Volcanology (also spelled vulcanology) is the study of volcanoes, lava, magma, and related geological, geophysical and geochemical phenomena (volcanism). The term volcanology is derived from the Latin word vulcan. Vulcan was the ancient Roman god of fire.
A volcanologist is a geologist who studies the eruptive activity and formation of volcanoes, and their current and historic eruptions. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of enquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting eruptions, like predicting earthquakes, could save many lives.
Seismic observations are made using seismographs deployed near volcanic areas, watching out for increased seismicity during volcanic events, in particular looking for long period harmonic tremors, which signal magma movement through volcanic conduits.
Surface deformation monitoring includes the use of geodetic techniques such as leveling, tilt, strain, angle and distance measurements through tiltmeters, total stations and EDMs. This also includes GNSS observations and InSAR. Surface deformation indicates magma upwelling: increased magma supply produces bulges in the volcanic center's surface.
Gas emissions may be monitored with equipment including portable ultra-violet spectrometers (COSPEC, now superseded by the miniDOAS), which analyzes the presence of volcanic gases such as sulfur dioxide; or by infra-red spectroscopy (FTIR). Increased gas emissions, and more particularly changes in gas compositions, may signal an impending volcanic eruption.
Temperature changes are monitored using thermometers and observing changes in thermal properties of volcanic lakes and vents, which may indicate upcoming activity.
Satellites are widely used to monitor volcanoes, as they allow a large area to be monitored easily. They can measure the spread of an ash plume, such as the one from Eyjafjallajökull's 2010 eruption, as well as SO2 emissions. InSAR and thermal imaging can monitor large, scarcely populated areas where it would be too expensive to maintain instruments on the ground.
Other geophysical techniques (electrical, gravity and magnetic observations) include monitoring fluctuations and sudden change in resistivity, gravity anomalies or magnetic anomaly patterns that may indicate volcano-induced faulting and magma upwelling.
Volcanology has an extensive history. The earliest known recording of a volcanic eruption may be on a wall painting dated to about 7,000 BCE found at the Neolithic site at Çatal Höyük in Anatolia, Turkey. This painting has been interpreted as a depiction of an erupting volcano, with a cluster of houses below shows a twin peaked volcano in eruption, with a town at its base (though archaeologists now question this interpretation). The volcano may be either Hasan Dağ, or its smaller neighbour, Melendiz Dağ.
The classical world of Greece and the early Roman Empire explained volcanoes as sites of various gods. Greeks considered that Hephaestus, the god of fire, sat below the volcano Etna, forging the weapons of Zeus. The Greek word used to describe volcanoes was etna, or hiera, after Heracles, the son of Zeus. The Roman poet Virgil, in interpreting the Greek mythos, held that the giant Enceladus was buried beneath Etna by the goddess Athena as punishment for rebellion against the gods; the mountain's rumblings were his tormented cries, the flames his breath and the tremors his railing against the bars of his prison. Enceladus' brother Mimas was buried beneath Vesuvius by Hephaestus, and the blood of other defeated giants welled up in the Phlegrean Fields surrounding Vesuvius.
The Greek philosopher Empedocles (c. 490-430 BCE) saw the world divided into four elemental forces, of Earth, Air, Fire and Water. Volcanoes, Empedocles maintained, were the manifestation of Elemental Fire. Plato contended that channels of hot and cold waters flow in inexhaustible quantities through subterranean rivers. In the depths of the earth snakes a vast river of fire, the Pyriphlegethon, which feeds all the world's volcanoes. Aristotle considered underground fire as the result of "the...friction of the wind when it plunges into narrow passages."
Wind played a key role in volcano explanations until the 16th century. Lucretius, a Roman philosopher, claimed Etna was completely hollow and the fires of the underground driven by a fierce wind circulating near sea level. Ovid believed that the flame was fed from "fatty foods" and eruptions stopped when the food ran out. Vitruvius contended that sulfur, alum and bitumen fed the deep fires. Observations by Pliny the Elder noted the presence of earthquakes preceded an eruption; he died in the eruption of Vesuvius in 79 CE while investigating it at Stabiae. His nephew, Pliny the Younger gave detailed descriptions of the eruption in which his uncle died, attributing his death to the effects of toxic gases. Such eruptions have been named Plinian in honour of the two authors.
Nuées ardentes were described from the Azores in 1580. Georgius Agricola argued the rays of the sun, as later proposed by Descartes had nothing to do with volcanoes. Agricola believed vapor under pressure caused eruptions of 'mointain oil' and basalt.
Jesuit Athanasius Kircher (1602–1680) 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.
Johannes Kepler considered volcanoes as conduits for the tears and excrement of the Earth, voiding bitumen, tar and sulfur. Descartes, pronouncing that God had created the Earth in an instant, declared he had done so in three layers; the fiery depths, a layer of water, and the air. Volcanoes, he said, were formed where the rays of the sun pierced the earth.
Science wrestled with the ideas of the combustion of pyrite with water, that rock was solidified bitumen, and with notions of rock being formed from water (Neptunism). Of the volcanoes then known, all were near the water, hence the action of the sea upon the land was used to explain volcanism.
Tribal legends of volcanoes abound from the Pacific Ring of Fire and the Americas, usually invoking the forces of the supernatural or the divine to explain the violent outbursts of volcanoes. Taranaki and Tongariro, according to Māori mythology, were lovers who fell in love with Pihanga, and a spiteful jealous fight ensued. Māori will not to this day live between Tongariro and Taranaki for fear of the dispute flaring up again.
In the Hawaiian religion, Pele (/ˈpeɪleɪ/ Pel-a; [ˈpɛlɛ]) is the goddess of volcanoes and a popular figure in Hawaiian mythology. Pele was used for various scientific terms as for Pele's hair, Pele's tears, and Limu o Pele (Pele's seaweed). A volcano on the Jovian moon Io is also named Pele.
Saint Agatha is patron saint of Catania, close to mount Etna, and an important highly venerated (till today) example of virgin martyrs of Christian antiquity. In 253 CE, one year after her violent death, the stilling of an eruption of Mt. Etna was attributed to her intercession. Catania was however nearly completely destroyed by the eruption of Mt. Etna in 1169, and over 15,000 of its inhabitants died. Nevertheless, she was invoked again 1669 and, for an outbreak danginering Nicolosi in 1886. The way she is invoked and dealt with in Italian Folk religion, a sort of quid pro quo way approach to saints, has been related (in the tradition of James Frazer) to earlier pagan believes.
In 1660 the eruption of Vesuvius rained twinned pyroxene crystals and ash upon the nearby villages. The crystals resembled the crucifix and this was interpreted as the work of Saint Januarius. In Naples, the relics of St Januarius are paraded through town at every major eruption of Vesuvius. The register of these processions and the 1779 and 1794 diary of Father Antonio Piaggio allowed British diplomat and amateur naturalist Sir William Hamilton to provide a detailed chronology and description of Vesuvius' eruptions.
For the extinct cephalopod genus, see Andesites.
Andesite ( or ) is an extrusive igneous, volcanic rock, of intermediate composition, with aphanitic to porphyritic texture. In a general sense, it is the intermediate type between basalt and rhyolite, and ranges from 57 to 63% silicon dioxide (SiO2) as illustrated in TAS diagrams. The mineral assemblage is typically dominated by plagioclase plus pyroxene or hornblende. Magnetite, zircon, apatite, ilmenite, biotite, and garnet are common accessory minerals. Alkali feldspar may be present in minor amounts. The quartz-feldspar abundances in andesite and other volcanic rocks are illustrated in QAPF diagrams.
Classification of andesites may be refined according to the most abundant phenocryst. Example: hornblende-phyric andesite, if hornblende is the principal accessory mineral.
Andesite can be considered as the extrusive equivalent of plutonic diorite. Characteristic of subduction zones, andesite represents the dominant rock type in island arcs. The average composition of the continental crust is andesitic. Along with basalts they are a major component of the Martian crust. The name andesite is derived from the Andes mountain range.Basaltic andesite
Basaltic andesite is a volcanic rock containing about 55% silica. It is distinct from basalt and andesite in having a different percentage of silica content. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America.Dike (geology)
A dike or dyke, in geological usage, is a sheet of rock that is formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack then solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack.Ejecta
Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (Tephra) that came out of a volcanic explosion and magma eruption volcanic vent, or crater, has traveled through the air or under water, and fell back on the ground surface or on the ocean floor.Extrusive rock
Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the atmosphere to fall back as pyroclastics or tuff. This is as opposed to intrusive rock formation, in which magma does not reach the surface.The main effect of extrusion is that the magma can cool much more quickly in the open air or under seawater, and there is little time for the growth of crystals. Sometimes, a residual portion of the matrix fails to crystallize at all, instead becoming a natural glass or obsidian.
If the magma contains abundant volatile components which are released as free gas, then it may cool with large or small vesicles (bubble-shaped cavities) such as in pumice, scoria, or vesicular basalt. Examples of extrusive rocks include basalt, rhyolite, andesite, obsidian and pumice, scoria, and feldspar.Global Volcanism Program
The Smithsonian Institution's Global Volcanism Program (GVP) documents Earth's volcanoes and their eruptive history over the past 10,000 years. The GVP reports on current eruptions from around the world as well as maintaining a database repository on active volcanoes and their eruptions. In this way, a global context for the planet's active volcanism is presented. Smithsonian reporting on current volcanic activity dates back to 1968, with the Center for Short-Lived Phenomena (CSLP). The GVP is housed in the Department of Mineral Sciences, part of the National Museum of Natural History, on the National Mall in Washington, D.C.
During the early stages of an eruption, the GVP acts as a clearing house of reports, data, and imagery which are accumulated from a global network of contributors. The early flow of information is managed such that the right people are contacted as well as helping to sort out vague and contradictory aspects that typically arise during the early days of an eruption.
The Weekly Volcanic Activity Report is a cooperative project between the Smithsonian's Global Volcanism Program and the United States Geological Survey's Volcano Hazards Program. Notices of volcanic activity posted on the report website are preliminary and subject to change as events are studied in more detail. Detailed reports on various volcanoes are published monthly in the Bulletin of the Global Volcanism NetworkThe GVP also documents the last 10,000 years of Earth's volcanism. The historic activity can guide perspectives on possible future events and on volcanoes showing activity. GVP's volcano and eruption databases constitute a foundation for all statistical statements concerning locations, frequencies, and magnitudes of Earth's volcanic eruptions during the past recent 10,000 years.
Two editions of Volcanoes of the World, a regional directory... (1981) and (1994) were published based on the GVP data and interpretations.Igneous petrology
Igneous petrology is the study of igneous rocks—those that are formed from magma. As a branch of geology, igneous petrology is closely related to volcanology, tectonophysics, and petrology in general. The modern study of igneous rocks utilizes a number of techniques, some of them developed in the fields of chemistry, physics, or other earth sciences. Petrography, crystallography, and isotopic studies are common methods used in igneous petrology.Ituxi Vallis
Ituxi Vallis is a valley in the Elysium quadrangle of Mars, located at 25.4° N and 207° W. It is 62 km long and was named after the Ituxi River in Brazil.Magma chamber
A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is under great pressure, and, given enough time, that pressure can gradually fracture the rock around it, creating a way for the magma to move upward. If it finds its way to the surface, then the result will be a volcanic eruption; consequently, many volcanoes are situated over magma chambers.
These chambers are hard to detect deep within the Earth, and therefore most of those known are close to the surface, commonly between 1 km and 10 km down.Philippine Institute of Volcanology and Seismology
The Philippine Institute of Volcanology and Seismology (PHIVOLCS Tagalog pronunciation: [ˈfivolks]; Filipino: Surian ng Pilipinas sa Bulkanolohiya at Sismolohiya) is a Philippine national institution dedicated to provide information on the activities of volcanoes, earthquakes, and tsunamis, as well as other specialized information and services primarily for the protection of life and property and in support of economic, productivity, and sustainable development. It is one of the service agencies of the Department of Science and Technology.
PHIVOLCS monitors volcano, earthquake, and tsunami activity, and issues warnings as necessary. It is mandated to mitigate disasters that may arise from such volcanic eruptions, earthquakes, tsunamis, and other related geotectonic phenomena.Rhyodacite
Rhyodacite is an extrusive volcanic rock intermediate in composition between dacite and rhyolite. It is the extrusive equivalent of granodiorite. Phenocrysts of sodium-rich plagioclase, sanidine, quartz, and biotite or hornblende are typically set in an aphanitic to glassy light to intermediate-colored matrix.
Rhyodacite is a high silica rock containing 20% to 60% quartz with the remaining constituents being mostly feldspar. The feldspar is a mix of alkaline feldspar and plagioclase, with plagioclase forming 35% to 65% of the mix.
Rhyodacite often exists as explosive pyroclastic volcanic deposits.
Rhyodacite lava flows occur, for example, in northwestern Ferry County (Washington), and at An Sgùrr on the island of Eigg in Scotland.Rhyolite
Rhyolite ( RY-ə-lyte, RY-oh-) is an igneous, volcanic rock, of felsic (silica-rich) composition (typically > 69% SiO2 – see the TAS classification). It may have any texture from glassy to aphanitic to porphyritic. The mineral assemblage is usually quartz, sanidine and plagioclase (in a ratio > 2:1 – see the QAPF diagram). Biotite and hornblende are common accessory minerals. It is the extrusive equivalent to granite.Rootless cone
A rootless cone, also formerly called a pseudocrater, is a volcanic landform which resembles a true volcanic crater, but differs in that it is not an actual vent from which lava has erupted. They are characterised by the absence of any magma conduit which connects below the surface of a planet.
Rootless cones are formed by steam explosions as flowing hot lava crosses over a wet surface, such as a swamp, a lake, or a pond. The explosive gases break through the lava surface in a manner similar to a phreatic eruption, and the tephra builds up crater-like forms which can appear very similar to real volcanic craters.
Well known examples are found in Iceland like the craters in the lake Mývatn (Skútustaðagígar), the Rauðhólar in the region of the capital city Reykjavík or the Landbrotshólar located in South-Iceland in the Katla UNESCO Global Geopark in the vicinity of Kirkjubæjarklaustur. Rootless cones have also been discovered in the Athabasca Valles region of Mars, where lava flows superheated groundwater in the underlying rocks.Volcanologists witnessed the formation of a rootless cone for the first time in history during a steam explosion in connection with the first eruption of Eyjafjallajökull in March 2010.Supervolcano
A supervolcano is a large volcano that has had an 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 kilometers (240 cubic miles).
Supervolcanoes occur when magma in the mantle rises into the crust but is unable to break through it and pressure builds in a large and growing magma pool until the crust is unable to contain the pressure. This can occur at hotspots (for example, Yellowstone Caldera) or at subduction zones (for example, Toba). Large-volume supervolcanic eruptions are also often associated with large igneous provinces, which can cover huge areas with lava and volcanic ash. These can cause long-lasting climate change (such as the triggering of a small ice age) and threaten species with extinction. The Oruanui eruption of New Zealand's Taupo Volcano (about 26,500 years ago) was the world's most recent VEI-8 eruption.Volcanic field
A volcanic field is an area of the Earth's crust that is prone to localized volcanic activity. They usually contain 10 to 100 volcanoes such as cinder cones and are usually in clusters. Lava flows may also occur. They may occur as a monogenetic volcanic field or a polygenetic volcanic field.Volcanic glass
Volcanic glass is the amorphous (uncrystallized) product of rapidly cooling magma. Like all types of glass, it is a state of matter intermediate between the close-packed, highly ordered array of a crystal and the highly disordered array of gas. Volcanic glass can refer to the interstitial, or matrix, material in an aphanitic (fine grained) volcanic rock or can refer to any of several types of vitreous igneous rocks. Most commonly, it refers to obsidian, a rhyolitic glass with high silica (SiO2) content.
Other types of volcanic glass include:
Pumice, which is considered a glass because it has no crystal structure.
Apache tears, a kind of nodular obsidian.
Tachylite (also spelled tachylyte), a basaltic glass with relatively low silica content.
Sideromelane, a less common form tachylyte.
Palagonite, a basaltic glass with relatively low silica content.
Hyaloclastite, a hydrated tuff-like breccia of sideromelane and palagonite.
Pele's hair, threads or fibers of volcanic glass, usually basaltic.
Pele's tears, tear-like drops of volcanic glass, usually basaltic.
Limu o Pele (Pele's seaweed), thin sheets and flakes of brownish-green to near-clear volcanic glass, usually basaltic.Volcanologist
A volcanologist or vulcanologist is a geologist who studies the processes involved in the formation and eruptive activity of volcanoes and their current and historic eruptions, known as volcanology. Volcanologists frequently visit volcanoes, especially active ones, to observe volcanic eruptions, collect eruptive products including tephra (such as ash or pumice), rock and lava samples. One major focus of inquiry is the prediction of eruptions; there is currently no accurate way to do this, but predicting eruptions could alleviate the impact on surrounding populations.Volcanology of Italy
Italy is a volcanically active country, containing the only active volcanoes in mainland Europe. The country's volcanism is due chiefly to the presence, a short distance to the south, of the boundary between the Eurasian Plate and the African Plate. The magma erupted by Italy's volcanoes is thought to result from the subduction and melting of one plate below another.
Three main clusters of volcanism exist: a line of volcanic centres running northwest along the central part of the Italian mainland (see: Campanian volcanic arc); a cluster in the northeast of Sicily; and another cluster around the Mediterranean island of Pantelleria.Volcanology of Western Canada
Volcanology of Western Canada includes lava flows, lava plateaus, lava domes, cinder cones, stratovolcanoes, shield volcanoes, greenstone belts, submarine volcanoes, calderas, diatremes and maars, along with examples of more less common volcanic forms such as tuyas and subglacial mounds.