Vesuvius in History

Mount Vesuvius today stands over 1,200m. It is still active and is actually in two parts - an external crater, Monte Somma and the main cone, Gran Cono, which was produced by the eruption of AD79. The slopes of the mountain bear witness to the many lava flows that have taken place over the centuries. However, on these apparently hostile slopes vegetation grows abundantly, especially on the lower slopes, due to the richness of the fertile soil (the volcanic ash contains high percentages of soil enriching nutrients potassium, calcium and sodium). Prior to 79 little is known of volcanic activity with the exception of a massive eruption in about 1800 BC. Since then major eruptions have occurred in 203, 472, 512, 685, 787, 968, 1037 and 1139. Between 1139 and 1631 there was relatively little activity.

In December 1631 a major eruption buried many villages under lava flows, killing around 3,000 people. Vesuvius then entered a more continuous period of activity with over 20 major eruptions, culmination in the eruption of March, 1944, which destroyed the villages of San Sebastiano al Vesuvio, Massa di Somma, Ottaviano, and an area of San Giorgio a Cremano. .. Mount Vesuvius is being constantly monitored for seismic activity and although it is not thought that Vesuvius will erupt in the immediate future, emergency procedures have been put in place to evacuate the population living in the areas of greatest risk to pyroclasic flows.

.. Since 1944 Vesuvius has remained ominously quiet for over 60 years. In recent times the quiet periods have only lasted from between 18 months to 7½ years, so the current lack of activity is abnormal. ..

.. The plans assume that Vesuvius would give sufficient warning to allow for the evacuation of over 600,000. 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. Pyroclastic Flow

.. The majority of the samples tested returned temperatures between 240–340°C. (Cioni, R., L. Gurioli, R. Lanza, and E. Zanella (2004), Temperatures of the A.D. 79 pyroclastic density current deposits (Vesuvius, Italy)). The video opposite is of Mt Unzen near the city of Shimabara, on the island of Kyūshū, Japan’s southernmost main island. On June 3, 1991, the volcano erupted violently, possibly as a result of depressurization of the magma column after a landslide. The resulting pyroclastic flow reached 4.5kilometres from the crater and claimed the lives of 43scientists and journalists, (contrary to what the commentary says) including volcanologists Katia and Maurice Krafft and Harry Glicken.

Pyroclastic flows are fast-moving currents of hot gas, ash, and rock, which can travel away from the volcano at up to 700 kph. They may result from the explosive eruption of molten or solid rock fragments, or, as in the case of Vesuvius in AD79, the collapse of the vertical eruption column. The gas, ash and rock fragments can reach some extremely high temperatures. The temperature of the deposits left by the AD79 eruption was estimated by examining more than 200 lava clasts and roof tile fragments collected at varying distances from the vent. ..

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Most pyroclastic flows consist of two parts: a basal flow of coarse fragments that moves along the ground, downhill, spreading laterally, and a turbulent cloud of ash that rises above the basal flow. The photograph above (left) is of a pyroclastic flow sweeping down the Mayon Volcano in the Philippines in 1984.

Phlegraean Fields

Vesuvius is not the only sign of vulcanism in the region. The area, known as the Phlegraean Fields, lies to the west of Naples. It is a large 13km wide caldera, mostly submerged today. However the caldera does contain the town of Pozzuoli and the crater of Solfatara. ,,

The area round Solfatara has a large number of fumeroles emitting columns of steam and several pools of boiling mud (left). Prior to Roman times the Greeks had colonised the area with towns at Cumae as well as Paestum further to the south. The photograph above is courtesy of NASA. Pozzuoli is in the centre of the photograph, Cumae was on the south western coastal strip while the naval base of Misenum was on the peninsula to the south.

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