Abstract
Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome. They move away from the volcano at high speed, causing devastation. The impact is generally associated with flow dynamic pressure and temperature. Little emphasis has yet been given to flow duration, although it is emerging that the survival of people engulfed in a current strongly depends on the exposure time. The AD 79 event of Somma-Vesuvius is used here to demonstrate the impact of pyroclastic density currents on humans during an historical eruption. At Herculaneum, at the foot of the volcano, the temperature and strength of the flow were so high that survival was impossible. At Pompeii, in the distal area, we use a new model indicating that the current had low strength and low temperature, which is confirmed by the absence of signs of trauma on corpses. Under such conditions, survival should have been possible if the current lasted a few minutes or less. Instead, our calculations demonstrate a flow duration of 17 min, long enough to make lethal the breathing of ash suspended in the current. We conclude that in distal areas where the mechanical and thermal effects of a pyroclastic density currents are diminished, flow duration is the key for survival.
Highlights
Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome
In the vicinity of the volcano the main effect was related to dynamic pressure and temperature[19,26]
This conclusion is corroborated by our observations at Herculaneum (Fig. 1a), where the current left a massive layer formed by a highly concentrated and hot flow that was capable of breaking and toppling thick walls and of charring wood
Summary
Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome They move away from the volcano at high speed, causing devastation. The impact of pyroclastic density currents (PDCs) is generally attributed to the combination of flow temperature and dynamic pressure[1,2,3]. Currents moving in the vicinity of a volcano can have a high concentration of hot magmatic particles that confer high temperature and high dynamic pressure to the flow. This can cause burning of buildings, breaking of windows and toppling of walls, which make survival impossible[6]
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