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50-507: The almost circular caldera is a nested structure formed as a result of three separate caldera collapse episodes, each associated with explosive eruptions . These caldera collapse episodes occurred following explosive eruptions that formed the Risco , Bretanha and Santa Barbara pyroclastic fields. The first phase occurred 35,700 years ago, and ceased with the collapse of the principal volcano. A secondary phase began around 28,750 years ago and

100-414: 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 ,

150-466: A key role in volcano explanations until the 16th century after Anaxagoras , in the fifth century BC, had proposed eruptions were caused by a great wind. 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

200-820: 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 SO 2 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. Stratigraphic analyses includes analyzing tephra and lava deposits and dating these to give volcano eruption patterns, with estimated cycles of intense activity and size of eruptions. Compositional analysis has been very successful in

250-417: A phreatic eruption which does not. One mechanism for explosive cryovolcanism is cryomagma making contact with clathrate hydrates . Clathrate hydrates, if exposed to warm temperatures, readily decompose. A 1982 article pointed out the possibility that the production of pressurised gas upon destabilisation of clathrate hydrates making contact with warm rising magma could produce an explosion that breaks through

300-512: A spiteful jealous fight ensued. Some Māori will not to this day live on the direct line between Tongariro and Taranaki for fear of the dispute flaring up again. In the Hawaiian religion , Pele ( / ˈ p eɪ l eɪ / 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

350-481: A tectonic structure aligned in a northwest to southeast orientation following the fault of the Terceira Rift zone. These faults and regional fractures have given way to radial faults resulting in scoria cones and lava domes throughout the serra. The volcano of Sete Cidades is distinguished by two stratigraphic layers: Notes Sources Explosive eruption In volcanology , an explosive eruption

400-468: A variety of all-embracing systems. Volcanic eruptions and earthquakes were generally linked in these systems to the existence of great open caverns under the Earth where inflammable vapours could accumulate until they were ignited. According to Thomas Burnet , much of the Earth itself was inflammable, with pitch, coal and brimstone all ready to burn. In William Whiston 's theory the presence of underground air

450-530: 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 or forecasting eruptions, like predicting earthquakes, could save many lives. In 1841,

500-575: Is a volcanic eruption of the most violent type. A notable example is the 1980 eruption of Mount St. Helens . Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when pressure is suddenly lowered at the vent. Sometimes a lava plug will block the conduit to the summit, and when this occurs, eruptions are more violent. Explosive eruptions can expel as much as 1,000 kg (2,200 lb) per second of rocks, dust, gas and pyroclastic material, averaged over

550-472: Is depressurised. Depressurisation reduces the boiling point of the water, so when depressurised the water suddenly boils. Or it may happen when groundwater is suddenly heated, flashing to steam suddenly. When the water turns into steam, it expands at supersonic speeds, up to 1,700 times its original volume. This can be enough to shatter solid rock, and hurl rock fragments hundreds of metres. A phreatomagmatic eruption contains magmatic material, in contrast to

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600-455: The 1631 eruption of Mount Vesuvius (1632 and later editions) and Francesco Serao 's account of the eruption of Vesuvius in 1737 (1737, with editions in French and English). The 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

650-525: 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,

700-400: The Earth was an animal, and that its internal heat, earthquakes and eruptions were all signs of life. This animistic philosophy was waning by the end of the seventeenth century, but traces continued well into the eighteenth. 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

750-501: The Sete Cidades volcano, resulting in fallout and hydromagmatic eruptions. Location of these eruptions vary, but they generally took on a southerly dispersal. Yet, there is geological evidence for pyroclastic density currents associated with three or four explosive events, but high concentrations of pyroclastic flows are sparse. It may be likely that: The last intra-caldera eruption occurred approximately 500 years A.D., resulting in

800-742: The advance had occurred in another field of science. For example, the study of radioactivity only commenced in 1896, and its application to the theory of plate tectonics and radiometric dating took about 50 years after this. Many other developments in fluid dynamics , experimental physics and chemistry, techniques of mathematical modelling , instrumentation and in other sciences have been applied to volcanology since 1841. 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

850-428: The bubble walls may have time to reform into spherical liquid droplets. The final state of the emulsions depends strongly on the ratio of liquid to gas. Gas-poor magmas end up cooling into rocks with small cavities, becoming vesicular lava . Gas-rich magmas cool to form rocks with cavities that nearly touch, with an average density less than that of water, forming pumice . Meanwhile, other material can be accelerated with

900-530: The burning of sulfur, bitumen and coal. He published his view of this in Mundus Subterraneus with volcanoes acting as a type of safety valve. The causes of these phenomena were discussed in the large number of theories of the Earth that were published in the hundred years after 1650. The authors of these theories were not themselves observers, but combined the observations of others with Newtonian, Cartesian, Biblical or animistic science to produce

950-558: The creation of the Caldeira Seca cone. At the base of the caldera, there exist six Holocene era pyroclastic cones . Further, a large group of Pleistocene post-caldera trachytic lava domes, lava flows, and pyroclastic-flow deposits have been discovered on the northwestern flanks of the massif. Along historical eruptions have generally been basaltic in quality, with effusive characteristics that were less explosive, but generally Hawaiian or Strombolian in nature, occurring along

1000-509: 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

1050-405: The duration of eruption, that travels at several hundred meters per second as high as 20 km (12 mi) into the atmosphere. This cloud may subsequently collapse, creating a fast-moving pyroclastic flow of hot volcanic matter. Viscous magmas cool beneath the surface before they erupt. As they do this, bubbles exsolve from the magma. Because the magma is viscous, the bubbles remain trapped in

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1100-464: 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

1150-416: The eruption progresses, a chain reaction causes the magma to be ejected at higher and higher speeds. The violently expanding gas disperses and breaks up magma, forming an emulsion of gas and magma called volcanic ash . The cooling of the gas in the ash as it expands chills the magma fragments, often forming tiny glass shards recognisable as portions of the walls of former liquid bubbles. In more fluid magmas

1200-592: The first volcanological observatory, the Vesuvius Observatory , was founded in the Kingdom of the Two Sicilies . Volcanology advances have required more than just structured observation, and the science relies upon the understanding and integration of knowledge in many fields including geology , tectonics , physics , chemistry and mathematics , with many advances only being able to occur after

1250-495: 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

1300-471: The flanks of the crater and conditioned by regional and radial faults. Unlike Furnas , Sete Cidades has no active fumaroles , and most secondary manifestations occur in the submarine vents off the coast of Ponta da Ferraria and the coast of Mosteiros, as well as zones of natural degasification. The most recent historical eruption dates back to the 15th century; Sete Cidades has not erupted historically, although an eruption may have occurred immediately prior to

1350-447: The flow's path, including wood, vegetation, and buildings. Alternately, when an eruption has contact with snow, crater lakes, or wet soil in large amounts, water mixing into the flow can create lahars , which pose significant known risks worldwide. An explosive eruption is usually triggered by exsolution of volatiles but there are other ways to create an explosive eruption. A phreatic eruption can occur when hot water under pressure

1400-485: The fracture, creating a plume. This is thought to be partially responsible for Enceladus's ice plumes. Volcanology 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

1450-599: The gas, becoming volcanic bombs. These can travel with so much energy that large ones can create craters when they hit the ground. When an emulsion of volcanic gas and magma falls back to the ground, it can create a density current called a pyroclastic flow. The emulsion is somewhat fluidised by the gas, allowing it to spread. These can often climb over obstacles, and devastate human life. Earthly pyroclastic flows can travel at up to 80 km (50 mi) per hour and reach temperatures of 200 to 700 °C (392 to 1,292 °F). The high temperatures can burn flammable materials in

1500-468: The geomorphological forms in this region, as does a rift zone characterized by abundant scoria cones extending to the southeast from the caldera. This rift zone is uncharacteristically 200 metres (660 ft) higher than the crater rim, that it could shield Ponta Delgada from all but pyrcolastic flows associated with any future eruption. The northwestern flank is marked by the Mosteiros Graben,

1550-464: 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,

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1600-426: The grouping of volcanoes by type, origin of magma, including matching of volcanoes to a mantle plume of a particular hotspot , mantle plume melting depths, the history of recycled subducted crust, matching of tephra deposits to each other and to volcanoes of origin, and the understanding the formation and evolution of magma reservoirs, an approach which has now been validated by real time sampling. Some of

1650-418: The island and corresponds to a circular central caldera 6 by 5 kilometres (3.7 mi × 3.1 mi), whose interior is occupied by various lakes and volcanic cones of pumice , lava domes and maars. The depth of the caldera varies between 200 metres (660 ft) in the west to 500 metres (1,600 ft) in the east, although this varies at about 300 metres (980 ft) median. Regional tectonics influence

1700-496: The island's first colonisation, associated with a rift zone immediately southeast of the Sete Cidades Massif. Other eruptions have occurred within the caldera and from submarine vents along the western coast of the island; there have been four Strombolian eruptions and three Surtseyan eruptions in occupied history within a short distance of the shoreline. The Sete Cidades Massif occupies the northwestern portion of

1750-444: The last 5000 years, which makes it the most active in the archipelago. The intra-calderan activity has been essentially marked by trachyte sub- Plinian and Plinian eruptions , with some having hydromagmatic characteristics. These formations date to 35,700 B.C., 28,750 B.C. and 15,740 B.C. Numerous smaller explosive eruptions then occurred between these paroxysmal events. In the last 5000 years, 17 explosive eruptions took place within

1800-547: The magma. As the magma nears the surface, the bubbles and thus the magma increase in volume. The pressure of the magma builds until the blockage is blasted out in an explosive eruption through the weakest point in the cone, usually the crater. (However, in the case of the eruption of Mount St. Helens , the pressure was released on the side of the volcano, rather than the crater. ). The release of pressure causes more gas to exsolve, doing so explosively. The gas may expand at hundreds of metres per second, expanding upward and outward. As

1850-468: 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

1900-479: 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

1950-520: The next initial onset time of an eruption, as it might also address the size of a future eruption, and evolution of an eruption once it has begun. 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

2000-466: The rediscovery of Classical descriptions of them by wtiters like Lucretius and Strabo . Vesuvius, Stromboli and Vulcano provided an opportunity to study the nature of volcanic phenomena. Italian natural philosophers living within reach of these volcanoes wrote long and learned books on the subject: Giovanni Alfonso Borelli 's account of the eruption of Mount Etna in 1669 became a standard source of information, as did Giulio Cesare Recupito's account of

2050-665: The rise of molten rock to the surface. During the Renaissance, observers as Bernard Palissy , Conrad Gessner , and Johannes Kentmann (1518–1568) showed a deep intense interest in the nature, behavior, origin and history of the terrestrial globe. Many theories of volcanic action were framed during the late sixteenth mid-seventeenth centuries. 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. Johannes Kepler considered volcanoes as conduits for

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2100-475: The saint was invoked again for the 1669 Etna eruption and, for an outbreak that was endangering the town of Nicolosi in 1886. The way the saint is invoked and dealt with in Italian folk religion , in a quid pro quo manner, or bargaining approach which is sometimes used in prayerful interactions with saints, has been related (in the tradition of James Frazer ) to earlier pagan beliefs and practices. In 1660

2150-446: The surface, resulting in explosive cryovolcanism. If a fracture reaches the surface of an icy body and the column of rising water is exposed to the near-vacuum of the surface of most icy bodies, it will immediately start to boil, because its vapor pressure is much more than the ambient pressure. Not only that, but any volatiles in the water will exsolve. The combination of these processes will release droplets and vapor, which can rise up

2200-399: 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. The volcanoes of southern Italy attracted naturalists ever since the Renaissance led to

2250-464: The techniques mentioned above, combined with modelling, have proved useful and successful in the forecasting of some eruptions, such as the evacuation of the locality around Mount Pinatubo in 1991 that may have saved 20,000 lives. Short-term forecasts tend to use seismic or multiple monitoring data with long term forecasting involving the study of the previous history of local volcanism. However, volcanology forecasting does not just involve predicting

2300-423: The two authors. Thirteenth century Dominican scholar Restoro d'Arezzo devoted two entire chapters (11.6.4.6 and 11.6.4.7) of his seminal treatise La composizione del mondo colle sue cascioni to the origin of the endogenous energy of the Earth. Restoro maintained that the interior of the Earth was very hot and insisted, following Empedocles , that the Earth had a molten center and that volcanoes erupted through

2350-433: 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

2400-548: 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

2450-466: Was necessary if ignition were to take place, while John Woodward stressed that water was essential. Athanasius Kircher maintained that the caverns and sources of the heat were deep, and reached down towards the centre of the Earth, while other writers, notably Georges Buffon , believed they were relatively superficial, and that volcanic fires were seated well up within the volcanic cone itself. A number of writers, most notably Thomas Robinson, believed that

2500-468: Was responsible for the collapse of the northwest portion of the primitive caldera. Around 15,740 years ago the last phase, marked by the collapse of the northern and northeastern portions of the crater occurred. In each of these formational phases, lapilli fallout (resulted from Plinian eruptions ) and the pyroclastic flow deposits were transformed into ignimbrites , from melting. The Sete Cidades Massif has experienced 17 intra-caldera eruptions within

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