A dark cloud was rapidly approaching the city. The pyroclastic flow had descended the slopes of Mount Vesuvius at great speed and was threatening small and wealthy Herculaneum, Pompeii’s neighbor. Being closer to the volcano, the ash accumulation reached it with greater virulence, with temperatures that exceeded 550º Celsius.
For its inhabitants, this difference was brutal. The merchant and merchant cults of Herculaneum perished without a trace in 79 AD, something that intrigued archaeologists for decades. Now, a team from Roma Tre University claims to have discovered the answer.
As explained in an article published in the journal Scientific Reports, a short-lived ash cloud, with temperatures between 495 and 555 degrees, reached the city just a few minutes after the eruption. The currents were capable of causing instant death to everything in their path, leaving just a few centimeters of dust on the ground.
Experts point out that, unlike what happened in Pompeii, where its residents were entombed in ashes, the bodies in Herculaneum most likely vaporized due to this searing explosion of gas and particles, leaving virtually no trace of its inhabitants. .
The newly published work began in 2018 when archaeologists uncovered the first compelling evidence that some Herculaneum residents suffered a gruesome death: Their soft tissues and blood boiled in an instant when struck by extreme heat and their skulls burst.
Two years later, researchers discovered another skull containing fragments of a material that led to the belief that the person’s brain had been turned to glass. Scorching temperatures of around 500°C could have produced all these gruesome effects: vitrified brains, shattered teeth, shrunken limbs, charred bones, and cracked skulls.
But there was other evidence of preserved soft tissue in some ribs that pointed to cooler temperatures. Hence, the geologist Alessandra Pensa and her team decided to reconstruct the temperatures that hit the city of Herculaneum in the year 79.
To do this, they analyzed the amount of light reflected from 40 samples of charred wood excavated in the 1960s at five different sites in the Roman metropolis to see the temperature at which coal formed. This ‘thermometer’ showed that the heat initially exceeded 500 degrees and could even reach 555.
The highest temperature signals were detected in wood samples from the northern part of the city, in the Collegium Augustalium, where the vitrified brain was found. The cooler measurements detected offshore to the southwest could be explained by interactions between seawater and the ash cloud when the plume first came ashore.
According to the researchers, the first wave of pyroclastic flow was criminal and the following ones, which gradually buried the city, had slightly lower thermal waves, between 465 and 390 degrees and between 350 and 315°C.
These highly turbulent and unpredictable ground-hugging currents of dilute pyroclastic density traveling at speeds of hundreds of meters per second have been linked to some of the deadliest volcanic disasters, including the 1902 eruption of Mount Pelée, which killed almost 30,000 people almost instantly.
