Extreme heat of Vesuvius eruption vaporized body fluids, exploded skulls

The catastrophic eruption of Mount Vesuvius in 79 AD wiped out several nearby towns and killed thousands of people. It has long been supposed that the vast majority died from asphyxiation, choking on the thick clouds of noxious gas and ash. But a recent paper by Italian archaeologists concludes that at least some of the Vesuvian victims died instantaneously from the intense heat of fast-moving lava flows, with temperatures high enough to boil brains and explode skulls.

As bioarchaeologist Kristina Killgrove notes over at Forbes, this new analysis, led by Pierpaolo Petrone of the University of Naples, builds on the Italian team's short 2001 paper in Nature. This is when they first broached their hypothesis, noting that the body postures of many victims unearthed in waterfront chambers in the town of Herculaneum, near the foot of Vesuvius, showed evidence of thermal shock. There were telltale flexed body parts, like curled toes and charred bones, indicating sudden death from a blast of extreme heat.

It is estimated that the eruption of Vesuvius released 100,000 times the thermal energy of the atomic bombs dropped on Hiroshima and Nagasaki in 1945, ejecting many tons of molten rock, pumice, and hot ash over the course of two days. In the first phase, immediately after the eruption, a long column of ash and pumice blanketed the surrounding towns, most notably Pompeii and Herculaneum. By late night or early morning, pyroclastic flows (fast-moving hot ash, lava fragments, and gases) swept through and obliterated what remained, leaving the bodies of the victims frozen in seeming suspended action.

Remains of a child and a young adult male excavated from the ash surge deposits at Herculaneum.

Credit: P. Petrone et al.

The only surviving eyewitness account is that of Pliny the Younger, who wrote two letters to his friend, the historian Tacitus, describing the cataclysmic event. He described "broad sheets of flame" visible from Vesuvius and a rain of ash blanketing the area like snow. He and his uncle, Pliny the Elder, also witnessed a dense cloud "filled with earth and cinders" rising above the mountain like a pine tree, "for it shot up to a great height in the form of a tall trunk, which spread out at the top as though into branches."

Archaeologists have made casts from the impressions victims' bodies left in the ash deposits around Pompeii (roughly 1,044) and collected bones from another 100 victims. A little over a third are believed to have been killed by roof collapses or falling rocks. Archaeologists also recovered the remains of around 332 bodies in the ash fall deposits at the Herculaneum site, located closer to the crater than Pompeii, likely killed by the pyroclastic surges.

It got hot

Most scientists assumed the Pompeii victims not killed by falling debris suffocated from the thick clouds of ash and gas, believing the temperatures of the material spewed forth by Vesuvius would not have been hot enough to cause outright death. There was good cause to think so, given the state of the bodies, the outline of clothing still visible on some. But a 2010 study by volcanologists estimated that the temperatures of the pyroclastic surge that destroyed Pompeii could have been as high as 572°F, killing the populace in fractions of a second. "The contorted postures are not the effects of a long agony, but of the cadaveric spasm, a consequence of heat shock on corpses," lead author Giuseppe Mastrolorenzo told National Geographic at the time.