Researchers say they’ve solved a nearly 2,000-year-old cold case, sparked by the catastrophic volcanic eruption that destroyed the ancient Roman cities of Pompeii and Herculaneum: What caused a victim’s brain to fuse into bits of glass?
The victim’s remains were unearthed in the 1960s, amid the ruins of a building in Herculaneum known as the Collegium Augustalium. In 2020, researchers announced that obsidian-like glass fragments found in the victim’s skull were actually vitrified bits of brain.
Archaeologists suspect that the victim was a guard who was caught up in the aftermath of Mount Vesuvius’ eruption in the year 79. The man died instantly, but how? For years, scientists have been debating the scenarios for vitrifying the brain in a way that’s never been seen elsewhere. Now an Italian-German research team has laid out a plausible explanation in research published by Scientific Reports.
An annotated image shows the remains of a volcano victim in his bed in the Collegium Augustalium in Herculaneum. (Credit: Guido Giordano et al. / Scientific Reports)
The case is unusual because the brain couldn’t have turned to glass if the victim had been killed by typical pyroclastic flows. Instead, the soft tissue would have simply burned up, as was the case for other victims whose remains have been found in Pompeii and Herculaneum.
In order to create glass, the organic material would have to be heated quickly to a liquid form, and then cooled quickly to get the proper crystallization as it turned back into a solid.
To solve the mystery, the researchers analyzed fragments of the glass from the victim’s skull and spine. They heated the samples at different temperatures, and cooled them at different rates. They studied the physical structure of the bits as they liquefied and solidified. They checked the chemical composition using Raman spectrometry. Then they matched up their findings with what’s known about how an eruption like the one at Vesuvius would have gone down.
The team’s analysis led to the conclusion that the destruction of Herculaneum began with a super-heated ash cloud that swept over the city. The temperature of the ash cloud would have to have been well over 510 degrees Celsius (950 degrees Fahrenheit).
“It left a few centimeters of very fine ash on the ground, but the thermal impact was terrible and deadly, even if brief enough to leave – at least in the only case of the discovery in the Collegium Augustalium – brain remains still intact,” lead author Guido Giordano, a volcanologist at Roma Tre University, said in a news release. “The cloud must have then dissipated just as quickly, allowing these remains to cool so quickly as to trigger the vitrification process.”
The bones of the skull and the spine probably protected the brain bits from breaking down completely — and shielded the glass fragments when the follow-up flows of hot ash and rocks buried Herculaneum. The preservation was so complete that some of the structure of individual brain cells could be seen in the glass centuries later.
“This scenario is of great importance not only for historical and volcanological reconstruction, but also for civil protection purposes,” Giordano said, “because it defines a very high danger even for very diluted flows that do not have great impacts on the structures but that can be lethal due to their temperatures, knowledge of which can translate into effective prevention and mitigation measures.”
In this photomicrograph of a glass fragment, the white arrows highlight the preserved structures of neural axons. (Credit: Guido Giordano et al. / Scientific Reports)
In addition to Giordano, the authors of the study in Scientific Reports, “Unique Formation of Organic Glass From a Human Brain in the Vesuvius Eruption of 79 CE,” include Alessandra Pensa, Alessandro Vona, Danilo Di Genova, Raschid Al-Mukadam, Claudia Romano, Joachim Deubener, Alessandro Frontoni and Pier Paolo Petrone.
