Exploring the tsunamigenic potential of unstable masses in the Gulf of Pozzuoli (Naples, Italy)

The recent resumption of the unrest at the Campi Flegrei caldera, located near the large metropolitan area of Naples (southern Italy), has raised significant concerns about the potential effects of volcanic events in such a densely urbanized environment. This volcanic structure is well documented in historical records, and its peculiar volcanic and seismic activity, manifesting by uplift cycles and the phenomenon of “bradyseism”, is intensively studied and continuously monitored.

One of the least considered volcanic-related phenomena is the potential mass destabilization, which in turn can interact with water and generate tsunamis. In particular, the Campi Flegrei caldera extends beneath the Gulf of Pozzuoli, a 20-km wide sub-basin of the larger Gulf of Naples, whose coasts are characterized by a high degree of anthropization, including both industrial structures and tourist facilities, which significantly increases exposure and vulnerability.

In this work, four landslide scenarios are defined, three of which are in the submarine domain. These are realized based on the limited bathymetric and geophysical studies and data available for the area. The reconstructed volumes span 2 to 4 million cubic meters and are in shallow water, in three distinct locations within the basin. The fourth scenario, with a smaller volume of around half million cubic meters, is positioned onshore, near a coastal stretch which recently experienced the collapse of cliffs induced by an earthquake. The dynamics of these landslides and the ensuing tsunamigenic impulse are reconstructed through dedicated numerical codes, developed and maintained by the University of Bologna research team; the propagation of the respective waves is simulated through the code JAGURS [1]. This approach provides insights into the tsunami energy distribution in the basin and its interaction with the coastlines.

The results show that the submarine landslides do not generate catastrophic waves; however, they are able to damage small boats and induce resonance effects in small sub-basins, posing a potential hazard. In contrast, the subaerial scenario, while characterized by a minor volume, can generate local catastrophic waves, exceeding 4 m in amplitude. The role of wave dispersion in landslide-tsunami propagation, and the way if affects much more this last case in comparison with the submarine ones is discussed as well.

[1] Baba, T., Takahashi, N., Kaneda, Y., Ando, K., Matsuoka, D., & Kato, T. (2015). Parallel implementation of dispersive tsunami wave modeling with a nesting algorithm for the 2011 Tohoku tsunami. Pure and Applied Geophysics, 172(12), 3455-3472.