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Mount Vesuvius
Highest point
Elevation	1,281 m (4,203 ft)
Prominence	1,232 m (4,042 ft)

Mount Vesuvius (Italian: Monte Vesuvio, Latin: Mons Vesuvius) is a volcano 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.

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 the Bay of Naples, when seen from the sea, with Naples in the foreground. 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:

• Hercules was son of the god Zeus and Alcmene of Thebes. Zeus was also known as Huēs (Template:Polytonic) in his aspect as the god of rains and dews. Hercules was thus alternatively known as Huēsou huios (Template:Polytonic), "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"

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 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 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 kilometers 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

Vesuvius has erupted many times. The famous eruption in 79 was preceded by numerous others in prehistory, including at least 3 significantly larger ones, the best known being the Avellino eruption around 1800 BC which engulfed several Bronze Age settlements. Since 79, 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 naturalist who observed the 79 eruption, to which his uncle Pliny the Elder possibly fell victim. 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 km away. A few times since 1944, landslides in the crater raised clouds of ash dust, which caused false alarms of an eruption.

Before 79

Eruption of 79

Date of the eruption

Later eruptions

Since the eruption of 79, Vesuvius has erupted around three dozen times. It erupted again in 203, during the lifetime of the historian Cassius Dio. In 472, it ejected such a volume of ash that ashfalls were reported as far away as Constantinople. The eruptions of 512 were so severe that those inhabiting the slopes of Vesuvius were granted exemption from taxes by Theodoric the Great, the Gothic king of Italy. Further eruptions were recorded in 787, 968, 991, 999, 1007 and 1036 with the first recorded lava flows. The volcano became quiescent at the end of the 13th century and in the following years it again became covered with gardens and vineyards as of old. Even the inside of the crater was filled with shrubbery.

Vesuvius entered a new and particularly destructive phase in December 1631, when a major eruption buried many villages under lava flows, killing around 3,000 people. Torrents of boiling water were also ejected, adding to the devastation. Activity thereafter became almost continuous, with relatively severe eruptions occurring in 1660, 1682, 1694, 1698, 1707, 1737, 1760, 1767, 1779, 1794, 1822, 1834, 1839, 1850, 1855, 1861, 1868, 1872, 1906, 1926, 1929, and 1944. The eruption of 1906 was particularly destructive, killing over 100 people and ejecting the most lava ever recorded from a Vesuvian eruption. Its last major eruption as of 2007 came in March 1944, destroying the villages of San Sebastiano al Vesuvio, Massa di Somma, Ottaviano, and part of San Giorgio a Cremano, as well as all 88 planes in a U.S. B-25 bomber group , as World War II continued to rage in Italy.

The volcano has been quiescent ever since. Over the past few centuries, the quiet stages have varied from 18 months to 7½ years, making the current lull in activity the longest in nearly 500 years. While Vesuvius is not thought likely to erupt in the immediate future, the danger posed by future eruptions is seen as very high in light of the volcano's tendency towards sudden extremely violent explosions and the very dense human population on and around the mountain.

The future

Large plinian eruptions which emit magma in quantities of about 1 km³ or more, the most recent of which overwhelmed Pompeii, have happened after periods of inactivity of a few thousand years. Subplinian eruptions producing about 0.1 km³, such as those of 472 and 1631, have been more frequent with a few hundred years between them. Following the 1631 eruption until 1944 every few years saw a comparatively small eruption which emitted 0.001-0.01 km³ of magma. It seems that for Vesuvius the amount of magma expelled in an eruption increases very roughly linearly with the interval since the previous one, and at a rate of around 0.001 km³ for each year. This gives an extremely approximate figure of 0.06 km³ for an eruption after 60 years of inactivity.

Magma sitting in an underground chamber for many years will start to see higher melting point constituents such as olivine crystallising out. The effect is to increase the concentration of dissolved gases (mostly steam 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 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, the volume of gas increasing explosively from nothing to perhaps many times that of the accompanying magma. Additionally, the removal of the lower 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 emergency plan for an eruption therefore assumes that the worst case will be an eruption of similar size and type to the 1631 VEI 4 one. In this scenario the slopes of the mountain, extending out to about 7 kilometres (4.3 miles) from the vent, may be exposed to pyroclastic flows sweeping down them, whilst much of the surrounding area could suffer from tephra falls. Because of prevailing winds, towns to the south and east of the volcano are most at risk from this, and it is assumed that tephra accumulation exceeding 100 kg/m² – 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. Towards Naples, to the north west, this tephra fall hazard is assumed to extend barely past the slopes of the volcano. The specific areas actually affected by the ash cloud will depend upon the particular 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 trains, ferries, cars, and buses is planned to take about seven days, and the evacuees will mostly be sent to other parts of 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, since if it is left too late then many people could be killed, whilst if it is started too early then the precursors of the eruption may turn out to have been a false alarm. In 1984, 40,000 people were evacuated from the Campi Flegrei area, another volcanic complex near Naples, but no eruption occurred.

Ongoing efforts are being made to reduce the population living in the red zone, by demolishing illegally constructed buildings, establishing a national park around the upper flanks of the volcano to prevent the erection of further buildings and by offering financial incentives to people for moving away. The underlying goal is to reduce the time needed to evacuate the area, over the next 20 or 30 years, to two or three days.

The volcano is closely monitored by the Osservatorio Vesuvio in Naples with extensive networks of seismic and gravimetric stations, a combination of a GPS-based geodetic array and satellite-based synthetic aperture radar to measure ground movement, and by local surveys and chemical analyses of gases emitted from fumaroles. All of this is intended to track magma rising underneath the volcano. So far, no magma has been detected within 10 km of the surface, and so the volcano was, in 2001, at worst only in the very early stages of preparing for an eruption. This status has apparently not changed much to date.

Vesuvius today

The area around Vesuvius was officially declared a national park on 5 June 1995. The summit of Vesuvius is open to visitors and there is a small network of paths around the mountain that are maintained by the park authorities on weekends.

There is access by road to within 200 metres of the summit (measured vertically), but thereafter access is on foot only. There is a spiral walkway around the mountain from the road to the crater.

References

1. "Summary of the eruptive history of Mt. Vesuvius". Osservatorio Vesuviano, Italian National Institute of Geophysics and Volcanology. Retrieved 2006-12-08.
2. "The Pomici Di Base Eruption". Osservatorio Vesuviano, Italian National Institute of Geophysics and Volcanology. Retrieved 2006-12-08.
3. Vesuvius, Italy, Volcano World
4. The world's top volcanoes, Scentia
5. ^ "Vesuvius". Global Volcanism. Retrieved 2006-12-08.
6. "Definition of somma volcano". Volcano Live. Retrieved 2006-12-11.
7. Aviation and the effects of Volcano Ash, Federal Aviation Authority
8. ^ Kilburn, Chris & McGuire, Bill (2001). Italian Volcanoes. Terra Publishing. ISBN 1-903544-04-1.{{cite book}}: CS1 maint: multiple names: authors list (link)
9. de Boer, Jelle Zeilinga & Sanders, Donald Theodore (2002). Volcanoes in Human History. Princeton University Press. ISBN 0-691-05081-3.{{cite book}}: CS1 maint: multiple names: authors list (link)
10. "Activity of Vesuvio between 1631 and 1799". Explore Italian Volcanoes. Retrieved 2006-12-09.
11. "Emergency plan (Italian)". Retrieved 2006-12-09.
12. In the shadow of the volcano, UK Guardian newspaper, 16 October 2003
13. ^ "Italians trying to prevent a modern Pompeii". USA Today. 21 October 2003. Retrieved 2006-12-08.
14. "Early Warning of Volcanic eruptions and Earthquakes in the neapolitan area, Campania Region, South Italy" (pdf). Second International Conference on Early Warning, Bonn, Germany, 16-18 October 2003. Retrieved 2007-01-26. {{cite conference}}: Unknown parameter |booktitle= ignored (|book-title= suggested) (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
15. "ESA press release on satellite monitoring of Vesuvius". Retrieved 2007-01-26.
16. "Monitoring of Mount Vesuvius". Osservatorio Vesuviano, Italian National Institute of Geophysics and Volcanology. Retrieved 2006-12-08.
17. "Present level of alert on Vesuvius". Osservatorio Vesuviano, Italian National Institute of Geophysics and Volcanology. Retrieved 2006-12-08.
18. Vesuvius portal website

40°49′14″N 14°25′47″E / 40.82056°N 14.42972°E / 40.82056; 14.42972

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