Vesuvius

Perhaps one of the most well-known volcanoes in the world for the catastrophic eruption that wiped out Pompeii and Herculaneum in 79 A.D., Vesuvius is considered to have evolved some 17000 years ago as a result of geological disturbances in the Earth's crust. The tectonic plates underneath have, over the centuries, been pushing against one another, fracturing the crust in the process and causing perceptible geographical changes. In this case, the fracture resulting from the African Plate pushing beneath the Eurasian Plate perhaps first gave shape to a submerged volcano in the Bay of Naples, which later surfaced as an island and became connected to the mainland by the periodic depositing of its eruption fall-outs.

Going by some of the carbon-dated rocks from Vesuvius, the first eruptions are thought to have occurred in the Ice Age. One of the earliest recorded eruptions is in about 900 B.C. In 320 B.C., the volcano, which then perhaps rose to 9000 feet, erupted again. Four more centuries were to go before the next eruption and in this time it became densely covered with forest growth and came to be generally regarded as dormant. Poets waxed eloquent about the beauty of its broad, flat-topped appearance and the rich built large villas at its base and along the coast. For a period in 73 B.C., after the famous Spartacus uprising, it even sheltered the rebellious gladiators and slaves. Virgil, writing the Aeneid in 30 B.C., made reference to the mythical giant Mimas, who had been imprisoned by the Gods under Vesuvius and whose tormented movements supposedly caused the earthquakes in the region. There is also reference by the Greek scientist Strabo, who wrote in 10 A.D. about the 'craters of fire' of Vesuvius. On 5 January 62 A.D., a severe earthquake rocked the towns of Pompeii and Herculaneum, taking a heavy toll of life and property. Another somewhat milder earthquake followed in Naples in 64 A.D. These were indications of the coming trouble, but the Romans, keen observers as they were, failed to take heed. Finally, on 24 and 25 August 79 A.D., Vesuvius, which was about 6000 feet then, erupted spectacularly in an eruption that was called 'perhaps the most violent and destructive in Europe' and the one which gave it its notoriety. An eyewitness account of this, the very first detailed information of a volcanic eruption, has been left by Pliny the Younger, a Roman Historian and Nobleman, who witnessed it from his villa at Misenum, across the Naples Bay and 30 km west of the volcano. His observations, recorded later in two letters to the historian Tacitus, together with modern scientific data can give us an idea of what exactly took place.

All volcanoes have an underground magma chamber (a cache of molten rock), which generally expands over time and gives rise to ground 'uplift', earthquakes, and heated ground water in the vicinity. Due to these disturbances, fine cracks develop in the rock covering of the magma chamber and the magma is able to ooze out to the surface through these, resulting in a lava-flow. However, if the volcano has been long inactive, the cracks become clogged and prevent the passage of the magma. This leads to a massive build-up of pressure, together with gaseous emanations, in the magma chamber. Finally this escalating pressure bursts the cracks wide open and the molten rock is spewed sky high in a tremendous blowup. It hardens on contact with the atmosphere and forms pumice, tons of it, which then rain down on the surrounding countryside as happened in the case of Pompeii. However in Pompeii, along with the pumice shower, there was a rare and complex phenomenon called Surge Cloud or Pyroclastic Flow. In this, the force of the eruption gave rise to a tall column (possibly 32 km in height) of hot pumice, dust and ashes, which Pliny the Younger and his uncle Pliny the Elder saw from Misenum. It collapsed into what the Pliny the Younger described as a 'black and dreadful cloud' that spread over a huge area, completely destroying everything. This was followed by a heavy pumice shower that caused further devastation. Pompeii was completely buried, except for some building roofs, while Herculaneum totally vanished from sight. A huge crater was formed atop Vesuvius.

Along with Pompeii and Herculaneum, the towns of Stabiae, Oplontis, Sora, Tora, Taurania, Cossa and Leucopetra too were annihilated. Emperor Titus, who had visited the area only a month earlier, ordered some salvage work to be carried out, but the towns were never rebuilt and their sites were eventually forgotten. It was only by chance that they were discovered in 1595 and centuries of looting followed after that. In between though, Vesuvius remained active. There were several eruptions after 79 A.D., all of them notably mentioned by many of the writers of the period.

In 91 A.D., a Roman poet referred to Vesuvius as 'once the haunt of dancing satyrs but now crowned by flames'. The Roman Historian Dio Cassius mentions eruptions in 203 A.D. and 472 A.D., the latter of which caused much panic in Constantinople. 1036 A.D. was the first occasion in which lava-flow was recorded, and on 16 December 1631 A.D., preceded by earthquakes and drying springs, there was a violent eruption paralleling the one in 79 A.D.; thousands perished in the ensuing mud-flows and lava-flows and the volcanic crater widened from 1 mile to 3 miles across and the level of the Bay of Naples dropped dramatically to give rise to an enormous tidal wave that crashed ashore, causing additional havoc. The warning tablet erected afterwards by the Spanish reads :'As soon as an eruption begins, you must escape as quickly as you can. If you worry about your chattels, your greed and recklessness will be punished. Listen to the voice of this marble. Flee without hesitation'. In 1660 A.D. Vesuvius threw out cross-shaped pyroxene crystals which the surrounding populace took for a miracle brought about by the patron saint of Naples, San Gennaro. The next explosion, in 1707 A.D., took place during the Austrian take-over of Naples from the Spanish, and the one after that, in 1737 A.D., sent out a lava stream a mile wide. Diderot's famous Encyclopédie had illustrations of the 1754 A.D. eruption, and the 1760 A.D. one formed a new crater on the side of the mountain. The eruptions between 28-31 March 1766 A.D. were witnessed by the British Ambassador, Sir William Hamilton (famous as the husband of Lord Nelson's mistress Emma), who made a series of engravings of what he saw and wrote that 'the lava had the appearance of a river of red-hot and liquid metal forming a most beautiful and uncommon cascade'. The eruption on 29 October 1767 A.D. was so terrible that the lava-flow endangered even the Naples Royal Palace and the King himself only narrowly escaped. The Neapolitans resorted to carrying a relic of San Gennaro in a procession to the safest vicinity of the volcano, and this apparently calmed Vesuvius. The most recent eruptions were between 1913 and 1944.

Vesuvius is still a pretty hazardous and unpredictable volcano, and future eruptions are quite likely to happen. Modern Volcanologists however monitor the geological changes closely and this will enable them to issue early warnings and in this way minimize the resulting damage. At present around 4 to 5 million people reside in the areas that could be possibly affected by an eruption.