Mount Vesuvius eruption turned a victim’s brain into glass

The eruption of Mount Vesuvius in 79 CE presented its surrounding ancient Roman communities with a number of terrifying ways to die: falling debris, collapsing buildings, asphyxiation from superheated dust plumes, etc.. And while attention is often focused on the destruction of Pompeii and its thousands of victims, the fate of nearby Herculaneum wasn’t much better. According to recent analysis of unique samples recovered from the seaside archeological site, the Vesuvius eruption even caused one person’s brain to flash-fry into a rare form of organic glass.

The theory, laid out in a study published February 27 in the journal Scientific Reports, is based on examinations of tiny shards found in 2020 inside the skull and spinal column of an individual at Herculaneum–a small port town with a population of around 5,000 people at the time. The victim is believed to have been a roughly 20-year-old man who worked as a guard at the Collegium Augustalium, a public building dedicated to worshipping Emperor Augustus. At the time of his death, however, the guard was laying in his bed—and it was this environment that likely fostered the extremely specific conditions needed for brain and spinal fluid vitrification.

While glass is a foundational component in many industries today,  it only naturally occurs in rare circumstances. This is because glass is only created when its liquid state cools fast enough to prevent crystallization as it solidifies. In order to accomplish this, there must be a major temperature difference between the substance itself and its environment. Not only that, but the liquid material must also solidify at a much higher temperature than its surroundings. Because most organic matter is largely water, conditions rarely allow for natural glass formation given its freezing point.

“It would therefore be impossible to find organic glass embedded in volcanic deposits that have reached several hundred of Celsius degrees,” wrote the study’s authors.

Using X-ray analysis and electron microscopy, the team confirmed the guard’s brain could only have turned to glass if it was heated “well above” 950 degrees Fahrenheit (510 degrees Celsius) before quickly cooling. But the majority of the eruption’s known after-effects cannot account for brain and spinal fluid vitrification. The eruption’s pyroclastic flows, for example, did not exceed 869℉ (465 ℃) and cooled far too slowly to create the glass.  

The study authors therefore concluded that “the body was exposed to the passage and vanishing of a short-lived, dilute and much hotter pyroclastic flow” that offered an early, quick flash-heating before subsequent rapid cooling.

“The glass that formed as a result of such a unique process attained a perfect state of preservation of the brain and its microstructures,” they wrote, adding that it is now the “only such occurrence” known on Earth.  And according to Guido Giordano, the study’s lead author at Italy’s Università Roma Tre, it’s unlikely they will find another example anytime soon.

“In principle it is possible. There is more to be excavated below the modern city that may have preserved a similar occurrence,” Giordano tells Popular Science. “However conditions must have been very, very specific because the organic tissue must have experienced a heating fast enough not to entirely destroy it (which is instead the most common occurrence) and then fast-cool to turn into glass.”

Giordano believes the building and room in which the guard died offered just the right conditions. But if additional brain glass is to be found, it will be in the ruins of Herculaneum and not Pompeii.

“Such [a] hot ash cloud hit Herculaneum during the night when Pompeii was still under the fallout of pumice,” he says. “The early pyroclastic flows arrived and buried Pompeii the day after, but at lower temperatures.”

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