Wednesday, October 27, 2010

Researchers say Heat Not Ash Killed Pompeiians and Call For Extended Evacuation zones

An analysis of the body postures and bone modifications of 93 victims of Pompeii has convinced an Italian research team that heat in the range of 250-300 degrees Centigrade from the fourth pyroclastic flow emitted from Vesuvius instantly killed the remaining residents of Pompeii in 79 CE.

The team, led by  Giuseppe Mastrolorenzo, Pierpaolo Petrone, Lucia Pappalardo and Fabio M. Guarino divided the remains into five posture groups, those exhibiting a ‘‘life-like’’ stance - victims that appear in suspended action like those labeled a1, a2, b, c, 3b at right).; those in a ‘‘sleep-like’’ stance - victims laying on their back, on their right or left side in an apparent relaxed posture like those in a3, d; those who appear to have suffered debris impact with corpse displacement and/or rupture of body elements, those whose limbs contracted with iperflexion of hands and feet (e1, e2) and those with a ‘‘pugilistic attitude’’ in which their limbs were flexed as a result of dehydration and shortening of tendons and muscles (f). 
"...in Pompeii and surroundings most of the victims are typically frozen in suspended actions (73% life-like stance, 27% sleep-like stance), showing as well as limb contraction (76%) and a large number of corpses presenting the pugilistic attitude (64%). Even if different postures often coexist in the same victims group, the prevalence of people frozen in suspended actions (life-like stance) is univocally indicative of a condition known as cadaveric spasm." - Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii
Unfortunate Animal victims of Vesuvius discove...Image by mharrsch via Flickr
Unfortunate Animal victim of
Vesuvius discovered near
Boscoreale Italy
The researchers go on to point out that cadaveric spasm, the rare stiffening of the entire body in its last position associated with violent instant death, is the key evidence that all victims suffered the same lethal event.  But to definitively isolate heat as the cause rather than suffocation, the team examined bone samples with an electronic microsope to see if the microscopic structure of the victims bones revealed the level of heat the victims suffered.

They established the pattern of coloration change and structural degradation by exposing modern bone samples from both humans and horses to varying degrees of heat.  When the heat applied reached 200 degrees Centigrade bone tissue yellowed.  As heat increased the bone tissue changed from yellow to bright brown then black, dark-brownish grey and finally light grey-white observed at 800 degrees Centigrade.  Bone structure likewise disintegrated from exhibiting linear microcracks at 200 degrees Centigrade to total dissolution into crystallized irregular globules at 500-800 degrees Centigrade.
Furthermore, researchers noted that DNA became undetectable above 300 degrees Centigrade as well.

In samples from the Pompeii victims, scientists found the bones yellowed and detected linear microcracks.  They also discovered intact DNA thus narrowing the temperature exposure during the 4th pyroclastic surge to 200 - 300 degrees Centigrade.  These temperatures, however, would have been lethal in microseconds, not the several minutes it would take to suffocate and no respiratory intervention would have been effective.  The researchers also point out that the calculated concentration of inhalable ash approached survivablility and the corpses would have exhibited the final floppy posture that characterize suffocation instead of the cadaveric spasm of instant death.
A parallel analysis was conducted on victims from the town of Herculaneum and the suburban Oplontis, both of which lie at about 7 kilometres from Vesuvius. The remains of victims here consist exclusively of skeletons (Herculaneum) or skeletons with only partial body imprint in the ash (Oplontis). The analyzed specimens from Herculaneum and Oplontis show bone colours ranging from black to grey-white, linear to polygonal microcracks and incipient to high recrystallization as well as complete DNA degradation . In contrast to Pompeii [10 kilometres from the vent] but similar to Herculaneum,  several victims at Oplontis show skull explosion, as testified by clear-cut fractures resulting from intracranial overpressure induced by exposure of the corpses to very high temperature. These features suggest temperatures of ca 500 degrees C in Herculaneum, which matches well with previous supporting evidence , and a temperature of ca 600 degrees C in Oplontis. - Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii
 What this all means to emergency evacuation planners in Naples and in other population centers near explosive volcanoes is that the radius of lethal exposure is much farther than originally thought and that respiratory intervention cannot be relied upon for survivability within these areas.
Pyroclastic flows at Mayon Volcano, Philippine...Image via Wikipedia"...while impact force and exposure time to dusty gas dropped below lethal conditions, the pyroclastic cloud retained its high temperature thus being the main cause of instantaneous mortality for the Vesuvius area inhabitants, including people who were sheltered within buildings as far as Pompeii. Definitely, a group of indoor victims found at Muregine, within the limit [of the 4th pyroclastic surge] about half kilometer south-east of Pompeii walls, suggests that even an extremely short exposure to the pyroclastic surge in the order of seconds to a few tents of seconds was lethal.  These facts and the evidence that the late, most powerful 79 AD PDCs reached distance exceeding 20 kilometres from the vent and the findings of several scattered groups of victims in Roman villas even as far as at least 15 kilometres in Stabiae highlight the need to strengthen the emergency plans for Vesuvius and other similar explosive volcanoes considering long-distance thermal effects even at the extreme PDCs periphery as primary cause of fatalities, " the research team ominously concluded.
The complete article can be read at Plosone.org
The Complete Pompeii (The Complete Series)   Pompeii - The Last Day/Colosseum - A Gladiator's Story   The Fires of Vesuvius: Pompeii Lost and Found   Pompeii: The History, Life and Art of the Buried City  The Mount St. Helens Volcanic Eruptions (Environmental Disasters)   La Catastrophe: The Eruption of Mount Pelee, the Worst Volcanic Disaster of the 20th Century
Volcanic Hazards and Disasters in Human Antiquity (Special Papers (Geological Society of America), 345.)
Enhanced by Zemanta
Post a Comment

Roman Archaeology Timeline