Mount Vesuvius
Mount Vesuvius is a somma–stratovolcano located on the Gulf of Naples in Campania, Italy, about 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 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, erupting molten rock and pulverized pumice at the rate of per second. More than 1,000 people are thought to have died in the eruption, though 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 the danger zone. Eruptions tend to be violent and explosive; these are known as Plinian eruptions.
Mythology
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 Vesuvio indicates that he 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", "from 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 AD 88 suggests that both Venus, patroness of Pompeii, and Hercules were worshipped in the region devastated by the eruption of 79.
Etymology
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 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:
- From Greek οὔ = 'not' prefixed to a root from or related to the Greek word σβέννυμι = 'I quench', in the sense of 'unquenchable'.
- From Greek ἕω = 'I hurl' and βίη 'violence' → 'hurling violence', vesbia, taking advantage of the collateral form.
- From an Indo-European root, eus- < ewes- <, 'shine', 'burn', sense "the one who lightens', through Latin or Oscan.
- From an Indo-European root wes = 'hearth'
Topography
The caldera started forming during an eruption around 17,000–18,000 years ago and 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 at Punta Nasone. The summit of the main cone of Vesuvius is above sea level and more than above the long valley of Atrio di Cavallo.
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.
Formation
Vesuvius is a stratovolcano and was formed as a result of the collision of two tectonic plates, the African and the Eurasian. The former 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 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, and Ischia, a volcanic island to the west, and several undersea volcanoes to the south. The arc forms the southern end of a larger chain of volcanoes produced by 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.
Eruptions
Mount Vesuvius has erupted many times. Numerous others preceded 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 the 18th century, eight times in the 19th century, 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 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, over 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 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 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 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.
Volcanic explosivity index
According to the Smithsonian Institution's Global Volcanism Program, Vesuvius has had 54 confirmed eruptions during the Holocene Epoch. A volcanic explosivity index has been assigned to all but one of these eruptions.Before AD 79
Scientific knowledge of the geologic history of Vesuvius comes from core samples taken from a plus borehole on 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.- 25,000 years ago: Vesuvius started forming in the Codola Plinian eruption.
- Vesuvius was then built up by a series of lava flows, with some smaller explosive eruptions interspersed between them. By this time, the volcano was 2,000 meters tall, with the summit being 500 meters east of the current summit.
- About 19,000 years ago: the style of eruption changed to a sequence of large explosive and caldera-forming Plinian eruptions, of which the AD 79 one was the most recent. The calderas are aligned in a roughly east–west direction, and all contributed to forming present-day's Somma caldera. The eruptions are named after the tephra deposits produced by them, which in turn are named after the place where the deposits were first identified:
- 18,300 years ago: the Basal Pumice eruption, VEI 6, the original formation of the Somma caldera. The caldera's formation was asymmetric towards the west. The eruption was followed by a period of much less violent, lava-producing eruptions.
- 16,000 years ago: the Green Pumice eruption, VEI 5.
- Around 11,000 years ago: the Lagno Amendolare eruption, smaller than the Mercato eruption.
- 8,000 years ago: the Mercato eruption – also known as Pomici Gemelle or Pomici Ottaviano, VEI 6.
- Around 5,000 years ago: two explosive eruptions smaller than the Avellino eruption.
- 3,800 years ago : the Avellino eruption, VEI 6; its vent was apparently west of the current crater and the eruption destroyed several Bronze Age settlements of the Apennine culture, including ancient Afragola. Several carbon dates on wood and bones offer a range of possible dates of about 500 years in the mid-2nd millennium BC. In May 2001, near Nola, Italian archaeologists using the technique of filling every cavity with plaster or substitute compound, recovered some remarkably well-preserved forms of perishable objects, such as fence rails, a bucket and especially in the vicinity, thousands of human footprints pointing into the Apennines to the north. The settlement had huts, pots and goats. The residents had hastily abandoned the village, leaving it to be buried under pumice and ash in much the same way that Pompeii and Herculaneum were later preserved. Pyroclastic surge deposits were distributed to the northwest of the vent, travelling as far as from it, and lie up to deep in the area now occupied by Naples.
- The volcano then entered a stage of more frequent, but less violent eruptions, until the most recent Plinian eruption, which destroyed Pompeii and Herculaneum. Evidence of these eruptions comes from badly preserved ashfall deposits that have been dubitatively assigned to either the Somma-Vesuvius complex, or the Phlegrean fields.
- The last of these may have been in 217 BC. There were earthquakes in Italy during that year and the sun was reported as being dimmed by gray haze or dry fog. Plutarch wrote of the sky being on fire near Naples, and Silius Italicus mentioned in his epic poem Punica that Vesuvius had thundered and produced flames worthy of Mount Etna in that year. However, both authors were writing around 250 years later. Greenland ice core samples of around that period show relatively high acidity, which is assumed to have been caused by atmospheric hydrogen sulfide.
- The volcano was then quiet and was described by Roman writers as having been covered with gardens and vineyards, except at the top, which was craggy. The volcano may have had only one summit at that time, judging by a wall painting, "Bacchus and Vesuvius", found in a Pompeian house, the House of the Centenary.
- The Greek historian Strabo described the mountain in Book V, Chapter 4 of his Geographica as having a predominantly flat, barren summit covered with sooty, ash-coloured rocks, and suggested that it might once have had "craters of fire". He also perceptively suggested that the fertility of the surrounding slopes may be due to volcanic activity, as at Mount Etna.
- In Book II of De architectura, the architect Vitruvius reported that fires had once existed abundantly below the peak and that it had spouted fire onto the surrounding fields. He described Pompeiian pumice as having been burnt from another species of stone.
- Diodorus Siculus, another Greek writer, wrote in Book IV of his Bibliotheca Historica that the Campanian plain was called fiery because of the peak, Vesuvius, which had spouted flames like Etna and showed signs of the fire that had burnt in ancient history.