Volcanic Activity and Processes

Abstract

The “reading” of an area by geologists inevitably leads to the nature of the physical processes that shaped it. It is in the variety of the landscape of Campania that one can recognize the various geological phenomena that have been operating for millions of years in this area, located on the eastern edge of the Tyrrhenian Basin and bordered by the limestone massifs of the Southern Apennines (Fig. 2.1). The two main geodynamic processes that characterize the Miocene, from 23 to 5.3 million years ago (mya), not only this area but throughout most of southern Italy, are the distension of the Tyrrhenian basin and the Apennine orogenesis (Fig. 2.2). These two processes are related to the counterclockwise rotation of the African plate to the south, converging on the Euroasian plate to the north. The border between the two plates is delimited by the Apennine chain, in the centre-south of Italy and, to the north, by the Alps, representing the zones of collision and corrugation due to convergence. The relative motion between the two plates has produced, since at least since the lower Pleistocene (between 2.5 mya and 11,700 years ago), predominantly extensional tectonic activity on the Tyrrhenian side, which becomes compressive as one moves across to the Adriatic. The Apennine is a watershed between these two different tectonic areas. The Apennine Rocks, which are Mesozoic-Tertiary in age, represent the ancient carbonate basement, formed in a shallow marine environment, and subsequently deformed by tectonic processes. Crustal relaxation on the Tyrrhenian margin during the Pleistocene is associated with a tectonic movement that incorporates a strongly vertical component, which caused the carbonate platform to sink as much as several thousand metres in the direction of the Tyrrhenian Sea. This resulted in the formation of horst and graben structures, which correspond to zones of upland topography and subsidence respectively. Within the setting of structures linked to the Tyrrenean distension system lies the Campania Plain which represents a graben, stretched in a northwesterly-southeasterly direction and filled by volcanoclastic deposits and alluvial sediments, the latter resulting from the collapse of the Apennines, for a total thickness of more than 3000 m in the area of ​​maximum subsidence. The plain itself develops between Monte Massico to the northwest, the Campanian Apennines (the Tifatini mountains of the area around Nola and Caserta) to the east and the Lattari Mountains of the Sorrento peninsula to the southeast. Monte Massico borders to the northwest with the extinct volcano of Roccamonfina, the last eruptive activity of which dates back to about 50,000 years ago (Fig. 1.3). In the central and southern part of the plain emerge the volcanic complexes of the Campi Flegrei and Vesuvius, which together with the island of Ischia, just to the west, constitute the active volcanoes of Campania. The tectonic distension of this area, ongoing over the course of several million years, has produced a progressive stretching and thinning of the crust, with the rise of the Moho which represents the rheological discontinuity between the lower crust and the upper mantle. This process has allowed magmas in the mantle to rise through the crust, halting at a range of depths and thus feeding Neapolitan volcanism (Fig. 2.3).