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103-506: Abbasanta sits on a lava plateau rich in cork oaks , olive trees and lentischi ( mastic trees ). The plateau arose from the lava flow of the Montiferru volcano . The landscape of the lava plateau is characterised by pastures that are enclosed by stone walls that surround the tancas built in the 18th century. In the surrounding countryside, there are still some typical shelters ( pinnete ) made of stones and boughs by

206-419: A continued supply of lava and its pressure on a solidified crust. Most basaltic lavas are of ʻaʻā or pāhoehoe types, rather than block lavas. Underwater, they can form pillow lavas , which are rather similar to entrail-type pahoehoe lavas on land. Ultramafic lavas, such as komatiite and highly magnesian magmas that form boninite , take the composition and temperatures of eruptions to the extreme. All have

309-455: A darker groundmass , including amphibole or pyroxene phenocrysts. Mafic or basaltic lavas are typified by relatively high magnesium oxide and iron oxide content (whose molecular formulas provide the consonants in mafic) and have a silica content limited to a range of 52% to 45%. They generally erupt at temperatures of 1,100 to 1,200 °C (2,010 to 2,190 °F) and at relatively low viscosities, around 10 to 10 cP (10 to 100 Pa⋅s). This

412-494: A detailed description of the AD 79 eruption, including his uncle's death. On occasion, eruptions from Vesuvius have been so large that the whole of southern Europe has been blanketed by ash; in 472 and 1631, Vesuvian ash fell on Constantinople ( Istanbul ), over 1,200 kilometres (750 mi) away. A few times since 1944, landslides in the crater have raised clouds of ash dust, raising false alarms of an eruption. Since 1750, seven of

515-420: A dome forms on an inclined surface it can flow in short thick flows called coulées (dome flows). These flows often travel only a few kilometres from the vent. Lava tubes are formed when a flow of relatively fluid lava cools on the upper surface sufficiently to form a crust. Beneath this crust, which being made of rock is an excellent insulator, the lava can continue to flow as a liquid. When this flow occurs over

618-533: A high-altitude column from which ash and pumice began to fall, blanketing the area. Rescues and escapes occurred during this time. At some time in the night or early the next day, pyroclastic surges in the close vicinity of the volcano began. Lights were seen on the peak, interpreted as fires. People as far away as Misenum fled for their lives. The flows were rapid-moving, dense and very hot, knocking down, wholly or partly, all structures in their path, incinerating or suffocating all population remaining there and altering

721-465: A massive dense core, which is the most active part of the flow. As pasty lava in the core travels downslope, the clinkers are carried along at the surface. At the leading edge of an ʻaʻā flow, however, these cooled fragments tumble down the steep front and are buried by the advancing flow. This produces a layer of lava fragments both at the bottom and top of an ʻaʻā flow. Accretionary lava balls as large as 3 metres (10 feet) are common on ʻaʻā flows. ʻAʻā

824-567: A phonolitic tephrite ). According to the Smithsonian Institution 's Global Volcanism Program , Vesuvius has had 54 confirmed eruptions during the Holocene Epoch (the last 11,700 years). A volcanic explosivity index (VEI) has been assigned to all but one of these eruptions. Scientific knowledge of the geologic history of Vesuvius comes from core samples taken from a 2,000 m (6,600 ft) plus borehole on

927-648: A prolonged period of time the lava conduit can form a tunnel-like aperture or lava tube , which can conduct molten rock many kilometres from the vent without cooling appreciably. Often these lava tubes drain out once the supply of fresh lava has stopped, leaving a considerable length of open tunnel within the lava flow. Lava tubes are known from the modern day eruptions of Kīlauea, and significant, extensive and open lava tubes of Tertiary age are known from North Queensland , Australia , some extending for 15 kilometres (9 miles). Vesuvius Mount Vesuvius ( / v ɪ ˈ s uː v i ə s / viss- OO -vee-əs )

1030-960: A silica content greater than 63%. They include rhyolite and dacite lavas. With such a high silica content, these lavas are extremely viscous, ranging from 10 cP (10 Pa⋅s) for hot rhyolite lava at 1,200 °C (2,190 °F) to 10 cP (10 Pa⋅s) for cool rhyolite lava at 800 °C (1,470 °F). For comparison, water has a viscosity of about 1 cP (0.001 Pa⋅s). Because of this very high viscosity, felsic lavas usually erupt explosively to produce pyroclastic (fragmental) deposits. However, rhyolite lavas occasionally erupt effusively to form lava spines , lava domes or "coulees" (which are thick, short lava flows). The lavas typically fragment as they extrude, producing block lava flows. These often contain obsidian . Felsic magmas can erupt at temperatures as low as 800 °C (1,470 °F). Unusually hot (>950 °C; >1,740 °F) rhyolite lavas, however, may flow for distances of many tens of kilometres, such as in

1133-450: A silica content under 45%. Komatiites contain over 18% magnesium oxide and are thought to have erupted at temperatures of 1,600 °C (2,910 °F). At this temperature there is practically no polymerization of the mineral compounds, creating a highly mobile liquid. Viscosities of komatiite magmas are thought to have been as low as 100 to 1000 cP (0.1 to 1 Pa⋅s), similar to that of light motor oil. Most ultramafic lavas are no younger than

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1236-441: A similar manner to ʻaʻā flows but their more viscous nature causes the surface to be covered in smooth-sided angular fragments (blocks) of solidified lava instead of clinkers. As with ʻaʻā flows, the molten interior of the flow, which is kept insulated by the solidified blocky surface, advances over the rubble that falls off the flow front. They also move much more slowly downhill and are thicker in depth than ʻaʻā flows. Pillow lava

1339-530: A solid crust that insulates the remaining liquid lava, helping to keep it hot and inviscid enough to continue flowing. The word lava comes from Italian and is probably derived from the Latin word labes , which means a fall or slide. An early use of the word in connection with extrusion of magma from below the surface is found in a short account of the 1737 eruption of Vesuvius , written by Francesco Serao , who described "a flow of fiery lava" as an analogy to

1442-575: A temperature of 1,100 to 1,200 °C (2,010 to 2,190 °F). On the Earth, most lava flows are less than 10 km (6.2 mi) long, but some pāhoehoe flows are more than 50 km (31 mi) long. Some flood basalt flows in the geologic record extend for hundreds of kilometres. The rounded texture makes pāhoehoe a poor radar reflector, and is difficult to see from an orbiting satellite (dark on Magellan picture). Block lava flows are typical of andesitic lavas from stratovolcanoes. They behave in

1545-501: A volcano extrudes silicic lava, it can form an inflation dome or endogenous dome , gradually building up a large, pillow-like structure which cracks, fissures, and may release cooled chunks of rock and rubble. The top and side margins of an inflating lava dome tend to be covered in fragments of rock, breccia and ash. Examples of lava dome eruptions include the Novarupta dome, and successive lava domes of Mount St Helens . When

1648-616: Is a somma – stratovolcano located on the Gulf of Naples in Campania , Italy , about 9 km (5.6 mi) east of Naples and a short distance from the shore. It is one of several volcanoes forming the Campanian volcanic arc . Vesuvius consists of a large cone partially encircled by the steep rim of a summit caldera , resulting from the collapse of an earlier, much higher structure. The eruption of Mount Vesuvius in 79 AD destroyed

1751-447: Is a "humpbacked" peak, consisting of a large cone ( Gran Cono ) partially encircled by the steep rim of a summit caldera caused by the collapse of an earlier (and originally much higher) structure called Mount Somma . The Gran Cono was produced during the A.D. 79 eruption. For this reason, the volcano is also called Somma-Vesuvius or Somma-Vesuvio . The caldera started forming during an eruption around 17,000–18,000 years ago and

1854-402: Is a large subsidence crater, can form in a stratovolcano, if the magma chamber is partially or wholly emptied by large explosive eruptions; the summit cone no longer supports itself and thus collapses in on itself afterwards. Such features may include volcanic crater lakes and lava domes after the event. However, calderas can also form by non-explosive means such as gradual magma subsidence. This

1957-456: Is also often called lava . A lava flow is an outpouring of lava during an effusive eruption . (An explosive eruption , by contrast, produces a mixture of volcanic ash and other fragments called tephra , not lava flows.) The viscosity of most lava is about that of ketchup , roughly 10,000 to 100,000 times that of water. Even so, lava can flow great distances before cooling causes it to solidify, because lava exposed to air quickly develops

2060-403: Is assumed that tephra accumulation exceeding 100 kilograms per square metre (20 lb/sq ft)—at which point people are at risk from collapsing roofs—may extend out as far as Avellino to the east or Salerno to the south-east. Near Naples, this tephra fall hazard is assumed to extend barely past the volcano's slopes to the northwest. The specific areas affected by the ash cloud depend upon

2163-415: Is basaltic lava that has a smooth, billowy, undulating, or ropy surface. These surface features are due to the movement of very fluid lava under a congealing surface crust. The Hawaiian word was introduced as a technical term in geology by Clarence Dutton . A pāhoehoe flow typically advances as a series of small lobes and toes that continually break out from a cooled crust. It also forms lava tubes where

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2266-719: Is concentrated in a thin layer in the toothpaste next to the tube and only there does the toothpaste behave as a fluid. Thixotropic behavior also hinders crystals from settling out of the lava. Once the crystal content reaches about 60%, the lava ceases to behave like a fluid and begins to behave like a solid. Such a mixture of crystals with melted rock is sometimes described as crystal mush . Lava flow speeds vary based primarily on viscosity and slope. In general, lava flows slowly, with typical speeds for Hawaiian basaltic flows of 0.40 km/h (0.25 mph) and maximum speeds of 10 to 48 km/h (6 to 30 mph) on steep slopes. An exceptional speed of 32 to 97 km/h (20 to 60 mph)

2369-546: Is mostly determined by composition but also depends on temperature and shear rate. Lava viscosity determines the kind of volcanic activity that takes place when the lava is erupted. The greater the viscosity, the greater the tendency for eruptions to be explosive rather than effusive. As a result, most lava flows on Earth, Mars, and Venus are composed of basalt lava. On Earth, 90% of lava flows are mafic or ultramafic, with intermediate lava making up 8% of flows and felsic lava making up just 2% of flows. Viscosity also determines

2472-444: Is one of three basic types of flow lava. ʻAʻā is basaltic lava characterized by a rough or rubbly surface composed of broken lava blocks called clinker. The word is Hawaiian meaning "stony rough lava", but also to "burn" or "blaze"; it was introduced as a technical term in geology by Clarence Dutton . The loose, broken, and sharp, spiny surface of an ʻaʻā flow makes hiking difficult and slow. The clinkery surface actually covers

2575-474: Is similar to the viscosity of ketchup , although it is still many orders of magnitude higher than that of water. Mafic lavas tend to produce low-profile shield volcanoes or flood basalts , because the less viscous lava can flow for long distances from the vent. The thickness of a solidified basaltic lava flow, particularly on a low slope, may be much greater than the thickness of the moving molten lava flow at any one time, because basaltic lavas may "inflate" by

2678-454: Is the lava structure typically formed when lava emerges from an underwater volcanic vent or subglacial volcano or a lava flow enters the ocean. The viscous lava gains a solid crust on contact with the water, and this crust cracks and oozes additional large blobs or "pillows" as more lava emerges from the advancing flow. Since water covers the majority of Earth 's surface and most volcanoes are situated near or under bodies of water, pillow lava

2781-409: Is to increase the concentration of dissolved gases (mostly sulfur dioxide and carbon dioxide ) in the remaining liquid magma, making the subsequent eruption more violent. As gas-rich magma approaches the surface during an eruption , the huge drop in internal pressure caused by the reduction in weight of the overlying rock (which drops to zero at the surface) causes the gases to come out of solution,

2884-422: Is typical of many shield volcanoes. Cinder cones and spatter cones are small-scale features formed by lava accumulation around a small vent on a volcanic edifice. Cinder cones are formed from tephra or ash and tuff which is thrown from an explosive vent. Spatter cones are formed by accumulation of molten volcanic slag and cinders ejected in a more liquid form. Another Hawaiian English term derived from

2987-516: Is usually of higher viscosity than pāhoehoe. Pāhoehoe can turn into ʻaʻā if it becomes turbulent from meeting impediments or steep slopes. The sharp, angled texture makes ʻaʻā a strong radar reflector, and can easily be seen from an orbiting satellite (bright on Magellan pictures). ʻAʻā lavas typically erupt at temperatures of 1,050 to 1,150 °C (1,920 to 2,100 °F) or greater. Pāhoehoe (also spelled pahoehoe , from Hawaiian [paːˈhoweˈhowe] meaning "smooth, unbroken lava")

3090-646: Is very common. Because it is formed from viscous molten rock, lava flows and eruptions create distinctive formations, landforms and topographical features from the macroscopic to the microscopic. Volcanoes are the primary landforms built by repeated eruptions of lava and ash over time. They range in shape from shield volcanoes with broad, shallow slopes formed from predominantly effusive eruptions of relatively fluid basaltic lava flows, to steeply-sided stratovolcanoes (also known as composite volcanoes) made of alternating layers of ash and more viscous lava flows typical of intermediate and felsic lavas. A caldera , which

3193-481: The Bay of Naples . A massive black cloud glistering with lightning obscured the early-morning light, a scene Pliny describes as sheet lightning . The cloud obscured Point Misenum near at hand and the island of Capraia ( Capri ) across the bay. Fearing for their lives, the population began to flee the shore along the road. An ash rain fell, causing Pliny to shake it off periodically to avoid being buried. Later that same day,

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3296-494: The Hawaiian language , a kīpuka denotes an elevated area such as a hill, ridge or old lava dome inside or downslope from an area of active volcanism. New lava flows will cover the surrounding land, isolating the kīpuka so that it appears as a (usually) forested island in a barren lava flow. Lava domes are formed by the extrusion of viscous felsic magma. They can form prominent rounded protuberances, such as at Valles Caldera . As

3399-889: The Proterozoic , with a few ultramafic magmas known from the Phanerozoic in Central America that are attributed to a hot mantle plume . No modern komatiite lavas are known, as the Earth's mantle has cooled too much to produce highly magnesian magmas. Some silicate lavas have an elevated content of alkali metal oxides (sodium and potassium), particularly in regions of continental rifting , areas overlying deeply subducted plates , or at intraplate hotspots . Their silica content can range from ultramafic ( nephelinites , basanites and tephrites ) to felsic ( trachytes ). They are more likely to be generated at greater depths in

3502-450: The Roman cities of Pompeii , Herculaneum , Oplontis , Stabiae and other settlements. The eruption ejected a cloud of stones , ash and volcanic gases to a height of 33 km (21 mi), erupting molten rock and pulverized pumice at the rate of 6 × 10 cubic metres (7.8 × 10  cu yd) per second. More than 1,000 people are thought to have died in the eruption, though

3605-591: The Roman Iron Age , the etymology depends to a large degree on the presumption of what language was spoken there at the time. Naples was settled by Greeks, as the name Nea-polis , "New City", testifies. The Oscans , an Italic people, lived in the countryside. The Latins also competed for the occupation of Campania. Etruscan settlements were in the vicinity. Other peoples of unknown provenance are said to have been there at some time by various ancient authors. Some theories about its origin are: Vesuvius

3708-520: The Snake River Plain of the northwestern United States. Intermediate or andesitic lavas contain 52% to 63% silica, and are lower in aluminium and usually somewhat richer in magnesium and iron than felsic lavas. Intermediate lavas form andesite domes and block lavas and may occur on steep composite volcanoes , such as in the Andes . They are also commonly hotter than felsic lavas, in

3811-418: The most abundant elements of the Earth's crust , with smaller quantities of aluminium , calcium , magnesium , iron , sodium , and potassium and minor amounts of many other elements. Petrologists routinely express the composition of a silicate lava in terms of the weight or molar mass fraction of the oxides of the major elements (other than oxygen) present in the lava. The silica component dominates

3914-458: The pilgrims during the religious feasts. Lava Lava is molten or partially molten rock ( magma ) that has been expelled from the interior of a terrestrial planet (such as Earth ) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust , on land or underwater, usually at temperatures from 800 to 1,200 °C (1,470 to 2,190 °F). The volcanic rock resulting from subsequent cooling

4017-400: The shepherds . In the village the stone houses are characteristic. They are low and with few floors, without sheds, but usually with a back courtyard where some space is reserved for the domestic animals. This is a quite common architectural dwelling in an area traditionally involved in sheep farming rather than agriculture. The front room of the house is often a courtyard for chickens, in

4120-484: The subduction process described above, which extends northwest along the length of Italy as far as Monte Amiata in Southern Tuscany . Vesuvius is the only one to have erupted in recent history, although some of the others have erupted within the last few hundred years. Many are either extinct or have not erupted for tens of thousands of years. Mount Vesuvius has erupted many times. Numerous others preceded

4223-535: The thermal energy released by the Hiroshima-Nagasaki bombings . The cities of Pompeii and Herculaneum were destroyed by pyroclastic surges and the ruins buried under tens of metres of tephra . The AD 79 eruption was preceded by a powerful earthquake in 62 , which caused widespread destruction around the Bay of Naples, and particularly to Pompeii. Some of the damage had still not been repaired when

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4326-533: The 18th century (including 1779 and 1794), eight times in the 19th century (notably in 1872), and in 1906, 1929 and 1944. There have been no eruptions since 1944, and none of the eruptions after AD 79 were as large or destructive as the Pompeian one. The eruptions vary greatly in severity but are characterized by explosive outbursts of the kind dubbed Plinian after Pliny the Younger , a Roman writer who published

4429-491: The 200 years preceding the AD 79 eruption describe the mountain as having had a volcanic nature, although Pliny the Elder did not depict the mountain in this way in his Natural History : In AD 79, Vesuvius erupted in one of the most catastrophic eruptions of all time. Historians have learned about the eruption from the eyewitness account of Pliny the Younger , a Roman administrator and poet. Several dates are given in

4532-519: The 5 km (3.1 mi) long valley of Atrio di Cavallo (the northern floor of Monte Somma's caldera). The volcano's slopes are scarred by lava flows, while the rest are heavily vegetated, with scrub and forests at higher altitudes and vineyards lower down. Vesuvius is a stratovolcano and was formed as a result of the collision of two tectonic plates , the African and the Eurasian . The former

4635-486: The Bay of Naples from the volcano, approximately 35 kilometres (22 mi), the elder Pliny launched a rescue fleet and went himself to the rescue of a personal friend. His nephew declined to join the party. One of the nephew's letters relates what he could discover from witnesses of his uncle's experiences. In a second letter, the younger Pliny details his own observations after the departure of his uncle. The two men saw an extraordinarily dense cloud rising rapidly above

4738-408: The Earth's surface, it broke through, thus forming the volcano. The volcano is one of several forming the Campanian volcanic arc . Others include Campi Flegrei , a large caldera a few kilometers to the north-west, Ischia , a volcanic island 20 kilometres (12 mi) to the west, and several undersea volcanoes to the south. The arc forms the southern end of a larger chain of volcanoes produced by

4841-493: The amount of magma expelled in an eruption increases roughly linearly with the interval since the previous one, and at a rate of around 0.001 cubic kilometres (0.00024 cu mi) for each year. This gives an approximate figure of 0.08 cubic kilometres (0.019 cu mi) for an eruption after 80 years of inactivity. Magma sitting in an underground chamber for many years will start to see higher melting point constituents such as olivine crystallizing out. The effect

4944-989: The aspect (thickness relative to lateral extent) of flows, the speed with which flows move, and the surface character of the flows. When highly viscous lavas erupt effusively rather than in their more common explosive form, they almost always erupt as high-aspect flows or domes. These flows take the form of block lava rather than ʻaʻā or pāhoehoe. Obsidian flows are common. Intermediate lavas tend to form steep stratovolcanoes, with alternating beds of lava from effusive eruptions and tephra from explosive eruptions. Mafic lavas form relatively thin flows that can move great distances, forming shield volcanoes with gentle slopes. In addition to melted rock, most lavas contain solid crystals of various minerals, fragments of exotic rocks known as xenoliths , and fragments of previously solidified lava. The crystal content of most lavas gives them thixotropic and shear thinning properties. In other words, most lavas do not behave like Newtonian fluids, in which

5047-404: The centre of which there is the hearth ( Sardinian : su foghile ), used for hanging and drying cured pork meat. Later, fireplaces replaced the hearths. In Roman times, the town, called Ad Medias , was in the territory of the Æchilenenses or Cornenses . The village was built all around the two churches of Santa Amada and Santa Caterina (dedicated to Catherine of Alexandria ). There

5150-446: The circumstances surrounding the eruption. The plan assumes between two weeks and 20 days notice of an eruption and foresees the emergency evacuation of 600,000 people, almost entirely comprising all those living in the zona rossa ("red zone"), i.e. at greatest risk from pyroclastic flows. The evacuation, by train, ferry, car, and bus, is planned to take about seven days, and the evacuees would mostly be sent to other parts of

5253-412: The city. The lowest temperatures were in rooms under collapsed roofs, at approximately 100 °C (212 °F). The only surviving eyewitness account of the event consists of two letters by Pliny the Younger to the historian Tacitus . Pliny the Younger describes, amongst other things, the last days in the life of his uncle, Pliny the Elder . Observing the first volcanic activity from Misenum across

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5356-428: The coast near the foot of the volcano, explaining that her party could only get away by sea and asking for rescue. Pliny ordered the immediate launching of the fleet galleys to the evacuation of the coast. He continued in his light ship to the rescue of Rectina's party. He set off across the bay but, in the shallows on the other side, encountered thick showers of hot cinders, lumps of pumice and pieces of rock. Advised by

5459-425: The column. The eruption alternated between Plinian and Peléan six times. Surges 3 and 4 are believed by the authors to have buried Pompeii. Surges are identified in the deposits by dune and cross-bedding formations, which are not produced by fallout. Another study used the magnetic characteristics of over 200 samples of roof-tile and plaster fragments collected around Pompeii to estimate the equilibrium temperature of

5562-423: The country, rather than to safe areas in the local Campania region, and may have to stay away for several months. However, the dilemma that would face those implementing the plan is when to start this massive evacuation: If it starts too late, thousands could be killed, whereas if it is started too early, the indicators of an eruption may turn out to be a false alarm . In 1984, 40,000 people were evacuated from

5665-411: The crater. Layers of lava , ash , scoria and pumice make up the volcanic peak. Their mineralogy is variable, but generally silica -undersaturated and rich in potassium , with phonolite produced in the more explosive eruptions (e.g. the eruption in 1631 displaying a complete stratigraphic and petrographic description: phonolite was firstly erupted, followed by a tephritic phonolite and finally

5768-587: The danger zone. This is the most densely populated volcanic region in the world. Eruptions tend to be violent and explosive; these are known as Plinian eruptions. Vesuvius has a long historic and literary tradition. It was considered a divinity of the Genius type at the time of the eruption of AD 79: it appears under the inscribed name Vesuvius as a serpent in the decorative frescos of many lararia , or household shrines, surviving from Pompeii . An inscription from Capua to IOVI VESVVIO indicates that he

5871-423: The eruption becoming more frequent over the next four days, but the warnings were not recognized. Reconstructions of the eruption and its effects vary considerably in the details but have the same overall features. The eruption lasted two days. The morning of the first day was perceived as normal by the only eyewitness to leave a surviving document, Pliny the Younger. In the middle of the day, an explosion threw up

5974-548: The eruption in AD 79 in prehistory, including at least three significantly larger; an example is the Avellino eruption around 1800 BC, which engulfed several Bronze Age settlements. Since AD 79, the volcano has also erupted repeatedly, in 172, 203, 222, possibly in 303, 379, 472, 512, 536, 685, 787, around 860, around 900, 968, 991, 999, 1006, 1037, 1049, around 1073, 1139, 1150, and there may have been eruptions in 1270, 1347, and 1500. The volcano erupted again in 1631, six times in

6077-418: The eruption. A cooling lava flow shrinks, and this fractures the flow. Basalt flows show a characteristic pattern of fractures. The uppermost parts of the flow show irregular downward-splaying fractures, while the lower part of the flow shows a very regular pattern of fractures that break the flow into five- or six-sided columns. The irregular upper part of the solidified flow is called the entablature , while

6180-415: The eruptions of Vesuvius have had durations of more than five years; only Mount Etna has had as many long-duration eruptions in the last 270 years. The two most recent eruptions of Vesuvius (1875–1906 and 1913–1944) each lasted more than 30 years. Vesuvius is still regarded as an active volcano, although its current activity produces little more than sulfur-rich steam from vents at the bottom and walls of

6283-430: The exact toll is unknown. The only surviving witness account consists of two letters by Pliny the Younger to the historian Tacitus . Vesuvius has erupted many times since. It is the only volcano on Europe's mainland to have erupted in the last hundred years. It is regarded as one of the most dangerous volcanoes in the world because 3,000,000 people live near enough to be affected by an eruption, with at least 600,000 in

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6386-561: The fabric control surfaces, the engines, the Plexiglas windscreens and the gun turrets of the 340th's B-25 Mitchell medium bombers. Estimates ranged from 78 to 88 aircraft destroyed. The eruption could be seen from Naples. Different perspectives and the damage caused to the local villages were recorded by USAAF photographers and other personnel based nearer to the volcano. Large Vesuvian eruptions which emit volcanic material in quantities of about 1 cubic kilometre (0.24 cu mi),

6489-440: The fields with pillows tied to their heads to protect them from the raining debris. They approached the beach again, but the wind prevented the ships from leaving. Pliny sat down on a sail that had been spread for him and could not rise even with assistance when his friends departed. Though Pliny the Elder died, his friends ultimately escaped by land. In the first letter to Tacitus, Pliny the Younger suggested that his uncle's death

6592-571: The flanks of the volcano, extending into Mesozoic rock. Cores were dated by potassium–argon and argon–argon dating . The area has been subject to volcanic activity for at least 400,000 years; the lowest layer of eruption material from the Somma caldera lies on top of the 40,000-year‑old Campanian ignimbrite produced by the Campi Flegrei complex. The volcanic complex stands on a large, sedimentary plain. Several surviving works written over

6695-654: The flood basalts of South America formed in this manner. Flood basalts typically crystallize little before they cease flowing, and, as a result, flow textures are uncommon in less silicic flows. On the other hand, flow banding is common in felsic flows. The morphology of lava describes its surface form or texture. More fluid basaltic lava flows tend to form flat sheet-like bodies, whereas viscous rhyolite lava flows form knobbly, blocky masses of rock. Lava erupted underwater has its own distinctive characteristics. ʻAʻā (also spelled aa , aʻa , ʻaʻa , and a-aa , and pronounced [ʔəˈʔaː] or / ˈ ɑː ( ʔ ) ɑː / )

6798-517: The flow of water and mud down the flanks of the volcano (a lahar ) after heavy rain . Solidified lava on the Earth's crust is predominantly silicate minerals : mostly feldspars , feldspathoids , olivine , pyroxenes , amphiboles , micas and quartz . Rare nonsilicate lavas can be formed by local melting of nonsilicate mineral deposits or by separation of a magma into immiscible silicate and nonsilicate liquid phases . Silicate lavas are molten mixtures dominated by oxygen and silicon ,

6901-499: The following years, it again became covered with gardens and vineyards as old. Even the inside of the crater was moderately filled with shrubbery. In March 1944, the United States Army Air Forces (USAAF) 340th Bombardment Group was based at Pompeii Airfield near Terzigno , Italy, just a few kilometres from the eastern base of the volcano. The tephra and hot ash from multiple days of the eruption damaged

7004-418: The former seashore by the first surge died of thermal shock. The rest were concentrated in arched chambers at a density of as high as three persons per square metre. As only 85 metres (279 ft) of the coast have been excavated, further casualties may be discovered. Since the eruption of AD 79, Vesuvius has erupted around three dozen times. The volcano became quiescent at the end of the 13th century, and in

7107-490: The helmsman to turn back, he stated, "Fortune favors the brave" and ordered him to continue to Stabiae (about 4.5 km from Pompeii). Pliny the Elder and his party saw what they believed to be flames coming from several parts of the crater. After staying overnight, the party was driven from the building by an accumulation of material, presumably tephra, which threatened to block all egress. They woke Pliny, who had been napping and emitting loud snoring. They elected to take to

7210-497: The icy satellites of the Solar System 's giant planets . The lava's viscosity mostly determines the behavior of lava flows. While the temperature of common silicate lava ranges from about 800 °C (1,470 °F) for felsic lavas to 1,200 °C (2,190 °F) for mafic lavas, its viscosity ranges over seven orders of magnitude, from 10 cP (10 Pa⋅s) for felsic lavas to 10 cP (10 Pa⋅s) for mafic lavas. Lava viscosity

7313-515: The landscape, including the coastline. Additional light tremors accompanied these and a mild tsunami in the Bay of Naples. By late afternoon of the second day, the eruption was over, leaving only haze in the atmosphere through which the sun shone weakly. The latest scientific studies of the ash produced by Vesuvius reveal a multi-phase eruption. The initial major explosion produced a column of ash and pumice ranging between 15 and 30 kilometres (49,000 and 98,000 ft) high, which rained on Pompeii to

7416-404: The lava's chemical composition. This temperature range is similar to the hottest temperatures achievable with a forced air charcoal forge. Lava is most fluid when first erupted, becoming much more viscous as its temperature drops. Lava flows quickly develop an insulating crust of solid rock as a result of radiative loss of heat. Thereafter, the lava cools by a very slow conduction of heat through

7519-610: The lava. Other cations , such as ferrous iron, calcium, and magnesium, bond much more weakly to oxygen and reduce the tendency to polymerize. Partial polymerization makes the lava viscous, so lava high in silica is much more viscous than lava low in silica. Because of the role of silica in determining viscosity and because many other properties of a lava (such as its temperature) are observed to correlate with silica content, silicate lavas are divided into four chemical types based on silica content: felsic , intermediate , mafic , and ultramafic . Felsic or silicic lavas have

7622-464: The lower and upper boundaries. These are described as pipe-stem vesicles or pipe-stem amygdales . Liquids expelled from the cooling crystal mush rise upwards into the still-fluid center of the cooling flow and produce vertical vesicle cylinders . Where these merge towards the top of the flow, they form sheets of vesicular basalt and are sometimes capped with gas cavities that sometimes fill with secondary minerals. The beautiful amethyst geodes found in

7725-467: The lower part that shows columnar jointing is called the colonnade . (The terms are borrowed from Greek temple architecture.) Likewise, regular vertical patterns on the sides of columns, produced by cooling with periodic fracturing, are described as chisel marks . Despite their names, these are natural features produced by cooling, thermal contraction, and fracturing. As lava cools, crystallizing inwards from its edges, it expels gases to form vesicles at

7828-422: The mantle than subalkaline magmas. Olivine nephelinite lavas are both ultramafic and highly alkaline, and are thought to have come from much deeper in the mantle of the Earth than other lavas. Tholeiitic basalt lava Rhyolite lava Some lavas of unusual composition have erupted onto the surface of the Earth. These include: The term "lava" can also be used to refer to molten "ice mixtures" in eruptions on

7931-521: The minimal heat loss maintains a low viscosity. The surface texture of pāhoehoe flows varies widely, displaying all kinds of bizarre shapes often referred to as lava sculpture. With increasing distance from the source, pāhoehoe flows may change into ʻaʻā flows in response to heat loss and consequent increase in viscosity. Experiments suggest that the transition takes place at a temperature between 1,200 and 1,170 °C (2,190 and 2,140 °F), with some dependence on shear rate. Pahoehoe lavas typically have

8034-452: The most recent of which overwhelmed Pompeii and Herculaneum, have happened after periods of inactivity of a few thousand years. Sub-Plinian eruptions producing about 0.1 cubic kilometres (0.024 cu mi), such as those of 472 and 1631, have been more frequent with a few hundred years between them. From the 1631 eruption until 1944, there was a comparatively small eruption every few years, emitting 0.001–0.01 km of magma. For Vesuvius,

8137-453: The mountain which of old spouted forth a huge fire [...] the mountain is called Vesuvius." It was inhabited by giant bandits, "the sons of the Earth. With the gods' assistance, he pacified the region and continued. The facts behind the tradition, if any, remain unknown, as does whether Herculaneum was named after it. An epigram by the poet Martial in 88 AD suggests that both Venus , patroness of Pompeii, and Hercules were worshipped in

8240-427: The peak. This cloud and a request by a messenger for an evacuation by sea prompted the elder Pliny to order rescue operations in which he sailed away to participate. His nephew attempted to resume a normal life, but that night a tremor awoke him and his mother, prompting them to abandon the house for the courtyard. Further tremors near dawn caused the population to abandon the village and caused disastrous wave action in

8343-446: The physical behavior of silicate magmas. Silicon ions in lava strongly bind to four oxygen ions in a tetrahedral arrangement. If an oxygen ion is bound to two silicon ions in the melt, it is described as a bridging oxygen, and lava with many clumps or chains of silicon ions connected by bridging oxygen ions is described as partially polymerized. Aluminium in combination with alkali metal oxides (sodium and potassium) also tends to polymerize

8446-459: The pumice and ash stopped falling, and the sun shone weakly through the cloud, encouraging Pliny and his mother to return to their home and wait for news of Pliny the Elder. Pliny's uncle, Pliny the Elder, was in command of the Roman fleet at Misenum and had meanwhile decided to investigate the phenomenon at close hand in a light vessel. As the ship was preparing to leave the area, a messenger came from his friend Rectina (wife of Tascius ) living on

8549-735: The pyroclastic flow. The magnetic study revealed that on the first day of the eruption a fall of white pumice containing clastic fragments of up to 3 centimetres (1.2 in) fell for several hours. It heated the roof tiles up to 140 °C (284 °F). This period would have been the last opportunity to escape. The collapse of the Plinian columns on the second day caused pyroclastic density currents (PDCs) that devastated Herculaneum and Pompeii. The depositional temperature of these pyroclastic surges reached up to 300 °C (572 °F). Any population remaining in structural refuges could not have escaped, as gases of incinerating temperatures surrounded

8652-440: The range of 850 to 1,100 °C (1,560 to 2,010 °F). Because of their lower silica content and higher eruptive temperatures, they tend to be much less viscous, with a typical viscosity of 3.5 × 10 cP (3,500 Pa⋅s) at 1,200 °C (2,190 °F). This is slightly greater than the viscosity of smooth peanut butter . Intermediate lavas show a greater tendency to form phenocrysts . Higher iron and magnesium tends to manifest as

8755-409: The rate of flow is proportional to the shear stress . Instead, a typical lava is a Bingham fluid , which shows considerable resistance to flow until a stress threshold, called the yield stress, is crossed. This results in plug flow of partially crystalline lava. A familiar example of plug flow is toothpaste squeezed out of a toothpaste tube. The toothpaste comes out as a semisolid plug, because shear

8858-470: The region devastated by the eruption of 79. Vesuvius was a name of the volcano in frequent use by the authors of the late Roman Republic and the early Roman Empire . Its collateral forms were Vesaevus , Vesevus , Vesbius and Vesvius . Writers in ancient Greek used Οὐεσούιον or Οὐεσούιος . Many scholars since then have offered an etymology . Given that peoples of varying ethnicity and language occupied Campania during

8961-625: The rocky crust. For instance, geologists of the United States Geological Survey regularly drilled into the Kilauea Iki lava lake, formed in an eruption in 1959. After three years, the solid surface crust, whose base was at a temperature of 1,065 °C (1,949 °F), was still only 14 m (46 ft) thick, even though the lake was about 100 m (330 ft) deep. Residual liquid was still present at depths of around 80 m (260 ft) nineteen years after

9064-442: The scattered bones of another 100. The remains of about 332 bodies have been found at Herculaneum (300 in arched vaults discovered in 1980). What percentage these numbers are of the total dead or the percentage of the dead to the total number at risk remain unknown. Thirty-eight percent of the 1,044 were found in the ash fall deposits, the majority inside buildings. These are thought to have been killed mainly by roof collapses, with

9167-445: The smaller number of victims found outside of buildings probably being killed by falling roof slates or by larger rocks thrown out by the volcano. The remaining 62% of remains found at Pompeii were in the pyroclastic surge deposits, and thus were probably killed by them – probably from a combination of suffocation from inhaling ashes and blast and debris thrown around. Examination of cloth, frescoes and skeletons shows that, in contrast to

9270-478: The southeast but not on Herculaneum upwind. The chief energy supporting the column came from the escape of steam superheated by the magma, created from seawater seeping over time into the deep faults of the region, which interacted with magma. Subsequently, the cloud collapsed as the gases expanded and lost their capability to support their solid contents, releasing it as a pyroclastic surge, which first reached Herculaneum but not Pompeii. Additional blasts reinstituted

9373-414: The surviving copies of the letters. The latest evidence supports earlier findings and indicates that the eruption occurred after 17 October. The volcano ejected a cloud of stones , ashes and volcanic gases to a height of 33 km (21 mi), spewing molten rock and pulverized pumice at the rate of 6 × 10 cubic metres (7.8 × 10  cu yd) per second, ultimately releasing 100,000 times

9476-580: The values of honesty, friendship, fidelity (of the woman), loyalty, parsimony and obedience to the divine will. The whole of the Abbasanta plateau is rich in archaeological sites. Very close to the village is the nuraghe Losa . A country church is set on the site of Sant'Agostino (dedicated to Augustine of Hippo ). Around the rural church, there are some characteristic small houses (in Sardinian language muristenes or cumbessias ) that host

9579-399: The victims found at Herculaneum, it is unlikely that high temperatures were a significant cause of the destruction at Pompeii. Herculaneum, much closer to the crater, was saved from tephra falls by the wind direction but was buried under 23 metres (75 ft) of material deposited by pyroclastic surges. Likely, most of the known victims in this town were killed by the surges. People caught on

9682-485: The volcano erupted. The deaths of 600 sheep from "tainted air" in the vicinity of Pompeii indicates that the earthquake of AD 62 may have been related to new activity by Vesuvius. The Romans grew accustomed to minor earth tremors in the region; the writer Pliny the Younger even wrote that they "were not particularly alarming because they are frequent in Campania". Small earthquakes started taking place four days before

9785-407: The volume of gas increasing explosively from nothing to perhaps many times that of the accompanying magma. Additionally, the removal of the higher melting point material will raise the concentration of felsic components such as silicates , potentially making the magma more viscous , adding to the explosive nature of the eruption. The government emergency plan for an eruption therefore assumes that

9888-429: The worst case will be an eruption of similar size and type to the 1631 VEI 4 eruption. In this scenario, the volcano's slopes, extending out to about 7 kilometres (4.3 mi) from the vent, may be exposed to pyroclastic surges sweeping down them, whilst much of the surrounding area could suffer from tephra falls. Because of prevailing winds , towns and cities south and east of the volcano are most at risk from this. It

9991-463: Was subducted at a convergent boundary beneath the latter, deeper into the earth. As the water-saturated sediments of the African oceanic plate were pushed to hotter depths inside the planet, the water boiled off and lowered the melting point of the upper mantle enough to partially melt the rocks. Because magma is less dense than the solid rock around it, it was pushed upward. Finding a weak spot at

10094-428: Was a clear separation between social classes . Until the 1950s the use of Italian and Sardinian language had distinct and complementary functions. Italian was the official language , used by the public administration , while Sardinian was the language spoken at home and among friends. The characteristic expressions of the dialect are usually inspired by the peasant and pastoral world. Many proverbs refer to

10197-399: Was due to the reaction of his weak lungs to a cloud of poisonous, sulphurous gas that wafted over the group. However, Stabiae was 16 km from the vent (roughly where the modern town of Castellammare di Stabia is situated), and his companions were unaffected by the volcanic gases. It is more likely that the corpulent Pliny died from another cause, such as a stroke or heart attack. His body

10300-492: Was enlarged by later paroxysmal eruptions, ending in the one of AD 79. This structure has given its name to the term " somma volcano ", which describes any volcano with a summit caldera surrounding a newer cone. The cliffs forming the northern ridge of Monte Somma's caldera rim reach a maximum height of 1,132 m (3,714 ft) at Punta Nasone. The summit of the main cone of Vesuvius is 1,281 m (4,203 ft) above sea level and more than 400 m (1,300 ft) above

10403-491: Was found with no apparent injuries the next day, after dispersal of the plume. Along with Pliny the Elder, the only other noble casualties of the eruption to be known by name were Agrippa (a son of the Herodian Jewish princess Drusilla and the procurator Antonius Felix ) and his wife. By 2003, around 1,044 casts made from impressions of bodies in the ash deposits had been recovered in and around Pompeii, with

10506-480: Was recorded following the collapse of a lava lake at Mount Nyiragongo . The scaling relationship for lavas is that the average speed of a flow scales as the square of its thickness divided by its viscosity. This implies that a rhyolite flow would have to be about a thousand times thicker than a basalt flow to flow at a similar speed. The temperature of most types of molten lava ranges from about 800 °C (1,470 °F) to 1,200 °C (2,190 °F) depending on

10609-469: Was worshipped as a power of Jupiter ; that is, Jupiter Vesuvius . The Romans regarded Mount Vesuvius as being devoted to Hercules . The historian Diodorus Siculus relates a tradition that Hercules, in the performance of his labors, passed through the country of nearby Cumae on his way to Sicily and found there a place called "the Phlegraean Plain" ( Φλεγραῖον πεδίον , "fiery"), "from

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