Mount Vesuvius
Overview
Mount Vesuvius is a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the Gulf of Naples
Gulf of Naples
The Gulf of Naples is a c. 15 km wide gulf located in the south western coast of Italy, . It opens to the west into the Mediterranean Sea. It is bordered on the north by the cities of Naples and Pozzuoli, on the east by Mount Vesuvius, and on the south by the Sorrentine Peninsula and the main...

, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, about 9 kilometres (5.6 mi) east of Naples
Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

 and a short distance from the shore. It is the only volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 on the Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an mainland to have erupted within the last hundred years, although it is not currently erupting. The two other major active volcanoes in Italy, Etna
Mount Etna
Mount Etna is an active stratovolcano on the east coast of Sicily, close to Messina and Catania. It is the tallest active volcano in Europe, currently standing high, though this varies with summit eruptions; the mountain is 21 m higher than it was in 1981.. It is the highest mountain in...

 and Stromboli
Stromboli
Stromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy. It is one of the eight Aeolian Islands, a volcanic arc north of Sicily. This name is a corruption of the Ancient Greek name Strongulē which was given to it...

, are located the islands of Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

 and Stromboli respectively.

Mount Vesuvius is best known for its eruption in AD 79
79
Year 79 was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Vespasianus...

 that led to the burying and destruction of the Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 cities of Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

 and Herculaneum
Herculaneum
Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...

.
Encyclopedia
Mount Vesuvius is a stratovolcano
Stratovolcano
A stratovolcano, also known as a composite volcano, is a tall, conical volcano built up by many layers of hardened lava, tephra, pumice, and volcanic ash. Unlike shield volcanoes, stratovolcanoes are characterized by a steep profile and periodic, explosive eruptions...

 in the Gulf of Naples
Gulf of Naples
The Gulf of Naples is a c. 15 km wide gulf located in the south western coast of Italy, . It opens to the west into the Mediterranean Sea. It is bordered on the north by the cities of Naples and Pozzuoli, on the east by Mount Vesuvius, and on the south by the Sorrentine Peninsula and the main...

, Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

, about 9 kilometres (5.6 mi) east of Naples
Naples
Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

 and a short distance from the shore. It is the only volcano
Volcano
2. Bedrock3. Conduit 4. Base5. Sill6. Dike7. Layers of ash emitted by the volcano8. Flank| 9. Layers of lava emitted by the volcano10. Throat11. Parasitic cone12. Lava flow13. Vent14. Crater15...

 on the Europe
Europe
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

an mainland to have erupted within the last hundred years, although it is not currently erupting. The two other major active volcanoes in Italy, Etna
Mount Etna
Mount Etna is an active stratovolcano on the east coast of Sicily, close to Messina and Catania. It is the tallest active volcano in Europe, currently standing high, though this varies with summit eruptions; the mountain is 21 m higher than it was in 1981.. It is the highest mountain in...

 and Stromboli
Stromboli
Stromboli is a small island in the Tyrrhenian Sea, off the north coast of Sicily, containing one of the three active volcanoes in Italy. It is one of the eight Aeolian Islands, a volcanic arc north of Sicily. This name is a corruption of the Ancient Greek name Strongulē which was given to it...

, are located the islands of Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

 and Stromboli respectively.

Mount Vesuvius is best known for its eruption in AD 79
79
Year 79 was a common year starting on Friday of the Julian calendar. At the time, it was known as the Year of the Consulship of Augustus and Vespasianus...

 that led to the burying and destruction of the Roman
Ancient Rome
Ancient Rome was a thriving civilization that grew on the Italian Peninsula as early as the 8th century BC. Located along the Mediterranean Sea and centered on the city of Rome, it expanded to one of the largest empires in the ancient world....

 cities of Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

 and Herculaneum
Herculaneum
Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...

. They were never rebuilt, although surviving townspeople and probably looters did undertake extensive salvage work after the destructions. The towns' locations were eventually forgotten until their accidental rediscovery in the 18th century.

The eruption also changed the course of the Sarno River
Sarno River
The Sarno, known as Sarnus to the Romans, is a stream that passes through Pompeii to the south of the Italian city of Naples. It is considered the most polluted river in Europe. It flows about 24 km from Mt. Sarno to Naples.-References:...

 and raised the sea beach, so that Pompeii was now neither on the river nor adjacent to the coast. Vesuvius itself underwent major changes – its slopes were denuded of vegetation and its summit changed considerably due to the force of the eruption.
Vesuvius 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 living nearby and its tendency towards explosive (Plinian
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

) eruptions. It is the most densely populated volcanic region in the world.

Mythology

Vesuvius has a long historic and literary tradition. It was considered a divinity of the Genius
Genius (mythology)
In ancient Roman religion, the genius was the individual instance of a general divine nature that is present in every individual person, place or thing.-Nature of the genius:...

 type at the time of the eruption of 79 AD: it appears under the inscribed name Vesuvius as a serpent in the decorative fresco
Fresco
Fresco is any of several related mural painting types, executed on plaster on walls or ceilings. The word fresco comes from the Greek word affresca which derives from the Latin word for "fresh". Frescoes first developed in the ancient world and continued to be popular through the Renaissance...

s of many lararia, or household shrines, surviving from Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

. An inscription from Capua
Capua
Capua is a city and comune in the province of Caserta, Campania, southern Italy, situated 25 km north of Naples, on the northeastern edge of the Campanian plain. Ancient Capua was situated where Santa Maria Capua Vetere is now...

 to IOVI VESVVIO indicates that he was worshipped as a power of Jupiter
Jupiter (mythology)
In ancient Roman religion and myth, Jupiter or Jove is the king of the gods, and the god of the sky and thunder. He is the equivalent of Zeus in the Greek pantheon....

; that is, Jupiter Vesuvius.

The historian Diodorus Siculus
Diodorus Siculus
Diodorus Siculus was a Greek historian who flourished between 60 and 30 BC. According to Diodorus' own work, he was born at Agyrium in Sicily . With one exception, antiquity affords no further information about Diodorus' life and doings beyond what is to be found in his own work, Bibliotheca...

 relates a tradition that Hercules
Hercules
Hercules is the Roman name for Greek demigod Heracles, son of Zeus , and the mortal Alcmene...

, in the performance of his labors, passed through the country of nearby Cumae
Cumae
Cumae is an ancient Greek settlement lying to the northwest of Naples in the Italian region of Campania. Cumae was the first Greek colony on the mainland of Italy , and the seat of the Cumaean Sibyl...

 on his way to Sicily
Sicily
Sicily is a region of Italy, and is the largest island in the Mediterranean Sea. Along with the surrounding minor islands, it constitutes an autonomous region of Italy, the Regione Autonoma Siciliana Sicily has a rich and unique culture, especially with regard to the arts, music, literature,...

 and found there a place called "the Phlegraean Plain" (phlegraion pedion, "plain of fire"), "from a hill which anciently vomited out fire ... now called Vesuvius." It was inhabited by bandits, "the sons of the Earth," who were giants. With the assistance of the gods he pacified the region and went on. The facts behind the tradition, if any, remain unknown, as does whether Herculaneum
Herculaneum
Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...

 was named after it. An epigram
Epigram
An epigram is a brief, interesting, usually memorable and sometimes surprising statement. Derived from the epigramma "inscription" from ἐπιγράφειν epigraphein "to write on inscribe", this literary device has been employed for over two millennia....

 by the poet Martial
Martial
Marcus Valerius Martialis , was a Latin poet from Hispania best known for his twelve books of Epigrams, published in Rome between AD 86 and 103, during the reigns of the emperors Domitian, Nerva and Trajan...

 in 88 AD suggests that both Venus
Venus (mythology)
Venus is a Roman goddess principally associated with love, beauty, sex,sexual seduction and fertility, who played a key role in many Roman religious festivals and myths...

, patroness of Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

, and Hercules were worshipped in the region devastated by the eruption of 79. Whether Hercules was ever considered some sort of patron of the volcano itself is debatable.

Origin of the name

Vesuvius was a name of the volcano in frequent use by the authors of the late Roman Republic
Roman Republic
The Roman Republic was the period of the ancient Roman civilization where the government operated as a republic. It began with the overthrow of the Roman monarchy, traditionally dated around 508 BC, and its replacement by a government headed by two consuls, elected annually by the citizens and...

 and the early Roman Empire
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

. Its collateral forms
Synonym
Synonyms are different words with almost identical or similar meanings. Words that are synonyms are said to be synonymous, and the state of being a synonym is called synonymy. The word comes from Ancient Greek syn and onoma . The words car and automobile are synonyms...

 were Vesaevus, Vesevus, Vesbius and Vesvius. Writers in ancient Greek used Οὐεσούιον or Οὐεσούιος. Many scholars since then have offered an etymology
Etymology
Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...

. As peoples of varying ethnicity and language occupied Campania
Campania
Campania is a region in southern Italy. The region has a population of around 5.8 million people, making it the second-most-populous region of Italy; its total area of 13,590 km² makes it the most densely populated region in the country...

 in the Roman Iron Age
Roman Iron Age
The Roman Iron Age is the name that Swedish archaeologist Oscar Montelius gave to a part of the Iron Age in Scandinavia, Northern Germany and the Netherlands....

, 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, a native Italic
Italic languages
The Italic subfamily is a member of the Indo-European language family. It includes the Romance languages derived from Latin , and a number of extinct languages of the Italian Peninsula, including Umbrian, Oscan, Faliscan, and Latin.In the past various definitions of "Italic" have prevailed...

 people, lived in the countryside. The Latins also competed for the occupation of Campania. Etruscan
Etruscan civilization
Etruscan civilization is the modern English name given to a civilization of ancient Italy in the area corresponding roughly to Tuscany. The ancient Romans called its creators the Tusci or Etrusci...

 settlements were in the vicinity. Other peoples of unknown provenience are said to have been there at some time by various ancient authors.

On the presumption that the language is Greek, Vesuvius might be a Latinization of the negative οὔ (ve) prefixed to a root from or related to the Greek word σβέννυμι = "I quench", in the sense of "unquenchable". In another derivation it might be from ἕω "hurl" and βίη "violence", "hurling violence", *vesbia, taking advantage of the collateral form.

Some other theories about its origin are:
  • From an Indo-European root, *eus- < *ewes- < *(a)wes-, "shine" sense "the one who lightens", through Latin or
  • From an Indo-European root *wes = "hearth
    Hearth
    In common historic and modern usage, a hearth is a brick- or stone-lined fireplace or oven often used for cooking and/or heating. For centuries, the hearth was considered an integral part of a home, often its central or most important feature...

    " (compare e.g. Vesta
    Vesta (mythology)
    Vesta was the virgin goddess of the hearth, home, and family in Roman religion. Vesta's presence was symbolized by the sacred fire that burned at her hearth and temples...

    )

Physical appearance

Vesuvius is a distinctive "humpbacked" mountain, consisting of a large cone
Volcanic cone
Volcanic cones are among the simplest volcanic formations. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and size of the fragments ejected during the eruption...

 (Gran Cono) partially encircled by the steep rim of a summit caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 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
Somma volcano
A somma volcano is a volcanic caldera that has been partially filled by a new central cone. The name comes from Mount Somma , a stratovolcano in southern Italy with a summit caldera in which the cone of Mount Vesuvius has grown.A number of the world's best examples of somma volcanoes are found on...

", 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 is 1,281 m (4,202 ft) at present. 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 and forest at higher altitudes and vineyard
Vineyard
A vineyard is a plantation of grape-bearing vines, grown mainly for winemaking, but also raisins, table grapes and non-alcoholic grape juice...

s 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
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...

 where the African Plate
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 is being subducted
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 beneath the Eurasian Plate
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

. Layers of lava, scoria
Scoria
Scoria is a volcanic rock containing many holes or vesicles. It is most generally dark in color , and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity...

, volcanic ash
Volcanic ash
Volcanic ash consists of small tephra, which are bits of pulverized rock and glass created by volcanic eruptions, less than in diameter. There are three mechanisms of volcanic ash formation: gas release under decompression causing magmatic eruptions; thermal contraction from chilling on contact...

, and pumice
Pumice
Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

 make up the mountain. Their mineralogy is variable, but generally silica-undersaturated and rich in potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...

, with phonolite
Phonolite
Phonolite is a rare igneous, volcanic rock of intermediate composition, with aphanitic to porphyritic texture....

 produced in the more explosive eruptions.

Formation

Vesuvius was formed as a result of the collision of two tectonic plates, the African
African Plate
The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:...

 and the Eurasian
Eurasian Plate
The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia...

. The former was pushed beneath the latter, deeper into the earth. As the water-saturated sediments of the oceanic African plate were pushed to hotter depths in the earth, the water boiled off and caused the melting point of the upper mantle to drop enough to create partial melting of the rocks. 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
Campanian volcanic arc
The Campanian volcanic arc is a volcanic arc that consists of a number of active, dormant, and extinct volcanoes in the Campania region of Italy. The Campanian volcanic arc centers on the bay of Naples and includes:...

. Others include Campi Flegrei
Campi Flegrei
The Phlegraean Fields, also known as Campi Flegrei, , is a large wide caldera situated to the west of Naples, Italy. It was declared a regional park in 2003. Lying mostly underwater, the area comprises 24 craters and volcanic edifices. Hydrothermal activity can be observed at Lucrino, Agnano and...

, a large caldera
Caldera
A caldera is a cauldron-like volcanic feature usually formed by the collapse of land following a volcanic eruption, such as the one at Yellowstone National Park in the US. They are sometimes confused with volcanic craters...

 a few kilometres to the north west, Mount Epomeo
Mount Epomeo
Mount Epomeo is the highest mountain on the volcanic island of Ischia, in the Gulf of Naples, Italy. Epomeo is believed to be a volcanic horst....

, 20 kilometres (12.4 mi) to the west on the island of Ischia
Ischia
Ischia is a volcanic island in the Tyrrhenian Sea. It lies at the northern end of the Gulf of Naples, about 30 km from the city of Naples. It is the largest of the Phlegrean Islands. Roughly trapezoidal in shape, it measures around 10 km east to west and 7 km north to south and has...

, and several undersea volcanoes to the south. The arc forms the southern end of a larger chain of volcanoes produced by the subduction
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...

 process described above, which extends northwest along the length of Italy as far as Monte Amiata
Monte Amiata
Mount Amiata is the largest of the lava domes in the Amiata lava dome complex located about 20 km NW of Lake Bolsena in the southern Tuscany region of Italy.-Geology:...

 in Southern Tuscany
Tuscany
Tuscany is a region in Italy. It has an area of about 23,000 square kilometres and a population of about 3.75 million inhabitants. The regional capital is Florence ....

. 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
Avellino eruption
The Avellino eruption of Mount Vesuvius refers to a Plinian-type eruption that occurred in the 2nd millennium BC and is estimated to have had a VEI of 6...

 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 as the Pompeian one.

The eruptions vary greatly in severity but are characterized by explosive outbursts of the kind dubbed Plinian
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

 after Pliny the Younger
Pliny the Younger
Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo , better known as Pliny the Younger, was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and educate him...

, 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
Constantinople
Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

 (Istanbul
Istanbul
Istanbul , historically known as Byzantium and Constantinople , is the largest city of Turkey. Istanbul metropolitan province had 13.26 million people living in it as of December, 2010, which is 18% of Turkey's population and the 3rd largest metropolitan area in Europe after London and...

), over 1200 kilometres (745.6 mi) away. A few times since 1944, landslides in the crater have raised clouds of ash dust, raising false alarms of an eruption.

Before AD 79

Scientific knowledge of the geologic history of Vesuvius comes from core sample
Core sample
A core sample is a cylindrical section of a naturally occurring substance. Most core samples are obtained by drilling with special drills into the substance, for example sediment or rock, with a hollow steel tube called a core drill. The hole made for the core sample is called the "core hole". A...

s taken from a 2000 m (6,561.7 ft) plus bore hole on the flanks of the volcano, extending into Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 rock. Cores were dated by potassium-argon and argon-argon dating
Argon-argon dating
Argon-argon dating is a radiometric dating method invented to supersede potassium-argon dating in accuracy. The older method required two samples for dating while the newer method requires only one...

. 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 Campania
Campania
Campania is a region in southern Italy. The region has a population of around 5.8 million people, making it the second-most-populous region of Italy; its total area of 13,590 km² makes it the most densely populated region in the country...

n Ignimbrite
Ignimbrite
An ignimbrite is the deposit of a pyroclastic density current, or pyroclastic flow, a hot suspension of particles and gases that flows rapidly from a volcano, driven by a greater density than the surrounding atmosphere....

 produced by the Campi Flegrei
Campi Flegrei
The Phlegraean Fields, also known as Campi Flegrei, , is a large wide caldera situated to the west of Naples, Italy. It was declared a regional park in 2003. Lying mostly underwater, the area comprises 24 craters and volcanic edifices. Hydrothermal activity can be observed at Lucrino, Agnano and...

 complex, and was the product of the Codola 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, which in turn are named after the location where the deposits were first identified:
  • The Basal Pumice (Pomici di Base) eruption, 18,300 years ago, VEI
    Volcanic Explosivity Index
    The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

     6, 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 (Pomici di Mercato) — also known as Pomici Gemelle or Pomici Ottaviano — 8000 years ago, VEI
    Volcanic Explosivity Index
    The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

     6, followed a smaller explosive eruption around 11,000 years ago (called the Lagno Amendolare eruption).
  • The Avellino eruption
    Avellino eruption
    The Avellino eruption of Mount Vesuvius refers to a Plinian-type eruption that occurred in the 2nd millennium BC and is estimated to have had a VEI of 6...

     (Pomici di Avellino), 3800 years ago, VEI 5, 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
    Bronze Age
    The Bronze Age is a period characterized by the use of copper and its alloy bronze as the chief hard materials in the manufacture of some implements and weapons. Chronologically, it stands between the Stone Age and Iron Age...

     settlements of the Apennine culture
    Apennine culture
    The Apennine culture or Italian Bronze Age is a technology complex of central and southern Italy spanning the Chalcolithic and Bronze Age proper. It is preceded by the Neolithic and succeeded by the Iron Age Villanovan culture. Apennine culture pottery is a black, burnished ware incised and...

    . Several carbon dates on wood and bone offer a range of possible dates of about 500 years in the mid-2nd millennium BC. In May 2001 near Nola
    Nola
    Nola is a city and comune of Campania, southern Italy, in the province of Naples, situated in the plain between Mount Vesuvius and the Apennines...

     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
    Pumice
    Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

     and ash in much the same way that Pompeii was later preserved. Pyroclastic surge
    Pyroclastic surge
    A pyroclastic surge is a fluidized mass of turbulent gas and rock fragments which is ejected during some volcanic eruptions. It is similar to a pyroclastic flow but it has a lower density or contains a much higher proportion of gas to rock ratio, which makes it more turbulent and allows it to rise...

     deposits were distributed to the northwest of the vent, travelling as far as 15 km (9.3 mi) from it, and lie up to 3 m (9.8 ft) 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
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

, which destroyed Pompeii
Pompeii
The city of Pompeii is a partially buried Roman town-city near modern Naples in the Italian region of Campania, in the territory of the comune of Pompei. Along with Herculaneum, Pompeii was destroyed and completely buried during a long catastrophic eruption of the volcano Mount Vesuvius spanning...

.

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
Plutarch
Plutarch then named, on his becoming a Roman citizen, Lucius Mestrius Plutarchus , c. 46 – 120 AD, was a Greek historian, biographer, essayist, and Middle Platonist known primarily for his Parallel Lives and Moralia...

 wrote of the sky being on fire near Naples and Silius Italicus
Silius Italicus
Silius Italicus, in full Tiberius Catius Asconius Silius Italicus , was a Roman consul, orator, and Latin epic poet of the 1st century CE,...

 mentioned in his epic poem Punica
Punica (poem)
The Punica is a Latin epic poem in seventeen books in dactylic hexameter written by Silius Italicus comprising some twelve thousand lines . It is the longest surviving Latin poem from antiquity...

that Vesuvius had thundered and produced flames worthy of Mount Etna
Mount Etna
Mount Etna is an active stratovolcano on the east coast of Sicily, close to Messina and Catania. It is the tallest active volcano in Europe, currently standing high, though this varies with summit eruptions; the mountain is 21 m higher than it was in 1981.. It is the highest mountain in...

 in that year, although both authors were writing around 250 years later. Greenland
Greenland
Greenland is an autonomous country within the Kingdom of Denmark, located between the Arctic and Atlantic Oceans, east of the Canadian Arctic Archipelago. Though physiographically a part of the continent of North America, Greenland has been politically and culturally associated with Europe for...

 ice core
Ice core
An ice core is a core sample that is typically removed from an ice sheet, most commonly from the polar ice caps of Antarctica, Greenland or from high mountain glaciers elsewhere. As the ice forms from the incremental build up of annual layers of snow, lower layers are older than upper, and an ice...

 samples of around that period show relatively high acidity, which is assumed to have been caused by atmospheric hydrogen sulfide
Hydrogen sulfide
Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

.

The mountain was then quiet for hundreds of years and was described by Roman
Roman Empire
The Roman Empire was the post-Republican period of the ancient Roman civilization, characterised by an autocratic form of government and large territorial holdings in Europe and around the Mediterranean....

 writers as having been covered with garden
Garden
A garden is a planned space, usually outdoors, set aside for the display, cultivation, and enjoyment of plants and other forms of nature. The garden can incorporate both natural and man-made materials. The most common form today is known as a residential garden, but the term garden has...

s and vineyard
Vineyard
A vineyard is a plantation of grape-bearing vines, grown mainly for winemaking, but also raisins, table grapes and non-alcoholic grape juice...

s, 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
Spartacus
Spartacus was a famous leader of the slaves in the Third Servile War, a major slave uprising against the Roman Republic. Little is known about Spartacus beyond the events of the war, and surviving historical accounts are sometimes contradictory and may not always be reliable...

 in 73 BC. This area was doubtless a crater
Volcanic crater
A volcanic crater is a circular depression in the ground caused by volcanic activity. It is typically a basin, circular in form within which occurs a vent from which magma erupts as gases, lava, and ejecta. A crater can be of large dimensions, and sometimes of great depth...

. 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
House of the Centenary
The House of the Centenary was the house of a wealthy resident of Pompeii, preserved by the eruption of Mount Vesuvius in 79 AD. The house was discovered in 1879, and was given its modern name to mark the 18th centenary of the disaster...

 (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
    Greece
    Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....

     historian Strabo
    Strabo
    Strabo, also written Strabon was a Greek historian, geographer and philosopher.-Life:Strabo was born to an affluent family from Amaseia in Pontus , a city which he said was situated the approximate equivalent of 75 km from the Black Sea...

     (ca 63 BC–AD 24
    24
    Year 24 was a leap year starting on Saturday of the Julian calendar. At the time, it was known as the Year of the Consulship of Cethegus and Varro...

    ) described the mountain in Book V, Chapter 4 of his Geographica
    Geographica (Strabo)
    The Geographica , or Geography, is a 17-volume encyclopedia of geographical knowledge written in Greek by Strabo, an educated citizen of the Roman empire of Greek descent. Work can have begun on it no earlier than 20 BC...

    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
    De architectura
    ' is a treatise on architecture written by the Roman architect Vitruvius and dedicated to his patron, the emperor Caesar Augustus, as a guide for building projects...

    , the architect
    Architect
    An architect is a person trained in the planning, design and oversight of the construction of buildings. To practice architecture means to offer or render services in connection with the design and construction of a building, or group of buildings and the space within the site surrounding the...

     Vitruvius
    Vitruvius
    Marcus Vitruvius Pollio was a Roman writer, architect and engineer, active in the 1st century BC. He is best known as the author of the multi-volume work De Architectura ....

     (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
    Pumice
    Pumice is a textural term for a volcanic rock that is a solidified frothy lava typically created when super-heated, highly pressurized rock is violently ejected from a volcano. It can be formed when lava and water are mixed. This unusual formation is due to the simultaneous actions of rapid...

     as having been burnt from another species of stone.
  • Diodorus Siculus
    Diodorus Siculus
    Diodorus Siculus was a Greek historian who flourished between 60 and 30 BC. According to Diodorus' own work, he was born at Agyrium in Sicily . With one exception, antiquity affords no further information about Diodorus' life and doings beyond what is to be found in his own work, Bibliotheca...

     (ca 90 BC–ca 30 BC), another Greek writer
    Writer
    A writer is a person who produces literature, such as novels, short stories, plays, screenplays, poetry, or other literary art. Skilled writers are able to use language to portray ideas and images....

    , 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.

Precursors and foreshocks

The AD 79 eruption was preceded by a powerful earthquake
Earthquake
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...


seventeen years beforehand on 5 February, AD 62
62 Pompeii earthquake
The 62 Pompeii earthquake occurred on 5 February. It had an estimated magnitude of between 5 and 6 and a maximum intensity of XI or X on the Mercalli intensity scale. The towns of Pompeii and Herculaneum were severely damaged. The earthquake may have been a precursor to the eruption of Mount...

, 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. The deaths of 600 sheep from "tainted air" in the vicinity of Pompeii reported by Seneca the Younger
Seneca the Younger
Lucius Annaeus Seneca was a Roman Stoic philosopher, statesman, dramatist, and in one work humorist, of the Silver Age of Latin literature. He was tutor and later advisor to emperor Nero...

 leads Haraldur Sigurdsson
Haraldur Sigurdsson
Haraldur Sigurðsson is an Icelandic volcanologist and geochemist. Sigurðsson studied geology and geochemistry in the United Kingdom, where he obtained a Bachelors degree from Queen's University, Belfast, followed by a Ph.D. degree from the University of Durham in 1970...

 to compare them to similar deaths of sheep in Iceland from pools of volcanic carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

 and to speculate that the earthquake of 62 was related to new activity by Vesuvius.

Another smaller earthquake took place in 64 AD; it was recorded by Suetonius
Lives of the Twelve Caesars
De vita Caesarum commonly known as The Twelve Caesars, is a set of twelve biographies of Julius Caesar and the first 11 emperors of the Roman Empire written by Gaius Suetonius Tranquillus.The work, written in AD 121 during the reign of the emperor Hadrian, was the most popular work of Suetonius,...

 in his biography of Nero
Nero
Nero , was Roman Emperor from 54 to 68, and the last in the Julio-Claudian dynasty. Nero was adopted by his great-uncle Claudius to become his heir and successor, and succeeded to the throne in 54 following Claudius' death....

, and by Tacitus
Tacitus
Publius Cornelius Tacitus was a senator and a historian of the Roman Empire. The surviving portions of his two major works—the Annals and the Histories—examine the reigns of the Roman Emperors Tiberius, Claudius, Nero and those who reigned in the Year of the Four Emperors...

 in Annales
Annals (Tacitus)
The Annals by Tacitus is a history of the reigns of the four Roman Emperors succeeding Caesar Augustus. The surviving parts of the Annals extensively cover most of the reigns of Tiberius and Nero. The title Annals was probably not given by Tacitus, but derives from the fact that he treated this...

because it took place while Nero was in Naples performing for the first time in a public theatre
Theatre
Theatre is a collaborative form of fine art that uses live performers to present the experience of a real or imagined event before a live audience in a specific place. The performers may communicate this experience to the audience through combinations of gesture, speech, song, music or dance...

. Suetonius recorded that the emperor continued singing through the earthquake until he had finished his song, while Tacitus wrote that the theatre collapsed shortly after being evacuated.

The Romans grew accustomed to minor earth tremors in the region; the writer
Writer
A writer is a person who produces literature, such as novels, short stories, plays, screenplays, poetry, or other literary art. Skilled writers are able to use language to portray ideas and images....

 Pliny the Younger
Pliny the Younger
Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo , better known as Pliny the Younger, was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and educate him...

 even wrote that they "were not particularly alarming because they are frequent in Campania". Small earthquakes started taking place on 20 August, 79 becoming more frequent over the next four days, but the warnings were not recognised.

Nature of the eruption

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
Pliny the Younger
Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo , better known as Pliny the Younger, was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and educate him...

. In the middle of the day an explosion threw up a high-altitude column from which ash 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 flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

s in the close vicinity of the volcano began. Lights were seen on the mountain 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 the landscape, including the coastline. These were accompanied by additional light tremors and a mild tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

 in the Bay of Naples.

By evening of the second day the eruption was over, leaving only haze in the atmosphere through which the sun shone weakly. Those are the historical facts as far as they can be discovered. Many studies both scientific and speculative have attempted to fill in additional detail, most claiming to be based "on new evidence." Much of this evidence is scientifically cogent, but the authors of the studies present different views. How to reconcile them remains an on-going concern.
Stratigraphic studies

According to a stratigraphic study (a study of the layers of ash) by Sigurdsson, Cashdollar and Sparks
Steve Sparks (volcanologist)
Robert Stephen John Sparks, FRS, CBE , is Chaning Wills Professor of Geology in the Department of Earth Sciences at the University of Bristol. He is one of the world's leading volcanologists and has been widely recognised for his work in this field.-Career:Steve Sparks is a graduate of Imperial...

, published in 1982, and now a standard reference, the eruption of Vesuvius of 79 AD unfolded in two phases: a Plinian eruption
Plinian eruption
Plinian eruptions, also known as 'Vesuvian eruptions', are volcanic eruptions marked by their similarity to the eruption of Mount Vesuvius in AD 79 ....

 that lasted eighteen to twenty hours and produced a rain of pumice southward of the cone that built up to depths of 2.8 metres (9.2 ft) at Pompeii, followed by a pyroclastic flow
Pyroclastic flow
A pyroclastic flow is a fast-moving current of superheated gas and rock , which reaches speeds moving away from a volcano of up to 700 km/h . The flows normally hug the ground and travel downhill, or spread laterally under gravity...

 or nuée ardente in the second, Peléan phase
Pelean eruption
Peléan eruptions are a type of volcanic eruption. They can occur when viscous magma, typically of rhyolitic or andesitic type, is involved, and share some similarities with Vulcanian eruptions. The most important characteristics of a Peléan eruption is the presence of a glowing avalanche of hot...

 that reached as far as Misenum but was concentrated to the west and northwest. Two pyroclastic flows engulfed Pompeii, burning and asphyxiating the stragglers who had remained behind. Oplontis
Oplontis
Oplontis was a town near Pompeii, in the Roman Empire. On August 24, AD 79, the eruption of Mount Vesuvius buried it under a deep layer of ash. It is today the location of the Villa Poppaea, the villa of the wife of Emperor Nero, which was excavated in the mid-20th century and is open to the...

 and Herculaneum
Herculaneum
Herculaneum was an ancient Roman town destroyed by volcanic pyroclastic flows in AD 79, located in the territory of the current commune of Ercolano, in the Italian region of Campania in the shadow of Mt...

 received the brunt of the flows and were buried in fine ash and pyroclastic deposits.

In an article published in 2002 Sigurdsson and Casey elaborate on the stratigraphic evidence based on excavations and surveys up until then. In this interpretation, the quasi-initial explosion (not quite initial) produced a column of ash and pumice ranging between 15 kilometres (49,212.6 ft) and 30 kilometres (98,425.2 ft) high, which, due to northwest winds, rained on Pompeii to the southeast but not on Herculaneum upwind. The eruption is viewed as primarily phreatic
Phreatic eruption
A phreatic eruption, also called a phreatic explosion or ultravulcanian eruption, occurs when rising magma makes contact with ground or surface water. The extreme temperature of the magma causes near-instantaneous evaporation to steam, resulting in an explosion of steam, water, ash, rock, and...

; that is, the chief energy supporting the column came from the escape of steam superheated by the magma, created from ground water seeping over time into the deep faults of the region.

Subsequently the cloud collapsed as the gases expanded and lost their capability to support their solid contents, releasing it as a pyroclastic surge, which reached Herculaneum but not Pompeii. Additional explosions reinstituted the column. The eruption alternated between Plinian and Peléan six times. Surges 3 and 4 are believed by the authors to have destroyed Pompeii. Surges are identified in the deposits by dune and cross-bedding formations, which are not produced by fallout.

The authors suggest that the first ash falls are to be interpreted as early-morning, low-volume explosions not seen from Misenum, causing Rectina to send her messenger on a ride of several hours around the Bay of Naples, then passable, providing an answer to the paradox of how the messenger might miraculously appear at Pliny's villa so shortly after a distant eruption that would have prevented him.
Magnetic studies


A 2006 study by Zanella, Gurioli, Pareschi and Lanza used the magnetic characteristics of over 200 samples of lithic, roof-tile and plaster fragments collected from pyroclastic deposits in and around Pompeii to estimate the equilibrium temperatures of the The deposits were placed by pyroclastic density currents (PDCs) resulting from the collapses of the Plinian column. The authors argue that fragments over 2–5 cm were not in the current long enough to acquire its temperature, which would have been much higher, and therefore they distinguish between the depositional temperatures, which they estimated, and the emplacement temperatures, which in some cases based on the cooling characteristics of some types and fragment sizes of rocks they believed they also could estimate. Final figures are considered to be those of the rocks in the current just before deposition.

All crustal rock contains some iron or iron compounds, rendering it ferromagnetic, as do Roman roof tiles and plaster. These materials may acquire a residual field from a number of sources. When individual molecules, which are magnetic dipole
Magnetic dipole
A magnetic dipole is the limit of either a closed loop of electric current or a pair of poles as the dimensions of the source are reduced to zero while keeping the magnetic moment constant. It is a magnetic analogue of the electric dipole, but the analogy is not complete. In particular, a magnetic...

s, are held in alignment by being bound in a crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...

line structure, the small fields reinforce each other to form the rock's residual field. Heating the material adds internal energy
Internal energy
In thermodynamics, the internal energy is the total energy contained by a thermodynamic system. It is the energy needed to create the system, but excludes the energy to displace the system's surroundings, any energy associated with a move as a whole, or due to external force fields. Internal...

 to it. At the Curie temperature
Curie point
In physics and materials science, the Curie temperature , or Curie point, is the temperature at which a ferromagnetic or a ferrimagnetic material becomes paramagnetic on heating; the effect is reversible. A magnet will lose its magnetism if heated above the Curie temperature...

, the vibration of the molecules is sufficient to disrupt the alignment; the material loses its residual magnetism and assumes whatever magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...

 might be applied to it only for the duration of the application. The authors term this phenomenon unblocking. Residual magnetism is considered to "block out" non-residual fields.

A rock
Rock (geology)
In geology, rock or stone is a naturally occurring solid aggregate of minerals and/or mineraloids.The Earth's outer solid layer, the lithosphere, is made of rock. In general rocks are of three types, namely, igneous, sedimentary, and metamorphic...

 is a mixture of mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...

s, each with its own Curie temperature; the authors therefore looked for a spectrum
Spectrum
A spectrum is a condition that is not limited to a specific set of values but can vary infinitely within a continuum. The word saw its first scientific use within the field of optics to describe the rainbow of colors in visible light when separated using a prism; it has since been applied by...

 of temperatures rather than a single temperature. In the ideal sample, the PDC did not raise the temperature of the fragment beyond the highest blocking temperature. Some constituent material retained the magnetism imposed by the Earth's field when the item was formed. The temperature was raised above the lowest blocking temperature and therefore some minerals on recooling acquired the magnetism of the Earth as it was in 79 AD. The overall field of the sample was the vector sum of the fields of the high-blocking material and the low-blocking material.

This type of sample made possible estimation of the low unblocking temperature. Using special equipment that measured field direction and strength at various temperatures, the experimenters raised the temperature of the sample in increments of from 100 °C (212 °F) until it reached the low unblocking temperature. Deprived of one of its components, the overall field changed direction. A plot of direction at each increment identified the increment at which the sample's resultant magnetism had formed. That was considered to be the equilibrium temperature of the deposit. Considering the data for all the deposits of the surge arrived at a surge deposit estimate. The authors discovered that the city, Pompeii, was a relatively cool spot within a much hotter field, which they attributed to interaction of the surge with the "fabric" of the city.

The investigators reconstruct the sequence of volcanic events as follows. 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 to 120 °C (248 °F) to 140 °C (284 °F). This period would have been the last opportunity to escape. Subsequently a second column deposited a grey pumice with clastics up to 10 cm (3.9 in), temperature unsampled, but presumed to be higher, for 18 hours. These two falls were the Plinian phase. The collapse of the edges of these clouds generated the first dilute PDCs, which must have been devastating to Herculaneum, but did not enter Pompeii.

Early in the morning of the second day the grey cloud began to collapse to a greater degree. Two major surges struck and destroyed Pompeii. Herculaneum and all its population no longer existed. The emplacement temperature range of the first surge was 180 °C (356 °F) to 220 °C (428 °F), minimum temperatures; of the second, 220 °C (428 °F) to 260 °C (500 °F). The depositional temperature of the first was 140 °C (284 °F) to 300 °C (572 °F). Upstream and downstream of the flow it was 300 °C (572 °F) to 360 °C (680 °F).

The variable temperature of the first surge was due to interaction with the buildings. Any population remaining in structural refuges could not have escaped, as the city was surrounded by gases of incinerating temperatures. The lowest temperatures were in rooms under collapsed roofs. These were as low as 100 °C (212 °F), the boiling point of water. The authors suggest that elements of the bottom of the flow were decoupled from the main flow by topographic irregularities and were made cooler by the introduction of ambient turbulent air. In the second surge the irregularities were gone and the city was as hot as the surrounding environment.

During the last surge, which was very dilute, one meter more of deposits fell over the region.

The Two Plinys

The only surviving eyewitness account of the event consists of two letters by Pliny the Younger
Pliny the Younger
Gaius Plinius Caecilius Secundus, born Gaius Caecilius or Gaius Caecilius Cilo , better known as Pliny the Younger, was a lawyer, author, and magistrate of Ancient Rome. Pliny's uncle, Pliny the Elder, helped raise and educate him...

, who was 17 at the time of the eruption, to the historian, Tacitus
Tacitus
Publius Cornelius Tacitus was a senator and a historian of the Roman Empire. The surviving portions of his two major works—the Annals and the Histories—examine the reigns of the Roman Emperors Tiberius, Claudius, Nero and those who reigned in the Year of the Four Emperors...

. Observing the first volcanic activity from Misenum across the Bay of Naples from the volcano, approximately 35 kilometres (21.7 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.
Pliny the Younger

The two men saw an extraordinarily dense cloud rising rapidly above the mountain:
These events and a request by 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, continuing to study, and bathing, but that night a tremor awoke him and his mother, prompting them to abandon the house for the courtyard. At another tremor near dawn the population abandoned the village. After still a third "the sea seemed to roll back upon itself, and to be driven from its banks ...," which is evidence for a tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...

. There is, however, no evidence of extensive damage from wave action.

The early light was obscured by a black cloud through which shone flashes, which Pliny likens to sheet lightening, but more extensive. The cloud obscured Point Misenum near at hand and the island of Capraia (Capri
Capri
Capri is an Italian island in the Tyrrhenian Sea off the Sorrentine Peninsula, on the south side of the Gulf of Naples, in the Campania region of Southern Italy...

) across the bay. Fearing for their lives the population began to call to each other and move back from the coast along the road. Pliny's mother requested him to abandon her and save his own life, as she was too corpulent and aged to go further, but seizing her hand he led her away as best he could. A rain of ash fell. Pliny found it necessary to shake off the ash periodically to avoid being buried. Later that same day the 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. The letter compares the ash to a blanket of snow. Evidently the earthquake and tsunami damage at that location were not severe enough to prevent continued use of the home.
Pliny the Elder

Pliny’s uncle Pliny the Elder
Pliny the Elder
Gaius Plinius Secundus , better known as Pliny the Elder, was a Roman author, naturalist, and natural philosopher, as well as naval and army commander of the early Roman Empire, and personal friend of the emperor Vespasian...

 was in command of the Roman fleet
Roman Navy
The Roman Navy comprised the naval forces of the Ancient Roman state. Although the navy was instrumental in the Roman conquest of the Mediterranean basin, it never enjoyed the prestige of the Roman legions...

 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 Bassus) living on the coast near the foot of the volcano explaining that her party could only get away by sea and asking for rescue. How the messenger escaped remains unexplained. Suddenly grasping the full significance of events, 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 the helmsman to turn back he stated "Fortune favors the brave" and ordered him to continue on to Stabiae
Stabiae
Stabiae was an ancient Roman town, located close to the modern town of Castellammare di Stabia approximately 4.5 km southwest of Pompeii. It was positioned on a 50 m high headland overlooking the Gulf of Naples...

 (about 4.5 km from Pompeii), where Pomponianus was. It is not clear whether he was abandoning the effort to reach Rectina's villa or believed Pompianus was a member of Rectina's party. Pliny does not mention her again. Pomponianus had already loaded a ship with possessions and was preparing to leave, but the same onshore wind that brought Pliny's ship to the location had prevented anyone from leaving.

Pliny and his party saw flames coming from several parts of the mountain, which Pliny and his friends attributed to burning villages. After staying overnight, the party was driven from the building by an accumulation of material, presumably, tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

, which threatened to block all egress. They woke Pliny, who had been napping and emitting loud snoring. They elected to take to the fields with pillows tied to their heads to protect them from rockfall. They approached the beach again but the wind had not changed. Pliny sat down on a sail that had been spread for him and could not rise even with assistance when his friends departed, escaping ultimately by land. Very likely, he had collapsed and died, which is the most popular explanation of why his friends abandoned him, although Suetonius offers an alternative story of his ordering a slave to kill him to avoid the pain of incineration. How the slave would have escaped to tell the tale remains a mystery. There is no mention of such an event in his nephew's letters.

In the first letter to Tacitus his nephew suggested that his death was due to the reaction of his weak lungs to a cloud of poisonous, sulphuric gas that wafted over the group. However, Stabiae was 16 km from the vent (roughly where the modern town of Castellammare di Stabia
Castellammare di Stabia
Castellammare di Stabia is a comune in the province of Naples, Campania region, southern Italy. It is situated on the Bay of Naples about 30 kilometers southeast of Naples, on the route to Sorrento.-History:...

 is situated) and his companions were apparently unaffected by the fumes, and so it is more likely that the corpulent Pliny died from some other cause, such as a stroke
Stroke
A stroke, previously known medically as a cerebrovascular accident , is the rapidly developing loss of brain function due to disturbance in the blood supply to the brain. This can be due to ischemia caused by blockage , or a hemorrhage...

 or heart attack
Myocardial infarction
Myocardial infarction or acute myocardial infarction , commonly known as a heart attack, results from the interruption of blood supply to a part of the heart, causing heart cells to die...

.
An asthmatic attack is also not out of the question. His body was found with no apparent injuries on the next day, after dispersal of the plume.

Casualties from the eruption

Along with Pliny the Elder, the only other noble casualties of the eruption to be known by name were Agrippa (a son of the Jewish princess
Princess
Princess is the feminine form of prince . Most often, the term has been used for the consort of a prince, or his daughters....

 Drusilla
Drusilla (daughter of Agrippa I)
Drusilla was a daughter of Herod Agrippa I and thus sister to Berenice, Mariamne and Herod Agrippa II.-First marriage:She was six years of age at the time of her father's death at Caesarea in 44...

 and the procurator Antonius Felix
Antonius Felix
Marcus Antonius Felix was the Roman procurator of Iudaea Province 52-58, in succession to Ventidius Cumanus.- Life :...

) and his wife.

It is not known how many people the eruption killed. By 2003 around 1,044 casts made from impressions of bodies in the ash deposits had been recovered in and around Pompeii, with 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 completely unknown.

Thirty-eight percent of the 1044 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 metres (75.5 ft) of material deposited by pyroclastic surges. It is likely that most, or all, of the known 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.

These people were all caught on the former seashore by the first surge and died of thermal shock but not of carbonization, although some were partly carbonized by later and hotter surges. Death was not immediate; the remains show some evidence of final agony. The arched vaults were most likely boathouses, as the crossbeams in the overhead were probably for the suspension of boats. No boats have been found, indicating they may have been used for the earlier escape of some of the population. The rest were concentrated in the chambers at a density of as high as 3 persons per square meter. As only 85 metres (278.9 ft) of the coast have been excavated, the casualties waiting to be excavated may well be as high as the thousands.

Date of the eruption

The year of the eruption of AD 79 was referred to by contemporary writers (apart from being described by Pliny) and has never been seriously questioned, being determined by the well-known events of the reign of Titus
Titus
Titus , was Roman Emperor from 79 to 81. A member of the Flavian dynasty, Titus succeeded his father Vespasian upon his death, thus becoming the first Roman Emperor to come to the throne after his own father....

. Vespasian
Vespasian
Vespasian , was Roman Emperor from 69 AD to 79 AD. Vespasian was the founder of the Flavian dynasty, which ruled the Empire for a quarter century. Vespasian was descended from a family of equestrians, who rose into the senatorial rank under the Emperors of the Julio-Claudian dynasty...

 died that year. When Titus visited Pompeii to give orders for the relief of the displaced population, he was the sole ruler. In the year after the eruption, 80 AD, he faced another disaster, a great fire at Rome.

The time of year is stated once in one historical document, the first letter of Pliny the Younger to Tacitus, as which is not a produced meaning and has no syntax (the grammarians say, indeclinable), but would seem to be an abbreviation of a standard date, which was an abbreviation. By 79 the Julian Calendar
Roman calendar
The Roman calendar changed its form several times in the time between the founding of Rome and the fall of the Roman Empire. This article generally discusses the early Roman or pre-Julian calendars...

 was in use. The inscribing of dates was abbreviational and formulaic. Whether anyone knew exactly what the abbreviation stood for is questionable (compare English Mr. and Mrs.); certainly, literary representations such as Pliny's left out or misinterpreted key elements that would be required for the understanding of a produced meaning. Pliny's date (if it was Pliny's) would have been a.d. IX kal. sept., to be interpreted as "the ninth day before the Kalends
Kalends
The Calends , correspond to the first days of each month of the Roman calendar. The Romans assigned these calends to the first day of the month, signifying the start of the new moon cycle...

 of September", which would have been 8 days before Sept. 1, or August 24 (the Romans counted Sept. 1 as one of the nine).

August 24 is not necessarily the date given by Pliny. It represents an editorial collusion to use the text of Codex
Codex
A codex is a book in the format used for modern books, with multiple quires or gatherings typically bound together and given a cover.Developed by the Romans from wooden writing tablets, its gradual replacement...

 Laurentianus Mediceus (a manuscript
Manuscript
A manuscript or handwrite is written information that has been manually created by someone or some people, such as a hand-written letter, as opposed to being printed or reproduced some other way...

), which also appears in the 1508 printed edition of Aldus Manutius
Aldus Manutius
Aldus Pius Manutius , the Latinised name of Aldo Manuzio —sometimes called Aldus Manutius, the Elder to distinguish him from his grandson, Aldus Manutius, the Younger—was an Italian humanist who became a printer and publisher when he founded the Aldine Press at Venice.His publishing legacy includes...

, in all recension
Recension
Recension is the practice of editing or revising a text based on critical analysis. When referring to manuscripts, this may be a revision by another author...

s since then, even though the numerous Pliny manuscripts as well as the works of other authors offer many alternatives. Archaeological dissent from this view began with the work of Carlo Maria Rosini in 1797, to be followed by a succession of archaeologists putting forward evidence to the contrary. Archaeological evidence from Pompeii suggest that the town was buried about two or three months later. For example, people interred in the ashes appear to be wearing warmer clothing than the light summer clothes that would be expected in August. The fresh fruit, olives and vegetables in the shops are typical of October, and conversely the summer fruit that would have been typical of August was already being sold in dried, or conserved form. Wine fermenting jars had been sealed over, and this would have happened around the end of October. The coins found in the purse of a woman buried in the ash include a commemorative coin that should have been minted at the end of September.

A 2007 study by Rolandi, De Lascio and Stefani of 20 years of data concerning wind direction at meteorological stations in Rome and Brindisi
Brindisi
Brindisi is a city in the Apulia region of Italy, the capital of the province of Brindisi, off the coast of the Adriatic Sea.Historically, the city has played an important role in commerce and culture, due to its position on the Italian Peninsula and its natural port on the Adriatic Sea. The city...

 established wind patterns in the Vesuvius area above 14 kilometres (45,931.8 ft) with more precision than was previously known. From June through August the winds blow strongly from the west, for the rest of the time, from the east. This fact was known, but the easterly winds of the eruption were considered anomalous in August, caused (conjecturally) by the weak and shifting winds of the transition. The authors established that the winds of 79 produced long depositional patterns and were therefore not weak, and that the transition occurs in September, not August. The authors therefore reject the August date as being inconsistent with the patterns of nature.

The rejection is not of Pliny's eyewitness account or of Pliny's date, whatever it was. They focus on manuscript variants looking for possible sources of copyist alteration of Pliny's date. In many manuscripts the month has been omitted. If some original had no month then the copyists may have felt obliged to provide one, but chose wrongly. The authors suggest an original date of a.d. IX kal dec (November 23) or a.d. ix kal nov (October 24) more in line with the evidence of nature. This view is currently gaining wide acceptance. In its index of volcanic activity on Earth, the Global Volcanism Program
Global Volcanism Program
The Smithsonian Institution's Global Volcanism Program documents Earth's volcanoes and their eruptive history over the past 10,000 years. The GVP reports on current eruptions from around the world as well as maintaining a database repository on active volcanoes and their eruptions. In this way, a...

 of the Smithsonian Institution
Smithsonian Institution
The Smithsonian Institution is an educational and research institute and associated museum complex, administered and funded by the government of the United States and by funds from its endowment, contributions, and profits from its retail operations, concessions, licensing activities, and magazines...

 takes the view that the eruption did start around October 24 (?), 79 AD and ended on October 28 ±1 day.

Later eruptions from the 3rd to the 19th century

Since the eruption of 79 AD, 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
Constantinople
Constantinople was the capital of the Roman, Eastern Roman, Byzantine, Latin, and Ottoman Empires. Throughout most of the Middle Ages, Constantinople was Europe's largest and wealthiest city.-Names:...

. The eruptions of 512 were so severe that those inhabiting the slopes of Vesuvius were granted exemption from taxes by Theodoric the Great
Theodoric the Great
Theodoric the Great was king of the Ostrogoths , ruler of Italy , regent of the Visigoths , and a viceroy of the Eastern Roman Empire...

, the Gothic
Goths
The Goths were an East Germanic tribe of Scandinavian origin whose two branches, the Visigoths and the Ostrogoths, played an important role in the fall of the Roman Empire and the emergence of Medieval Europe....

 king of Italy. Further eruptions were recorded in 787, 968, 991, 999, 1007 and 1036 with the first recorded lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 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 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.

Eruptions in the 20th century

The eruption of 1906 killed over 100 people and ejected the most lava ever recorded from a Vesuvian eruption.

The last major eruption was in March 1944. It destroyed the villages of San Sebastiano al Vesuvio
San Sebastiano al Vesuvio
San Sebastiano al Vesuvio is a comune in the province of Naples, located on the western slopes of Mount Vesuvius. Its elevation means that it is often a few degrees cooler than the neighbouring metropolis of Naples....

, Massa di Somma
Massa di Somma
Massa di Somma is a comune in the Province of Naples in the Italian region Campania, located about 10 km east of Naples. As of 31 December 2004, it had a population of 5,929 and an area of 3.5 km²....

, Ottaviano
Ottaviano
Ottaviano is a comune in the Province of Naples in the Italian region Campania, located about 20 km east of Naples and is located in the Vesuvian Area. Ottaviano was in Roman times a hamlet of houses within a vast estate belonging to the gens Octavia, Augustus's family...

, and part of San Giorgio a Cremano
San Giorgio a Cremano
San Giorgio a Cremano is a primarily residential town and comune in the province of Naples, in the Campania region of southern Italy. It is located on the foothills of Mount Vesuvius to the west of the volcano, and is six kilometres to the south east of the centre of Naples...

. From 18 March to 23 March 1944, lava flows appeared within the rim. There were outflows. Small explosions then occurred until the major explosion took place on 18 March 1944.

At the time of the eruption, the United States Army Air Force (USAAF) 340th Bombardment Group was based at Pompeii Airfield near Terzigno, Italy, just a few kilometers from the eastern base of the mountain. The tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

 and hot ash damaged the fabric control surfaces, the engines, the Plexiglass windshields and the gun turrets of the 340th's B-25 Mitchell
B-25 Mitchell
The North American B-25 Mitchell was an American twin-engined medium bomber manufactured by North American Aviation. It was used by many Allied air forces, in every theater of World War II, as well as many other air forces after the war ended, and saw service across four decades.The B-25 was named...

 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.

The future

Large plinian eruptions which emit lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...

 in quantities of about 1 cubic kilometre (0.239912758604287 cu mi), the most recent of which overwhelmed Pompeii, have happened after periods of inactivity of a few thousand years. Subplinian eruptions producing about 0.1 cubic kilometre (0.0239912758604287 cu mi), 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 cubic kilometre (0.000239912758604287 cu mi) for each year. This gives an extremely approximate figure of 0.06 cubic kilometre (0.0143947655162572 cu mi) for an eruption after 60 years of inactivity.

Magma sitting in an underground chamber
Magma chamber
A magma chamber is a large underground pool of molten rock found beneath the surface of the Earth. The molten rock in such a chamber is under great pressure, and given enough time, that pressure can gradually fracture the rock around it creating outlets for the magma...

 for many years will start to see higher melting point constituents such as olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....

 crystallising out. The effect is to increase the concentration of dissolved gases (mostly steam
Steam
Steam is the technical term for water vapor, the gaseous phase of water, which is formed when water boils. In common language it is often used to refer to the visible mist of water droplets formed as this water vapor condenses in the presence of cooler air...

 and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...

) 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
Pressure
Pressure is the force per unit area applied in a direction perpendicular to the surface of an object. Gauge pressure is the pressure relative to the local atmospheric or ambient pressure.- Definition :...

 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
Felsic
The word "felsic" is a term used in geology to refer to silicate minerals, magma, and rocks which are enriched in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium....

 components such as silicate
Silicate
A silicate is a compound containing a silicon bearing anion. The great majority of silicates are oxides, but hexafluorosilicate and other anions are also included. This article focuses mainly on the Si-O anions. Silicates comprise the majority of the earth's crust, as well as the other...

s potentially making the magma more viscous, adding to the explosive nature of the eruption.

The government emergency plan for an eruption therefore assumes that the worst case will be an eruption of similar size and type to the 1631 VEI
Volcanic Explosivity Index
The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....

 4 one. In this scenario the slopes of the mountain, extending out to about 7 kilometres (4.3 mi) from the vent, may be exposed to pyroclastic flows sweeping down them, whilst much of the surrounding area could suffer from tephra
Tephra
200px|thumb|right|Tephra horizons in south-central [[Iceland]]. The thick and light coloured layer at center of the photo is [[rhyolitic]] tephra from [[Hekla]]....

 falls. Because of prevailing winds
Prevailing winds
Prevailing winds are winds that blow predominantly from a single general direction over a particular point on Earth's surface. The dominant winds are the trends in direction of wind with the highest speed over a particular point on the Earth's surface. A region's prevailing and dominant 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
Avellino
Avellino is a town and comune, capital of the province of Avellino in the Campania region of southern Italy. It is situated in a plain surrounded by mountains 42 km north-east of Naples and is an important hub on the road from Salerno to Benevento.-History:Before the Roman conquest, the...

 to the east or Salerno
Salerno
Salerno is a city and comune in Campania and is the capital of the province of the same name. It is located on the Gulf of Salerno on the Tyrrhenian Sea....

 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
Emergency evacuation
Emergency evacuation is the immediate and rapid movement of people away from the threat or actual occurrence of a hazard. Examples range from the small scale evacuation of a building due to a bomb threat or fire to the large scale evacuation of a district because of a flood, bombardment or...

 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
Train
A train is a connected series of vehicles for rail transport that move along a track to transport cargo or passengers from one place to another place. The track usually consists of two rails, but might also be a monorail or maglev guideway.Propulsion for the train is provided by a separate...

s, ferries
Ferry
A ferry is a form of transportation, usually a boat, but sometimes a ship, used to carry primarily passengers, and sometimes vehicles and cargo as well, across a body of water. Most ferries operate on regular, frequent, return services...

, car
Čar
Čar is a village in the municipality of Bujanovac, Serbia. According to the 2002 census, the town has a population of 296 people.-References:...

s, and bus
Bus
A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...

es 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
Campania
Campania is a region in southern Italy. The region has a population of around 5.8 million people, making it the second-most-populous region of Italy; its total area of 13,590 km² makes it the most densely populated region in the country...

 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 thousands could be killed, while if it is started too early then the precursors of the eruption may turn out to have been a false alarm
False alarm
A false alarm, also called a nuisance alarm, is the fake report of an emergency, causing unnecessary panic and/or bringing resources to a place where they are not needed. Over time, repeated false alarms in a certain area may cause occupants to start to ignore all alarms, knowing that each time it...

. In 1984, 40,000 people were evacuated from the Campi Flegrei
Campi Flegrei
The Phlegraean Fields, also known as Campi Flegrei, , is a large wide caldera situated to the west of Naples, Italy. It was declared a regional park in 2003. Lying mostly underwater, the area comprises 24 craters and volcanic edifices. Hydrothermal activity can be observed at Lucrino, Agnano and...

 area, another volcanic complex near Naples, but no eruption occurred.

Ongoing efforts are being made by the government at various levels (especially of Regione Campania) 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 building
Building
In architecture, construction, engineering, real estate development and technology the word building may refer to one of the following:...

s and by offering financial incentives to people for moving away. One of the underlying goals 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
Vesuvius Observatory
The Vesuvius Observatory is the surveillance centre for monitoring the three volcanoes which threaten the Campanian region of Italy: Mount Vesuvius, Campi Flegrei and Ischia. Founded in 1841 on the slopes of Mount Vesuvius , it is the oldest volcanology institute in the world....

 in Naples with extensive networks of seismic and gravimetric stations, a combination of a GPS-based geodetic array and satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....

-based synthetic aperture radar
Synthetic aperture radar
Synthetic-aperture radar is a form of radar whose defining characteristic is its use of relative motion between an antenna and its target region to provide distinctive long-term coherent-signal variations that are exploited to obtain finer spatial resolution than is possible with conventional...

 to measure ground movement, and by local surveys
Geophysical survey
Geophysical survey is the systematic collection of geophysical data for spatial studies. Geophysical surveys may use a great variety of sensing instruments, and data may be collected from above or below the Earth's surface or from aerial or marine platforms. Geophysical surveys have many...

 and chemical analyses of gas
Gas
Gas is one of the three classical states of matter . Near absolute zero, a substance exists as a solid. As heat is added to this substance it melts into a liquid at its melting point , boils into a gas at its boiling point, and if heated high enough would enter a plasma state in which the electrons...

es emitted from fumarole
Fumarole
A fumarole is an opening in a planet's crust, often in the neighborhood of volcanoes, which emits steam and gases such as carbon dioxide, sulfur dioxide, hydrochloric acid, and hydrogen sulfide. The steam is created when superheated water turns to steam as its pressure drops when it emerges from...

s. All of this is intended to track magma rising underneath the volcano. Currently no magma has been detected within 10 km of the surface, and so the volcano is classified by the Observatory as at a Basic or Green Level.

Vesuvius today

The area around Vesuvius was officially declared a national park
Vesuvius National Park
Vesuvius National Park is a national park centered around the volcano, Mount Vesuvius, east of Naples, Italy. The park was founded in 1995 and covers an area of around 135 square kilometers all located within the Province of Naples....

 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 (656.2 ft) 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.

See also

  • List of volcanic eruptions by death toll
  • List of volcanoes in Italy
  • Vesuvius National Park
    Vesuvius National Park
    Vesuvius National Park is a national park centered around the volcano, Mount Vesuvius, east of Naples, Italy. The park was founded in 1995 and covers an area of around 135 square kilometers all located within the Province of Naples....

  • Volcanic Explosivity Index
    Volcanic Explosivity Index
    The Volcanic Explosivity Index was devised by Chris Newhall of the U.S. Geological Survey and Stephen Self at the University of Hawaii in 1982 to provide a relative measure of the explosiveness of volcanic eruptions....


External links

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