Perhaps the most famous volcanic catastrophe in all of history was the eruption of Mount Vesuvius in 79AD. It was an extraordinarily violent event: The volcano exploded, heaving ash, stones and fumes 33 kilometres (20.5 miles) into the air, and ejecting crushed pumice and lava at a rate of 1.5 million tons per second.
The eruption lasted 18 hours, spewing several billion tons of debris. This fell on the nearby towns of Pompeii and Herculaneum and several smaller settlements. While many citizens were able to evacuate and survive, others took shelter in buildings. This move was ultimately to prove fatal. As the ash and pumice accumulated on rooftops, the buildings collapsed under the weight, burying and suffocating those inside. The bodies were sealed inside when lava flowed and hardened over the top of the ash and pumice.
Herculaneum, which was the closer of the two cities, was buried under 23 metres (75.4ft) of material, including lava flows. Pompeii was buried under 2.5-3 metres (8.2-9.8ft) of material, consisting mainly of pumice and ash. Both cities were considered too damaged to rebuild and were simply abandoned, the bodies left buried.
In the 19th century, excavation workers found cavities in the ash with bones inside. In 1863, Giuseppe Fiorelli, the new director of the excavation, changed the system so that the excavation took place from the top down. This allowed the team to pour plaster into the cavities, which created a plaster cast of the impression in the ash. This process (called the Fiorelli process) was used on some 1,044 humans (and several animals) by 2003.
This year, a team of researchers under the appointment of the Archaeological Superintendence of Pompeii, Herculaneum and Stabia began CT scanning 86 of those plaster casts to take a look at the bones inside without damaging the plaster.
The casts hadn't previously been examined in this way because they were in poor shape. The old plaster from the 19th century casts had been degrading, exposing the bones inside; the Great Pompeii Project earlier this year restored 86 plaster casts. These 86 casts were the subject of the CT scan project.
In addition, while CT scanning has been in archaeological use since the 1970s, it is only recently that the technology has become good enough to be used on the plaster casts, the density of which varies from restoration jobs over the years. In some parts, the plaster can be as dense as bone, which can make separating the bone from the plaster tricky. To scan the casts, the team borrowed a 16-layer CT scanner designed for people with prosthetics and implants from Philips SpA Healthcare.
The result is a multidisciplinary project that is seeing radiologists, orthodontists, computer engineers and archaeologists all working together to solve the technical problems involved in the scanning process, and piece together what they find.
To date, the team has scanned 30 casts of men, women, children, a dog and a boar. The initial results reveal a healthy population that had exceptionally good teeth, probably partially due to the presence of the volcano, partially due to diet.
"They ate better than we did," orthodontist Elisa Vanacore said at a press conference, reported by Italian news service The Local. "They have really good teeth -- they ate a diet that contained few sugars, and was high in fruit and vegetables. The initial results also show the high levels of fluorine that are present in the air and water here, near the volcano."
The scans also found fractured bones, revealing that at least some of the deaths were caused by falling roofs instead of suffocation. A cast of a body thought to have been that of a pregnant woman because of a rounded stomach showed no sign of foetal bones or adult bones; likewise the famous cast of a dog was found to contain no bones. It's possible these bones were removed from the cavity prior to the Fiorelli process.
Because the aperture of the CT scanner measures just 70 centimetres (27.5in) in diameter, some of the casts won't fit all the way, but the team plans to scan, or at least partially scan, as many of the 86 casts as they can.
"It will reveal much about the victims: their age, sex, what they ate, what diseases they had and what class of society they belonged to," said archaeological superintendant of Pompeii Maximo Osanna. "This will be a great step forward in our knowledge of antiquity."