecules having the che ...

hydrogen
,
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...

carbon monoxide
,
halocarbonHalocarbon compounds are chemicals in which one or more carbon atoms are linked by covalent bonds with one or more halogen atoms (fluorine, chlorine, bromine or iodine – ) resulting in the formation of organofluorine compounds, organochlorine ...
s, organic compounds, and volatile metal chlorides.


Lava flows


Composition

The form and style of eruption of a volcano is largely determined by the composition of the lava it erupts. The viscosity (how fluid the lava is) and the amount of dissolved gas are the most important characteristics of magma, and both are largely determined by the amount of silica in the magma. Magma rich in silica is much more viscous than silica-poor magma, and silica-rich magma also tends to contain more dissolved gases. Lava can be broadly classified into four different compositions: * If the erupted
magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, rock types, the others ...

magma
contains a high percentage (>63%) of
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
, the lava is described as ''
felsic In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (geology), rocks of which it is composed, and the processes ...
''. Felsic lavas (
dacite Dacite () is a volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a formed from erupted from a . In other words, it differs from other by being of origin. Like all rock types, the concept of volcanic rock ...
s or
rhyolite Rhyolite ( ) is the most silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and ...

rhyolite
s) are highly
viscous The viscosity of a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, ...
and are erupted as domes or short, stubby flows.
Lassen Peak Lassen Peak, commonly referred to as Mount Lassen, is the southernmost Volcano#Active, active volcano in the Cascade Range of the Western United States. Located in the Shasta Cascade region of Northern California, it is part of the Cascade Volca ...
in California is an example of a volcano formed from felsic lava and is actually a large lava dome. :Because felsic magmas are so viscous, they tend to trap
volatiles Volatiles are the group of chemical elements and chemical compounds that can be readily Volatility (chemistry), vaporized. In contrast with volatiles, elements and compounds that are not readily vaporized are known as Refractory (planetary scien ...
(gases) that are present, which leads to explosive volcanism.
Pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies ...
s (
ignimbrite Ignimbrite is a variety of hardened tuff. Ignimbrites are igneous rocks made up of crystal and rock fragments in a glass-shard Matrix (geology), groundmass, albeit the original Texture (geology), texture of the groundmass might be obliterated du ...

ignimbrite
s) are highly hazardous products of such volcanoes, since they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 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 many meters thick.
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
's
Valley of Ten Thousand Smokes The Valley of Ten Thousand Smokes is a valley within Katmai National Park and Preserve in Alaska which is filled with volcanic ash, ash flow from the eruption of Novarupta on June 6–8, 1912. Following the eruption, thousands of fumaroles ven ...
, formed by the eruption of
Novarupta Novarupta (meaning "newly erupted" in Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as Latium. Through ...

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 The atmosphere of Earth is the layer of gas Gas is one of the four fundamental states of matter (the others being solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The mo ...

Earth's atmosphere
as an
eruption column An eruption column or eruption plume is a cloud of super-heated Volcanic ash, ash and tephra suspended in volcanic gas, gases emitted during an explosive volcanic eruption. The volcanic materials form a vertical column or Plume (fluid dynamics), p ...
may travel hundreds of kilometers before it falls back to ground as a fallout
tuff Tuff is a type of Rock (geology), rock made of volcanic ash ejected from a Volcano, vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is consider ...

tuff
. Volcanic gases may remain in the
stratosphere The stratosphere () is the second layer of the atmosphere of the Earth, located above the troposphere The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphe ...

stratosphere
for years. :Felsic magmas are formed within the crust, usually through melting of crust rock from the heat of underlying mafic magmas. The lighter felsic magma floats on the mafic magma without significant mixing. Less commonly, felsic magmas are produced by extreme fractional crystallization of more mafic magmas. This is a process in which mafic minerals crystallize out of the slowly cooling magma, which enriches the remaining liquid in silica. * If the erupted magma contains 52–63% silica, the lava is of ''
intermediate compositionIn igneous petrologyIgneous petrology is the study of igneous rock Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was origina ...
'' or ''
andesitic Andesite ( or ) is an extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extrusive rock ref ...

andesitic
''. Intermediate magmas are characteristic of stratovolcanoes. They are most commonly formed at convergent boundaries between
tectonic plate This is a list of tectonic plates on Earth's surface Earth is the third planet A planet is an astronomical body orbiting a star or Stellar evolution#Stellar remnants, stellar remnant that is massive enough to be Hydrostatic equilibri ...
s, by several processes. One process is hydration melting of mantle peridotite followed by fractional crystallization. Water from a subducting
slab Slab or SLAB may refer to: Physical materials * Concrete slab, a flat concrete plate used in construction * Stone slab, a flat stone used in construction * Slab (casting), a length of metal * Slab (geology), that portion of a tectonic plate that is ...
rises into the overlying mantle, lowering its melting point, particularly for the more silica-rich minerals. Fractional crystallization further enriches the magma in silica. It has also been suggested that intermediate magmas are produced by melting of sediments carried downwards by the subducted slab. Another process is 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 A mafic mineral or rock is a silicate mineral Silicate minerals are rock-forming mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composit ...
'' (because it contains higher percentages of
magnesium Magnesium is a chemical element upright=1.0, 500px, The chemical elements ordered by link=Periodic table In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science ...

magnesium
(Mg) and iron (Fe)) or
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

basalt
ic. These lavas are usually hotter and much less viscous than felsic lavas. Mafic magmas are formed by partial melting of dry mantle, with limited fractional crystallization and assimilation of crustal material. :Mafic lavas occur in a wide range of settings. These include
mid-ocean ridge A mid-ocean ridge (MOR) is a seafloor mountain system formed by plate tectonics File:Earth cutaway schematic-en.svg, upright=1.35, Diagram of the internal layering of Earth showing the lithosphere above the asthenosphere (not to scale) Plate ...
s; Shield volcanoes (such the
Hawaiian Islands The Hawaiian Islands ( haw, Mokupuni o Hawai‘i) are an archipelago An archipelago ( ), sometimes called an island group or island chain, is a chain, cluster or collection of island An island (or isle) is an isolated pie ...
, including
Mauna Loa Mauna Loa ( or ; Hawaiian Hawaiian may refer to: * Hawaii state residents, regardless of ancestry * Native Hawaiians, the current term for the indigenous people of the Hawaiian Islands or their descendants * Hawaiian language Historic uses * ...

Mauna Loa
and ), on both
oceanic Oceanic may refer to: *Of or relating to the ocean *Of or relating to Oceania **Oceanic climate **Oceanic languages **Oceanic person or people, also called "Pacific Islander(s)" Places *Oceanic, British Columbia, a settlement on Smith Island, Br ...
and
continental crust Continental crust is the layer of igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the ...
; and as continental
flood basalt A flood basalt is the result of a giant volcanic eruption Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, ...
s. * Some erupted magmas contain <=45% silica and produce ''
ultramafic Ultramafic rocks (also referred to as ultrabasic rocks, although the terms are not wholly equivalent) are igneous Igneous rock (derived from the Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch o ...
'' lava. Ultramafic flows, also known as
komatiite Komatiite () is a type of ultramafic mantle-derived volcanic rock Volcanic rock (often shortened to volcanics in scientific contexts) is a Rock (geology), rock formed from lava erupted from a volcano. In other words, it differs from other igne ...
s, are very rare; indeed, very few have been erupted at the Earth's surface since the
Proterozoic The Proterozoic () is a geological eon spanning the time interval from 2500 to 541million years ago. It is the most recent part of the Precambrian The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest par ...
, when the planet's heat flow was higher. They are (or were) the hottest lavas, and were probably more fluid than common mafic lavas, with a viscosity less than a tenth that of hot basalt magma.


Lava texture

Mafic lava flows show two varieties of surface texture: Aa (pronounced ) and
pāhoehoe of pāhoehoe lava, Hawaii, United States Hawaii ( ; haw, Hawaii or ) is a U.S. state in the Western United States, in the Pacific Ocean about 2,000 miles (3,200 km) from the U.S. mainland. It is the only state outside North America, ...
(), both
Hawaiian Hawaiian may refer to: * Hawaii state residents, regardless of ancestry * Native Hawaiians, the current term for the indigenous people of the Hawaiian Islands or their descendants * Hawaiian language Historic uses * things and people of the Kingdo ...
words. Aa is characterized by a rough, clinkery surface and is the typical texture of cooler basalt lava flows. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Pāhoehoe flows are sometimes observed to transition to aa flows as they move away from the vent, but never the reverse. More silicic lava flows take the form of block lava, where the flow is covered with angular, vesicle-poor blocks.
Rhyolitic Rhyolite ( ) is the most silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and ...
flows typically consist largely of
obsidian Obsidian (; ) is a naturally occurring volcanic glass formed when lava extrusive rock, extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. Obsidian is produced from felsic lava, rich in the lighter element ...

obsidian
.


Tephra

Tephra is made when magma inside the volcano is blown apart by the rapid expansion of hot volcanic gases. Magma commonly explodes as the gas dissolved in it comes out of solution as the pressure decreases . These violent explosions produce particles of material that can then fly from the volcano. Solid particles smaller than 2 mm in diameter ( or smaller) are called volcanic ash. Tephra and other
volcaniclastics Volcaniclastics are geologic materials composed of broken fragments ( clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...
(shattered volcanic material) make up more of the volume of many volcanoes than do lava flows. Volcaniclastics may have contributed as much as a third of all sedimentation in the geologic record. The production of large volumes of tephra is characteristic of explosive volcanism.


Types of volcanic eruptions

Eruption styles are broadly divided into magmatic, phreatomagmatic, and phreatic eruptions.


Magmatic eruptions

Magmatic eruptions are driven primarily by gas release due to decompression. Low-viscosity magma with little dissolved gas produces relatively gentle effusive eruptions. High-viscosity magma with a high content of dissolved gas produces violent explosive eruptions. The range of observed eruption styles is expressed from historical examples. ''Hawaiian'' eruptions are typical of volcanoes that erupt mafic lava with a relatively low gas content. These are almost entirely effusive, producing local fire fountains and highly fluid lava flows but relatively little tephra. They are named after the . ''Strombolian'' eruptions are characterized by moderate viscosities and dissolved gas levels. They are characterized by frequent but short-lived eruptions that can produce eruptive columns hundreds of meters high. Their primary product is
scoria Scoria is a highly , dark-colored that may or may not contain crystals (s). It is typically dark in color (generally dark brown, black or purplish-red), and ic or in composition. Scoria is relatively low in as a result of its numerous macros ...
. They are named after
Stromboli Stromboli ( , ; scn, Struògnuli ; grc, Στρογγύλη, Strongýlē) is an island in the Tyrrhenian Sea The Tyrrhenian Sea (; it, Mar Tirreno , french: Mer Tyrrhénienne , sc, Mare Tirrenu, co, Mari Tirrenu, scn, Mari Tirrenu, nap, ...

Stromboli
. ''Vulcanian'' eruptions are characterized by yet higher viscosities and partial crystallization of magma, which is often intermediate in composition. Eruptions take the form of short-lived explosions over the course of several hours, which destroy a central dome and eject large lava blocks and bombs. This is followed by an effusive phase that rebuilds the central dome. Vulcanian eruptions are named after
Vulcano Vulcano ( scn, Vurcanu) or Vulcan is a small volcanic island Geologically, a high island or volcanic island is an island of volcano, volcanic origin. The term can be used to distinguish such islands from low islands, which are formed fr ...

Vulcano
. ''Peléan'' eruptions are more violent still, being characterized by dome growth and collapse that produces various kinds of pyroclastic flows. They are named after . ''Plinian'' eruptions are the most violent of all volcanic eruptions. They are characterized by sustained huge eruption columns whose collapse produces catastrophic pyroclastic flows. They are named after
Pliny the Younger Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo (61 – c. 113), better known as Pliny the Younger (), was a lawyer, author, and magistrate of Ancient Rome In historiography, ancient Rome is Roman people, Rom ...

Pliny the Younger
, who chronicled the Plinian
eruption of Mount Vesuvius in 79 Of the many eruptions of Mount Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma-stratovolcano A stratovolcano, also known as a composite volcano, is a conical volcano ...
AD. The intensity of explosive volcanism is expressed using the
Volcanic Explosivity Index The Volcanic Explosivity Index (VEI) is a relative measure of the explosiveness of volcanic eruptions Several types of volcanic eruptions—during which lava of pāhoehoe lava, Hawaii, United States , Iceland in 1984 Lava is molten Roc ...
(VEI), which ranges from 0 for Hawaiian-type eruptions to 8 for supervolcanic eruptions.


Phreatomagmatic eruptions

Phreatomagmatic eruptions are characterized by interaction of rising magma with
groundwater Groundwater is the water Water (chemical formula H2O) is an , transparent, tasteless, odorless, and , which is the main constituent of 's and the s of all known living organisms (in which it acts as a ). It is vital for all known form ...

groundwater
. They are driven by the resulting rapid buildup of pressure in the groundwater.


Phreatic eruptions

Phreatic eruptions are characterized by superheating of groundwater that comes in contact with hot rock or magma. They are distinguished from phreatomagmatic eruptions because the erupted material is all
country rock Country rock is a subgenre of , formed from the fusion of and . It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal ...
; no magma is erupted.


Volcanic activity

Volcanoes vary greatly in their level of activity, with individual volcanic systems having an ''eruption recurrence'' ranging from several times a year to once in tens of thousands of years. Volcanoes are informally described as active, dormant, or extinct, but these terms are poorly defined.


Active

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.


Dormant and reactivated

It is difficult to distinguish an extinct volcano from a dormant (inactive) one. Dormant volcanoes are those that have not erupted for thousands of years, but are likely to erupt again in the future. 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 Yellowstone National Park is an American national park located in the western United States, largely in the northwest corner of Wyoming and extending into Montana and Idaho. It was established by the U.S. Congress and signed into law by ...

Yellowstone
has a repose/recharge period of around 700,000 years, and of around 380,000 years.
Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma- stratovolcano located on the Gulf of Naples in Campania, Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repub ...

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 Herculaneum ( it, Ercolano) was an ancient town, located in the modern-day ''comune The (; plural: ) is a basic Administrative division, constituent entity of Italy, roughly equivalent to a township or municipality. Importance and f ...

Herculaneum
and
Pompeii Pompeii (, ) was an ancient city located in what is now the ''comune The (; plural: ) is a of , roughly equivalent to a or . Importance and function The provides essential public services: of births and deaths, , and maintenan ...

Pompeii
. Before its catastrophic eruption of 1991,
Pinatubo Mount Pinatubo ( xsb, Bakil nin Pinatobo; pam, Bunduk/Bulkan ning Pinatubu, Bunduk ning Apu Malyari; pag, Palandey/Bulkan na Pinatubu; ilo, Bantay Pinatubo; tgl, Bundok/Bulkang Pinatubo ) is an active volcano, active stratovolcano in the ...

Pinatubo
was an inconspicuous volcano, unknown to most people in the surrounding areas. Two other examples are the long-dormant
Soufrière Hills The Soufrière Hills are an active Active may refer to: Music * Active (album), ''Active'' (album), a 1992 album by Casiopea * Active Records, a record label Ships * Active (ship), ''Active'' (ship), several commercial ships by that ...

Soufrière Hills
volcano on the island of
Montserrat Montserrat ( ) is a British Overseas Territory The British Overseas Territories (BOTs), also known as United Kingdom Overseas Territories (UKOTs), are fourteen dependent territory, territories all with a constitutional and historical lin ...

Montserrat
, thought to be extinct before activity resumed in 1995 (turning its capital
Plymouth Plymouth () is a port city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: ...

Plymouth
into a
ghost town A ghost town or alternatively deserted city or abandoned city is an abandoned village, town, or city, usually one that contains substantial visible remaining buildings and infrastructure such as roads. A town often becomes a ghost town because ...
) and Fourpeaked Mountain in
Alaska Alaska (; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Central Alaskan Yup'ik language, Yup'ik: ''Alaskaq''; tli, Anáaski) is a U.S. state in the Western United States, on the northwest extremity of the country's West Coast of the United State ...

Alaska
, which, before its September 2006 eruption, had not erupted since before 8000 BCE and had long been thought to be extinct.


Extinct

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 Hawaiian may refer to: * Hawaii state residents, regardless of ancestry * Native Hawaiians, the current term for the indigenous people of the Hawaiian Islands or their descendants * Hawaiian language Historic uses * things and people of the Kingdo ...
in the Pacific Ocean (although some volcanoes at the eastern end of the chain are active),
Hohentwiel Hohentwiel is an extinct volcano A volcano is a rupture in the Crust (geology), crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and Volcanic gas, gases to escape from a magma chamber below the surface. ...

Hohentwiel
in
Germany ) , image_map = , map_caption = , map_width = 250px , capital = Berlin Berlin (; ) is the Capital city, capital and List of cities in Germany by population, largest city of Germany by both area and population. Its 3,769,495 inh ...

Germany
,
Shiprock Shiprock ( nv, , "rock with wings" or "winged rock") is a monadnock An inselberg or monadnock () is an isolated rock hill, knob, ridge, or small mountain A mountain is an elevated portion of the Earth's crust, generally with steep ...
in
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Greater Albuquerque , OfficialLang = None , Languages = English English usually refer ...

New Mexico
, , Zuidwal volcano in the
Netherlands ) , national_anthem = ( en, "William of Nassau") , image_map = EU-Netherlands.svg , map_caption = , image_map2 = BES islands location map.svg , map_caption2 = , image_map3 ...

Netherlands
, and many volcanoes in
Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repubblica Italiana, links=no ), is a country consisting of a peninsula delimited by the Alps The Alps ; german: Alpen ; it, Alpi ; rm, Alps; sl, Alpe ) are the highest ...

Italy
such as .
Edinburgh Castle Edinburgh Castle is a historic castle in Edinburgh, Scotland Edinburgh (; sco, Edinburgh; gd, Dùn Èideann ) is the capital city A capital or capital city is the municipality holding primary status in a Department (country subdi ...

Edinburgh Castle
in Scotland is located atop an extinct volcano, which forms Castle Rock. Whether a volcano is truly extinct is often difficult to determine. Since "supervolcano"
caldera A caldera is a large cauldron A cauldron (or caldron) is a large cast iron Cast iron is a group of iron-carbon alloys with a carbon content more than 2%. Its usefulness derives from its relatively low melting temperature. The alloy cons ...

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 may be considered dormant instead of extinct.


Volcanic-alert level

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.


Decade volcanoes

The Decade Volcanoes are 16 volcanoes identified by the
International Association of Volcanology and Chemistry of the Earth's Interior The International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) is a learned society that focuses on research in volcanology, efforts to mitigate volcanic Disasters#Volcanic eruption, disasters, and research into closely ...
(IAVCEI) as being worthy of particular study in light of their history of large, destructive eruptions and proximity to populated areas. They are named Decade Volcanoes because the project was initiated as part of the United Nations-sponsored
International Decade for Natural Disaster ReductionThe United Nations General Assembly The United Nations General Assembly (UNGA or GA; french: link=no, Assemblée générale, AG) is one of the six principal organs of the United Nations (UN), serving as the main deliberative, policy-making, an ...
(the 1990s). The 16 current Decade Volcanoes are : The Deep Earth Carbon Degassing Project, an initiative of the , monitors nine volcanoes, two of which are Decade volcanoes. The focus of the Deep Earth Carbon Degassing Project is to use 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 volcanic activityPrediction of volcanic eruption, or volcanic eruption forecasting, is an interdisciplinary monitoring and research effort to predict the time and severity of a volcano's eruption. Of particular importance is the prediction of hazardous eruptions tha ...
.


Volcanoes and humans

Volcanic eruptions pose a significant threat to human civilization. However, volcanic activity has also provided humans with important resources.


Hazards

There are many different
types of volcanic eruptions Several types of volcanic eruptions—during which lava Lava is magma once it has been expelled from the interior of a terrestrial planet (such as Earth) or a Natural satellite, moon onto its surface. Lava may be erupted at a volcano or ...
and associated activity:
phreatic eruptions A phreatic eruption, also called a phreatic explosion, ultravulcanian eruption or steam-blast eruption, occurs when magma 300px, Lava flow on Hawaii (island), Hawaii. Lava is the extrusive equivalent of magma. Magma (from Ancient Greek μάγ ...
(steam-generated eruptions), explosive eruption of high-
silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any su ...

silica
lava (e.g.,
rhyolite Rhyolite ( ) is the most silica Silicon dioxide, also known as silica, is an oxide An oxide () is a chemical compound A chemical compound is a chemical substance A chemical substance is a form of matter In classical physics and ...

rhyolite
), effusive eruption of low-silica lava (e.g.,
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

basalt
),
pyroclastic flow A pyroclastic flow (also known as a pyroclastic density current or a pyroclastic cloud) is a fast-moving current of hot gas Gas is one of the four fundamental states of matter In physics Physics is the natural science that studies ...
s,
lahar A lahar (, from jv, ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow A mudflow or mud flow is a form of mass wasting involving "very rapid to extremely rapid surging flow" of debris that has become partially or fully liquified by the addition ...
s (debris flow) and
carbon dioxide emission Greenhouse gas emissions are emissions of greenhouse gases A greenhouse gas (sometimes abbreviated GHG) is a gas that absorbs and emits radiant energy In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ ( ...
. All of these activities can pose a hazard to humans. Earthquakes,
hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of w ...

hot spring
s,
fumarole __NOTOC__ Sampling gases at a fumarole on Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** Federal government of the United States (metonym) ** Washington metr ...

fumarole
s,
mud pot Mud is soil File:Stagnogley.JPG, Surface-water-Gley soil, gley developed in glacial till, Northern Ireland. Soil is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Earth's body of soil, called ...
s and
geyser A geyser (, ) is a spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric ...

geyser
s often accompany volcanic activity. Volcanic gases can reach the stratosphere, where they form
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthogra ...

sulfuric acid
aerosols that can reflect solar radiation and lower surface temperatures significantly. Sulfur dioxide from the eruption of
Huaynaputina Huaynaputina ( ; ) is a volcano in a volcanic high plateau in southern Peru. Lying in the Central Volcanic Zone of the Andes, it was formed by the subduction of the oceanic Nazca Plate under the continental South American Plate. Huaynaputina is ...

Huaynaputina
may have caused the Russian famine of 1601–1603. Chemical reactions of sulfate aerosols in the stratosphere can also damage the , and acids such as
hydrogen chloride The compound Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above fortified with ...

hydrogen chloride
(HCl) and hydrogen fluoride (HF) can fall to the ground as
acid rain Acid rain is a rain or any other form of Precipitation (meteorology), precipitation that is unusually acidic, meaning that it has elevated levels of hydrogen ions (low pH). It can have harmful effects on plants, aquatic animals, and infras ...
. Explosive volcanic eruptions release the greenhouse gas
carbon dioxide Carbon dioxide (chemical formula A chemical formula is a way of presenting information about the chemical proportions of s that constitute a particular or molecule, using symbols, numbers, and sometimes also other symbols, such as pare ...

carbon dioxide
and thus provide a deep source of
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
for
biogeochemical cycle In ecology Ecology (from el, οἶκος, "house" and el, -λογία, label=none, "study of") is the study of the relationships between living organisms, including humans, and their physical environment. Topics of interest include the bi ...
s. Ash thrown into the air by eruptions can present a hazard to aircraft, especially
jet aircraft A jet aircraft (or simply jet) is an aircraft An aircraft is a vehicle that is able to flight, fly by gaining support from the Atmosphere of Earth, air. It counters the force of gravity by using either Buoyancy, static lift or by using th ...
where the particles can be melted by the high operating temperature; the melted particles then adhere to the
turbine A turbine ( or ) (from the Greek , ''tyrbē'', or Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', ...

turbine
blades and alter their shape, disrupting the operation of the turbine. This can cause major disruptions to air travel. A
volcanic winter A volcanic winter is a reduction in global temperatures caused by volcanic ash , Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a continent A continent is ...
is thought to have taken place around 70,000 years ago after the
supereruption A supervolcano is a large volcano that has had an volcanic eruption, eruption with a Volcanic Explosivity Index (VEI) of 8, the largest recorded value on the index. This means the volume of deposits for that eruption is greater than 1,000 cubic k ...
of
Lake Toba Lake Toba ( id, Danau Toba) is a large natural lake A lake is an area filled with water, localized in a basin, surrounded by land, apart from any river A river is a natural flowing watercourse, usually freshwater, flowing towards ...

Lake Toba
on Sumatra island in Indonesia, This may have created a
population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as specicide, widespread violen ...
that affected the genetic inheritance of all humans today. Volcanic eruptions may have contributed to major extinction events, such as the End-Ordovician, Permian-Triassic, and
Late Devonian The Devonian ( ) is a period (geology), geologic period and system of the Paleozoic, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, ...
mass extinction An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity Biodiversity is the biological variety and Genetic variability, variability of life, life on Earth. Biodiversity ...
s. The 1815 eruption of
Mount Tambora Mount Tambora, or Tomboro, is an active stratovolcano in West Nusa Tanagra, Sumbawa, Indonesia in one of the Lesser Sunda Islands The Lesser Sunda Islands ( id, Kepulauan Nusa Tenggara "southeastern archipelago" or "lesser sunda archip ...
created global climate anomalies that became known as the " Year Without a Summer" because of the effect on North American and European weather. The freezing winter of 1740–41, which led to widespread
famine A famine is a widespread scarcity of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual con ...
in northern Europe, may also owe its origins to a volcanic eruption.


Benefits

Although volcanic eruptions pose considerable hazards to humans, past volcanic activity has created important economic resources. Volcanic ash and weathered basalt produce some of the most fertile soil in the world, rich in nutrients such as iron, magnesium, potassium, calcium, and phosphorus. Tuff formed from volcanic ash is a relatively soft rock, and it has been used for construction since ancient times.Marcari, G., G. Fabbrocino, and G. Manfredi. "Shear seismic capacity of tuff masonry panels in heritage constructions." Structural Studies, Repairs and Maintenance of Heritage Architecture X 95 (2007): 73. The Romans often used tuff, which is abundant in Italy, for construction. The
Rapa Nui Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile Chile (, ; ), officially the Republic of Chile (), is a country in western South America. It occupies a long, narrow strip of land between ...
people used tuff to make most of the ''
moai Moai or moʻai ( es, moái, rap, moʻai, meaning "statue" in Rapa Nui language, Rapa Nui) are monolithic human figures carved by the Rapa Nui people on Easter Island in eastern Polynesia between the years 1250 and 1500. Nearly half are still ...

moai
'' statues in
Easter Island Easter Island ( rap, Rapa Nui; es, Isla de Pascua) is an island and special territory of Chile Chile, officially the Republic of Chile, is a country in the western part of South America South America is a continent ...

Easter Island
.Richards, Colin. 2016
"Making Moai: Reconsidering Concepts of Risk in the Construction of Megalithic Architecture in Rapa Nui (Easter Island)"
''Rapa Nui–Easter Island: Cultural and Historical Perspectives'', pp.150-151
Volcanic activity is responsible for emplacing valuable mineral resources, such as metal ores. Volcanic activity is accompanied by high rates of heat flow from the Earth's interior. These can be tapped as
geothermal power Geothermal power is electrical power generated from geothermal energy Geothermal energy is the thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. The geothermal energy ...
.


Volcanoes on other celestial bodies

The Earth's
Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia (continent), Australia), it is the largest natural satellite in the Solar System relative to the size of its plane ...

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 Maria may refer to: People * Maria (given name), a popular given name in many languages Placenames Extraterrestrial *170 Maria, a Main belt S-type asteroid discovered in 1877 *Lunar maria (plural of ''mare''), large, dark basaltic plains on Eart ...
(the darker patches seen on the Moon),
rille Rille (German for 'groove') is typically used to describe any of the long, narrow depressions in the surface of the Moon The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the wi ...
s and
domes A dome () is an architectural element similar to the hollow upper half of a sphere. There is significant overlap with the term cupola, which may also refer to a dome or a structure on top of a dome. The precise definition of a dome has been a m ...
. The planet
Venus Venus is the second planet from the Sun. It is named after the Venus (mythology), Roman goddess of love and beauty. As List of brightest natural objects in the sky, the brightest natural object in Earth's night sky after the Moon, Venus can ...

Venus
has a surface that is 90%
basalt Basalt (, ) is a fine-grained extrusive A volcanic rock from Italy with a relatively large six-sided phenocryst (diameter about 1 mm) surrounded by a fine-grained groundmass, as seen in thin section under a petrographic microscope Extr ...

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 Lava is magma Magma () is the molten or semi-molten natural material from which all igneous rock Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main The three types of rocks, ro ...

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. However, the interpretation of the flows as ash flows has been questioned. 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.
Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...

Jupiter
's Natural satellite, moon Io (moon), Io is the most volcanically active object in the Solar System because of tides, tidal interaction with Jupiter. It is covered with volcanoes that erupt
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
,
sulfur dioxide Sulfur dioxide (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the autho ...
and silicate rock, and as a result, Io (moon), 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 (moon), 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 , one of the most reliably identified cryovolcanoes on Saturn's moon Titan (moon), Titan A cryovolcano (sometimes informally called an ice volcano) is a type of volcano that erupts volatiles such as water, ammonia or methane, instead of lava, molte ...
es (ice volcanoes) on Triton (moon), Triton, a Natural satellite, moon of
Neptune Neptune is the eighth and farthest-known Solar planet from the Sun. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times the mass of Earth, slightly mo ...

Neptune
, and in 2005 the ''Cassini–Huygens'' probe photographed Enceladus (moon)#Cryovolcanism, fountains of frozen particles erupting from Enceladus, a moon of
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It only has one-eighth the average density of Earth; how ...

Saturn
. The ejecta may be composed of water, liquid nitrogen, ammonia, dust, or methane compounds. ''Cassini–Huygens'' also found evidence of a methane-spewing cryovolcano on the
Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It only has one-eighth the average density of Earth; how ...

Saturn
ian moon Titan (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 50000 Quaoar, Quaoar. A 2010 study of the exoplanet COROT-7b, which was detected by transit method, 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.


History of volcanology

Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of deity, 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 Society of Jesus, Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and
Stromboli Stromboli ( , ; scn, Struògnuli ; grc, Στρογγύλη, Strongýlē) is an island in the Tyrrhenian Sea The Tyrrhenian Sea (; it, Mar Tirreno , french: Mer Tyrrhénienne , sc, Mare Tirrenu, co, Mari Tirrenu, scn, Mari Tirrenu, nap, ...

Stromboli
, then visited the crater of
Vesuvius Mount Vesuvius ( ; it, Vesuvio ; nap, 'O Vesuvio , also or ; la, Vesuvius , also , or ) is a somma- stratovolcano located on the Gulf of Naples in Campania, Italy Italy ( it, Italia ), officially the Italian Republic ( it, Repub ...

Vesuvius
and published his view of an Earth with a central fire connected to numerous others caused by the burning of
sulfur Sulfur (in nontechnical British English: sulphur) is a chemical element In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: th ...

sulfur
, bitumen and coal. Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle (geology), 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.


See also

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References


Further reading

* * * * This is a reference aimed at geologists, but many articles are accessible to non-professionals.


External links

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U.S. Federal Emergency Management Agency Volcano advice

Volcano World
{{Authority control Volcanoes, * Geological hazards Volcanism Plate tectonics Volcanic landforms Volcanoes by status, * Volcanic rocks, * Volcanology Articles containing video clips