Mount Vesuvius

Mount Vesuvius is one of the world's most famous, most studied, and most scientifically influential volcanoes. The science of volcanology began with reports of its activity, and several key terms and concepts originated from its example. The science of archaeology also began with Vesuvius because of its most famous eruption in 79 Common Era (CE), which preserved the ruins of Pompeii and Herculaneum.

Mediterranean Volcanoes

When most people think of a volcano, they think of the kind of volcano that Vesuvius is—a distinctly conical mountain that erupts spectacularly at intervals, blowing rocks and ash high into the air while sending fiery lava down its slopes. In actuality, however, there are several different kinds of volcanoes and several different kinds of eruptions. Vesuvius, the best-known example of a stratovolcano, or composite volcano. It features a prominent cone made up of lava, craters, and ash. Like most stratovolcanoes, it has erupted in more than one way. Two of the variously classified eruption types, the Plinian and the Vesuvian (or Vulcanian), were either first or best observed here.

Vesuvius is one of a series of volcanoes irregularly aligned throughout the Mediterranean region, from southern Greece down to central and southern Italy and then to Sicily and its adjacent islands. The best-known Greek volcano, now extinct, is the crater-remnant island of Santorini (or Thera), the eruption of which is sometimes credited with the destruction of Minoan Crete. Aside from Vesuvius, the best-known Italian volcanoes, all of them recently active, are Mount Etna in Sicily and the two Aeolian island volcanoes, Vulcano (for which all other volcanoes are named) and Stromboli, which has been in constant eruption for more than 2,500 years. Geologists explain this Mediterranean lineage of volcanoes through plate tectonics. According to this theory, the African plate is slowly moving northward, colliding with, and sliding under the European plate. Its leading edge plunges downward beneath the European plate and eventually melts, creating large accumulations of liquid rock (magma) that later ascend to express themselves as volcanoes. This level of understanding, however, has only been achieved since about 1970, when plate tectonics theory was accepted.

Vesuvius, located 11 kilometers south of Naples and easily visible from there, is part of a larger volcanic complex surrounding that city. Other parts of the complex include the Phlegraean Fields, a group of nineteen small, closely grouped craters (regarded as the entrance to Hell in classical times); the so-called Temple of Jupiter Serapis at Puzzuoli, a Roman ruin that shows unmistakable evidence of abrupt vertical displacement within historical times (Charles Lyell utilized it as the frontispiece to all twelve editions of his Principles of Geology, 1830–75); the Solfatara, a large, steaming crater whose last eruption (in 1198) probably displaced the Temple of Jupiter Serapis; and the buried cities of Pompeii and Herculaneum. All these phenomena are closely associated with Vesuvius and have been immensely influential in forming ideas about volcanoes and how they work.

Vesuvius is the most recently active (1944) member of a group of volcanoes—many now deeply eroded and scarcely recognizable—lying roughly parallel to the Apennine Mountains and the Italian peninsula's Tyrrhenian (west) coast. In mid-Tertiary times (about 30 million years ago), the Apennine chain began to rise through the agency of plate tectonics and the Tyrrhenian Basin to subside. The Bay of Naples is also essentially a downwarp, with the Triassic and Cretaceous limestone rocks of the Sorrento peninsula forming one of its uptilted edges; Vesuvius, the Solfatara, and the Phlegraean Fields are located roughly atop its center. Vesuvius probably began as a submarine volcano in the Bay of Naples, emerged as an island, and finally became part of the mainland through the constructive effects of its own eruptions.

Birth of Vesuvius

Vesuvius originated about ten thousand years ago; there were several cones before the present one. Archaeological evidence attesting to the human occupation of its slopes goes back to the seventh century Before the Common Era (BCE). The name “Vesuvius” (its origin is unknown) was used around 45 BCE by Diodorus Siculus, a Sicilian writer who recognized the mountain as a former volcano. By around 30 BCE, however, the geographer Strabo regarded Vesuvius as a scene of local fires only. He described a flat-topped, barren summit and fertile slopes teeming with agriculture. Thus, no actual eruptions of Vesuvius had been recorded in historic times, and its identification as a volcano had been forgotten.

A destructive earthquake struck the Naples region on February 5, 63 CE, causing extensive havoc at Pompeii and Herculaneum. Subsequent tremors continued intermittently for the next sixteen years, with one of the strongest occurring on August 24, 79 CE. It is apparent to modern scientists that such earthquakes are often caused by the upward movement of magma in the vent of an active volcano, but no such understanding prevailed at the time. Therefore, the most famous volcanic eruption in history took the population it affected almost entirely by surprise.

Plinian Eruptions

The first reason the Vesuvian eruption of 79 CE is so well known is that Pliny the Younger wrote an eyewitness description of it some years after the event in two letters to the historian Tacitus regarding the death of Pliny the Elder, the writer's unclear who was a distinguished naturalist and public figure. This two-part epistolary account, often reprinted in translation, is the first volcanological field report and more exciting than geological papers tend to be.

According to the younger Pliny, at about one o'clock in the afternoon on August 24, a strange, unusually large, and rapid pine-tree-shaped cloud began to ascend over Vesuvius. Unlike North American pines, the Italian pine tree is narrow at the base and becomes increasingly broad as it grows upward. Pliny's description is so apt that an eruption cloud of the same shape today is still called a pino (Italian for pine tree); eruptions of this type are called Plinian. Realizing that a natural disaster was at hand, Pliny the Elder went by water to a friend's home, where he slept until tremors and falling ejecta from the volcano awakened everyone. An overweight man, he then died suddenly the following day from asphyxiation or possibly a heart attack—the first “scientist” ever to be killed by a volcano. Other portions of his nephew's account describe, for the first time, phenomena now frequently associated with volcanic eruptions: preternatural darkness, the retreat of the sea from its established shores, and repeated bursts of lightning within the eruption cloud.

Destruction of Pompeii and Herculaneum

The other reason the Vesuvian eruption of 79 CE is so famous is that the nearby cities of Pompeii and Herculaneum were destroyed (and their remains preserved) by it. Pliny the Younger does not mention either city, though Tacitus may have in a portion of his history no longer extant. There is not another written account before about 230 CE, when Dio Cassius erroneously claimed that the Pompeiians died while sitting in their theater, a scene later dramatized in Edward Bulwer-Lytton's novel The Last Days of Pompeii (1834) and numerous films. Archaeological evidence, however, has proved that Dio Cassius's account is false.

Except for some immediate posteruption attempts at salvage, Pompeii and Herculaneum lay essentially untouched beneath their respective volcanic coverings until well into the eighteenth century, when organized attempts at treasure hunting began. Skeletons of the deceased were then discovered rather frequently, especially at Pompeii, where the modern science of archaeology evolved. The destruction there had occurred so rapidly that the city's life ended with food still on tables and bread baking in ovens. Pompeii is one of Europe's most often visited monuments because the evidence of its everyday life and the drama of its abrupt termination are apparent to all.

Pompeii and Herculaneum were destroyed in different ways. The greater number of bodies—some of them skeletons, others cast in plaster—are from Pompeii, and they often appear to indicate death by asphyxiation. No lava reached the city, though it was bombarded with ash to a depth of about 1 meter. It is believed, however, that even such an ashfall could not have killed the more than two thousand persons known to have perished there. Current theorizing holds that at least one phase of Vesuvius's eruption (which lasted two days in all) included a nuée ardente, a sudden basal surge of incandescent, heavier-than-air gas that poured out of the crater and ran down its slope like an avalanche instantly searing and suffocating whatever animate life lay in its path. Pliny the Elder may have died because of it.

Herculaneum, probably a slightly later victim, was inundated not by lava or ash but by mud. The torrential rains that sometimes follow a volcanic eruption (which ejects huge volumes of water vapor) can gather newly deposited loose particles of ash upon the volcano's slopes into a precipitous mudslide (lahar) that will then flow rapidly and in great volume for kilometers. Such a mudslide buried the city of Herculaneum, which remains less excavated than Pompeii. Its eruption cover is much harder to dig through, and the modern city of Resina sits atop most of it. Both Pompeii and Herculaneum have fundamentally influenced archaeology, history, and the fine arts.

Plinian eruptions, such as that of 79 CE, are noted for their explosive violence. The cones of stratovolcanoes are surprisingly fragile and will often change significantly from one eruption to the next. In 79 CE, this fragility was more than usually apparent, as the entire upper cone of Vesuvius was completely destroyed, leaving behind only an incompletely circular ring now known as Mount Somma. The more general term “somma,” which applies to similar structures everywhere, is derived from it. Although some disagreement exists, for most volcanologists, the mountain that erupted in 79 CE is the present-day Mount Somma, and the cone within it, now called Vesuvius, did not arise until the quieter eruption of 172 CE.

Later Eruptions

Since then, there have been dozens of further Vesuvian eruptions, most of them from the central vent and a few from the flanks. Various literary sources tell of eruptions in 203, 472, 512, 685, 993, 1036, 1049, 1138, and 1139; there was then nothing of importance for almost five hundred years, though the overnight eruption in the Phlegraean Fields that produced Monte Nuovo in 1538 is attested by no fewer than four eyewitness accounts. This extended period of inactivity ended on December 16, 1631, when, after an explosive beginning, seven streams of lava poured down the slopes of Vesuvius, destroying a dozen villages and killing some eighteen thousand people. Several accounts of this disastrous eruption were written, some of them book-length. It is the first volcanic eruption in history for which there is published literature.

Vesuvius has been under almost constant observation ever since, with many subsequent outbursts. From 1631 until 1944, however, activity remained unusually frequent. During most of this time (including major eruptions in 1676, 1694, 1707, 1737, 1751, and 1760), Vesuvius was unquestionably the premier geological attraction in the world; it soon became a necessary destination for anyone who aspired to authority regarding the natural history of the earth. This prominence intensified due to the work of Sir William Hamilton, the British representative at Naples, who published highly influential accounts of the Vesuvian eruptions of 1766, 1767, 1770, and 1779. He is arguably the first person who might properly be described as a modern volcanologist.

Other major eruptions followed in 1793–94, 1822, 1834, 1855, 1867–68, 1872, 1906, and 1944. During these 150 years, the nature of observations changed gradually from those of the intrepid amateur (such as Hamilton) to fully sophisticated, rigorous science. One may cite in particular the establishment in 1844 of the Royal Vesuvian Observatory, a then unique (but since copied) institution located on the very slopes of the volcano. Under Macedonio Melloni, the observatory initially made ongoing monitoring of day-to-day volcanic activity possible. It became the training ground for a distinguished series of internationally known volcanologists, who naturally derived many of their concepts from Vesuvius itself. Luigi Palmieri, R. V. Matteucci, Giuseppe Mercalli, Frank Perret, and Giuseppe Imbo have all made important contributions.

In early 2016, a new official assessment created a "yellow zone" in addition to the "red zone" identified years earlier to establish the extent of people living near Vesuvius who would be most at risk if it were to erupt once more. This assessment placed a list of sixty-three towns and villages in the provinces of Naples and Salerno in the new zone. Despite uncertainty about when and if the volcano will erupt again, as it has been dormant for decades, Italian authorities began creating more concrete evacuation plans for as many as 700,000 people in preparation later that year. At the same time, some expressed concern that those at the local level responsible for implementing such plans would not be familiar enough with them to be adequately prepared to do so effectively. As seismic activity continued in the region in the early 2020s, local officials constantly tweaked and updated plans in cooperation with scientists and government officials. As the 2020s progressed, scientists predicted Vesuvius would likely remain dormant for the next few centuries before experiencing another powerful eruption. These conclusions were based on the volcano’s historical activity and monitoring of its magma composition. Constant geophysical monitoring allows scientists to make such predictions. However, the nearby Campi Flegrei supervolcano has shown signs of increased seismic activity since late 2022, raising concerns about its potential for eruption nearer in the future. 

Principal Terms

cone: the hill or mountain, more or less conical, surrounding a volcanic vent and created by its ejecta; it is normally surmounted by a crater

crater: the circular depression atop a volcanic cone

eruption: volcanic activity of such force as to propel significant amounts of magmatic products over the rim of the crater

lava: molten rock (as opposed to ash) erupted by a volcano; the term originated concerning Vesuvius

magma: molten rock, normally subterranean

stratovolcano, or composite volcano: a noticeably conical volcano composed of interbedded lava flows, ash, and cinders; also, the remnant of such a volcano

volcanology: the study of volcanoes

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