The duration of the pyroclastic currents that hit Pompeii during the eruption of Vesuvius in 79 AD lasted about fifteen minutes: the volcanic ashes, inhaled by the inhabitants, were fatal, causing asphyxiation.

The inhabited area around Vesuvius volcano in a 3D perspective view from West; DTM overlaid with digital colour orthophoto [Credit: Laboratory of Geomatics and Cartography, INGV-OV]

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 of Geophysics and Volcanology (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".

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 kilometres per hour, at high temperatures and with a high particles concentration.

Pyroclastic deposits within the Pompeii inhabited area including stratified layer with tractional structures formed by the Pyroclastic Density Currents [Credit: Laboratory of Geomatics and Cartography, INGV-OV]

“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 ".

“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 National Major Risks Commission. "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 behaviour of Vesuvius also in terms of civil protection".

Source: National Institute of Geophysics and Volcanology [March 22, 2021]