**5. The chronology of AD 79 eruption: How the eruption impacted on the Roman population**

Pliny the Younger observed the eruptive column from Miseno at about 13 h of the day of October 24 (**Figure 9**) [1, 11]. Probably, the start of the AD 79 Pompeii eruption (**Figure 10**) and the eruptive column begin to rise probably at 12 h of October 24 and appear just as strange phenomena for the Pompeii people (**Figure 11**). Fall-out products from the AD 79 eruption can be found both in the surrounding area and at a distance, stretching in a SE direction as far as Cilento: October 24 (the first day of eruption): "…a cloud appeared of unusual size and shape… The cloud advanced in height; and I cannot give you a more just representation than the form of a pine tree*…*" [1]. Eruptive column of the white pumice was sustained for about 8 h. Pliny the Younger, in its letters to the historian Tacito,

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**Figure 10.**

*Modified volcanic section of the AD 79 [20].*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk*

*DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 9.** *The younger Pliny reproved.*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 10.** *Modified volcanic section of the AD 79 [20].*

*Forecasting Volcanic Eruptions*

**4. Date of the AD 79 eruption**

Vesuvius ([11]; references therein).

**Roman population**

The south-easterly trend of the AD 79 products appears to be anomalous, because the eruption is conventionally believed to have occurred on August 24, when its southeast dispersive trend falls in a transitional period from the summer to autumnal wind regimes [11]. In fact, the AD 79 tephra dispersive direction toward the southeast is not in agreement with the June–August high-altitude wind directions in the region that are rather toward the west. This poses serious doubt about the date of the eruption and the mismatch raises the hypothesis that the eruption occurred in the Autumnal climatic period (October), when high-altitude winds were also blowing toward the southeast. New archaeological findings presented in the [11] study definitively place the date of eruption in the Autumn (October), in good agreement with the prevailing high-altitude wind directions above Somma-

**5. The chronology of AD 79 eruption: How the eruption impacted on the** 

Pliny the Younger observed the eruptive column from Miseno at about 13 h of the day of October 24 (**Figure 9**) [1, 11]. Probably, the start of the AD 79 Pompeii eruption (**Figure 10**) and the eruptive column begin to rise probably at 12 h of October 24 and appear just as strange phenomena for the Pompeii people (**Figure 11**). Fall-out products from the AD 79 eruption can be found both in the surrounding area and at a distance, stretching in a SE direction as far as Cilento: October 24 (the first day of eruption): "…a cloud appeared of unusual size and shape… The cloud advanced in height; and I cannot give you a more just representation than the form of a pine tree*…*" [1]. Eruptive column of the white pumice was sustained for about 8 h. Pliny the Younger, in its letters to the historian Tacito,

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**Figure 9.**

*The younger Pliny reproved.*

#### **Figure 11.**

*Cartoon shows how the Romans were surprised at the begin of the AD 79 eruption. They were unaware of the volcanic hazard.*

**Figure 12.** *The route of Pliny the Elder; after that, he realized the start of Somma activity (AD 79 eruption).*

writes that his uncle Pliny the Elder "… was at Misenum where he had the command of a fleet which was stationed there. At about 15 h Pliny the elder received a request of help by his friend Rectina and decided to start from Misenum with four Liburnae. After 4 h, he arrived near the coast of Oplonti but he cannot disembark because the effects of the eruption and decided to move toward Stabie, where his friend Pomponiano was located (**Figure 12**). At Pompeii, roof collapse due to the weight of the white pumice level begins between 17 and 18 h (**Figure 13**). After that, the Pompeii eruption changed from white pumice to grey pumice. This transition also changed the composition of the eruption (**Figure 14**). During the first day of the eruption Herculaneum was spared by pumice fall phase and people could observe the pyroclastic cloud diverted toward SE by winds. From about 1 to 8 h of

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**Figure 14.**

**Figure 13.**

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk*

*Cartoon shows the moment when Pompeii home start to collapse by the load of fall-out volcanic phase.*

October 25, the Plinian column of grey pumice assumed a collapsing character giving rise to surge and pyroclastic flows currents. Pliny the younger wrote I believe, while the vapor was fresh, it (the cloud) more easily ascended; but when the vapor

*Classic section of the AD 79 eruption with white and grey pumice fall-out.*

*DOI: http://dx.doi.org/10.5772/intechopen.89989*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 14.** *Classic section of the AD 79 eruption with white and grey pumice fall-out.*

October 25, the Plinian column of grey pumice assumed a collapsing character giving rise to surge and pyroclastic flows currents. Pliny the younger wrote I believe, while the vapor was fresh, it (the cloud) more easily ascended; but when the vapor

*Forecasting Volcanic Eruptions*

**Figure 11.**

*volcanic hazard.*

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**Figure 12.**

writes that his uncle Pliny the Elder "… was at Misenum where he had the command of a fleet which was stationed there. At about 15 h Pliny the elder received a request of help by his friend Rectina and decided to start from Misenum with four Liburnae. After 4 h, he arrived near the coast of Oplonti but he cannot disembark because the effects of the eruption and decided to move toward Stabie, where his friend Pomponiano was located (**Figure 12**). At Pompeii, roof collapse due to the weight of the white pumice level begins between 17 and 18 h (**Figure 13**). After that, the Pompeii eruption changed from white pumice to grey pumice. This transition also changed the composition of the eruption (**Figure 14**). During the first day of the eruption Herculaneum was spared by pumice fall phase and people could observe the pyroclastic cloud diverted toward SE by winds. From about 1 to 8 h of

*The route of Pliny the Elder; after that, he realized the start of Somma activity (AD 79 eruption).*

*Cartoon shows how the Romans were surprised at the begin of the AD 79 eruption. They were unaware of the* 

#### **Figure 15.**

*Herculaneum with Roman community hit by pyroclastic density currents at the end of white and white and grey pumice fall-out.*

was wasted the cloud became loose, or, perhaps, oppressed by its own gravity, and dilated itself into a greater breath…"

October 25 (the second day of eruption): pyroclastic flows bury the town (Herculaneum) under a 15-m-thick ash deposit. The inhabitants, in the vain attempt to escape by boat, take refuge in the barrel-vaults along the seaside where they will die (**Figure 15**). The Pompeii and Herculaneum towns, before the eruption, nearly looked out directly over the sea. The AD 79 eruption was a natural event that strongly affected the perivolcanic area of Somma-Vesuvio. The paleogeographic and socioeconomic variations that it caused were huge. After the eruption, the area was completely buried with the consequent progradation of the coast line [12]. Trading in the Nola and Acerra areas was badly affected as communication routes to the sea through the port of Pompeii no longer existed. Toward Stabia, the Pomponiano house was highly damaged by white and grey pumice fall, and the courtyard was filled by pumice deposits, so that early in morning of October 25, Pliny the elder decided to move toward the beach. In the meantime, a phase of eruptive calm had been registered and, in the Pompeii area, people who had managed to escape the

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**Figure 17.**

**Figure 16.**

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk*

*DOI: http://dx.doi.org/10.5772/intechopen.89989*

*Cartoon shows how the PDC were severe by hitting Roman villages.*

*Engraving showing Pliny the Elder found death on the beach of Stabie village.*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 16.** *Cartoon shows how the PDC were severe by hitting Roman villages.*

**Figure 17.** *Engraving showing Pliny the Elder found death on the beach of Stabie village.*

*Forecasting Volcanic Eruptions*

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**Figure 15.**

*grey pumice fall-out.*

was wasted the cloud became loose, or, perhaps, oppressed by its own gravity, and

*Herculaneum with Roman community hit by pyroclastic density currents at the end of white and white and* 

October 25 (the second day of eruption): pyroclastic flows bury the town (Herculaneum) under a 15-m-thick ash deposit. The inhabitants, in the vain attempt to escape by boat, take refuge in the barrel-vaults along the seaside where they will die (**Figure 15**). The Pompeii and Herculaneum towns, before the eruption, nearly looked out directly over the sea. The AD 79 eruption was a natural event that strongly affected the perivolcanic area of Somma-Vesuvio. The paleogeographic and socioeconomic variations that it caused were huge. After the eruption, the area was completely buried with the consequent progradation of the coast line [12]. Trading in the Nola and Acerra areas was badly affected as communication routes to the sea through the port of Pompeii no longer existed. Toward Stabia, the Pomponiano house was highly damaged by white and grey pumice fall, and the courtyard was filled by pumice deposits, so that early in morning of October 25, Pliny the elder decided to move toward the beach. In the meantime, a phase of eruptive calm had been registered and, in the Pompeii area, people who had managed to escape the

dilated itself into a greater breath…"

#### *Forecasting Volcanic Eruptions*

effects of the pumice fall phase tried to return to their homes by walking over the pumice deposits which had become as high as the rooftops. As they made their way home, accompanied by some soldiers, hot toxic cloud swamps departed by the hot avalanche that are invading Herculaneum, and kills them (**Figures 16** and **17**).

October 26 (the day after the eruption): Pliny the Elder's body was found dead on the beach "…when the light returned, which was not till the third day after his death, his body was found untouched by the fire, without any visible hurt, in the dress in which he fell, appearing rather like a person sleeping than like one who was dead*"* (Pliny's letters).

The destructive action of pyroclastic products on constructions is exerted in two main ways. Fall products, which are emplaced grain by grain, falling down from the eruptive cloud, blanket roofs with a layer of granular deposit, whose thickness is a function of both the intensity of the eruption and the distance from the vent. The pyroclastic fall layer loads the roofs with an extra weight that, when the maximum sustainable load threshold value is exceeded, can cause the roof to collapse. Pyroclastic density currents (PDC), on the other hand, generally originating from the collapse of the eruptive column, are gas clouds rich in both lithic and juvenile fragments that, running over the ground, exert a dynamic overpressure on the obstacles encountered on their way and are capable to destroy the buildings (**Figure 18**) [13]. Actually, the first damage was made by white pumice fall deposits,

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**Figure 19.**

*Romans' body-mould made by gypsum in modern age.*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk*

weighing on the roofs, leading to collapse them. The first pyroclastic density currents occurred during the late deposition of white pumice fall products; successively, grey pumice fall and pyroclastic flow and then PDC. The broken columns of the main atrium lie on the pumice fall deposits. The collapsing angle of the columns points out also the direction of the diluted currents (**Figure 18**). Around Somma-Vesuvius volcano, there is also a petrified tree that by its curvature shows the direction of the PDC. The first day of eruption produced 3 m of pyroclastic fell products blanket Pompeii, and some inhabitants fell asleep, and were buried by the collapse of their houses. Steps needed to obtain a mould of a body buried by pumice fall are: (1) the body was covered by pumice fall during the eruption; (2) organic matter was destroyed by heat, and the vacuum had been filled later on, in modern age, by gypsum; and (3) the shape of the body was then recovered (**Figure 19**).

**6. The Somma-Vesuvius history after the AD 79 eruption**

The history of ancient stratovolcano that suffered a caldera-like collapse, Somma [8, 10], ended with the AD 472 eruption. In Middle Ages, from AD 500 to AD 1100,

*DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 18.** *Effects of AD 79 eruption on Roman buildings: Villa 6 at Terzigno.*

*The Somma-Vesuvius Activity with a Focus to the AD 79 Eruption: Hazard and Risk DOI: http://dx.doi.org/10.5772/intechopen.89989*

**Figure 19.** *Romans' body-mould made by gypsum in modern age.*

weighing on the roofs, leading to collapse them. The first pyroclastic density currents occurred during the late deposition of white pumice fall products; successively, grey pumice fall and pyroclastic flow and then PDC. The broken columns of the main atrium lie on the pumice fall deposits. The collapsing angle of the columns points out also the direction of the diluted currents (**Figure 18**). Around Somma-Vesuvius volcano, there is also a petrified tree that by its curvature shows the direction of the PDC. The first day of eruption produced 3 m of pyroclastic fell products blanket Pompeii, and some inhabitants fell asleep, and were buried by the collapse of their houses. Steps needed to obtain a mould of a body buried by pumice fall are: (1) the body was covered by pumice fall during the eruption; (2) organic matter was destroyed by heat, and the vacuum had been filled later on, in modern age, by gypsum; and (3) the shape of the body was then recovered (**Figure 19**).
