Mount Vesuvius

Mount Vesuvius is a stratovolcano east of Naples, Italy. It is the only volcano on the European mainland to have erupted within the last hundred years, although it is not currently erupting. The two other volcanoes in Italy Etna and Stromboli are located on islands. Mount Vesuvius is on the coast of the Bay of Naples, about 9 kms or 6 miles east of Naples and a short distance from the shore. It is conspicuous in the beautiful landscape presented by that bay, when seen from the sea, with Naples in the foreground.

Mount Vesuvius is best known for its eruption in AD 79 that led to the destruction of the Roman cities of Pompeii and Herculaneum and the death of 10,000 to 25,000 people. It has erupted many times since and is today regarded as one of the most dangerous volcanoes in the world because of the population of 3,000,000 people living nearby and its tendency towards explosive eruptions. It is the most densely populated volcanic region in the world. Mount Vesuvius was regarded by the Greeks and Romans as being sacred to the hero and demigod Heracles or Hercules, and the town of Herculaneum, built at its base, was named after him.

Vesuvius is a distinctive humpbacked mountain, consisting of a large cone partially encircled by the steep rim of a summit caldera caused by the collapse of an earlier and originally much higher structure called Monte Somma. The Gran Cono was produced during the eruption of 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 years ago and was enlarged by later paroxysmal eruptions. This structure has given its name to the term somma volcano, which describes any volcano with a summit caldera surrounding a newer cone.

The height of the main cone has been constantly changed by eruptions but presently is 1,281 m or 4,202 ft. Monte Somma is 1,149 m or 3,770 ft high, separated from the main cone by the valley of Atrio di Cavallo, which is some 3 miles or 5 km long. The slopes of the mountain are scarred by lava flows but are heavily vegetated, with scrub at higher altitudes and vineyards lower down. Vesuvius is still regarded as an active volcano at the convergent boundary where the African Plate is being subducted beneath the Eurasian Plate. Its lava is composed of viscous andesite. Layers of lava, scoria, volcanic ash, and pumice make up the mountain.

Vesuvius was formed as a result of the collision of two tectonic plates, the African and the Eurasian. The former was pushed beneath the latter, deeper into the earth. The crust material became heated until it melted, forming magma, a type of liquid rock. Because magma is less dense than the solid rock around it, it was pushed upward. Finding a weak place at the Earth's surface it broke through, producing the volcano.

The volcano is one of several which form the Campanian volcanic arc. Others include Campi Flegrei, a large caldera a few kilometres to the north west, Mount Epomeo, 20 kms or 12 miles to the west on the island of Ischia, and several undersea volcanoes to the south. The arc forms the southern end of a larger chain of volcanoes produced by the subduction process described above, which extends northwest along the length of Italy as far as Monte Amiata in Southern Tuscany. Vesuvius is the only one to have erupted within recent history, although some of the others have erupted within the last few hundred years. Many are either extinct or have not erupted for tens of thousands of years.

The eruptions vary greatly in severity but are characterized by explosive outbursts of the kind dubbed Plinian after Pliny the Younger, 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 in Istanbul, over 1,200 kms or 750 miles away. A few times since 1944, landslides in the crater have raised clouds of ash dust, raising false alarms of an eruption.

The area around Vesuvius was officially declared a national park on 5 June 1995.The summit of Vesuvius is open to visitors and there is a small network of paths around the mountain that are maintained by the park authorities on weekends. The efforts are being made to reduce the population living in the red zone, by demolishing illegally constructed buildings, establishing a national park around the upper flanks of the volcano to prevent the erection of further buildings and by offering financial incentives to people for moving away. The underlying goal is to reduce the time needed to evacuate the area, over the next 20 or 30 years, to two or three days.

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