Bombs and volcano

A bomb is any of a range of explosive devices that typically rely on the exothermic chemical reaction of an explosive material to produce an extremely sudden and violent release of energy. The word comes from the Greek word βόμβος (bombos), an onomatopoetic term with approximately the same meaning as "boom" in English. A nuclear weapon employs chemical-based explosives to initiate a much larger nuclear-based explosion.
The term "bomb" is not usually applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as bombs. The military use of the term "bomb", or more specifically aerial bomb, typically refers to airdropped, unpowered explosive weapons most commonly used by air forces and naval aviation. Other military explosive devices not classified as "bombs" include grenades, shells, depth charges (used in water), warheads when in missiles, or land mines. In unconventional warfare, "bomb" can refer to any of a limitless range of explosive devices used as boobytraps or offensive weapons.
Contents[hide]
1 Effects
2 Types
3 Delivery
4 References
5 External links
//

[edit] Effects
Detonation causes injury and/or death within the blast radius through three distinct yet inter-related phenomena: shock wave (a.k.a. detonation wave, pressure wave or overpressure), thermal wave and fragmentation.
A shock wave is produced when an explosive event suddenly displaces a volume of air spherically outward from the point of detonation. At its initial creation this phenomenon might best be visualized as a round, thick "shell" of highly compressed air enclosing a vacuum. This shell of pressurized air will expand outward at a speed described by the Chapman-Jouguet condition, typically several to many times the speed of sound.
Even brief exposure to overpressure conditions can cause severe damage, crush injury and death. 1psi overpressure can shatter windows, 5psi can rupture eardrums and shatter a 12-inch concrete wall, and 15psi can cause severe lung damage. Shock waves dissipate as they expand, and the greatest defense against shock injuries is distance from the source of shock.[1] As a point of reference, the overpressure at the Oklahoma City bombing was estimated in the range of 4000psi.[2]
Shock waves produced by explosive events actually have two distinct components, the positive and negative wave. The positive wave shoves outward from the point of detonation, followed by the trailing vacuum space which "sucks back" towards the point of origin as the shock bubble collapses back on itself. This is most clearly observed in footage from the Trinity nuclear test where both the positive and negative effects on buildings are evident.[3]
A thermal wave is created by the sudden release of heat caused by an explosion. Military bomb tests have documented temperatures of 3000 to 4500˚F. While capable of inflicting severe to catastrophic burns and causing secondary fires, thermal wave effects are considered very limited in range compared to shock and fragmentation. This rule has been challenged, however, by military development of thermobaric weapons, which employ a combination of negative shock wave effects and extreme temperature to incinerate objects within the blast radius.
Fragmentation is produced by the acceleration of shattered pieces of bomb casing and adjacent physical objects. This is technically distinct, although practically indistinguishable, from shrapnel, which is physical objects, such as steel balls or nails, added to a bomb specifically to increase injury. While conventionally viewed as small metal shards moving at super- to hypersonic speeds, fragmentation can occur in epic proportions and travel for extensive distances. When the S.S. Grandcamp exploded in the Texas City Disaster on April 16, 1947, one "fragment" of that blast was a two ton anchor which was hurled nearly two miles inland to embed itself in the parking lot of the Pan American refinery.

[edit] Types

Device originally thought to be a pipe bomb, found to be a time bomb. From a United States government publication.
Experts commonly distinguish between civilian and military bombs. The latter are almost always mass-produced weapons, developed and constructed to a standard design out of standard components and intended to be deployed in a standard way each time. By contrast, civilian bombs are usually custom-made, developed to any number of designs, use a wide range of explosives of varying levels of power and chemical stability, and are used in many different ways. For this reason, civilian-made bombs are generally referred to as improvised explosive devices (IEDs). IEDs are divided into three basic categories by basic size and delivery. Type 1 IEDs are hand-carried parcel or suitcase bombs, type 2 are "suicide vests" worn by a bomber, and type 3 devices are vehicles laden with explosives to act as large-scale stationary or self-propelled bombs, also known as VBIED (vehicle-borne IEDs).
Improvised explosive materials are typically very unstable and subject to spontaneous, unintentional detonation triggered by a wide range of environmental effects ranging from impact and friction to electrostatic shock. Even subtle motion, change in temperature, or the nearby use of cellphones or radios, can trigger an unstable or remote-controlled device. Any interaction with explosive materials or devices by unqualified personnel should be considered a grave and immediate risk of death or dire injury. The safest response to finding an object believed to be an explosive device is to get as far away from it as possible.
The term dirty bomb refers to a specialized device that relies on a comparatively low explosive yield to scatter harmful material over a wide area. Most commonly associated with radiological or chemical materials, dirty bombs seek to kill or injure and then to deny access to a contaminated area until a thorough clean-up can be accomplished. In the case of urban settings, this clean-up may take extensive time, rendering the contaminated zone virtually uninhabitable in the interim.
The most powerful kind of bomb in existence is the hydrogen bomb, a nuclear weapon with destructive power measured in TNT equivalent. The most powerful bombs ever used in combat were the two bombs dropped by the United States to attack Hiroshima and Nagasaki, and the most powerful ever tested was the Tsar Bomba. The most powerful non-nuclear bombs are the United States Air Force's MOAB (officially Massive Ordnance Air Blast, or more commonly known as the "Mother of All Bombs") and the Russian "Father of All Bombs".[4]
Bombs can also be classified according to the way they are set off and radius of effect.

[edit] Delivery

A Japanese bomb explodes on the flight deck of USS Enterprise, 24 August 1942, during the Battle of the Eastern Solomons, causing minor damage.
The first air-dropped bombs were used by the Austrians in the 1849 siege of Venice. Two hundred unmanned balloons carried small bombs, few bombs actually hit Venice.[5]
The first bombing from a fixed wing aircraft took place in 1911 when the Italians fought Arabs in what is now Libya. The bombs were dropped by hand.[6]
The first significant terrorist bombing in the United States took place nine years later at noon on September 16, 1920 when an explosives-laden horse-drawn wagon, detonated on the lunchtime-crowded streets of New York's financial district. The Wall Street bombing employed many aspects of modern terrorist devices, such as cast-iron slugs added for shrapnel, in a horrific attack that killed 38 and injured some 400 others.
Modern military bomber aircraft are designed around a large-capacity internal bomb bay while fighter bombers usually carry bombs externally on pylons or bomb racks, or on multiple ejection racks which enable mounting several bombs on a single pylon. Modern bombs, precision-guided munitions, may be guided after they leave an aircraft by remote control, or by autonomous guidance. When bombs such as nuclear weapons are mounted on a powered platform, they are called guided missiles.
Some bombs are equipped with a parachute, such as the World War II "parafrag", which was an 11 kg fragmentation bomb, the Vietnam-era daisy cutters, and the bomblets of some modern cluster bombs. Parachutes slow the bomb's descent, giving the dropping aircraft time to get to a safe distance from the explosion. This is especially important with airburst nuclear weapons, and in situations where the aircraft releases a bomb at low altitude.[7]
A hand grenade is delivered by being thrown. Grenades can also be projected by other means using a grenade launcher, such as being launched from the muzzle of a rifle using the M203 or the GP-30 or by attaching a rocket to the explosive grenade as in a rocket propelled grenade (RPG).
A bomb may also be positioned in advance and concealed.
A bomb destroying a rail track just before a train arrives causes a train to derail. Apart from the damage to vehicles and people, a bomb exploding in a transport network often also damages, and is sometimes mainly intended to damage that network. This applies for railways, bridges, runways, and ports, and to a lesser extent, depending on circumstances, to roads.
In the case of suicide bombing the bomb is often carried by the attacker on his or her body, or in a vehicle driven to the target.
The Blue Peacock nuclear mines, which were also termed "bombs", were planned to be positioned during wartime and be constructed such that, if they were disturbed, they would explode within ten seconds.
The explosion of a bomb may be triggered by a detonator or a fuse. Detonators are triggered by clocks, remote controls like cell phones or some kind of sensor, such as pressure (altitude), radar, vibration or contact. Detonators vary in ways they work, they can be electrical, fire fuze or blast initiated detonators and others.

[edit] References

This article needs additional citations for verification. Please help improve this article by adding reliable references (ideally, using inline citations). Unsourced material may be challenged and removed. (April 2007)
^ Marks, Michael E. (2002). The Emergency Responder's Guide to Terrorism. Red Hat Publishing Co., Inc.. pp. 30. ISBN 1-932235-00-0.
^ Wong, Henry (2002). "Blast-Resistant Building Design Technology Analysis of its Application to Modern Hotel Design". WGA Wong Gregerson Architects, Inc.. pp. 5.
^ "The House in the Middle". Federal Civil Defense Administration. 1954. http://www.archive.org/details/Houseint1954. Retrieved on 2008-07-16.
^ Solovyov, Dmitry (2007-09-12). "Russia tests superstrength bomb, military says". Reuters. http://www.reuters.com/article/worldNews/idUSL1155952320070912?feedType=RSS&feedName=worldNews&rpc=22&sp=true. Retrieved on 2008-06-02.
^ Murphy, Justin; contributed by Tucker, Spencer (2005). Military Aircraft, Origins to 1918: An Illustrated History of their Impact. ABC-CLIO. pp. 10. ISBN 1851094881. http://books.google.ca/books?id=7pS1QpH8FRgC&pg=PA10&dq=Venice+bombing+1849&lr=&sig=mCN924uCybWfcThJuN2nRryGtNg. Retrieved on 2008-05-26.
^ Lindqvist, Sven (2004). "Guernica". Shock and Awe: War on Words. published by Van Eekelen, Bregje. North Atlantic Books. pp. 76. ISBN 0971254605. http://books.google.ca/books?id=R-I3Zsdm14wC&pg=PA76&dq=Lindqvist+Bombing+Libya&lr=&sig=BZhmF-8ew2loSKwVQj30Aq9Yu9Y#PPA76,M1. Retrieved on 2008-05-26.
^ Jackson, S.B. (June 1968). The Retardation of Weapons for Low Altitude Bombing. United States Naval Institute Proceedings.

[edit] External links

Wikimedia Commons has media related to: Bombs


And,A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot ash, and gases Volcanic activity involving the extrusion of rock tends to form mountains or features like mountains over a period of time. The Ancient Romans called volcanoes Vulcano, after Vulcan, their fire god.[1]
Volcanoes are generally found where tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not created where two tectonic plates slide past one another. Volcanoes can also form where there is stretching and thinning of the Earth's crust (called "non-hotspot intraplate volcanism"), such as in the African Rift Valley, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America and the European Rhine Graben with its Eifel volcanoes.
Volcanoes can be caused by mantle plumes. These so-called hotspots, for example at Hawaii, can occur far from plate boundaries. Hotspot volcanoes are also found elsewhere in the solar system, especially on rocky planets and moons.
Contents[hide]
1 Plate tectonics and hotspots
1.1 Divergent plate boundaries
1.2 Convergent plate boundaries
1.3 Hotspots
2 Volcanic features
2.1 Fissure vents
2.2 Shield volcanoes
2.3 Lava domes
2.4 Volcanic cones (cinder cones)
2.5 Stratovolcanoes (composite volcanoes)
2.6 Supervolcanoes
2.7 Submarine volcanoes
2.8 Subglacial volcanoes
2.8.1 Antarctica eruption
2.9 Mud volcanoes
3 Erupted material
3.1 Lava composition
3.2 Lava texture
4 Volcanic activity
4.1 Active
4.2 Extinct
5 Notable volcanoes
6 Effects of volcanoes
7 Volcanoes on other planetary bodies
8 Etymology
9 In culture
9.1 Past beliefs
9.2 Heraldry
10 Panoramas
11 See also
12 Further reading
13 Notes
14 External links
//

[edit] Plate tectonics and hotspots

Map showing the divergent plate boundaries (OSR – Oceanic Spreading Ridges) and recent sub aerial volcanoes.

Lava enters the Pacific at the Big Island of Hawaii

Indonesia - Lombok: Mount Rinjani - outbreak in 1994

[edit] Divergent plate boundaries
Main article: divergent boundary
At the mid-oceanic ridges, two tectonic plates diverge from one another. New oceanic crust is being formed by hot molten rock slowly cooling and solidifying. The crust is very thin at mid-oceanic ridges due to the pull of the tectonic plates. The release of pressure due to the thinning of the crust leads to adiabatic expansion, and the partial melting of the mantle causing volcanism and creating new oceanic crust. Most divergent plate boundaries are at the bottom of the oceans, therefore most volcanic activity is submarine, forming new seafloor. Black smokers or deep sea vents are an example of this kind of volcanic activity. Where the mid-oceanic ridge is above sea-level, volcanic islands are formed, for example, Iceland.

[edit] Convergent plate boundaries
Main article: convergent boundary
Subduction zones are places where two plates, usually an oceanic plate and a continental plate, collide. In this case, the oceanic plate subducts, or submerges under the continental plate forming a deep ocean trench just offshore. Water released from the subducting plate lowers the melting temperature of the overlying mantle wedge, creating magma. This magma tends to be very viscous due to its high silica content, so often does not reach the surface and cools at depth. When it does reach the surface, a volcano is formed. Typical examples for this kind of volcano are Mount Etna and the volcanoes in the Pacific Ring of Fire.

[edit] Hotspots
Main article: hotspot (geology)
Hotspots are not usually located on the ridges of tectonic plates, but above mantle plumes, where the convection of the Earth's mantle creates a column of hot material that rises until it reaches the crust, which tends to be thinner than in other areas of the Earth. The temperature of the plume causes the crust to melt and form pipes, which can vent magma. Because the tectonic plates move whereas the mantle plume remains in the same place, each volcano becomes dormant after a while and a new volcano is then formed as the plate shifts over the hotspot. The Hawaiian Islands are thought to be formed in such a manner, as well as the Snake River Plain, with the Yellowstone Caldera being the part of the North American plate currently above the hotspot.

[edit] Volcanic features
The most common perception of a volcano is of a conical mountain, spewing lava and poisonous gases from a crater at its summit. This describes just one of many types of volcano, and the features of volcanoes are much more complicated. The structure and behavior of volcanoes depends on a number of factors. Some volcanoes have rugged peaks formed by lava domes rather than a summit crater, whereas others present landscape features such as massive plateaus. Vents that issue volcanic material (lava, which is what magma is called once it has escaped to the surface, and ash) and gases (mainly steam and magmatic gases) can be located anywhere on the landform. Many of these vents give rise to smaller cones such as Puʻu ʻŌʻō on a flank of Hawaii's Kīlauea.
Other types of volcano include cryovolcanoes (or ice volcanoes), particularly on some moons of Jupiter, Saturn and Neptune; and mud volcanoes, which are formations often not associated with known magmatic activity. Active mud volcanoes tend to involve temperatures much lower than those of igneous volcanoes, except when a mud volcano is actually a vent of an igneous volcano.

Skjaldbreiður, a shield volcano whose name means "broad shield"

[edit] Fissure vents
Main article: fissure vent
Volcanic fissure vents are flat, linear cracks through which lava emerges.

[edit] Shield volcanoes
Main article: shield volcano
Shield volcanoes, so named for their broad, shield-like profiles, are formed by the eruption of low-viscosity lavas that can flow a great distance from a vent, but not generally explode catastrophically. The Hawaiian volcanic chain is a series of shield cones, and they are common in Iceland, as well.

[edit] Lava domes
Main article: lava dome
Lava domes are built by slow eruptions of highly viscous lavas. They are sometimes formed within the crater of a previous volcanic eruption (as in Mount Saint Helens), but can also form independently, as in the case of Lassen Peak. Like stratovolcanoes, they can produce violent, explosive eruptions, but their lavas generally do not flow far from the originating vent.

[edit] Volcanic cones (cinder cones)

Holocene cinder cone volcano on State Highway 18 near Veyo, Utah.
Main articles: volcanic cone and cinder cone
Volcanic cones or cinder cones result from eruptions that erupt mostly small pieces of scoria and pyroclastics (both resemble cinders, hence the name of this volcano type) that build up around the vent. These can be relatively short-lived eruptions that produce a cone-shaped hill perhaps 30 to 400 meters high. Most cinder cones erupt only once. Cinder cones may form as flank vents on larger volcanoes, or occur on their own. Parícutin in Mexico and Sunset Crater in Arizona are examples of cinder cones. In New Mexico, Caja del Rio is a volcanic field of over 60 cinder cones.

Mayon Volcano, a stratovolcano

[edit] Stratovolcanoes (composite volcanoes)
Main article: stratovolcano
Stratovolcanoes or composite volcanoes are tall conical mountains composed of lava flows and other ejecta in alternate layers, the strata that give rise to the name. Stratovolcanoes are also known as composite volcanoes, created from several structures during different kinds of eruptions. Strato/composite volcanoes are made of cinders, ash and lava. Cinders and ash pile on top of each other, lava flows on top of the ash, where it cools and hardens, and then the process begins again. Classic examples include Mt. Fuji in Japan, Mount Mayon in the Philippines, and Mount Vesuvius and Stromboli in Italy. In recorded history, explosive eruptions by stratovolcanoes have posed the greatest hazard to civilizations.[citation needed]

The Lake Toba volcano created a caldera 100 km long

[edit] Supervolcanoes
Main article: supervolcano
A supervolcano is a large volcano that usually has a large caldera and can potentially produce devastation on an enormous, sometimes continental, scale. Such eruptions would be able to cause severe cooling of global temperatures for many years afterwards because of the huge volumes of sulfur and ash erupted. They are the most dangerous type of volcano. Examples include Yellowstone Caldera in Yellowstone National Park and Valles Caldera in New Mexico (both western United States), Lake Taupo in New Zealand and Lake Toba in Sumatra, Indonesia. Supervolcanoes are hard to identify centuries later, given the enormous areas they cover. Large igneous provinces are also considered supervolcanoes because of the vast amount of basalt lava erupted, but are non-explosive (basalt lava is produced only in non-explosive eruptions; see Kilauea).

Pillow lava (NOAA)

[edit] Submarine volcanoes
Main article: submarine volcano
Submarine volcanoes are common features on the ocean floor. Some are active and, in shallow water, disclose their presence by blasting steam and rocky debris high above the surface of the sea. Many others lie at such great depths that the tremendous weight of the water above them prevents the explosive release of steam and gases, although they can be detected by hydrophones and discoloration of water because of volcanic gases. Pumice rafts may also appear. Even large submarine eruptions may not disturb the ocean surface. Because of the rapid cooling effect of water as compared to air, and increased buoyancy, submarine volcanoes often form rather steep pillars over their volcanic vents as compared to above-surface volcanoes. They may become so large that they break the ocean surface as new islands. Pillow lava is a common eruptive product of submarine volcanoes.

Herðubreið, one of the tuyas in Iceland

[edit] Subglacial volcanoes
Main article: subglacial volcano
Subglacial volcanoes develop underneath icecaps. They are made up of flat lava flows atop extensive pillow lavas and palagonite. When the icecap melts, the lavas on the top collapse leaving a flat-topped mountain. Then, the pillow lavas also collapse, giving an angle of 37.5 degrees[citation needed]. These volcanoes are also called table mountains, tuyas or (uncommonly) mobergs. Very good examples of this type of volcano can be seen in Iceland, however, there are also tuyas in British Columbia. The origin of the term comes from Tuya Butte, which is one of the several tuyas in the area of the Tuya River and Tuya Range in northern British Columbia. Tuya Butte was the first such landform analyzed and so its name has entered the geological literature for this kind of volcanic formation. The Tuya Mountains Provincial Park was recently established to protect this unusual landscape, which lies north of Tuya Lake and south of the Jennings River near the boundary with the Yukon Territory.

[edit] Antarctica eruption
In January 2008, the British Antarctic Survey (BAS) scientists led by Hugh Corr and David Vaughan, reported (in the journal Nature Geoscience) that 2,200 years ago, a volcano erupted under the Antarctica ice sheet (based on airborne survey with radar images). The biggest eruption in Antartica in the last 10,000 years, the volcanic ash was found deposited on the ice surface under the Hudson Mountains, close to Pine Island Glacier.[2]

[edit] Mud volcanoes
Main article: mud volcano
Mud volcanoes or mud domes are formations created by geo-excreted liquids and gases, although there are several different processes which may cause such activity. The largest structures are 10 kilometers in diameter and reach 700 meters high.

[edit] Erupted material

[edit] Lava composition

Pāhoehoe Lava flow at Hawaii (island). The picture shows few overflows of a main lava channel.

The Stromboli volcano off the coast of Sicily has erupted continuously for thousands of years, giving rise to the term strombolian eruption ejecting lava bombs
Another way of classifying volcanoes is by the composition of material erupted (lava), since this affects the shape of the volcano. Lava can be broadly classified into 4 different compositions (Cas & Wright, 1987):
If the erupted magma contains a high percentage (>63%) of silica, the lava is called felsic.
Felsic lavas (or rhyolites) tend to be highly viscous (not very fluid) and are erupted as domes or short, stubby flows. Viscous lavas tend to form stratovolcanoes or lava domes. Lassen Peak in California is an example of a volcano formed from felsic lava and is actually a large lava dome.
Because siliceous magmas are so viscous, they tend to trap volatiles (gases) that are present, which cause the magma to erupt catastrophically, eventually forming stratovolcanoes. Pyroclastic flows (ignimbrites) are highly hazardous products of such volcanoes, since they are composed of molten volcanic ash too heavy to go up into the atmosphere, so they hug the volcano's slopes and travel far from their vents during large eruptions. Temperatures as high as 1,200 °C are known to occur in pyroclastic flows, which will incinerate everything flammable in their path and thick layers of hot pyroclastic flow deposits can be laid down, often up to many meters thick. Alaska's Valley of Ten Thousand Smokes, formed by the eruption of Novarupta near Katmai in 1912, is an example of a thick pyroclastic flow or ignimbrite deposit. Volcanic ash that is light enough to be erupted high into the Earth's atmosphere may travel many kilometres before it falls back to ground as a tuff.
If the erupted magma contains 52–63% silica, the lava is of intermediate composition.
These "andesitic" volcanoes generally only occur above subduction zones (e.g. Mount Merapi in Indonesia).
If the erupted magma contains <52%>45% silica, the lava is called mafic (because it contains higher percentages of magnesium (Mg) and iron (Fe) or basaltic. These lavas are usually much less viscous than rhyolitic lavas, depending on their eruption temperature; they also tend to be hotter than felsic lavas. Mafic lavas occur in a wide range of settings:
At mid-ocean ridges, where two oceanic plates are pulling apart, basaltic lava erupts as pillows to fill the gap;
Shield volcanoes (e.g. the Hawaiian Islands, including Mauna Loa and Kilauea), on both oceanic and continental crust;
As continental flood basalts.
Some erupted magmas contain <=45% silica and produce ultramafic lava. Ultramafic flows, also known as komatiites, are very rare; indeed, very few have been erupted at the Earth's surface since the Proterozoic, when the planet's heat flow was higher. They are (or were) the hottest lavas, and probably more fluid than common mafic lavas.

[edit] Lava texture
Two types of lava are named according to the surface texture: ʻAʻa (pronounced [ʔaʔa]) and pāhoehoe (pronounced [paːhoehoe]), both words having Hawaiian origins. ʻAʻa is characterized by a rough, clinkery surface and is what most viscous and hot lava flows look like. However, even basaltic or mafic flows can be erupted as ʻaʻa flows, particularly if the eruption rate is high and the slope is steep. Pāhoehoe is characterized by its smooth and often ropey or wrinkly surface and is generally formed from more fluid lava flows. Usually, only mafic flows will erupt as pāhoehoe, since they often erupt at higher temperatures or have the proper chemical make-up to allow them to flow at a higher fluidity.

[edit] Volcanic activity

A volcanic fissure and lava channel

Mount St. Helens in May 1980, shortly after the eruption of May 18

Shiprock, the erosional remnant of the throat of an extinct volcano.

Map of Volcanoes

[edit] Active
A popular way of classifying magmatic volcanoes is by their frequency of eruption, with those that erupt regularly called active, those that have erupted in historical times but are now quiet called dormant, and those that have not erupted in historical times called extinct. However, these popular classifications—extinct in particular—are practically meaningless to scientists. They use classifications which refer to a particular volcano's formative and eruptive processes and resulting shapes, which was explained above.
There is no real consensus among volcanologists on how to define an "active" volcano. The lifespan of a volcano can vary from months to several million years, making such a distinction sometimes meaningless when compared to the lifespans of humans or even civilizations. For example, many of Earth's volcanoes have erupted dozens of times in the past few thousand years but are not currently showing signs of eruption. Given the long lifespan of such volcanoes, they are very active. By human lifespans, however, they are not.
Scientists usually consider a volcano to be active if it is currently erupting or showing signs of unrest, such as unusual earthquake activity or significant new gas emissions. Many scientists also consider a volcano active if it has erupted in historic time. It is important to note that the span of recorded history differs from region to region; in the Mediterranean, recorded history reaches back more than 3,000 years but in the Pacific Northwest of the United States and Canada, it reaches back less than 300 years, and in Hawaii and New Zealand, only around 200 years. The Smithsonian Global Volcanism Program's definition of active is having erupted within the last 10,000 years.

[edit] Extinct
Extinct volcanoes are those that scientists consider unlikely to erupt again, because the volcano no longer has a lava supply. Examples of extinct volcanoes are many volcanoes on the Hawaiian Islands in the U.S. (extinct because the Hawaii hotspot is centered near the Big Island), and Paricutin, which is monogenetic. Otherwise, whether a volcano is truly extinct is often difficult to determine. Since "supervolcano" calderas can have eruptive lifespans sometimes measured in millions of years, a caldera that has not produced an eruption in tens of thousands of years is likely to be considered dormant instead of extinct. For example, the Yellowstone Caldera in Yellowstone National Park is at least 2 million years old and hasn't erupted violently for approximately 640,000 years, although there has been some minor activity relatively recently, with hydrothermal eruptions less than 10,000 years ago and lava flows about 70,000 years ago. For this reason, scientists do not consider the Yellowstone Caldera extinct. In fact, because the caldera has frequent earthquakes, a very active geothermal system (i.e. the entirety of the geothermal activity found in Yellowstone National Park), and rapid rates of ground uplift, many scientists consider it to be an active volcano.
It is difficult to distinguish an extinct volcano from a dormant one because volcanoes are usually considered to be extinct if there are no written records of its activity. Nevertheless volcanoes may remain dormant for a long period of time and it is not uncommon for a so-called "extinct" volcano to erupt again. Vesuvius was thought to be extinct before its famous eruption of AD 79, which destroyed the towns of Herculaneum and Pompeii. More recently, the long-dormant Soufrière Hills volcano on the island of Montserrat was thought to be extinct before activity resumed in 1995. The most recent example is Fourpeaked Mountain in Alaska, which prior to September 2006 is not believed to have erupted since before 8000 BCE and was long thought to be extinct.

[edit] Notable volcanoes
Main article: List of volcanoes
The 16 current Decade Volcanoes are:
Avachinsky-Koryaksky, Kamchatka, Russia
Nevado de Colima, Jalisco and Colima, Mexico
Mount Etna, Sicily, Italy
Galeras, Nariño, Colombia
Mauna Loa, Hawaii, USA
Mount Merapi, Central Java, Indonesia
Mount Nyiragongo, Democratic Republic of the Congo
Mount Rainier, Washington, USA
Sakurajima, Kagoshima Prefecture, Japan
Santamaria/Santiaguito, Guatemala
Santorini, Cyclades, Greece
Taal Volcano, Luzon, Philippines
Teide, Canary Islands, Spain
Ulawun, New Britain, Papua New Guinea
Mount Unzen, Nagasaki Prefecture, Japan
Vesuvius, Naples, Italy

[edit] Effects of volcanoes

Volcanic "injection"

Solar radiation reduction from volcanic eruptions

Sulfur dioxide emissions by volcanoes.

Average concentration of sulfur dioxide over the Sierra Negra Volcano (Galapagos Islands) from October 23–November 1, 2005
There are many different types of volcanic eruptions and associated activity: phreatic eruptions (steam-generated eruptions), explosive eruption of high-silica lava (e.g., rhyolite), effusive eruption of low-silica lava (e.g., basalt), pyroclastic flows, lahars (debris flow) and carbon dioxide emission. All of these activities can pose a hazard to humans. Earthquakes, hot springs, fumaroles, mud pots and geysers often accompany volcanic activity.
The concentrations of different volcanic gases can vary considerably from one volcano to the next. Water vapor is typically the most abundant volcanic gas, followed by carbon dioxide and sulfur dioxide. Other principal volcanic gases include hydrogen sulfide, hydrogen chloride, and hydrogen fluoride. A large number of minor and trace gases are also found in volcanic emissions, for example hydrogen, carbon monoxide, halocarbons, organic compounds, and volatile metal chlorides.
Large, explosive volcanic eruptions inject water vapor (H2O), carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride (HCl), hydrogen fluoride (HF) and ash (pulverized rock and pumice) into the stratosphere to heights of 16–32 kilometres (10–20 mi) above the Earth's surface. The most significant impacts from these injections come from the conversion of sulfur dioxide to sulfuric acid (H2SO4), which condenses rapidly in the stratosphere to form fine sulfate aerosols. The aerosols increase the Earth's albedo—its reflection of radiation from the Sun back into space - and thus cool the Earth's lower atmosphere or troposphere; however, they also absorb heat radiated up from the Earth, thereby warming the stratosphere. Several eruptions during the past century have caused a decline in the average temperature at the Earth's surface of up to half a degree (Fahrenheit scale) for periods of one to three years — sulfur dioxide from the eruption of Huaynaputina probably caused the Russian famine of 1601 - 1603. The sulfate aerosols also promote complex chemical reactions on their surfaces that alter chlorine and nitrogen chemical species in the stratosphere. This effect, together with increased stratospheric chlorine levels from chlorofluorocarbon pollution, generates chlorine monoxide (ClO), which destroys ozone (O3). As the aerosols grow and coagulate, they settle down into the upper troposphere where they serve as nuclei for cirrus clouds and further modify the Earth's radiation balance. Most of the hydrogen chloride (HCl) and hydrogen fluoride (HF) are dissolved in water droplets in the eruption cloud and quickly fall to the ground as acid rain. The injected ash also falls rapidly from the stratosphere; most of it is removed within several days to a few weeks. Finally, explosive volcanic eruptions release the greenhouse gas carbon dioxide and thus provide a deep source of carbon for biogeochemical cycles.

Rainbow and volcanic ash with sulfur dioxide emissions from Halema`uma`u vent.
Gas emissions from volcanoes are a natural contributor to acid rain. Volcanic activity releases about 130 to 230 teragrams (145 million to 255 million short tons) of carbon dioxide each year.[3] Volcanic eruptions may inject aerosols into the Earth's atmosphere. Large injections may cause visual effects such as unusually colorful sunsets and affect global climate mainly by cooling it. Volcanic eruptions also provide the benefit of adding nutrients to soil through the weathering process of volcanic rocks. These fertile soils assist the growth of plants and various crops. Volcanic eruptions can also create new islands, as the magma cools and solidifies upon contact with the water.

[edit] Volcanoes on other planetary bodies

Olympus Mons (Latin, "Mount Olympus") is the tallest known mountain in our solar system, located on the planet Mars.
Main articles: Geology of the Moon, Geology of Mars, Volcanism on Io, and Volcanism on Venus
The Earth's Moon has no large volcanoes and no current volcanic activity, although recent evidence suggests it may still possess a partially molten core.[4] However, the Moon does have many volcanic features such as maria (the darker patches seen on the moon), rilles and domes.
The planet Venus has a surface that is 90% basalt, indicating that volcanism played a major role in shaping its surface. The planet may have had a major global resurfacing event about 500 million years ago,[5] from what scientists can tell from the density of impact craters on the surface. Lava flows are widespread and forms of volcanism not present on Earth occur as well. Changes in the planet's atmosphere and observations of lightning, have been attributed to ongoing volcanic eruptions, although there is no confirmation of whether or not Venus is still volcanically active. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank.
There are several extinct volcanoes on Mars, four of which are vast shield volcanoes far bigger than any on Earth. They include Arsia Mons, Ascraeus Mons, Hecates Tholus, Olympus Mons, and Pavonis Mons. These volcanoes have been extinct for many millions of years,[6] but the European Mars Express spacecraft has found evidence that volcanic activity may have occurred on Mars in the recent past as well.[6]

The Tvashtar volcano erupts a plume 330 km (205 mi) above the surface of Jupiter's moon Io.
Jupiter's moon Io is the most volcanically active object in the solar system because of tidal interaction with Jupiter. It is covered with volcanoes that erupt sulfur, sulfur dioxide and silicate rock, and as a result, Io is constantly being resurfaced. Its lavas are the hottest known anywhere in the solar system, with temperatures exceeding 1,800 K (1,500 °C). In February 2001, the largest recorded volcanic eruptions in the solar system occurred on Io.[7] Europa, the smallest of Jupiter's Galilean moons, also appears to have an active volcanic system, except that its volcanic activity is entirely in the form of water, which freezes into ice on the frigid surface. This process is known as cryovolcanism, and is apparently most common on the moons of the outer planets of the solar system.
In 1989 the Voyager 2 spacecraft observed cryovolcanoes (ice volcanoes) on Triton, a moon of Neptune, and in 2005 the Cassini-Huygens probe photographed fountains of frozen particles erupting from Enceladus, a moon of Saturn.[8] The ejecta may be composed of water, liquid nitrogen, dust, or methane compounds. Cassini-Huygens also found evidence of a methane-spewing cryovolcano on the Saturnian moon Titan, which is believed to be a significant source of the methane found in its atmosphere.[9] It is theorized that cryovolcanism may also be present on the Kuiper Belt Object Quaoar.

[edit] Etymology
Volcano is thought to derive from Vulcano, a volcanic island in the Aeolian Islands of Italy whose name in turn originates from Vulcan, the name of a god of fire in Roman mythology. The study of volcanoes is called volcanology, sometimes spelled vulcanology.
The Roman name for the island Vulcano has contributed the word for volcano in most modern European languages.

[edit] In culture

[edit] Past beliefs

Kircher's model of the Earth's internal fires, from Mundus Subterraneus
Many ancient accounts ascribe volcanic eruptions to supernatural causes, such as the actions of gods or demigods. To the ancient Greeks, volcanoes' capricious power could only be explained as acts of the gods, while 16th/17th-century German astronomer Johannes Kepler believed they were ducts for the Earth's tears. [10] One early idea counter to this was proposed by Jesuit Athanasius Kircher (1602–1680), who witnessed eruptions of Mount Etna and Stromboli, then visited the crater of Vesuvius and published his view of an Earth with a central fire connected to numerous others caused by the burning of sulfur, bitumen and coal.
Various explanations were proposed for volcano behavior before the modern understanding of the Earth's mantle structure as a semisolid material was developed. For decades after awareness that compression and radioactive materials may be heat sources, their contributions were specifically discounted. Volcanic action was often attributed to chemical reactions and a thin layer of molten rock near the surface.

[edit] Heraldry
Volcanoes appear as a charge in heraldry.

[edit] Panoramas

Irazú Volcano, Costa Rica.

Black Rock Volcano an extinct cinder cone near Fillmore, Utah.

Crater of Sierra Negra volcano, Isabela island, Galapagos, Ecuador.

[edit] See also

Volcanoes portal
History of Volcanology
Plinian eruption
Prediction of volcanic activity
Volcano observatory
Geomorphology
Earth science
Volcanic field
Volcanic gas
Tsunami
Lists
List of volcanoes (terrestrial)
List of extraterrestrial volcanoes
List of famous volcanic eruption deaths
Volcanic Explosivity Index (includes list of large eruptions)
List of deadliest natural disasters
Specific locations
Iceland hotspot
Anahim hotspot
Kerguelen hotspot
East Australia hotspot
Hawaii hotspot
Bowie hotspot
Réunion hotspot
Galápagos hotspot
New England hotspot
Canary hotspot
Pacific Ring of Fire
Io (moon)
Triton (moon)
People
Category:Volcanologists

[edit] Further reading
Marti, Joan and Ernst, Gerald. (2005). Volcanoes and the Environment. Cambridge University Press. ISBN 0-521-59254-2.
Macdonald, Gordon A., and Agatin T. Abbott. (1970). Volcanoes in the Sea. University of Hawaii Press, Honolulu. 441 p.
Ollier, Cliff. (1988). Volcanoes. Basil Blackwell, Oxford, UK, ISBN 0-631-15664-X (hardback), ISBN 0-631-15977-0 (paperback).
Haraldur Sigurðsson, ed. (1999) Encyclopedia of Volcanoes. Academic Press. ISBN 0-12-643140-X. This is a reference aimed at geologists, but many articles are accessible to non-professionals.
Cas, R.A.F. and J.V. Wright, 1987. Volcanic Successions. Unwin Hyman Inc. 528p. ISBN 0-04-552022-4

[edit] Notes

This article needs additional citations for verification. Please help improve this article by adding reliable references (ideally, using inline citations). Unsourced material may be challenged and removed. (October 2008)
^ "What is a Volcano?". Education. Oracle Foundation. http://library.thinkquest.org/J003007/Disasters2/volcano/what/whatvol.htm. Retrieved on 2009-03-28.
^ BBC NEWS, Ancient Antarctic eruption noted Nature article: doi:10.1038/ngeo106
^ "Volcanic Gases and Their Effects" (HTML). U.S. Geological Survey. http://volcanoes.usgs.gov/Hazards/What/VolGas/volgas.html. Retrieved on 2007-06-16.
^ M. A. Wieczorek, B. L. Jolliff, A. Khan, M. E. Pritchard, B. P. Weiss, J. G. Williams, L. L. Hood, K. Righter, C. R. Neal, C. K. Shearer, I. S. McCallum, S. Tompkins, B. R. Hawke, C. Peterson, J, J. Gillis, B. Bussey (2006). "The Constitution and Structure of the Lunar Interior". Reviews in Mineralogy and Geochemistry 60 (1): 221–364. doi:10.2138/rmg.2006.60.3.
^ D.L. Bindschadler (1995). "Magellan: A new view of Venus' geology and geophysics". American Geophysical Union. http://www.agu.org/journals/rg/rg9504S/95RG00281/index.html. Retrieved on 2006-09-04.
^ a b "Glacial, volcanic and fluvial activity on Mars: latest images". European Space Agency. 2005-02-25. http://www.esa.int/esaMI/Mars_Express/SEMLF6D3M5E_0.html. Retrieved on 2006-08-17.
^ Exceptionally Bright Eruption on lo Rivals Largest in Solar System, Nov. 13, 2002
^ PPARC, Cassini Finds an Atmosphere on Saturn's Moon Enceladus
^ NewScientist, Hydrocarbon volcano discovered on Titan, June 8, 2005
^ Micheal Williams (11-2007). "Hearts of fire". Morning Calm (Korean Air Lines Co., Ltd.) (11-2007): 6.

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