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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.

A volcanic catastrophe even more devastating than the famous anno Domini 79 Pompeii eruption occurred during the Old Bronze Age at Vesuvius. The 3780-yr-B.P. Avellino plinian eruption produced an early violent pumice fallout and a late pyroclastic surge sequence that covered the volcano surroundings as far as 25 km away, burying land and villages. Here we present the reconstruction of this prehistoric catastrophe and its impact on the Bronze Age culture in Campania, drawn from an interdisciplinary volcanological and archaeoanthropological study. Evidence shows that a sudden, en masse evacuation of thousands of people occurred at the beginning of the eruption, before the last destructive plinian column collapse. Most of the fugitives likely survived, but the desertification of the total habitat due to the huge eruption size caused a social-demographic collapse and the abandonment of the entire area for centuries. Because an event of this scale is capable of devastating a broad territory that includes the present metropolitan district of Naples, it should be considered as a reference for the worst eruptive scenario at Vesuvius.archeoanthropology ͉ Bronze Age ͉ volcanic catastrophe ͉ volcanology P linian eruptions are highly destructive volcanic events that produce severe and long-lasting damage over thousands of squared kilometers of the territory surrounding volcanoes (1-4). Studies of the occurrence of plinian eruptions in densely populated areas reveal that most of the people who lived in the affected zones survived (3, 5). However, because of the habitat devastation and their inability to rehabilitate their homeland (5-7), many victims suffer social-economic crises and health status decline (3,5,8). Strong eruption precursors commonly alert the people days to months before the cataclysmic event; in the early phases of a plinian eruption, the slow escalation of the phenomena could allow them to escape from the volcano and flee beyond the lapilli fallout zone. The success of the evacuation depends mainly on its timeliness, because the early phase of a plinian eruption may not be lethal, even close to the volcano (2). Nevertheless, in most cases, the emplacement of billions of cubic meters of ash and lapilli in the form of a continuous blanket from decimeters to meters thick retards or prevents the recovery of the social-economical structure for decades to centuries, even tens of kilometers away from the vent (3, 9, 10).An extraordinary case that sheds light on such catastrophic consequences of an eruption is the Bronze Age Avellino plinian event at Vesuvius, dated by 14 C to Ϸ3780 yr B.P. (2, 10, 11). The eruption produced Ϸ4 km 3 of phonolitic ash and lapilli, a large subaqueous debris-flow avalanch in the gulf of Naples (12), and was even reported to have caused a global climatic disturbance (13). This event started with a moderate-sized explosive phase followed by a plinian column that in a few hours rose to 36 km in the stratosphere and, driven by westerly winds, produced a lapilli fallout covering thousands...

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