1631 eruption of Mount Vesuvius

Of the many eruptions of Mount Vesuvius, a major stratovolcano in Southern Italy, its eruption in 1631 is the most destructive episode in the recent history and one of the deadliest of all time.

History
Before 1631 Vesuvius had remained for about five centuries in a state of quiescence. From November to December 1631, considerable seismic activity occurred in the Vesuvius area culminating in a grade VII MCS shake on 15 December, followed by an intense earthquake swarm.

The eruption began on 16 December 1631, with the opening of a fissure vent on the western side of Vesuvius, close to the base of the volcanic cone. The explosion caused a giant eruption column, which pushed by high pressure inside the volcano reached about 13 km altitude. According to William Hamilton "Giulio Cesare Braccini measured with a quadrant the elevation of the mass of clouds that was formed over Vesuvius during the eruption, and found it to exceed thirty miles in height". The eruption column lasted around 8 hours. Fallout of vesiculated lapilli and lithic clasts occurred until the evening. During the night between 16 and 17 December the volcano produced discrete explosions accompanied by lapilli relapses.

In the morning of 17 December a violent earthquake occurred, lasting a few minutes. The earthquake was immediately followed by the most violent phase of the eruption, characterized by pyroclastic flow activity. The Volcanic Explosivity Index was VEI-5, and it was a Plinian eruption that buried many villages under the resulting lava flows. Large quantities of ashes and dust were ejected and several streams of molten lava poured out of the crater and down the sides of the mountain, overwhelming several villages, including Torre Annunziata, Torre del Greco and Ercolano. Torrents of lahar were also created, adding to the devastation.

The 1631 eruption was considered to be of minor proportions regarding its eruptive magnitude and erupted volumes compared to the AD 79 eruption, but the damage was not. It is estimated that between 4,000 people were killed by the eruption, making it the highest death toll for a volcanic disaster in the Mediterranean in the last 1800 years. The list of casualties might have been higher still, had it not been for a rescue mission conducted three days later to save stranded villagers. The town of Naples was not directly damaged by the eruption, but food supply from the Vesuvius neighbourhood was interrupted. Besides over 20,000 refugees invaded the town creating problems of public order.

Due to the proximity of Vesuvius to Naples, this eruption was broadly described by contemporary authors and its study affected the evolution of natural philosophy in the first half of the 17th century. Scholars flocked to Naples to study the phenomenon and to collect mineral specimens from the mountainside. Some historians argue that this investigation and engagement with Vesuvius was paramount to the development of modern volcanology.

By the 1631 eruption, the summit of Mount Vesuvius had been reduced by 450m, making its total height lower than that of Mount Somma. The eruption marked the beginning of a long period of almost continuous eruptive activity by Vesuvius, that lasted until the eighteenth century.