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Pompeii: the duration of pyroclastic currents generated by the eruption of Vesuvius in 79 AD has been determined

A research on the effects of the pyroclastic flows of the 79 AD eruption on Pompeii highlighted how their duration had a tragic impact on the population

About fifteen minutes was the duration of the pyroclastic currents that hit Pompeii during the eruption of Vesuvius in 79 AD: the volcanic ashes, inhaled by the inhabitants, were fatal, causing asphyxiation.
This is what reveals the study “The impact of pyroclastic density currents duration on humans: the case of the AD 79 eruption of Vesuvius”, conducted by the University of Bari – Department of Earth and Geo-environmental Sciences, in collaboration with the Istituto Nazionale di Geofisica e Vulcanologia (INGV) and the British Geological Survey of Edinburgh. The study has just been published ‘Scientific Reports’.
“The aim of the work”, says Roberto Isaia, senior researcher of the Vesuvian Observatory of the INGV “was to develop a model to try to understand and quantify the impact of pyroclastic flows on the inhabited area of Pompeii”.

The inhabited area around Vesuvius volcano in a 3D perspective view from West; DTM overlaid with digital color orthophoto (Laboratory of Geomatics and Cartography, INGV-OV)

Pyroclastic flows, in fact, are the most devastating phenomenon of the so-called explosive eruptions. Comparable to avalanches, they are generated by the collapse of the eruptive column. The resulting dense pyroclastic flows flow along the slopes of the volcano at speeds of hundreds of kilometers per hour, at high temperatures and with a high particles concentration.
“During our research”, continues Isaia, “we carried out filed and laboratory studies of the pyroclastic deposits recognized within the archaeological excavations of Pompeii which led to the measurement and definition of the physical-mechanical parameters of the rocks. The obtained data have been used as input parameters for a mathematical model that has allowed us to carry out numerical simulations. From these we obtained the physical parameters of the pyroclastic currents and, therefore, the effects on the territory, including people, have been estimated. The main result is that the persistence of the flow of pyroclastic currents took place over a period of time between 10 and 20 minutes”.

Pyroclastic deposits within the Pompeii inhabited area including stratified layer with tractional structures formed by the Pyroclastic Density Currents

“The developed model” adds the researcher, “can also be applied to other active volcanoes around the world,. The example of Pompeii in fact, about 10 km far from Vesuvius, suggests how the use of this model could be very valuable for understanding the duration of pyroclastic flows and, therefore, the damage deriving from an eruption even at distances where the temperature and the pressure of the pyroclastic currents no longer causes harmful effects on humans and the environment. The applied methodology can therefore provide new elements of knowledge in the context of the hazard assessment of an active volcanic structure “, concludes Roberto Isaia.
“It is very important to be able to reconstruct what happened in the past eruptions of Vesuvius starting from the geological record, in order to trace the characteristics of the pyroclastic currents and the impact on population” declares Professor Pierfrancesco Dellino of the University of Bari, referent for the sector volcanic activity of the Commissione Grandi Rischi nazionale. “The adopted scientific approach in this study reveals information that are contained by the pyroclastic deposits and that clarifies new aspects of the eruption of Pompeii and provides valuable insights for interpreting the behavior of Vesuvius also in terms of civil protection”.

Briefly

Who: Università degli Studi di Bari, Istituto Nazionale di Geofisica e Vulcanologia (INGV) e British Geological Survey, Edinburgh (UK)
What: A model was developed that allowed to calculate that in Pompeii the persistence of the passage of pyroclastic currents occurred in a period of time between 10 and 20 minutes, causing lethal effects on its inhabitants.
Where: The research The impact of pyroclastic density currents duration on humans: the case of the AD 79 eruption of Vesuvius in ‘Scientific Reports’.
Link: https://www.nature.com/articles/s41598-021-84456-7

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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.

 

 

Press release from the Istituto Nazionale di Geofisica e Vulcanologia (INGV)