Vesuvius

Mount Vesuvius (in Italian Monte Vesuvio and in Latin Mons Vesuvius) is an active stratovolcano east of Naples, Italy. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting. The two other volcanoes in Italy, (Etna and Stromboli) are located on islands.

Mount Vesuvius is on the coast of the Bay of Naples, about nine kilometres (six miles) east of Naples and a short distance from the shore. It is conspicuous in the beautiful landscape presented by that bay, when seen from the sea, with Naples in the foreground. Mount Vesuvius is best known for its eruption in AD 79 that led to the destruction of the Roman cities of Pompeii and Herculaneum. It has erupted many times since and is today regarded as one of the most dangerous volcanoes in the world because of the population of 3,000,000 people now living close to it and its tendency towards explosive eruptions. It is the most densely populated volcanic region in the world.

Mount Vesuvius was regarded by the Greeks and Romans as being sacred to the hero and demigod Heracles/Hercules and the town of Herculaneum, built at its base, was named after him.

Origin of the name

Some of the theories about the origin of the name Vesuvius include:

• Heracles was a son of the Greek god Zeus and the queen Alcmene of Thebes. Zeus was also known as Huēs (Ὓης) in his aspect as the god of rains and dews. Heracles was thus alternatively known as Huēsou huios (Ὓησου υἱός), "Son of Hues." Transliterating the "ου" as "V" (as is normally done), and the other upsilons (with rough breathing) also by V (rather than the usual "HY") and changing to the Latin nominative ending "us", gives VESVVIVS – Vesuvius.

• From the Oscan word festf which means "smoke".

• From the Proto-Indo-European root ves- = "hearth"[citation needed]

Physical appearance

Vesuvius is a distinctive "humpbacked" mountain, 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 Monte Somma. The Gran Cono was produced during the eruption of AD 79. For this reason, the volcano is also called Somma-Vesuvius or Somma-Vesuvio.

The caldera started forming during an eruption around 17,000 (or 18,300) 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 height of the main cone has been constantly changed by eruptions but presently is 1,281 m (4,202 ft). Monte Somma is 1,149 m (3,770 ft) high, separated from the main cone by the valley of Atrio di Cavallo, which is some 3 miles (5 km) long. The slopes of the mountain are scarred by lava flows but are heavily vegetated, with scrub at higher altitudes and vineyards lower down. Vesuvius is still regarded as an active volcano, although its current activity produces little more than steam from vents at the bottom of the crater. Vesuvius is a stratovolcano at the convergent boundary where the African Plate is being subducted beneath the Eurasian Plate. Its lava is composed of viscous andesite. Layers of lava, scoria, volcanic ash, and pumice make up the mountain.

Formation

Vesuvius was formed as a result of the collision of two tectonic plates, the African and the Eurasian. The former was pushed beneath the latter, deeper into the earth. The crust material became heated until it melted, forming magma, a type of liquid rock. Because magma is less dense than the solid rock around it, it was pushed upward. Finding a weak place at the Earth's surface it broke through, producing the volcano.

The volcano is one of several which form the Campanian volcanic arc. Others include Campi Flegrei, a large caldera a few kilometres to the north west, Mount Epomeo, 20 kilometres (12 mi) to the west on the island of Ischia, 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 within 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. The famous eruption in 79 AD was preceded by numerous others in prehistory, including at least three significantly larger ones, the best known being the Avellino eruption around 1800 BC which engulfed several Bronze Age settlements. Since 79 AD, the volcano has also erupted repeatedly, in 172, 203, 222, possibly 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 (notably in 1872), and in 1906, 1929, and 1944. There has been no eruption since 1944, and none of the post-79 eruptions were as large or destructive.

The eruptions vary greatly in severity but are characterized by explosive outbursts of the kind dubbed Plinian after Pliny the Younger, the Roman writer who observed the AD 79 eruption, during which his uncle, the naturalist Pliny the Elder, watched with him. However, Pliny the Elder died when his boat was trapped at a port when the pumice that was floating in the water pushed his boat and stranded it on the beach. On occasion, the eruptions 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 raised clouds of ash dust, which caused false alarms of an eruption.

Before 79 AD

The mountain started forming 25,000 years ago. Although the area has been subject to volcanic activity for at least 400,000 years, the lowest layer of eruption material from the Somma mountain lies on top of the 34,000 year-old Campanian Ignimbrite produced by the Campi Flegrei complex, and was the product of the Cordola plinian eruption 25,000 years ago.

It was then built up by a series of lava flows, with some smaller explosive eruptions interspersed between them. However, the style of eruption changed around 19,000 years ago to a sequence of large explosive plinian eruptions, of which the AD 79 one was the last. The eruptions are named after the tephra deposits produced by them:

• The Basal Pumice (Pomici di Base) eruption, 18,300 years ago, VEI 6, was probably the most violent of these eruptions and saw the original formation of the Somma caldera. The eruption was followed by a period of much less violent, lava producing eruptions.

• The Green Pumice (Pomici Verdoline) eruption, 16,000 years ago, VEI 5.

• The Mercato eruption also known as Pomici Gemelle or Ottaviano 8,000 years ago, VEI 6, followed a smaller explosive eruption around 11,000 years ago (called the Lagno Amendolare eruption).

• The Avellino eruption (Pomici di Avellino), 1660 BC ± 43 years, VEI 6, followed two smaller explosive eruptions around 5,000 years ago. The Avellino eruption vent was apparently 2 km west of the current crater, and the eruption destroyed several Bronze Age settlements. The remarkably well-preserved remains of one were discovered in May 2001 near Nola by Italian archaeologists, with huts, pots, livestock and even the footprints of animals and people, as well as skeletons. The residents had hastily abandoned the village, leaving it to be buried under pumice and ash in much the same way that Pompeii was later preserved.The eruption was larger than the ones of AD 79 (VEI 5) and 1631 (VEI 4) with pyroclastic surge deposits distributed to the northwest of the vent, the surges travelling as far as 15 km from it, and lie up to 3 m 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.

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 a 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, although 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 mountain was then quiet for hundreds of years and was described by Roman writers as having been covered with gardens and vineyards, except at the top which was craggy. Within a large circle of nearly perpendicular cliffs was a flat space large enough for the encampment of the army of the rebel gladiator Spartacus in 73 BC. This area was doubtless a crater. The mountain may have had only one summit at that time, judging by a wall painting, "Bacchus and Vesuvius", found in a Pompeiian house, the House of the Centenary (Casa del Centenario).

Several surviving works written over 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 Naturalis Historia:

• The Greek historian Strabo (ca 63 BC–AD 24) 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 (ca 80-70 BC -?) reported that fires had once existed abundantly below the mountain and that it had spouted fire onto the surrounding fields. He went on to describe Pompeiian Pumice as having been burnt from another species of stone.

• Diodorus Siculus (ca 90 BC–ca 30 BC), another Greek writer, wrote in Book IV of his Bibliotheca Historica that the Campanian plain was called fiery (Phlegrean) because of the mountain, Vesuvius, which had spouted flame like Etna and showed signs of the fire that had burnt in ancient history.

By AD 79 the area was, as now, densely populated with villages, towns and small cities like Pompeii, and its slopes were covered in vineyards and farms.

Credited to wikipedia