Vesuvius, the danger of mud flows on the Campania plain assessed:the study of Engv

The phenomenon, called lahar, represents one of the most dangerous among those that accompany or follow volcanic eruptions

NAPLES – With an ambitious project, a multidisciplinary team of researchers from the National Institute of Geophysics and Volcanology (Ingv), Heriot-Watt University (UK), the University of Pisa, the University of Turin and the University of Bari , And managed to quantitatively evaluate the danger on the Campania plain of possible mud flows caused by the re-mobilization of the fall deposits and pyroclastic flows during, or in the months immediately following, an eruption of Vesuvius similar to the sub-Plinian ones of 472 and 1631 AD.The results of the study, financed by the Department of Civil Protection (DPC), were published in three related articles in the international scientific journal 'Solid Earth', of the European Geophysical Union (EGU).

THE LAHAR PHENOMENON

Following a volcanic eruption the formation of a flow consisting of a mixture of fragments is possible, mainly volcanic, and water with the consistency of mud which tends to channel along the valleys and stop at the foot of the slopes. The phenomenon, called lahar, represents one of the most dangerous among those that accompany or follow volcanic eruptions:due to the destructive power that distinguishes them, they can cause significant changes in the landscape, with dramatic impacts on the population and infrastructure.The Campanian Plain, or the flat area that extends from the Tyrrhenian Sea to the Campanian Apennines, from the Garigliano to the Sorrento Peninsula, and which also includes the Campi Flegrei and Vesuvius, appears to be particularly subject to the effects of lahars, since the slopes of the volcanoes Vesuvius (properly, Somma-Vesuvius) and Campi Flegrei, together with the valleys and Apennine reliefs, are covered with pyroclastic deposits from the explosive eruptions of these volcanoes which are easily re-mobilised, especially after intense and/or prolonged rainfall .

The team of scientists, coordinated by INGV, for the first time in volcanology, evaluated the probabilistic danger of mud flows (lahar) as a whole.In particular, the first of the three studies, focused on field surveys, carried out an accurate field and laboratory study, the data of which were included in a complete database of the stratigraphic and sedimentological characteristics of the deposits of the eruptions of 472 AD.(CD.eruption of Pollena) and the more recent one in 1631, of the related lahar deposits and their impact on the territory, which in some cases was very disastrous.
Samples of these eruptions were extracted in approximately 500 points of the Campanian Plain located at varying distances from Vesuvius (from the nearest localities up to the Apennines), both through archaeological excavations already present in that area and with excavations carried out for the volcanological study.Their analysis allowed us to quantitatively define the large-scale and local effects of the events studied.The pyroclastic deposits recognized in the studied area represent very precise chronological levels, fundamental for the definition of the geological and archaeological evolution of the landscape.

The second study presents the new Imex-SfloW2D code for the numerical simulation of lahars, based on constitutive laws and equations that better describe some typical characteristics of the propagation of mud flows such as, for example, the deposition and erosion processes that occur during the flow of the casting, and which are capable of significantly modifying the distance traveled by the casting itself.The study also presents the calibration of the model based on the field data of the first study, identifying, through a rigorous analysis, the most relevant processes and parameters for the purposes of hazard estimation.
The third study, based on the results of the first two, provides the answer to the objective of the project financed by the Department of Civil Protection, with the development of probabilistic hazard maps of the invasion of mud flows on the Campania plain, considering different thresholds of thickness and dynamic pressure of the castings.Thickness and pressure, in fact, represent the main parameters with which the impact of the flows on buildings and the urban environment is quantified.The study also takes into account the uncertainties on the initial volume of the remobilised flows, on the availability of pyroclastic material in the event of an eruption (due, in turn, to the uncertainty on the direction and speed of the wind during the possible eruption), and on which of the various river basins that exist on the Campana Plain could give rise to the lahar.