Did Vesuvius vaporize its victims? Get the facts.

The infamous A.D. 79 eruption of Mount Vesuvius obliterated the surrounding landscape as well as residents of the Roman metropolises that stood in the volcano’s shadow. After heavy ash caused fatal building collapses in Pompeii, violent pyroclastic currents rocketed downslope and smothered the city, the nearby port town of Herculaneum, and several other sites.

Academics don’t debate the volcanic fury on display that day almost 2,000 years ago. Perhaps surprisingly, however, there is still considerable controversy about how most of its victims died. (Also find out what really happened to a headless Pompeii victim who made headlines in June.)

A team of Italian specialists recently revisited some of the most gruesome deaths in Herculaneum, in which people’s skulls had seemingly exploded. The researchers’ long-standing hypothesis has been that extreme heat was the predominant killer, causing the fluids in victims’ brains and soft tissues to quickly boil into oblivion. That notion is now supported by evidence presented in a PLOS ONE study published in September.

But the theory is not without its dissenters. Elżbieta Jaskulska, an osteoarcheologist at the University of Warsaw who wasn’t involved in the work, argues that the study’s claim “goes against everything I know about heat damage to the human body and skeletal remains.”

Death in ancient paradise

Pyroclastic flows are gravity-driven mixtures of ash, lava blobs, and noxious gases. They can be as hot as 1300°F and move at speeds of 50 miles an hour. Pyroclastic surges are much the same but have proportionally more gas.

Both flows and surges emerged from Vesuvius during that fateful eruption, and both could have killed people in a range of horrific ways. Flying debris can hit and slaughter people, and inhaling too much ash or breathing in volcanic gas can cause asphyxiation. The extremely high temperatures can also immediately flash-fry a person to death.

Pier Paolo Petrone, a paleobiologist at the Federico II University Hospital in Naples, has spent decades researching the victims of the A.D. 79 cataclysm. Several papers he contributed to, including a 2001 study in Nature and another in PLOS ONE in 2010, provided evidence suggesting that ash and gases were not the primary causes of death in the region, as other studies had concluded. Instead, Petrone argued that it was the heat itself that killed most people, affording them a quick and painless demise.

Importantly, what heat did to people’s bodies differed between those in Pompeii and those in Herculaneum. Seated six miles away from the volcano, Pompeii was initially hit by falling volcanic debris, causing houses to collapse and suffocate those inside. The city was then hit by a particularly gassy pyroclastic surge, which was responsible for the greatest number of fatalities. (See horses found in Pompeii that were likely harnessed to try and flee the eruption.)

Archaeologists have found that the bodies of the victims here remained largely intact. Based on how bones were damaged and various metals melted, Petrone and his colleagues figure that many of the people died suddenly of extreme thermal shock upon experiencing a pyroclastic surge no hotter than 572°F.

In Herculaneum and the nearby site of Oplontis, something more disturbing took place. These two settlements were located a couple miles closer to Vesuvius’s vent, and researchers have found victims here whose DNA was completely degraded, with heat-induced bone fractures and what appeared to be exploded skulls. Petrone’s team deduced that these victims were hit by hotter pyroclastic surges between 932°F and 1112°F, which caused their bodily fluids to suddenly boil, including those within their brains.

Turning up the heat

The new PLOS ONE study, led by Petrone, adds more evidence to this gruesome hypothesis. Researchers point to a dark, reddish residue found on the bones of several victims in Herculaneum. Chemical analysis revealed it to be rich in irons and iron oxides, most likely originating from the blood and bodily fluids of the victims.

These iron-rich compounds could have formed as hemoglobin present in the victim’s red blood cells broke down. Petrone suggests that extreme heat could certainly have caused that to happen, which would have also cracked bones and, he says, “completely vaporized the soft tissues of the victim’s corpses in not more than 10 minutes, causing the skulls to explode.”

In addition, many of the Pompeii victims were found in fully contorted poses, indicating that their muscles had contracted very quickly upon being exposed to high heat. Those in Herculaneum seemed to show muscle contraction in some limbs but not others. According to the new study, this supports the idea that extreme heat could have destroyed certain muscles faster than they could contract.

Jaskulska says that some independent forensic evidence supports the idea that red blood cell destruction can cause this sort of bone staining. However, as her comments under the original study reveal, she isn’t convinced the case is closed.

According to Jaskulska, red blood cell destruction can happen without the vaporization of skin, muscles, or fat, and it’s not clear whether soft tissue vaporization happened in Herculaneum at all.

Modern funerary cremation furnaces provide a grim window into the annihilation of human bodies, featuring temperatures up to 1832°F. This heat is comparable to what victims would have experienced in Herculaneum.

“In these conditions, soft tissues are not vaporizing,” Jaskulska says. “They are simply burning.”

Race for survival

She also raises other issues with the new study, including its suggestion that the body’s lower extremities disappeared faster than the upper extremities. This seems odd to her, considering that there are far more soft tissues to vaporize on legs than on arms. Jaskulska also expected that if these tissues disappeared due to sudden heat, the damage to the bones would be much more intense than it appears.

As far as the skulls go, she isn’t even sure that they can explode. Cremations show that skulls seem to fracture from the heat, but they don’t violently explode and send fragments flying. Jaskulska suggests it’s perfectly plausible that the fragmented skulls in Herculaneum were simply crushed.

“Any archaeologist will tell you,” she says, that even undamaged skulls collapse under the weight of heavy sediments.

Jaskulska isn’t saying that heat damage didn’t occur or that it couldn’t have been lethal. She’s just saying that there is no concrete evidence yet that it was the primary killer at Herculaneum. Even if heat-driven hemoglobin breakdown did occur, the pyroclastic surges might have caused the damage after the people had already died of asphyxiation or other causes.

Modern analogs may shed some light on the debate. Janine Krippner, a volcanologist at Concord University in Athens, West Virginia, points out that pyroclastic flows and surges still happen today, and they are not always a guarantee of a quick, painless demise. The outcome depends on how fast, hot, ashy, and gassy the currents are, among other things. If it is diluted enough, you might even be able to survive the severe heat-related trauma.

Still, to avoid ending up like the victims of Vesuvius, Krippner’s advice is simple: “If you see a grey cloud moving toward you, run.”