Precursors of the eruption (animation 193 Kb)

Before the eruption of 79, earthquakes occurred for some time, but were disregarded by local inhabitants because of their familiarity with the phenomenon. Seneca reports that an earthquake occurred on 5 February of 62 (according to Tacitus) or 63 AD.

The earthquake laid down Pompeii, made great ruins in Herculaneum, and caused minor damage in Nuceria and Naples, where the emperor Nero was performing in the theatre.

According to Seneca, the earthquakes lasted for several days ("non desiit enim assidue fremere Campania") until they became milder "but still caused great damage".

We presume that this earthquake swarm occurred at a shallow depth in the Vesuvian area, given the distribution and the area extent of damages.

In the last sentences of this writing, Seneca asked himself if this disaster in Campania had not "made every man strengthened and resulted (resolved) against all catastrophes."

The reply to his question probably came 17 years later, when Pliny the Elder went to the rescue of the people staying in the area that had been shaken for several days.

As the younger Pliny testified, "for several days before (the eruption) the earth had been shaken, but this fact did not cause fear because this was a feature commonly observed in Campania" (praecesserat per multos dies tremor terrae, minus formidolosus quia Campaniae solitus).

Repair work was underway in some houses at Pompeii and Oplonti Villa when the eruption occurred. This can be considered evidence of intensive seismic shaking of the buildings.

Dio Cassius (150-235 AD) also reports some precursors of the eruption. He tells that for several days before the eruptions there were earthquakes and subterranean rumblings and giants were seen wandering on the earth (giants are a common feature associated with earthquakes and volcanic eruptions; Scandone, 1987).
 
 

We do not know if the description made by Pliny the Younger of the eruption of 79 AD is reliable or not (he explicitly mentions in the end of the first letter that other persons reported to him most of the facts); we will however recall some of the more important points in his account.

We make use of the text of the letters of the "Scriptores Classicorum Bibliotheca Oxonensis" translated into italian by Marcello Gigante (1980). When necessary we made a literal translation into english.

The first letter

The beginning of the eruption is uncertain: the two Plinys observe the cloud at the seventh hour of the day (1 PM, Sigurdsson et al, 1985). We must presume that the eruption began sometime earlier to allow the arrival, at about the same hour, of a messenger sent from the vesuvian area.

Sigurdsson et al (1985) suggest that the event prompting Rectina, wife of Tascus, to send the messenger, was a phreatic explosion at the very beginning of the eruption.

The eruptive column was directly observed by Pliny the Younger from a distance of 21 km, so that he could fully appreciate its total extent and behavior. Subsequent scholars of Vesuvius eruptions have frequently used the same description for other eruptions. The description gives us the idea of the typical explosive eruption

"It resembled a pine {Mediterranean pine} more than any other tree. Like a very high tree, the cloud went high and expanded in different branches. I believe, because it was first driven by a sudden gust of air (recenti spiritu eiecta), then, with its diminution or because of the weight, the cloud expanded laterally, sometimes white, sometimes dark and stained by the sustained sand and ash (pondere suo victa in latitudinem vanescebat, candida interdum, interdum sordida et maculosa prout terram cineremque sustulerat)."

The route of Pliny the Elder

Pliny the Elder, on his course to the endangered area, has the wind blowing at his back, from the north-west. We do not know where he intended to land, but he changed his mind because a new shoal formed by the eruption prevented the landing.

At this moment he observes red-hot stones and pumice falling on the ships, so he must already be at the south-east of the volcano as suggested by the area distribution of pumice (Lirer et al, 1973).

We may infer that he was trying to reach the Pompeii port and that he could not land because of the floating pumice, so, he changed his mind and sailed toward Stabiae to reach the friend, Pomponianus, who could not leave because of the opposing wind.

The decision of reaching Stabiae was a fatal one because brought the rescuers to a place where sea escape was impossible. Stabiae was separated by the center of the gulf where the shore made a gentle arc and the waves rushed in ("Stabiis erat diremptus sinu medio (nam sensim circumactis curvatisque litoribus mare infunditur" ). The ancient coastline formed probably a more pronounced gulf than nowadays.

The northwestern wind favoured the entrance into the gulf ("Quo tunc avunculus meus secundissimo invectus" - most favourable to the route of my uncle-) but prevented the escape on the next day during the paroxismic phase of the eruption ("Placuit egredi in litus, et ex proximo adspicere, ecquid iam mare admitteret; quod adhuc vastum et adversum permanebat " - They decided to reach the shore and look if the sea permitted the escape. But the sea was still stormy and did not allowed the departure-).

The second letter

During the time of the eruption, Pliny the Younger stayed in the proximity of Misenum from where he observed the eruption along with his mother (Pliny the Elder's sister). In the second letter, he describes what occurred there.

Earthquakes - During the night of the first day of the eruption, and for most of the morning of the next day, the houses of Misenum where shaken by earthquakes that caused much panic. Pliny the Younger and his mother escaped; they reached a place from which Vesuvius, Capri and Cape Misenum were visible.

The only place where such view is possible is the "Monte di Procida" hill. On the top of the hill, wheeled-charts on flat land were shaken back and forth even if chocks were placed against the wheels. Given the distance from Vesuvius, we may presume that the seismic activity, or a strong seismic tremor, ranged in magnitude between 4 and 5.

Tsunami : ("Praeterea mare in se resorberi et tremore terrae quasi repelli videbamus "- Further on, we saw the sea retreating as if pushed by the earthquakes-) The retreat of the sea observed in Misenum is probably related with a tsunami associated with the climax of the eruption. A similar occurrence has been described during the eruption of Vesuvius of 1631.

Black clouds at Misenum: "Ab altero latere nubes atra et horrenda, ignei spiritus tortis vibratisque discursibus rupta, in longas flammarum figuras dehiscebat " - From the other side, black and horrible clouds, broken by sinuous shapes of flaming winds, were opening with long tongues of fire).

The description suggests strong explosions that - After a little while descended onto the land, opened the sea, covered Capri and prevented the sight of Misenum- ("Nec multos post illa nubes descendere in terras, operire maria; cinxerat Capreas et absconderat, Miseni quod procurrit abstulerat ").

The clouds reached the place where Pliny the Younger and his mother where ("densa caligo tergis imminebat, quae nos torrentis modo infusa terrae sequebatur. (...) et nox non qualis inlunis aut nubila, sed qualis in locis clausis lumine exstincto." - A dense haze was impending at our backs, following us like a stream flowing on land (...) and the night fell on us, not like a night with clouds or without stars, but like the night in a closed place without a lamp)-.

After a while they were reached by another cloud - Again the obscurity, again the ash, dense and heavy. We raised some time to shake away the ash as we could have been covered and choked by its weight- ("Tenebrae rursus, cinis rursus, multus et gravis. Hunc identidem adsurgentes excutiebamus; operti alioqui atque etiam oblisi pondere essemus ".

We can exclude that these phenomenona can be ascribed to air-fall ash. The distribution of the pumice driven by stratospheric winds is toward the south-eastern side of Vesuvius (Lirer et al, 1973, Sigurdsson et al, 1985). Low altitude winds were blowing from north-west (as the course of Pliny the Elder testifies).

We have to conclude that the phenomena in the proximity of Misenum were due to a pyroclastic surge as also suggested by Sigurdsson et al (1985). If such description is truthful, it raises however some new questions about the extent of damage caused by the eruption. Any pyroclastic surge reaching Misenum, causing breathing difficulties and obscuration of the sky must first have passed the city of Naples.

In the proximity of the volcano these phenomena caused severe damages and deaths. Most people living in the aerea probably escaped during the first phase of the eruption when the high eruption column deposited in the proximity of Pompei about 4 meters of pumice lapilli.

In the towns remained mostly animals like horses unable to walk in the thick cover of lapilli or dogs left to watch the unguarded houses. Only a few individuals probably died because of this.

The arrival of pyroclastic flows and surges caused instead the total destruction of that part of the houses that emerged above the pumice layer. Many people that were still in the towns or had come back were caught by surprise by this second phase and their bodies are found above the fall-pumice layer within the surge deposit.

The Damages

We do not have any evidence of extensive damages in Naples although the contemporary roman authors were rather obscure about the true extent of damages. We know (from Svetonius) that Emperor Titus appointed two ex-consuls (Curatores Restituendae Campaniae) to supervise the work of restoration of the damaged region and to solve the legal questions raised by the death of so many people.

We also know that the import to Rome of Campanian wine suffered a drastic decrease after the eruption (Videmann, 1987). We find an echo of such occurrence in a poem of Martial (40-104 AD) who describes Vesuvius, once covered by green grapes, now submerged under flames and lapilli.

Pliny the Younger does not mention any damages other than those suffered by himself or the uncle. However a record of the destruction of Herculaneum and Pompei is found in Marcus Aurelius (121-180 AD) and in Dio Cassius (AD 150-235). This last author also reports that the ashes of the eruption reached Africa (the modern Libya), Syria and Egypt, and caused pestilence.

Similarly the poet Papinius Statius (40- 96 AD) made many references to the ruins caused by Vesuvius in his collection of poems "Silvae". The poet lived in Naples for long time and was possibly there during the eruption, as he got a poetry premium in the town in 78 or 80 AD. Soon after he left and lived in Rome until 92. On that date he had to write a poem (Silvae III, 5) "Ad Claudiam Uxorem" to convince his wife to come back to Naples (Paratore, 1992).

In this poem we find informations on the state of the town at that date: "Non adeo Vesuvinus apex et flammea diri- montis hiems trepidas exhausit civibus urbes- stant populisque vigent (The summit of Vesuvius and the fire-storm did not made the anxious cities empty of men, they still live full of men); Hic auspice condita Phoebo tecta, Dicarchei portusque et litora mundi hospita; (Here you will see the temple of Phoebus and the port of Pozzuoli and its hospitable shores) (...) Nostra quoque et propris tenuis nec rara colonis Parthenope (Full of citizens and colonists is our dear Parthenope (Naples) (...) Has ego te sedes (...) transferre laboro, quas et mollis hiems et frigida temperat aestas, quas imbelle fretum torpentibus adluit undis (I want to to bring you to these places where the winter is sweet and the summer is fresh, where the sea lightly touches the land with lazy waves).

According to these verses, we get the impression that Naples and all the region of Campi Flegrei had completely recovered from the damages of the eruption. Different was the condition in the immediate surrounding of Vesuvius. Possibly only Stabiae had recovered at the time of Statius (Renna, 1992).

Renna (1992) suggests that the important road connecting Nuceria to Stabiae, covered by the deposits of the eruption, was restored already in 121 AD; this same author suggests that the areas of Portici and Torre del Greco were occupied between the II and IV-V century AD, and those of Pompei and Herculaneum between the III and V century AD.

The memory of the lost cities lasted for centuries. The vestiges of a lost town called "La Civita" (from the latin Civitas=town) were commonly found by farmers. The systematic excavation of Pompei started only in the XVIII century by the order of Charles III, King of the Two Sicilies.

1 - Herculaneum - Limit of excavated area. The deposits of pyroclastic flows covering the town are visible on the right
2 - Herculaneum -Close up of pyroclastic flows. At least two units are visible
3 - Herculaneum - Columns broken by the weight of volcanic products.
4 - Herculaneum -  Cardo V with a public fountain and a "thermopolium" (fast-food) .
5 - Herculaneum - Peristilium or inner garden . All these areas were originally filled by ashes.
6 - Herculaneum - The dark areas are the original woods and doors. The temperature of the pyroclastic flows was between 100 and 400°C and the carbonization was caused by mineralization processes more then by actual fires.
7 - Herculaneum - Food containers (dolia) in a thermopolium. Pompei was renown for a fish sauce called garum.
8 - Herculaneum - Paintings in the so-called Collegium Augustalis
9 - Herculaneum - Inner structure of an edifice decorated by paintings.
10 - Herculaneum - Paintings in the so-called Collegium Augustalis.
11 - Herculaneum -Original kids graffiti in the Samnitic house.
12 - Herculaneum - The 79 AD sea-shore of Herculaneum  . The level is now at a depth of 4 m below the present sea-level. In these area were found more the 300 skeletons and a boat.
13 - Herculaneum - View of the sea-front of the town. To the lower right is the area of Nonius Balbus and the sub-urban baths..
14 - Herculaneum - Several buildings have the holes made during the early excavation (1700-1800) when they dig tunnels in the deposits of pyroclastic flows.
15 - Herculaneum - A building with the original upper floor..
16 - Pompeii -  "Vesuvius Gate and Mount Vesuvius.
17 - Pompeii - The Anphitaetrum.
18 - Pompeii - Cast of victims. The cast is obtained by the filling the cavity in the ashes with liquid chalk. the method was inented in 1863 by Giuseppe Fiorelli.
19 - Pompeii - Cast of victims at Nocera gate. The position is suggestive of a death by asphixiation by the ingestion of hot ashes.
20 - Pompeii - Cast of victims with may children in the so called "orto dei fuggiaschi".
21 - Pompeii - Nocera gate: the deposits of the pumice fall and of the surges that destroyed the town.
22 - Oplontis - Villa of Poppea - In the swimming pool is visible the succession of deposits that destroyed the villa.
23 - Oplontis - Villa of Poppea , garden. The succession of deposits is visible on the wall. The cast of the tree show the effect of the arrival of pyroclastic flows that bended the part of the tree emerging above the pumice fall.

Bibliography 

• Other informations regarding Vesuvius or the other neapolitan volcanoes can be found in the homepage of Neapolitan volcanoes)
• The volcanological excursion of the area surrounding Vesuvius