01 Aug 2023
 | 01 Aug 2023
Status: this preprint is open for discussion.

Lahar events in the last 2,000 years from Vesuvius eruptions. Part 1: Distribution and impact on densely-inhabited territory estimated from field data analysis

Mauro A. Di Vito, Ilaria Rucco, Sandro de Vita, Domenico M. Doronzo, Marina Bisson, Mattia de' Michieli Vitturi, Mauro Rosi, Laura Sandri, Giovanni Zanchetta, Elena Zanella, and Antonio Costa

Abstract. Lahars represent some of the most dangerous phenomena in volcanic areas for their destructive power, causing dramatic changes in the landscape with no premonitory signs and impacting on population and infrastructures. In this regard, the Campanian Plain turns out to be very prone to the development of these phenomena, since the slopes of the Somma-Vesuvius and Campi Flegrei volcanoes, along with the Apennine reliefs are mantled by pyroclastic deposits that can be easily remobilised, especially after intense and/or prolonged rainfall.

This study focuses on the analysis of the pyroclastic fall and flow deposits and of the syn- and post-eruptive lahar deposits related to two sub-Plinian eruptions of Vesuvius, 472 AD (Pollena) and 1631. To begin with, historical and field data from the existing literature and from hundreds of outcrops were collected and organized into a database, which was integrated with several new pieces of data. In particular, stratigraphic, sedimentological (facies analysis and laboratory) and archaeological analyses were carried out, in addition to rock magnetic investigations and impact parameter calculations. The new data are mainly referred to the finding of ash beds in more distal areas, which was included into new isopach maps for the two sub-Plinian eruptions.

The results show that for both the eruptions the distribution of the primary deposits is wider than the one previously known. A consequence of these results is that a wider areal impact should be expected in terms of civil protection, as the sub-Plinian scenario is the reference one for a future large eruption of Vesuvius. Such distribution of the pyroclastic deposits directly affects the one of the lahar deposits, also because a significant remobilization took place during and after the studied eruptions which involved the distal phreatomagmatic ash. From these integrated analyses, it was possible to constrain the timing of the deposition and the kind of deposits remobilized (pyroclastic fall vs. flow), as well as was possible to calculate the velocities and dynamic pressures of the lahars, and ultimately infer the lahar transport and emplacement mechanisms.

The multidisciplinary approach adopted in this work shows how it is crucial to assess the impact of lahars in densely populated areas even at distances of several to tens of km from active volcanoes. This especially applies to large parts of the densely populated areas around Somma-Vesuvius up to the nearby Apennine valleys.

Mauro A. Di Vito et al.

Status: open (until 17 Oct 2023)

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  • RC1: 'Comment on egusphere-2023-1302', Ulrich Kueppers, 03 Sep 2023 reply

Mauro A. Di Vito et al.

Mauro A. Di Vito et al.


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Short summary
We study the distribution of two historical pyroclastic fall/flow and lahar deposits from the Vesuvius eruptions of 472 AD Pollena and 1631. The study motivation comes directly from the widely distributed impact that both the eruptions and lahar phenomena had on the territory, not only around the volcano but also down the nearby Apennine valleys in the Campanian Plain. All data get to a database of about 500 points, in some of which we estimate the lahar velocity and dynamic pressure.