Volcanologist Claudio Scarpati, and colleagues Giuseppe Luongo and Annamaria Perrotta of the University of Naples Federico II in Italy, analyzed layers of volcanic deposits in a Pompeian house and examined 13 skeletons found there on a carpet of pumice to reconstruct the events that occurred when the eruption was in progress. The team reported their findings at a recent international conference on ancient DNA in Naples.
Located in Pompeii's main street, Via dell'Abbondanza, the home of Iulius Polybius is one of the most studied in the ancient Roman town.
"This house has yielded rich and diverse archaeological findings. Moreover, it features the most complete stratified sections of Pompeii's volcanic deposit," Scarpati told Discovery News.
At around 1:00 p.m. on Aug. 24, 79 A.D., Pompeii residents saw a pine tree-shaped column of smoke bursting from Vesuvius. Reaching nine miles into the sky, the column began spewing a thick pumice rain. Many residents rushed in the streets, trying to leave the city.
"At that moment, Polybius' house was inhabited by 12 people, including a young woman in advanced pregnancy. They decided to remain in the house, most likely because it was safer for the pregnant woman. Given the circumstances, it was the right strategy," Scarpati said.
Once considered relatively innocuous by volcanologists, this first phase of the eruption in fact produced 38 percent of the deaths.
"Contrary to what was previously believed, a large number of deaths occurred in the first hours of the eruption. Many skeletons of those who tried to escape show fractured skulls, meaning that they died from collapsing roofs or large fragments falling from the eruptive column," Scarpati said.
By examining the density of volcanic deposits in relation to an accumulation rate of six inches per hour, the researchers concluded that it took up to six hours for the roofs of Polybius' house to collapse.
At around 7:00 p.m., by which time the front part the house had collapsed, the inhabitants took shelter in the rear rooms, whose steeper roofs had not been damaged by the falling material.
"There were three adult males, three adult females of various ages, four boys, one girl, one child and one fetus in the last month of intrauterine life. The fetus was associated with the skeleton of a young (16 to 18-year-old) female," Scarpati said.
Analysis of mitochondrial DNA, which is passed down through the maternal line, revealed that six individuals belonged to the same family.
"The age of five out of six individuals suggests that they were siblings. Another subject, about 25 to 30 years old, might have been a cousin. The three adult women were unrelated," molecular biologist Marilena Cipollaro, of the Second University of Naples, told Discovery News.
Cipollaro's analysis also revealed that two related subjects suffered from spina bifida, a birth defect resulting in an incomplete closure of the spinal column.
Most likely, the group of people in Polybius' house included the parents, their children, a cousin and his young, pregnant wife, plus a pair of servants.
They all witnessed the terrible evolution of the eruption. In the early hours of Aug. 25, a nearly 10-foot-thick carpet of pumice had already covered the streets and bottoms of buildings.
Polybius' family perished in their home's back rooms.
"The position of some skeletons on the volcanic deposit indicates that some individuals were lying on beds at the moment of death," Scarpati said.
When the first phase of the eruption ended, the eruptive column collapsed, producing a series of pyroclastic currents. These are fast-moving flows of hot gas and rock at temperatures ranging from 392 to 1,292 degrees Fahrenheit.
"The first pyroclastic currents arrived from the north and overtopped the rear part of the house. The currents moved into the garden and advanced toward the front of the house. No escape was possible for the people there. The ash reached every corner in the house and suffocated its inhabitants," Scarpati said.
Ash layers revealed that not all Pompeii residents were killed by the devastating wave of gas and rock.
"We found victims several centimeters above the basal ash layers related to this current. Some residents walked outdoors and survived until the second pyroclastic current," Scarpati said.
Between 7:00 and 8:00 a.m., a final phase, punctuated by more pumice rain, buried Pompeii.
The solid roofs of Polybius' house collapsed. What followed was a long, deathly silence.
"It was impossible to survive that eruption. Even though we calculated that 75 to 92 percent of the residents escaped the town at the first signs of the crisis, it is not possible to know how successful those fugitives were. Hundreds of victims were recovered from the relatively small excavations outside the city walls," Scarpati said.