Eruptions, earthquakes and geothermal resources at Campi Flegrei and Ischia

The volcanic activity of Campi Flegrei and Ischia ranges between 150 ka and the present. The last eruption at Ischia occurred in 1302 CE, and that in Campi Flegrei in 1538. Eruptions at Ischia were more frequent during Greek and Roman times, whereas Campi Flegrei was more active between 5000 and 3000 aBP. The use of thermal baths flourished at Campi Flegrei during  roman and the middle age, and balneo-therapy became a popular remedy that rivalled with the activity of the Salerno school of medicine. All this activity came to an end with the eruption of Monte Nuovo in 1538, that, although of modest magnitude, caused a strong commotion and altered the state of springs for long times. Soon after the eruption of Montenuovo, a calabrian physician, Giulio Iasolino (1588), wrote a treatise named “ De Rimedi Naturali che sono nell'Isola di Pithecusa; hoggi detta Ischia” ,  enumerating the springs of Ischia and describing their curative properties. Since then, the thermal springs of Ischia slowly became renown firstly in the kingdom of Naples and subsequently in Italy. Volcanic activity and earthquakes have strongly influenced the exploitation of the geothermal resources and the fears of possible eruptions has affected for long time the attitude of people against the benefits resulting from it.

The active volcanoes in the bay of Naples (Vesuvius, Campi Flegrei and Ischia) share a common behavior, in that they alternate long periods of quiescence lasting several centuries to millennia, with prolonged periods of activity with numerous eruptions in a relatively short span of time (centuries).
Vesuvius had its last period of activity between 1631 and 1944 preceded by a quiescence of several centuries and followed by a new quiescence lasting since 1944, and longer by an order of magnitude than any quiescence of the preceding period (Carta et al, 1981). A longer quiescence period preceded the eruption of 79 AD and the following eruptions.
Campi Flegrei in the last 15 ka had at least three periods of activity lasting several centuries with numerous explosive and effusive eruption; each period was followed by a period of quiescence lasting several millennia (Rosi andSbrana, 1987, Di Vito et al, 1999). The last period of activity between 4.8 and 3.8 ka Bp was followed by a quiescence until 1538 with the single eruption of Monte Nuovo and, since 1950, there has been a period of unrest with uplift of the ground and swarms of earthquakes (Del Gaudio et al, 2010).
Ischia island had at least two major periods characterized by numerous eruptions between 6 and 4.3 ka Bp and 2.9 and 1.6 ka Bp (De Vita et al, 2010, Vezzoli et al, 2009, with the last eruption occurring in 1302 CE. The causes of such periodization may be related with processes of magma ascent and stocking at shallow level in the crust; the activity period could represent the activation and evacuation of the magma emplaced in a shallow reservoir (Di Vito et al, 2016).
The succession of long period of quiescence followed by long period of activity had an economic impact on the communities living in the area, with period of prosperity followed by sudden economic decline.

2-Campi Flegrei and Ischia from Neolithic to Roman age
The Campanian plain has been the site of numerous human settlements since at least Neolithic age (Di Vito et al, 2013). The settlements are rarer in Campi Flegrei because of the frequent volcanic activity. It appears that the area was settled during the period of quiescence and abandoned as a consequence of volcanic activity.
The eruption of the Neapolitan Yellow Tuff at 15000 a BP left a wide gulf extending inland with respect to the present coastline (Scandone et al, 1991). A Neolithic village was settled on the border of the gulf at Monte di Procida and was subsequently buried by the products of Fondi di Baia eruption (Albore Livadié, 1986) dated at 8560 y BP belonging to the second Epoch of activity (Di Vito et al, 1999).
At Ischia, at Cilento locality, there are traces of a settlement of middle-late neolithic age overlain by a thick ash deposit called Piano Liguori Formation (Buchner andRittman, 1948, Buchner, 1986) dated between 5.1 and 5.5 ka. In locality S.Michele, there are traces of a more recent settlement dated between 5000 and 3000 a BP.
After the second epoch of activity, the central part of Campi Flegrei rose above sea level, living a large portion of land dry. New settlements of Eneolithic age, and Bronze age were located on the side of Gauro volcano, and at Montagna Spaccata and were buried by the deposits of the last phase of activity of Campi Flegrei (Albore Livadié, 1986).
At Ischia there are evidences of a Mycenaean trading post around 1000 BC (as shown in the archeological museum of Ischia) during a short lull of the volcanic activity. Subsequently Greek colonists from Euboea in 770 BC settled on the island on Monte Vico above the present village of Lacco Ameno. The settlement was called Pythecusa and was probably a port of commerce and trade before the large wave of Greek colonization in southern Italy. Greek and roman authors (Strabo, Plinius Seniore) report that seismic and volcanic activity, several times drove away the settlers from Ischia. Strabo reports that the Syracusans which established a garrison on the island after 474 BC, were driven away by an eruption and earthquakes, probably occurred, in 470 BC (Buchner, 1986). Frequent eruptions affected the island throughout this period, till late roman age (Buchner, 1986, De Vita et al, 2010, Vezzoli et al, 2009). The last eruption occurred in 1302 in a locality that was called Arso (Burned) and caused a widespread emigration from the island toward Pozzuoli. A testimony of the fact is the presence at Pozzuoli of the common surname "Schiano" deriving from the abbreviation of "Ischitano->Ischiano->Schiano" (Annecchino, 1960) .

3-The beginning of the exploitation of the thermal Baths
The abundance of thermal spring and hot pools recalled the attention of the Romans, who were very fond of the thermal baths, especially if the warm water was of natural origin, as recalled by Cassiodorus in 530 CE "hot thermal baths not heated by smoky furnaces but directly by Nature".
The first testimony of the use of the thermal waters of Campi Flegrei for therapy is referred by T.
Livii to 176 BC when, the consul Cneus Cornelius came to Campi Flegrei to cure arthritis, but the therapy did not have the desired effect "ad Aquas Cumanas profectus ingravescente morbo Cumis decessit".
Rich Roman patricians in the late republican period (Caius Marius, Caesar, Pompeius Magnus, Cicero, Antonius, etc) had their summer villas in the area which soon became a popular summer resort.
The luxury of the place caused the contempt of Propertius because of the betrayal of his girlfriend Cinthia "A pereant Baiae, crimen amoris, aquae". Similar words were used by Seneca to describe the place. Horatius remembers the place with better words "nullus in orbe sinus Baiis prelucet Amoenis", and the thermal baths were also mentioned by Martial and Plinius Senior.     (1667) identified all the 40 baths existing before the eruption from Naples to Miseno but ascertained that only 9 still remained in use and proposed the restoration of all the others. Unfortunately, the cost of restoration was too high to allow a total recovering of all the baths. The list of all the thermae was engraved in three marble epigraphs, two of which are still preserved in Naples and Pozzuoli.
The third was stolen in 1800 by English mariners and what still remain is the name of the place "Punta dell'Epitaffio" near Baia ( fig. 4).  Such works permitted a flourishing of the island, and of the balneotherapy also during the following period under the kingdom of Italy. During this period Ischia became a renown international resort and it is not a case that, among the 2333 casualties caused by the 28 July 1883 earthquake, 625 were foreigners (Placanica, 1998). In such a sense, the 1883 earthquake was the first "international catastrophe" affecting a wide number of different nationalities such as that, more than a century later, of the Sumatra earthquake and tsunami of 2004.
The temporary decline of Ischia thermal baths due to the earthquake led to a rapid revival of Campi  It would be desirable that, after the decline of such industrial activities, the Spa activities may flourish again in this area.

4-Conclusions
Earthquakes and eruptions have affected in different periods the area of Campi Flegrei and Ischia.
The temporal shift of the activity in the two areas caused that when one area flourished the other declined and vice-versa. Although such natural phenomena have been known, since at least three thousand years, people have always resettled after the eruptions and earthquakes, rebuilding their homes and the activity related with the natural resources.
In more recent times different dynamics related with the uncontrolled expansion of urban settlements have completely altered the delicate balance between environment and man, and even the recent seismic and deformation crises of Campi Flegrei (Luongo et al, 1985) have not prevented the continuous expansion of the city of Naples within the area at highest risk (Alberico et al, 2002).