Vesuvius, how the true date of the eruption was established (no, it was not in summer)

According to Pliny the Youngerwho lived at the time of events, it was August 24, 79 AD when the destructive fury of Vesuvius engulfed the entire surrounding area, razing cities such as Pompeii and Herculaneum. What we know so far about one of the most famous – and deadly – eruptions of all time, however, may not be entirely correct: the real date of the natural catastrophe, in fact, would be the 24 or 25 October 79 AD. This is what emerges from a study conducted by the National Institute of Geophysics and Volcanology (Ingv) and by the National Research Center (Cnr), which integrated data from numerous disciplines, from the study of sediments to the rereading of historical sources, to follow in detail all the phases of the eruption almost two thousand years ago. The results were published in the journal on Earth science reviews.

The date problem

The story of the eruption of Vesuvius in 79 AD is definitely known: suddenly, at one in the afternoon, when the inhabitants of cities south of Naples such as Pompeii, Herculaneum and Stabia were immersed in their activities, a very violent occurred explosive eruptionin which lava, ashes and incandescent lapilli poured into the surrounding areas, overwhelming everything they encountered, including homes, objects and people. Such events are part of what is said explosive volcanismwhich, indicates eruptions in which the violent and sudden expansion of the volcanic gases contained in the magma occurs. Among the most destructive phenomena of explosive volcanism are the Plinian eruptionscharacterized by high speed escape from the volcanic duct of a jet of incandescent gas together with pumice e ashes.

The most famous and documented Plinian eruption is that of Vesuvius in 79 AD, and not by chance: in fact, this type of eruption is so called because we have the first knowledge on the explosive eruption of Vesuvius just starting from a letter written by Pliny the Younger to Tacitusin which it describes in detail the volcanic events that destroyed Pompeii, date included. In fact, in the letter it appears that the eruption occurred “nine days before the Kalends of September”, Date corresponding to August 24 and that for a certain period of time it was considered the actual one of the catastrophic event. In reality it is from the eighteenth century – says Biagio Giaccio, co-author of the article – that it it is the subject of numerous debatesas there are various evidences that would refute the Plinian version: for example, finds in the typically autumn fruit area, the heavy tunics worn by the inhabitants of Pompeii, and finally the discovery of an inscription in charcoal on the wall of a building in the destroyed city which can be translated as’The sixteenth day before the calends of November – October 17, ed – he indulged in food in an immoderate way‘, making us assume that the eruption could not have occurred before that date.

A multidisciplinary approach

Basically, despite being one of the most studied eruptions and which has taught a lot to modern volcanology, that of Vesuvius still presents many open questions. This is why the study authors thought of a multidisciplinary approach that would integrate most of the studies on the subject, combining different investigation approaches (exploiting the analysis of historical, stratigraphic, petrological, geophysical and climate modeling data) e temporally following the events of eruption and debris deposition of 79 AD, even thousands of kilometers away from Vesuvius itself. The first result was that of date change of the eruptionnow estimated 24-25 October.

The authors of the study, in fact, have measured the impact of the individual phases of the eruption on the areas and archaeological sites near the volcano, then following the traces left by the deposits of volcanic material for miles and miles, as far as Greece. Not only that: the researchers also evaluated the effects of the rash on climate of time and its short-term variations. Thanks to these data, they it is hoped to find new perspectives useful for the study of similar events that may occur in the future.

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