Resurrecting Pompeii (16 page)
Read Resurrecting Pompeii Online
Authors: Estelle Lazer
An understanding of the form of the eruption enables us to establish the principal causes of death of the
AD
79 victims. It also helps determine the potential for individuals to have escaped. Until the last few decades, opinion was divided about the exact nature of the event that destroyed the towns in the region of Mt Vesuvius in
AD
79. Traditionally, it was considered that the rapid build up of air-fall ash and pumice, known as tephra, accounted for the majority of deaths.
111
This approach is exemplified in the volcanological work of Bullard, who described the
AD
79 eruption as a classic example of a Vulcanian type of eruption. There are several types of eruptions, each associated with specific phases and types of eruption material.
112
Bullard’s classification is consistent with Pliny the Younger’s description of the eruption process.
113
Pliny employed the shape of a Mediterranean umbrella pine as a metaphor for the shape of the cloud that rose above Vesuvius. Pliny’s description of what he viewed from Misenum has been considered to be a valuable contribution to volcanology and is commemorated by the descriptor ‘Plinian’ for explosive eruptions that are characterized by high eruption columns of ash pumice and volcanic gases.
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The second school of thought has become the accepted interpretation. This argues that there were, in fact, two phases in the
AD
79 eruption. The first was a Plinian period of pumice and ash fall. This was followed by a phase of
nuées ardentes
, or pyroclastic density currents, after the collapse of the eruption column.
Nuée ardente
is a blanket term that has been used to cover both pyroclastic surges and pyroclastic flows. These are respectively dilute turbulent clouds of particles that are suspended in gas and hot air and dense avalanches of concentrated particles. They are composed of pumice, ash and gas. The direction of a pyroclastic flow is determined by the underlying topography, whilst that of the low density, highly turbulent surge is not dependent on ground features. As a result, a surge can spread radially from the crater at greater speed than a pyroclastic flow.
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The notion of the
AD
79 event as a two-phase eruption dates back to the eruption of Mt Pelée, Martinique in 1902, when an estimated 29,000 people were killed by a series of hot gas avalanches and has provided the term ‘Peléan’ for similar types of events. Parallels with the
AD
79 Vesuvius eruption were recognized as early as 1903 and various scholars have propagated this view.
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The definitive work was done by Sigurdsson and his team, who made a detailed stratigraphic examination of the region, with specific reference to the
AD
79 layers and were able to clearly identify the different phases from the strata.
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The only real criticism that can be levelled at the work of Sigurdsson is his almost unquestioning use of the letters of the Younger Pliny as a totally reliable source for the sequence and chronology of the eruption.
118
This is probably the result of the influence of the key aim of his initial research project in the Vesuvian region, which was to tie in the evidence of Pliny the Younger’s account with the excavations in Herculaneum and Pompeii.
119
The widely accepted
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hour-by-hour, and sometimes even half-hour, chronology is essentially based on two events.
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The first is the time that Pliny the Elder’s sister is said to have pointed out the umbrella pine shaped cloud.
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This has been used to determine that the first violent phase of this explosive eruption began at about one o’clock in the afternoon. The second is the account of events in Pliny’s second letter.
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The current interpretation of this text is that he and his mother were forced to flee Misenum by a surge at about eight o’clock on the morning of the second day of the eruption. At the very least, it is misleading to describe the precise time of each event in the eruption sequence, as it gives the impression of greater certainty than is provided by the available evidence. The use of this chronology is problematic as it is predicated on the accuracy of Pliny the Younger’s memory after an interval of about a quarter of a century.
Most of the literature that deals with eyewitness accounts concerns crime scenes but the results of this work are still appropriate for appraising Pliny the Younger’s account. Memory is complex and can be unintentionally distorted to fulfil the expectations of the witness. Consequently, eyewitness memory is notoriously unreliable as demonstrated by numerous studies.
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Various factors affect central and peripheral memory and what is perceived as such, and, depending on the event, it is possible that central and peripheral information can be interchangeable. Details that are not of primary interest tend not to be so well remembered.
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The provision of a description of the eruption was by no means the principal agenda of Pliny the Younger’s account of his uncle’s death and the timing of the event was of even less importance. The reliability of Pliny’s retrieval of information that was so peripheral to the main story, especially after such a long period of time, can be questioned.
It is notable that the in fluence of an earlier interpretation of the account of Pliny the Younger probably was responsible for scholars, like Bullard, discounting the possibility that
nuées ardentes
were a feature of this eruption.
126
The weight given to Pliny’s account is a reflection of the emphasis that has traditionally been placed on primary literary sources over physical evidence.
According to Sigurdsson, the first phase of the eruption, as it was experienced in Pompeii, occurred over a period that he arguably estimated to have lasted at least eighteen hours and resulted in a layer of ash and pumice up to 2.8 metres. Since air-fall deposits do not tend to be lethal, Sigurdsson considered that there probably would have only been a relatively small number of deaths in this phase as a result of roofs collapsing due to the weight of lapilli. He estimated that ash and pumice were deposited in the first seven or eight hours at Pompeii at a rate of 12–15 cm an hour. The accumulated weight would probably have caused roofs to collapse after several hours, probably when about 40 cm had been deposited. It has been suggested that roof collapse would probably have provided substantial incentive for people who had taken refuge in their houses to consider evacuation of the town. Falling volcanic debris may also have been responsible for some loss of life. In addition to the ash and pumice, there were lithic clasts which are pieces of rock that derive from the walls of the vent of the volcano. They are far more dangerous than pumice due to their greater density. It has been estimated that some of the lithic clasts at Pompeii were travelling at speeds of 50 metres per second when they hit the ground. Nonetheless, Sigurdsson argued that these would not have accounted for many deaths as they were only observed in very small numbers in the deposit, thus lowering the probability of individuals being hit.
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Sigurdsson suggested that this phase was not only associated with a minimal number of fatalities but that the phenomenon of the ash fall would have alerted the inhabitants of the danger to which they were being exposed and encouraged most of them to escape before the lethal second stage of the eruption. He did concede that escape would have been difficult as fugitives from this phase of the eruption would have had to contend with a thick layer of loose pumice in a dark environment.
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The second eruption phase was marked by a series of hot gas avalanches or
nuées ardentes
. This was the most lethal period in the eruption as evidenced by the number of bodies that were found above the layer of pumice. It has been observed that
nuées ardentes
are associated with a particularly high death to injury ratio, especially when compared with other types of natural disasters.
129
Sigurdsson and his team examined the stratigraphy of the entire region that was affected by the
AD
79 eruption. He concentrated on establishing the cause of death of the victims from Herculaneum but argued that his findings were also applicable to Pompeii. He considered that variation in the physical appearance of the remains in the two sites only reflected differences in posteruption groundwater levels (also see Chapter 10). All the human bodies that were discovered at the waterfront of Herculaneum from the 1980s on were found in association with what Sigurdsson identified as the first surge layer (S1). The stratigraphic evidence indicates that the majority of the Herculaneum victims were killed by this surge (S1), which did not extend as far as Pompeii. A superficial examination of the positions of the bodies suggested that they met their fate fairly rapidly.
The second and third surges that Sigurdsson identi fied also did not affect Pompeii. The fourth surge (S4) reached Pompeii some hours later, followed only minutes later by the fifth surge (S5). The fourth surge was lethal and Sigurdsson argued that it would have been responsible for the death of any occupants who had remained in the town. It was observed that the majority of the documented victims have been found within the layers of the fourth and fifth surges (S4 and S5). The bodies of these victims were subsequently covered by the thick deposit associated with the sixth surge (S6). This surge was extremely destructive and was responsible for the collapse of the walls of the highest buildings and the displacement of building materials, as well as a few of the bodies of victims.
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It is notable that until consensus was reached in the latter part of the twentieth century, Pompeian skeletal evidence was used to support opposing theories about the eruption. Often the same skeletons were subjected to different interpretations as can be seen, for example, in the work of Bullard and Sigurdsson. Both scholars cited reports of a number of bodies that were uncovered at least three metres above ground level in 1812 in the presence of Queen Caroline Murat, along with discoveries of individuals with their hands in front of their mouths. Bullard employed this evidence in an attempt to prove that the
AD
79 eruption did not include
nuées ardentes
and that the main cause of death was asphyxiation due to ash and poisonous gases in the first few hours of the eruption, whilst Sigurdsson used it to support an interpretation of death from the effects of a pyroclastic surge.
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The evidence is clearly more consistent with the latter. It makes far more sense to explain bodies found above the layer of ash and lapilli as those of people who survived the initial phase of tephra fall only to succumb to the surge, which can easily be identified in exposed sections of the site.
132
Luongo
et al
., along with De Carolis and Patricelli, published the results of more recent stratigraphic studies of the region, in conjunction with the available information on the stratigraphic level and location of the victims that have been documented from the excavations in Pompeii since 1748.
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These indicate that some modification of Sigurdsson’s conclusions are required, especially in relation to number of deaths in each phase of the eruption.
Establishing the exact details of the deaths of the victims is dif ficult, though it is possible to gain a general picture of how the majority of the victims met their fate. Sigurdsson suggested that the stratigraphic evidence was consistent with that associated with eruptions like Mt St Helens in 1980, which in turn could be used to assess the likely relative causes of death of the victims.
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It is important, however, to remember that there can be considerable variation between individual mountains and eruptions, including those within the same volcanic category.
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Despite the fact that both the 1980 Mt St Helens and the
AD
79 eruption of Mt Vesuvius were probably Peléan in nature, it is quite possible that the major causes of death were not identical.
Autopsy reports of 26 of the 67 known victims of the 1980 eruption of Mt St Helens in North America revealed that the majority of deaths were caused by asphyxiation. The bodies were found to contain an occlusal plug of mucus and ash in the trachea, larynx and upper respiratory tract. Five of the victims were diagnosed as having died of thermal shock. In two of these cases, asphyxiation was also a contributing factor. The other three bodies displayed no evidence of asphyxiation but appeared to have been baked in the surge deposit. Their extremities were mummified and the internal organs showed signs of shrinkage and desiccation. Only three out of the 25 bodies that were autopsied were killed by projectiles, namely trees or rocks that were borne by the surge. Analysis of the blood of the victims indicated that they had not inhaled toxic gases from the surge cloud. This is probably because the victims were asphyxiated before they could have been affected by gases.
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Sigurdsson extrapolated the results from these autopsy reports onto the victims of the
AD
79 eruption of Vesuvius, suggesting that the stratigraphic evidence and the positions of the corpses were consistent with a rapid death from a volcanic surge. He did not consider that the temperatures were high enough for the victims to have succumbed to thermal shock (see below). He postulated that the majority of the victims died of burns and asphyxiation within a few minutes.
137
As mentioned above, Sigurdsson did not consider that the first phase of the eruption was associated with a high mortality rate. De Carolis and Patricelli
138
made an exhaustive study of the Pompeian excavation diaries and journals, dating from the first excavations, to determine where and when documented victims died. They established that the 394 victims in the pumice that was associated with the first phase of the eruption were found in the layer that spanned, depending on the underlying topography, from ground level up to 2.6 to 2.8 metres. These victims represent 38 per cent of the 1044 known victims from Pompeii, which is clearly at odds with Sigurdsson’s claim. It has been assumed that they were mostly killed by the collapse of walls and roofs as a result of the accumulation of ash and pumice. This argument is supported by the fact that 345 of these individuals were found inside buildings as compared to 49 discovered in outdoor locations. The outdoor deaths presumably occurred as a result of collapsing building material or victims being struck by larger lithic fragments, which could be up to 17 cm in size.
139
Luongo
et al
.
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stated that some of the skulls found in the deposit associated with the first phase of the eruption exhibited skull fractures. They cite this as evidence for tephra-related deaths due to falling structural elements. They do not provide a source for this claim but other scholars who have presented this argument have relied on the accounts of William Hamilton.
141
While Hamilton provides an invaluable source for the eighteenthcentury excavations he witnessed, he was not qualified to differentiate between perimortem fractures, which are those that occur at or around the time of death, and post-mortem breaks that may have resulted from the pressure of earth on a skull over a long period of time. I did not observe any unequivocal evidence for tephra-related deaths in the Pompeian skeletal record, though one skull displayed damage that was consistent with having received a blow at or about the time of death.
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Sigurdsson considered that the second phase of the eruption was the truly lethal phase. Surge clouds, for example, have been found to travel at speeds reaching 100 to 300 kilometres per hour. They are very turbulent and have been known to transport objects, such as rocks and building materials. In addition, they generally have very high temperatures, ranging from 100 to over 400 degrees Celsius. Volcanic surges tend to have low levels of free oxygen and can carry dangerous levels of toxic gases.
143
They are generally incompatible with survival, though recent modelling by Baxter
et al
. (1998), to determine survival prospects for people in a region exposed to pyroclastic density currents suggests that certain locations can provide significant protection. Pompeian skeletons and casts, especially those that were left
in situ
, combined with the stratigraphic evidence from Herculaneum, have been used to provide evidence for the majority of deaths having resulted from a
nuée ardente
or pyroclastic density current. Certainly, more recently excavated human remains, such as those from the
Casa di Stabianus
(I, xxii, 1–2), were found in the ash layer above the lapilli of the first eruption phase (Figures 1.1, 4.1).
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The number of documented bodies recovered from the ash of the second phase is considerably higher than those found in the deposit associated with the Plinian phase of the eruption. Of the 653 victims from this phase, 334 were found inside buildings and 319 were uncovered either along the roads or in open spaces.
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