Hundreds of millions of people live close to active volcanoes around the world, remaining there on the basis of a delicate balance that inherently considers benefits (fertile soils, raw materials, geothermal sources) and risks. The violence of the emplacement mechanisms (e.g., fall from a high eruptive column or pyroclastic currents from a collapsing plume) and the sudden burying of the landscape make these types of eruptions extremely dangerous, and able to wipe out whole towns (such as Pompeii and Herculaneum in Italy). Furthermore, even small eruptions produce well-known volcanic crisis when occur in close proximity to population centres (such as Montserrat, West Indies). Why people decide to confront such a dramatic scenario is difficult to answer. This note documents some case studies related to the impacts of eruptions of Neapolitan volcanoes on human settlements and provides new insight into human behaviour after different kinds of volcanic eruptions.
Campi Flegrei eruptive history
The complex volcanic history of this volcanic field is characterized by the superposition of minor effusive, main explosive, and some reworked volcanic products, together with the presence of volcano-tectonic structures (caldera rim) and several monogenetic volcanoes. The Campi Flegrei volcanic field is a vast area that includes a large part of the city of Naples and the Island of Procida; it is characterized by the presence of diffuse monogenetic volcanic cones and two nested calderas associated with the Campanian Ignimbrite (39 ka) (Perrotta et al., 2006) and the Neapolitan Yellow Tuff (15 ka; Scarpati et al., 1993) eruptions, respectively. The oldest volcanic rocks crop out well inside the city of Naples (San Martino hill) and are dated at ca. 78 ka. Numerous small volcanic centers have been identified, including lava domes and scattered monogenetic vents located in the city of Naples, along the morphological border of Campi Flegrei and on Procida Island. The products of this early activity are covered by tephra from different sources: (1) coarse fallout and flow deposits from Ischia Island; and (2) stratified fall deposits from the eastern part of Campi Flegrei. A ubiquitous succession formed by coarse welded beds (Piperno) and lithic breccia (Breccia Museo) associated with the Campanian Ignimbrite eruption covers the ancient sequence. These proximal deposits dated at 39 ka mark the oldest caldera rim that occupies the Campi Flegrei region and part of the city of Naples. A few small volcanoes (e.g., Solchiaro and Trentaremi) located inside and outside the caldera and some local tephra layers crop out below the Neapolitan Yellow Tuff. This huge pyroclastic deposit (50 km3 dense rock equivalent), which crops out extensively in the Neapolitan area, produced a second caldera collapse inside the preexisting Campanian Ignimbrite caldera. Tens of small volcanic edifices (most made up by lithified yellow tuff) were emplaced almost exclusively within the Neapolitan Yellow Tuff caldera both during prehistoric and historic times (e.g., Monte Nuovo volcano, 1538 A.D.).
Somma-Vesuvius eruptive history
The first phase of volcanic activity in the area of Somma–Vesuvius (as recorded in the unique 2072 m deep Trecase well) began about 0.4 myr B.P. and ended 0.3 myr B.P. with the emplacement of almost 400 m of lava flows. The oldest Plinian activity crop out in distal sites and is represented by Codola pumice fall deposit. Several plinian eruptions occurred every few thousands years with more frequent subplinian to strombolian and effusive episodes. A new fall deposit found in the Pollena quarry is a rare evidence of an ancient (>22 ka), well-preserved, proximal, Plinian deposit (Carcavone eruption) at Somma-Vesuvius (Sparice et al., 2017). The volcano's summit caldera has experienced incremental collapse associated with various plinian eruptions. The destructive impact of the major vesuvian eruptions on the surrounding volcanic territory is documented both by the numerous archaeological sites that suffered extensive damage and by historical chronicles of the more recent eruptive events. In fact, many villages, towns and rural farms in a large area around the volcano have been destroyed and buried under a blanket of tephra and mass flows in prehistoric and historic time. Some examples are the burying of a Bronze Age village entombed by the products of the Avellino plinian eruption in 3400 a BP and the most famous cities of Pompeii and Herculaneum destroyed during the 79 AD eruption. Thousands of people were killed in the few days of this eruption (Luongo et al., 2003). The next major eruptions after the 79 AD event were the major explosive eruptions (subplinian) of 472 AD and 1631. Historical records report over 4000 people killed and some 40,000 displaced in consequence of this latter eruption. A few other smaller explosive episodes were reported in 512 AD, the Medieval age and during the final 1631–1944 activity cycle.
The brief summary of the volcanic activity occurred in the Neapolitan area reported above defines the continuity and intensity of volcanic events that the prehistoric and historical populations have had to face. Do frequently erupting active volcanoes produce an area without settlements within the boundaries of a previously destroyed zone? And, if they initially do, how quickly do people come back to their original settlements? Incorporating new volcanological and archaeological results (Scarpati et al., 2013), it is possible to reveal a complex history of destruction of human settlements in the Neapolitan region extending over hundreds of years and how people re-used the same places few years after a violent explosive eruption.
Luongo, G., Perrotta, A., Scarpati, C., De Carolis, E., Patricelli, G., Ciarallo, A., 2003. Impact of 79AD explosive eruption on Pompeii II: causes of death of the inhabitants inferred by stratigraphical and areal distribution of the human corpses. J. Volcanol. Geotherm. Res. 126, 169–200.
Perrotta, A., Scarpati, C., Luongo, G., and Morra, V., 2006. The Campi Flegrei caldera boundary in the city of Naples. In De Vivo, B., ed., Volcanism in the Campania Plain: Vesuvius, Campi Flegrei and Ignimbrites: Amsterdam, the Netherlands, Elsevier, Developments in Volcanology 9, p. 85–96.
Scarpati, C., Cole, P., Perrotta, A., 1993, The Neapolitan Yellow Tuff— A large volume multiphase eruption from Campi Flegrei, southern Italy: Bulletin of Volcanology, v. 55, p. 343–356, doi: 10.1007/BF00301145.
Scarpati C., Perrotta, A., De Simone, F. G., 2016. Impact of explosive volcanic eruptions around Vesuvius: a story of resilience in Roman time. Bulletin of Volcanolology, 78:21. DOI: 10.1007/s00445-016-1017-4
Sparice, D., Scarpati, C., Mazzeo, F.C., Petrosino, P., Arienzo, I., Gisbert. G., Petrelli, M., 2017. New proximal tephras at Somma-Vesuvius: evidences of a pre-caldera, large (?) explosive eruptions Journal of Volcanology and Geothermal Research, 335: 71-81.