The most famous volcanic eruption of all time is probably that of Vesuvius in the year 79 c.e. Mount Vesuvius is the only active volcano on the European mainland, towering 4,195 feet (1,279 m) above the densely populated areas of Naples, Herculaneum, and surrounding communities in southern Italy. Vesuvius is an arc volcano related to the subduction of oceanic crust to the east of Italy beneath the Italian peninsula, and the volcano rises from the plain of Campania between the Apennine Mountains to the east and the Tyrrhenian sea to the west. The volcano developed inside the collapsed caldera of an older volcano known as Monte somma, only a small part of which remains along the northern rim of Vesuvius. Monte Somma and Vesuvius have had at least five major eruptions in the past 4,000 years, including 1550 and 217 b.c.e., and 79, 472, and 1631 c.e. There have been at least 50 minor eruptions of Vesuvius since 79 c.e.
Ash from the 79 c.e. eruption buried the towns of Pompeii, Herculaneum, and Stabiae in present-day Italy and killed tens of thousands of people. Before the eruption Pompeii was a well-known center of commerce, home to approximately 20,000. The area was known especially for its wines, cabbage, and fish sauce, and was also a popular resort area for wealthy Roman citizens. Pompeii became wealthy and homes were elaborately decorated with statues, patterned tile floors, and frescoes. The city built a forum, several theaters, and a huge amphitheater in which 20,000 spectators could watch gladiators fight each other or animals, with the loser usually being killed.
A large caldera north of Vesuvius presently has molten magma moving beneath the surface, causing a variety of volcanic phenomena that have inspired many legends. The Phlegraean Fields is the name given to a region where there are many steaming fumaroles spewing sulfurous gases and boiling mud-pots, which may have inspired the Roman poet Virgil's description of the entrance to the underworld. The land surface in the caldera rises and falls with the movement of magma below the surface. This is most evident near the sea, where shorelines have moved up and down relative to coastal structures. At Pozzuoli the ancient Temple of Serapis lies partly submerged near the coast. The marble pillars of the temple show evidence of having been previously submerged, as they are partly bored through by marine organisms, leaving visible holes in the pillars. Charles Lyell, in his famous treatise Principles of Geology, used this observation to demonstrate that land can subside and be uplifted relative to sea level. A few miles north of Pozzuoli the ancient town of Port Julius is completely submerged beneath the sea, showing that subsidence has been ongoing for thousands of years.
Before the cataclysmic eruption in 79, the Cam-panians of southern Italy had forgotten that Vesuvius was a volcano and did not perceive any threat from the mountain, even though 50 years earlier the geographer strabo had described many volcanic features of the mountain. The crater lake at the top of the mountain was used by the rebelling gladiator spar-ticus and his cohorts to hide from the Roman army in 72 c.e., neither side of whom was aware of the danger of the crater. There were other signs that the volcano was returning to life. In 62 c.e. a powerful earthquake shook the region, damaging many structures and causing the water reservoir for Pompeii to collapse, flooding the town and killing and injuring many. It is likely that poisonous volcanic gases also escaped through newly opened fractures at this time, as Roman historians and philosophers write of a flock of hundreds of sheep dying mysteriously near Pompeii by a pestilence from within the Earth. The descriptions are reminiscent of the poison carbon dioxide gases emitted from some volcanoes, such as the disasters of Lake Nyos in Cameroon in 1984 and 1986. More earthquakes followed, including one in 63 c.e. that violently shook the theater while the emperor Nero was singing to a captive audience. Instead of evacuating the theater, it was said that Nero was convinced his voice was ever stronger and perhaps excited the gods of the underworld.
On August 24, 79 c.e., Vesuvius erupted after several years of earthquakes. The initial blast launched two and a half cubic miles (10 km3) of pumice, ash, and other volcanic material into the air, forming a mushroom cloud that expanded in the stratosphere. This first phase of the eruption lasted 12 hours, during which time Pompeii's terrified residents were pelted with blocks of pumice and a rain of volcanic ash that was falling on the city at a rate of 7-8 inches (15-20 cm) per hour. People were hiding in buildings and fleeing through the artificially darkened streets, many collapsing and dying from asphyxiation. soon the weight of the ash caused roofs to collapse on structures throughout the city, killing thousands. The ash quickly buried Pompeii under 10 feet (3 m) of volcanic debris. About half a day after the eruption began, the eruption column began to collapse from decreasing pressure from the magma chamber, and the eruption entered a new phase. At this stage pyro-clastic flows known as nuées ardentes began flowing down the sides of the volcano. These flows consisted of a mixture of hot gases, volcanic ash, pumice, and other particles; they raced downhill at hundreds of miles (km) per hour while maintaining temperatures of 1,800°F (1,000°C) or more. These hot pyroclastic flows ripped up and ignited anything in their path, and Herculaneum was first in that path.
Successive pyroclastic flows together killed about 4,000 people in Herculaneum and Pompeii, and neighboring towns suffered similar fates after the initial blast. During the second phase of the massive eruption huge quantities of ash were blown up to 20 miles (32 km) into the atmosphere, alternately surging upward and dropping tons of ash onto the surrounding region and killing most of the people who were not killed in the initial eruption. Daylight was quickly turned into a dark, impenetrable night, and the town of Pompeii was buried under another 6 to 7 feet (~2 m) of ash. Thick ash also accumulated on the slopes of the volcano and was quickly saturated with water from rains created by the volcanic eruption. Water-saturated mudflows called lahars moved swiftly down the slopes of Vesuvius, burying the town of Herculaneum under additional volcanic layers up to 65 feet (20 m) thick, and covering Pompeii by up to 20 feet (5 m) of mud. The towns of Herculaneum and Pompeii were not uncovered until archaeologists discovered their ruins nearly 2,000 years later when, in 1699 the Italian scientist Giuseppe Marcrini dug into an elevated mound and discovered parts of the buried city of Pompeii. The public was not interested in the early 1700s, however, and the region's history remained obscure. For the next century wealthy landowners discovered that if they dug tunnels through the solidified ash, they could fund ancient statues, bronze pieces, and other valuables that they used to decorate their homes. It was not until Italy became unified in 1860 and the archaeologist Giuseppe Fiorelli was put in charge of excavations in southern Italy that looting changed to systematic excavation and study.
This area has since been rebuilt, with farmland covering much of Pompeii, and the town of Ercolano now lies on top of the 20 feet (6 m) of ash that buried Herculaneum. Archaeological investigation at both sites, however, has led to a wealth of information about life in ancient Italy, and Pompeii in particular has proven to be a valuable time capsule preserved in pristine condition by the encapsulating volcanic ash that entrapped so many people in their homes or trying to escape into the streets or elsewhere. Vesuvius is still active, and has experienced many eruptions since the famous eruption in 79 c.e.
The 72 c.e. eruption of Vesuvius is the source of some terms commonly used to describe features of volcanic eruptions. Pliny the Elder, the Roman naturalist and naval officer in charge of a squadron of vessels in the Bay of Naples during the eruption, commanded one of his vessels to move toward the mountain during the initial eruption for a better view and to rescue a friend. Both efforts failed, as the eruption was too intense to approach, so he sailed to Stabiae to the south to attempt to save another friend. Pliny the Elder died there, apparently from a heart attack brought on by struggling through the thick ash in the city. In an account of the death of his uncle and of the eruption given to the Roman historian Tacitus, Pliny the Younger (the Elder's nephew) described the mushroom cloud associated with the initial eruption as being like an umbrella where the lower column rose up in a thin pipe then expanded outward in all directions at the top. The common term Plinian eruption column is taken from these descriptions.
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