Nearly 2,000 years ago, Mount Vesuvius erupted catastrophically, killing thousands of people and destroying the Roman towns of Pompeii and Herculaneum.
The grisly fates of those caught by the volcano have been a boon to archaeologists, with their remains preserved by layers of ash.
One particularly unlucky victim experienced something that, so far, is unique to science: the eruption turned his brain to glass.
The "organic glass" brain, which was discovered in 2020, provides important insights into what happened to the victim — believed to be a male about 20 years old — and others on that fateful day in August 79 AD.
The man's remains were found in the Collegium Augustalium, a place of worship for Augustus, the first Roman emperor, in the town of Herculaneum.
As he lay on his bed he was most likely caught in a fast-moving superheated ash cloud that rushed down the volcano's slope to the coast, according to a new study published today in Scientific Reports.
This would have heated his brain to high temperatures and then abruptly cooled back down — allowing the "vitrification" (glass-forming) process to occur.
Lead author Guido Giordano, a researcher at Università Roma Tre, said the victim's final moments would have unfortunately been painful — albeit over fast.
"Conditions must have been very, very specific because the organic tissue must have experienced a heating fast enough not to entirely destroy it," Professor Giordano said.
While it's possible more organic glass is waiting under Herculaneum, Professor Giordano thinks it's unlikely.
The fate of Herculaneum
Herculaneum was buried by a pyroclastic flow: a burst of super-hot gas and matter ejected by a volcano at breakneck speeds.
While the ash and rocks from this pyroclastic flow preserved the town, the glass brain suggests the young man died well before this happened.
[map]"The very existence of a vitrified human brain within this deposit implies that the process of vitrification must have occurred prior to the entombment," Professor Giordano said.
For glass to form, a material needs to be heated up very quickly and then cooled down very fast. The rocks that buried the town wouldn't have cooled down quickly.
The study also suggests ash and rocks from the eruption wouldn't have been hot enough to vitrify the brain — the pyroclastic flow reached temperatures of 465 degrees Celsius, while the organic glass would only have formed above 510C.
Instead, the researchers think a hot ash cloud swept over the area first, killing inhabitants instantaneously but leaving buildings intact, and leaving cold air to rush through soon after.
Volcanologist Chris Firth, who wasn't involved with the research, said this was a common occurrence with big volcanic eruptions.
"Often when a big eruption like this happens, the opening phases are really powerful, violent blasts, but the volume of material is much smaller," Dr Firth said.
These smaller blasts move quickly, and carry less material than subsequent surges.
Dr Firth said the study was an exciting way to add to our understanding of the Vesuvius eruption.
"Most of what we know about [big eruptions] is not from directly observing them because they don't happen very regularly, so we have to forensically reconstruct what's happened," Dr Firth said.
This is useful information for predicting how future eruptions might happen, and protecting people from them, according to Dr Firth.
Professor Giordano said their research showed it was essential to heat-proof houses and shelters in active volcanic areas, like is done for bushfires.
"This way, should anyone be caught in a dilute hot ash cloud, there could be a possibility to survive and wait for rescue," Professor Giordano said.
