Pyroclastic flow8/5/2023 ![]() ![]() After a few hours, the plume became unstable and partially collapsed, generating small volume PDCs that hit the slopes of the volcano and buried the town of Herculaneum 9, 10 (Fig. The Roman towns and villages around Somma-Vesuvius and along the plume dispersal axis were covered by pumice lapilli and ash with thickness up to 3 m at Pompeii 9, which caused roof collapse of several houses. This short opening event heralded the main explosive phase, which started around noon of October 24th with the formation of a 25 km high eruptive column that, favored by stratospheric winds, caused the propagation of a south-eastwardly dispersed volcanic plume. The eruption started on October 24th, with the deposition of a thin bed of fine ash to the east 11. The 79 AD eruption of Vesuvius and associated deposits ![]() We study here the famous AD 79 eruption of Somma-Vesuvius 9, 10 and we reconstruct, for the first time, also the effect of flow duration on humans. The exposure time therefore plays a major role in determining the impact of PDCs on human beings, but, until now, it has not been quantified 2, 7. Exposure to pure hot air at 200–250 ☌ can be survived for 2–5 minutes 8, but the presence of inhalable hot fine ash drastically reduces survival times. The presence of fine-ash particles suspended in air for a long time, even in very small amounts, can be very harmful to human health, and represents one major cause of injury 2. ![]() This can cause burning of buildings, breaking of windows and toppling of walls, which make survival impossible 6.Ĭoncerning effects on humans, it is emerging that even in areas far from a volcano, where particle concentration, temperature and dynamic pressure strongly decrease, people engulfed in the flow have “high probability of receiving fatal skin burns and inhalation injury of the upper and lower respiratory tract, unless the duration is very brief” 7. 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. Particle volumetric concentration represents an important parameter too because dynamic pressure is proportional to it. 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.Įngineering investigations 1, 4, 5 show that dynamic pressures higher than 5 kPa produce significant damage, while pressures under 1 kPa have minimal to no consequence on structures or infrastructures. Instead, our calculations demonstrate a flow duration of 17 min, long enough to make lethal the breathing of ash suspended in the current. Under such conditions, survival should have been possible if the current lasted a few minutes or less. 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. At Herculaneum, at the foot of the volcano, the temperature and strength of the flow were so high that survival was impossible. The AD 79 event of Somma-Vesuvius is used here to demonstrate the impact of pyroclastic density currents on humans during an historical eruption. 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 impact is generally associated with flow dynamic pressure and temperature. They move away from the volcano at high speed, causing devastation. Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome. ![]()
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