The calamitous eruption of Mount Vesuvius in 79 CE completely obliterated people living in nearby Roman towns, including Pompeii and Herculaneum, earning it a reputation as one of history’s most bloodcurdling horror stories.
Now, scientists have discovered new and terrifying details about that day that could have real-world implications for the hundreds of thousands of people who still live in the blast zone of this tempestuous volcano, which could produce another disastrous blast again one day, reports a new study.
The research unveils previously unknown evidence that a cloud of hot gas–with temperatures of more than 555degC (1,031degF)–initially swept through Herculaneum, essentially vaporizing countless victims, before the area was deluged by currents made of thicker ash. This early surge of hot gas, known as a pyroclastic density current (PDC), could help explain some of the bone-chilling finds at Herculaneum, including a piece of brain that was transformed to glass by the shock of the heat.
Researchers led by Alessandra Pensa, a geologist at University of Roma Tre, reconstructed this new timeline of the disaster by examining charcoal deposits across the ruins of Herculaneum. According to a last week study, the results provided the first direct assessment on the “extremely high temperature impact from the very first Ash cloud, which caused deaths and damaged infrastructures,” the reports.
“Despite the 79 CE being one of the most studied eruptions, the exact timing, and the causes of death at Pompeii and Herculaneum are still debated, bearing implications for volcanological, archaeological and forensic anthropological studies,” Pensa and her colleagues said in the study.
“Charcoal proved to be the only proxy capable of recording multiple, ephemeral extreme thermal events, thus revealing for the first time the real thermal impact of the 79 CE eruption,” the researchers noted. “The lethal impact documented for diluted PDC produced during ancient and recent volcanic eruptions suggests that such hazard deserves greater consideration at Vesuvius and elsewhere, especially the underestimated hazard associated with hot detached ash cloud surges, which, though short lived, may expose buildings to severe heat damages and people to death.”
Pompeii is the most famous settlement destroyed by this ancient eruption, in part because layers of ash buried the town and its residents, leaving them eerily preserved for nearly 2,000 years. Researchers working in Herculaneum, a nearby town, have found many strange curiosities among the ruin ruins. One of these is a fragment of a human brain, which appears to be vitrified from the volcanic eruption. These clues indicate that Herculaneum’s victims may have suffered a more horrific fate than the ones at Pompeii.
“The heat-induced effects suffered by the victims, notably the explosion and charring of skulls, vaporization of brains, cracked and charred bones, cracked teeth, contraction of limbs and thermal degradation of blood hemoproteins indicate the occurrence of an early extremely high thermal event higher than the previously estimated temperature of about 500degC,” Pensa and her colleagues explained.
“Unlike Pompeii, where many bodies show the typical post-mortem stance known as pugilistic attitude, the lack of such corpse attitude at Herculaneum testifies to the rapid disappearance of soft tissue, as the pugilistic stance is due to dehydration and shortening of muscles induced by intense heat,” the researchers continued. “However, until now, no direct measures of such a high temperature early [pyroclastic current] event were made at Herculaneum.”
By analyzing the charcoal deposits, the team was able to estimate the temperature of the initial diluted current that decimated Herculaneum. This early blast of gas was, at minimum, 550degC making it at least 100degC hotter than the following ash clouds that later blanketed the landscape and subsumed buildings and communities. The results help to explain some of the scary finds at Herculaneum, including the piece of glassy brain.
“The occurrence of an early >550 degC short lived diluted PDC event leaving only a thin ash layer on the ground, and later followed by the deposition of lower temperature but thicker pyroclastic deposits, allows to understand the conditions for the formation and preservation of a vitrified brain recently discovered within a victim’s skull in the Collegium Augustalium,” the team said.
“The transformation into glass of fresh cerebral tissue in a hot environment is only possible if two conditions are met: (1) the heating event is short-lived, so that the tissue is not fully vaporized, and (2) once the diluted PDC has vanished, the body is not fully entombed in a hot deposit, a necessary condition to allow the very rapid cooling required to attain vitrification,” the researchers noted. “This allows us to recognize that [the first PDC] was an ephemeral, extremely hot, dilute event, and that a sufficient time interval occurred for the fast cooling of the body still partly exposed to air before the following [pyroclastic currents] progressively entered and covered the town.”
It’s frightening enough to imagine this cloud of hot gas incinerating the Roman-era populations surrounding Vesuvius, but the researchers also raise alarm about the “overlooked” thread of PDCs in a modern context.
The study notes that a similar sequence of deadly events has been observed in recent eruptions, such as the 1902 ash surge that destroyed Saint-Pierre, Martinique, killing tens of thousands of people. They warn that the communities around Vesuvius including Naples may not be ready for another ephemeral hot-dilutive event.
“The results of this study bear unprecedented implications for the mitigation of volcanic risk at Vesuvius and possibly elsewhere,” Pensa and her colleagues said. “The red zone at Vesuvius, where full evacuation of ca 700. 000 people is planned in case of a future eruption was designed based on the probability of [pyroclastic current] invasion derived from the geological record. While this is certainly the goal to be achieved, it remains uncertain whether the progression of the volcanic unrest will allow enough time to reach the expected full evacuation prior to eruption.”
“Given these premises, we suggest that the edifices within the red zone, irrespective of the need to evacuate all people before the eruption, should be reinforced to be able to shelter people from the thermal impact of ash cloud surges in case full evacuation is not achieved on time,” the team concluded. “This could allow people who may not have had the chance to evacuate earlier to survive and wait for rescue or be able to leave before other [pyroclastic currents] may impact the area.”
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