Lethal Thermal Impact at Periphery of Pyroclastic Surges: Evidences at Pompeii

Abstract

BackgroundThe evaluation of mortality of pyroclastic surges and flows (PDCs) produced by explosive eruptions is a major goal in risk assessment and mitigation, particularly in distal reaches of flows that are often heavily urbanized. Pompeii and the nearby archaeological sites preserve the most complete set of evidence of the 79 AD catastrophic eruption recording its effects on structures and people.Methodology/Principal FindingsHere we investigate the causes of mortality in PDCs at Pompeii and surroundings on the bases of a multidisciplinary volcanological and bio-anthropological study. Field and laboratory study of the eruption products and victims merged with numerical simulations and experiments indicate that heat was the main cause of death of people, heretofore supposed to have died by ash suffocation. Our results show that exposure to at least 250°C hot surges at a distance of 10 kilometres from the vent was sufficient to cause instant death, even if people were sheltered within buildings. Despite the fact that impact force and exposure time to dusty gas declined toward PDCs periphery up to the survival conditions, lethal temperatures were maintained up to the PDCs extreme depositional limits.Conclusions/SignificanceThis evidence indicates that the risk in flow marginal zones could be underestimated by simply assuming that very thin distal deposits, resulting from PDCs with poor total particle load, correspond to negligible effects. Therefore our findings are essential for hazard plans development and for actions aimed to risk mitigation at Vesuvius and other explosive volcanoes.

New evidence suggests pyroclastic flows are responsible for the remarkable preservation of the Jehol biota

“…11) [25][26][27][28][29][30][31][32] . The limb flexures of the skeletons are typical postures of PDC victims, which result from postmortem shortening of tendons and muscles 33,34 . Statistical documentation of head-tail axes of Confuciusornis carcasses revealed a distinct orientation (E-W) 7,12 , which is consistent with the preferred orientation of victims of PDCs, such as seen in the 1902 Mount Pelée eruptions 33 .…”

“…Vesuvius 34 . Similarly, these characteristics are consistent with experimental results from heating modern bones 34,39 .…”

“…Vesuvius 34 . Similarly, these characteristics are consistent with experimental results from heating modern bones 34,39 . The asymmetrically wavy abrasive pits on bone surfaces and loss of bone debris into embedding sediments may result from heat erosion during transport in PDCs as the susceptibility of bones to fragmentation is known to significantly increase after their being heated 39 .…”

Recovery and amplification of ancient DNA from Herculaneum victims killed by the 79 AD Vesuvius hot surges

“…That study showed greater difficulty in recovering and analyzing DNA from Herculaneum skeletal remains when compared with molecular analyses of Pompeii bone remains, likely due to exposure to higher thermal stress in the former case (Mastrolorenzo et al, 2001a(Mastrolorenzo et al, , 2010.…”

“…Using histochemical techniques, Mastrolorenzo et al (2010) showed the presence of DNA within osteocytic lacunae of bone samples experimentally heated up to 300 °C. Here we test the possibility of extracting and amplifying aDNA from human bone remains of Herculaneum victims showing macro-and microscopic evidence of exposure to temperatures of about 300 °C, using a combination of histological and molecular methods.…”