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Mount Vesuvius

2007 Schools Wikipedia Selection. Related subjects: European Geography

   Mount Vesuvius
   Mt. Vesuvius as seen from Pompeii, which was destroyed in the eruption
   of 79. The active cone is the high peak on the left side; the smaller
   one on the right is part of the Somma caldera wall.
   Elevation 1 281 m as of 1944
   Location Italy
   Coordinates 40°49′N 14°26′E
   Type Stratovolcano
   Age of rock Oldest 25,000 yr
   Last eruption 1944
   Easiest route walk

   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 only other two such 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 A.D. 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.

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

Origin of the name

   There are three theories about the origin of the name Vesuvius:-
     * Hercules was son of the god Zeus and Alcmene of Thebes. Zeus was
       also known as Ves (Ὓης) in his aspect as the god of rains and dews.
       Hercules was thus alternatively known as Vesouvios (Ὓσου υἱός),
       "Son of Ves." This name was corrupted into "Vesuvius".
     * From the Oscan word fesf which means "smoke".
     * From the Proto-Indo-European root ves- = " hearth"

Physical appearance

   View of the [crater] wall of Vesuvius, with Naples in the background
   Enlarge
   View of the [crater] wall of Vesuvius, with Naples in the background

   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 17000 (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, scoriae, ashes, and pumice make up
   the mountain.

Formation

   View of the crater wall of Vesuvius, from a convent in Napoli
   Enlarge
   View of the crater wall of Vesuvius, from a convent in Napoli

   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, becoming pushed deeper into the Earth. The crust material
   became heated until it melted, forming magma, one kind of liquid rock.
   Because magma is less dense than the solid rock around it, it became
   pushed upward, finding a weak place at the Earth's surface. It broke
   through, forming the volcano.

Eruptions

   Vesuvius has erupted repeatedly in recorded history, most famously in
   79 and subsequently in 472, 512, 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. 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, and whose uncle Pliny the
   Elder possibly fell victim to it. On occasion, the eruptions have been
   so large that the whole of southern Europe has been blanketed by ashes;
   in 472 and 1631, Vesuvian ashes 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.

Eruption of 79

   The eruption of Vesuvius in BBC/Discovery Channel's co-production
   Pompeii.
   Enlarge
   The eruption of Vesuvius in BBC/Discovery Channel's co-production
   Pompeii.

   By the 1st century, Pompeii was only one of a number of towns located
   around the base of Mount Vesuvius. The area had a substantial
   population which grew prosperous from the region's renowned
   agricultural fertility. Many of Pompeii's neighboring communities, most
   famously Herculaneum, also suffered damage or destruction during the 79
   eruption, which is thought to have lasted about 19 hours, in which time
   the volcano released about 1 cubic mile (4 cubic kilometres) of ash and
   rock over a wide area to the south and south-east of the crater, with
   about 3 m (10 ft) of tephra falling on Pompeii.The white pumiceous ash
   associated with this eruption was mainly of leucite phonolite
   composition.

Foreshocks

   Outbreak of the Vesuvius. Painting by Norwegian painter I.C. Dahl
   (1826)
   Enlarge
   Outbreak of the Vesuvius. Painting by Norwegian painter I.C. Dahl
   (1826)

   The 79 eruption was preceded by a powerful earthquake seventeen years
   beforehand on 5 February 62, which caused widespread destruction around
   the Bay of Naples, and particularly to Pompeii. Some of the damage had
   still not been repaired when the volcano erupted . However, this may
   have been a tectonic event rather than one associated with the
   re-awakening of the volcano.

   Another smaller earthquake took place in 64; it was recorded by
   Suetonius in his biography of Nero, in De Vita Caesarum, and by Tacitus
   in Book XV of Annales because it took place whilst Nero was in Naples
   performing for the first time in a public theatre. Suetonius recorded
   that the emperor continued singing through the earthquake until he had
   finished his song, whilst Tacitus wrote that the theatre collapsed
   shortly after being evacuated.

   The Romans grew used to minor earth tremors in the region; the writer
   Pliny the Younger writing that they "were not particularly alarming
   because they are frequent in Campania". In early August of 79, springs
   and wells dried up . Small earthquakes started taking place on 20
   August, 79, becoming more frequent over the next four days, but the
   warnings were not recognised (it is worth noting the Romans had no word
   for volcano, and only a hazy concept of other similar mountains like
   Mount Etna, home of Vulcan), and on the afternoon of August 24, a
   catastrophic eruption of the volcano started. The eruption devastated
   the region, burying Pompeii and other settlements. By coincidence it
   was the day after Vulcanalia, the festival of the Roman god of fire.

The Two Plinys

Pliny the Younger

   The only surviving reliable eyewitness account of the event was
   recorded by Pliny the Younger in two letters to the historian Tacitus.
   Observing it from Misenum (approximately 35 km from the volcano) whilst
   his uncle sailed closer, he saw an extraordinarily dense and
   rapidly-rising cloud appearing above the mountain:


   Mount Vesuvius

      I cannot give you a more exact description of its figure, than by
     resembling it to that of an umbrella pine tree; for it shot up to a
    great height in the form of a tall trunk, which spread out at the top
    into a sort of branches. It appeared sometimes bright, and sometimes
    dark and spotted, as it was either more or less filled with earth and
                                  cinders.


   Mount Vesuvius

   This was the eruption column, now estimated to have been more than 32
   km (20 miles) tall.

   After some time he described the cloud rushing down the flanks of the
   mountain and covered everything around it, including the surrounding
   sea. This is known today as a pyroclastic flow, which is a cloud of
   superheated gas, ash, and rock that erupts from a volcano. Geologists
   have used the magnetic characteristics of over 200 volcanic rocks and
   pieces of debris (eg roof tiles) found in Pompeii to estimate the
   temperature of this pyroclastic flow. (When molten rock solidifies,
   magnetic minerals in the rock record the direction of Earth's magnetic
   field. If the material is heated above a certain temperature, known as
   the Curie temperature, the magnetic field may be modified or completely
   reset.) Most of the materials analyzed experienced temperatures between
   240 °C and 340 °C (with a few areas showing lower temperatures of only
   180 °C). This suggests that the ash cloud had a temperature of 850 °C
   when emerging from the mouth of Vesuvius and had cooled to below 350 °C
   by the time it reached the city. It is theorized that turbulence may
   have mixed cool air into the ash cloud. (Cioni, et al., 2004). This is
   now called the Plinian stage of the eruption, named after both the
   younger and elder Plinys.

   Pliny stated that several earth tremors were felt at the time of the
   eruption and were followed by a very violent shaking of the ground. He
   also noted that ash was falling in very thick sheets and the village he
   was in had to be evacuated, and then that the sun was blocked out by
   the eruption and the daylight hours were left in darkness. Also, the
   sea was sucked away and forced back by an "earthquake", a phenomenon
   now called a tsunami.

Pliny the Elder

   Pliny’s uncle Pliny the Elder was in command of the Roman fleet at
   Misenum, on the far side of the bay, and had meanwhile decided to take
   several ships to investigate the phenomenon at close hand. The fleet
   also took on a rescue mission for those at the foot of the volcano
   when, as it was preparing to leave, a messenger arrived from a friend
   of Pliny’s living on the coast near the foot of the volcano imploring
   him to rescue her. He set off across the bay but encountered thick
   showers of hot cinders, lumps of pumice and pieces of rock which,
   altering the shoreline and water depths, blocked his approach to the
   shore and prevented him from landing there. The prevailing southerly
   wind also stopped him landing there, but he continued south under it to
   Stabiae (about 4.5 km from Pompeii) where he landed and took shelter
   with Pomponianus, a friend. Pomponianus had already loaded a ship with
   possessions and prepared to leave, but the wind was against him.

   Pliny and his party saw flames coming from several parts of the
   mountain (probably pyroclastic flows and surges, which would later
   destroy Pompeii and Herculaneum). After staying overnight, the party
   decided to evacuate in spite of the rain of tephra because of the
   continuing violent earth threatening to collapse the building. Pliny,
   Pomponianus and their companions made their way back towards the beach
   with pillows tied on their heads to protect them from the rockfall. By
   this time, there was so much ash in the air that the party could barely
   see through the murk and needed torches and lanterns to find their way.
   They made it to the beach but found the water too violently disturbed
   from the continuous earthquakes for them to escape safely by sea.

   Pliny the Elder collapsed and died, and in the first letter to Tacitus
   his nephew suggested that this was due to the inhalation of poisonous,
   sulphurous gases. However, Stabiae was 16 km from the vent (roughly
   where the modern town of Castellammare di Stabia is) and his companions
   were apparently unaffected by the fumes, and so it is more likely that
   the corpulent Pliny died through a different cause, such as a stroke or
   heart attack. His body was found with no apparent injuries on 26
   August, after the plume had dispersed sufficiently for daylight to
   return.

Casualties from the eruption

   Estimates of the population of Pompeii range from 10,000 to 20,000,
   whilst Herculaneum is thought to have had a population of about 5,000.
   It is not known how many people the eruption killed, although around
   1,150 remains of bodies have been recovered, or casts made of their
   impressions in the ash deposits in and around Pompeii. The remains of
   about 350 bodies have been found at Herculaneum (300 in arched vaults
   discovered in 1980). However these figures must represent a great
   underestimate of the total number of deaths over the region affected by
   the eruption.

   38% of the victims at Pompeii were found in the ash fall deposits; the
   majority inside buildings. These are thought to have been killed mainly
   by roof collapses, with 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. This differs from modern experience,
   since over the last four hundred years only around 4% of victims have
   been killed by ash falls during explosive eruptions. 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 through ash inhalation and blast and debris thrown around.
   In contrast to the victims found at Herculaneum, examination of cloth,
   frescoes and skeletons show that it is unlikely that high temperatures
   were a significant cause.

   Herculaneum, which was much closer to the crater, was saved from tephra
   falls by the wind direction, but was buried under 23 m (75 ft) of
   material deposited by pyroclastic surges. It is likely that most, or
   all, of the victims in this town were killed by the surges,
   particularly given evidence of high temperatures found on the skeletons
   of the victims found in the arched vaults, and the existence of
   carbonised wood in many of the buildings.

   Pompeii and Herculaneum were never rebuilt, although surviving
   townspeople and probably looters did undertake extensive salvage work
   after the destructions. The eruption changed the course of the River
   Sarno and raised the sea beach, so that Pompeii was now neither on the
   river nor adjacent to the coast.

   The towns' locations were eventually forgotten until their accidental
   rediscovery in the 18th century. Vesuvius itself underwent major
   changes — its slopes were denuded of vegetation and its summit had
   changed considerably due to the force of the eruption.

Later eruptions

   An eruption of Vesuvius seen from Portici, by Joseph Wright (ca.
   1774-6)
   Enlarge
   An eruption of Vesuvius seen from Portici, by Joseph Wright (ca.
   1774-6)

   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 2006 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 the light of
   the volcano's tendency towards sudden extremely violent explosions and
   the very dense human population on and around the mountain.

The future

   Depiction of the eruption of Vesuvius in 1822.
   Enlarge
   Depiction of the eruption of Vesuvius in 1822.

   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. Sub-plinian
   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 overlaying 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 one
   (which was VEI 4). 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 barely extend 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 20 days and two weeks 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 geodic 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 crater of Vesuvius
   Enlarge
   The crater of Vesuvius
   The crater of Vesuvius (clearer image)
   Enlarge
   The crater of Vesuvius (clearer image)

   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.

   You can also look around parts of Herculaneum and Pompeii which have
   been uncovered.
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