One more way to die: Tremors when Vesuvius erupted collapsed shelter walls

Archaeologists have hotly debated the precise cause of death of those who perished in Pompeii when Mount Vesuvius erupted in 79 CE. Did they die of asphyxiation, from the extreme heat, or from a combination of factors? A new paper published in the journal Frontiers in Earth Science examines the complicating effects of earthquakes that occurred just prior to and concurrently with the eruption. Of most interest was the discovery of two skeletons of people who likely died when their shelter collapsed around them, weakened by the seismic tremors.

As previously reported, the eruption of Mount Vesuvius released thermal energy roughly equivalent to 100,000 times the atomic bombs dropped on Hiroshima and Nagasaki at the end of World War II, spewing molten rock, pumice, and hot ash over the cities of Pompeii and Herculaneum in particular. Archaeologists believed that the vast majority of the victims died of asphyxiation, choking to death on the thick clouds of noxious gas and ash.

However, a 2001 study in Nature, co-authored by University of Naples archaeologist Pierpaolo Petrone, estimated a temperature of 500° Celsius (932° Fahrenheit) for the pyroclastic surge that destroyed Pompeii, sufficient to kill inhabitants in fractions of a second. In 2018, we reported on Petrone's conclusion that inhabitants of Herculaneum may have suffered a similar fate. He observed fracturing in the bones of some 100 excavated skeletons, as well as "cracking and explosion" of the skullcaps, consistent with forensic cases where skulls burst from extreme heat.

Petrone's 2020 follow-up study offered additional evidence that extreme heat killed many victims, based on analysis of one victim's skull in particular, first excavated in the 1960s from Herculaneum. There was evidence of brain matter remains in the skull. Usually such brain matter would be "saponified" by the extreme heat—that is, it turned to soap (glycerol and fatty acids). But this victim's brain matter had been vitrified, i.e., fused into glass. Later that year, Petrone reported fresh evidence that this might, indeed, have been the case, announcing his discovery of preserved human neurons in the victim with the "glassified" brain, although other scientists expressed skepticism about that finding.

A 2023 multidisciplinary analysis of seven plaster casts from Pompeii concluded that these victims, at least, likely survived the early eruption and died some 20 hours later from asphyxiation, although the authors were careful to emphasize that their findings were only applicable to these particular cases. "It is likely that the catastrophic eruption killed people in different ways," the authors of that 2023 study wrote, concluding that "generalizing and supporting a sole hypothesis of death becomes overly reductive."

Seismic shocks

Now we have yet another twist: Some Pompeii residents may have perished due to the cumulative effects of earthquakes and aftershocks. According to Domenico Sparice, a volcanologist at INGV-Osservatorio Vesuviana, and co-authors, there is historical evidence of seismic activity in the decades prior to the 79 CE eruption. For instance, an earthquake in 62–63 CE caused extensive damage to buildings in Pompeii such that repairs were still underway 17 years later.

Many houses in Pompeii had goods and furniture set aside, with piles of lime and other building materials stacked, as well as incomplete wall decorations and frescoes—all indications of ongoing repairs. "The picture that emerges is of a city that, between 62 and 79 CE, suffered the effects of recurring earthquakes and volcanic tremors that forced the inhabitants to undertake continuous reconstruction, renovation, and restoration works until the eruption," Sparice et al. wrote.

Pliny the Younger reported seismic shakings for several days before the eruption but noted that people weren't particularly alarmed because they were accustomed to it. During the eruption itself, Pliny reported tremors in Misenum, some 29 kilometers west of Vesuvius during the night of the first day of eruption, as well as violent aftershocks at the dawn of the second day. He wrote that the "earthquakes... that night became so intense that everything seemed not only to be shaken but overturning." As for the following morning. "the chariots we had ordered to be brought out, though on a level ground, were shaken back and forth and did not remain steady in their places even wedged with stones."

Seismic activity was clearly a factor, yet it can be difficult to identify specific evidence of seismic damage during archaeological excavations at Pompeii since most of the devastation was primarily caused by volcanic phenomena, and the two types of damage intertwine. "For example, earthquakes may trigger the collapse of buildings already conditioned by a vertical load of a fall deposit," Sparice et al. wrote. "Alternatively, the dynamic pressure of a pyroclastic current may affect buildings already weakened by seismic shakings."

The discovery of two male skeletons with traumatic injuries consistent with collapsing structures provides key evidence for this scenario. The remains were found at the Insula dei Casti Amanti, a name derived from a fresco depicting two lovers kissing. Excavations of the site have been ongoing, with the most recent efforts revealing two adjoining rooms (designated A and 22) with evidence of wall failures and damage consistent with structural collapse.

The two skeletons found in Room A were male, around 50 years of age. The first (Individual 1) was lying on its right side with wall debris covering the skull, torso, upper limbs, and part of the lower limbs; the back was exposed and facing the center of the room. The second (Individual 2) was lying on its left side on top of a heap of small rocks and ashes (pumice lapilli). A large masonry fragment lay on top of the right lower limb and pelvis, and the skeleton was covered in a layer of wall fragments and pumice.

The position of Individual 1 is consistent with a man being suddenly crushed by the collapse of a large wall, causing trauma that would have led to immediate death. Individual 2 met a similar fate but may have been trying to protect himself with some kind of round wooden object. Excavators found traces of such an object in the volcanic deposits. It seems unlikely these two men choked to death on thick clouds of hot ash, or perished from extreme heat, since their skeletons were found on top of the pumice lapilli layer rather than under it. According to the authors, it seems the two men survived the initial phase of the eruption and took temporary shelter, only to be crushed under collapsing walls weakened by all the seismic activity before the onset of the pyroclastic flows.

“These complexities are like a jigsaw puzzle in which all the pieces must fit together to unravel the complete picture,” said Sparice of their findings. “We proved that seismicity during the eruption played a significant role in the destruction of Pompeii and, possibly, influenced the choices of the Pompeiians who faced an inevitable death.”

Frontiers in Earth Science, 2024. DOI: 10.3389/feart.2024.1386960  (About DOIs).