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History, water and geology

History

The thermal waters of the Island are well known and used since ancient times. Already the first Euboeans settlers (eighth century AC), as evidenced by numerous archaeological finds at the site of Pithecusa and kept at the Archaeological Museum of Villa Arbusto in Lacco Ameno, appreciated and used the waters of hot springs on the island. The Greeks used the hot springs for restoring spirit and body and as a remedy for healing the aftereffects of war wounds (in pre-antibiotic age!) By attributing to the waters and vapors that bubbled up from the earth with supernatural powers, not by chance at each spa town stood temples dedicated to deities like Apollo at Delphi. Strabo, greek historian and geographer, mentions in his monumental work the geographical island of Ischia and the virtues of its hot springs (Geograph. Lib. V). If the Greeks were the first people to know the powers of hot springs, the Romans praised as a tool of healing and relaxation through the creation of public Thermae and the many safe and profitable source of the island (as the votive tablets found at Source Nitrodi Barano of Ischia, where stood a temple dedicated to Apollo and the Nymphs Nitrodi, guardians of the water) without lavish settlements. In fact, on the island has not been found, as instead in Rome and other ancient spas, majestic ruins of the Baths probably volcanic eruptions and earthquakes, which frequently have violently shaken the cliffs.

The decline of the power of Rome coincided with the abandonment of the use of bathing even in Ischia: there are indeed traces of water in use in the Middle Ages.

About Spa and thermae we can actively talking in the Renaissance and a decisive impetus to the modern spa medicine was given by Giulio Iasolino, a Calabrian physician, professor at the University of Naples, who towards the end of 1500, attracted by the climate and the phenomena of secondary volcanism (fumaroles and hot springs), realizing the therapeutic potential of the thermal medium, carried out a thorough survey of the sources, he identified the composition of the water and made detailed observations about their effects on many diseases that plagued his contemporaries.

Chemical composition of the water

During the ten-year period from 1988 to1998, 83 thermal establishments located near springs and wells that are important to the reconstruction of the water circulation plan were monitored. The samples were drawn periodically in the communes of Casamicciola (22 thermal establishments), Ischia (28 thermal establishments), Forio (17 thermal establishments), Serrara Fontana (7 thermal establishments), Lacco Ameno (7 thermal establishments) and Barano (2 thermal establishments).
The analysis concerned the determination of the main chemical-physical parameters (temperature, pH and electric conductibility) and that of a large series of anions and cations. The concentration of cations was determined through a spectrophotometry of atomic absorption, that of the anions through ionic chromatography and that of the silica through the colorimetric method. It was found that the subterranean waters of the island vary greatly and are generally characterised by:
- temperatures between 18 and 90?C;
- an electric conductibility between 841 and 56000 mS/cm; high levels of alkali and silica (up to about 600mg/l), the latter being typical of subterranean water circuits in volcanic potassium rocks.

Four water groups were recognised:
- bicarbonate-calcium;
- bicarbonate- alkaline;
- transitional waters;
- sulphate - chlorate ? alkaline

directly connectable to the geological-volcanic model of the Island.

The Geological model

The eruptive and tectonic history of the Island of Ischia is very complex and the surveyed age of its volcanic materials dates back to 150,000 years ago. Volcanic activity on the island of Ischia includes two distinct cycles: the first developed between 150,000 and 75,000 years ago and the second cycle started with the great eruption that generated the green tuff of Mount Epomeo and is characterised by consistent vertical movements that concern the central part of the island. Added to this volcanic activity are the volcanic-tectonic phenomena and those connected with the action of exogenous agents, the effects of which translate into the erosion, transportation and sedimentation of melted pyroclastic materials. The most commonly accepted hydrogeological model provides the existence of two basic superimposed tables (3): the lower one is fed by the ingression of seawater, therefore having a high saline content, and is delimited above by a concave surface that faces upwards; the other is nourished by rain water, which contains less minerals and ?floats? on the previous one due to its lower density and is delimited above by a convex surface, since it thickens as it departs from the coast and heads towards the internal part of the island. The area of contact between the two is characterised by a diffusion belt where the waters assume an intermediate chemism. The thickness of this belt varies from area to area and can even vary in the same area during the year. These variations are due to the different intensity of rainfall. Maximum rainfall takes place in the twomonth period of November and December, while minimum rainfall occurs during the quarter that goes from June to August. Water heating takes place through conduction (transfer of heat on contact between the waters and the hot acquifer rocks), but especially by convention, following the circulatory motions through the reticule of fissures (divergent faults and fractures) triggered by thermal imbalances.

Hydrogeological maps

Group A (facies bicarbonate - calcic)
Only a few samples belong to the faciescalcic type. This consists of waters drawn in correspondence of springs and superficial wells in the internal areas of the island, concerning perched water tables. The low temperature (from 18 to 25?C) (Figure 2) and conductibility values (from 831 to 1789 mS/cm) (Figure 3), when compared to the remaining standardisations are proof of the presence of relatively superficial and fast circuits, with minimum water-rock interaction.

Group B (Bicarbonate-alkaline)
These are bicarbonate-alkaline waters. They are characterised by high temperature values (from 40 to 90?C) and relatively contained conductibility (from 1800 to 6700 mS/cm), when compared to those in groups C and D. These waters were generally sampled in the internal areas of the island, particularly near the marginal faults of Mount Epomeo, at the top and at the foot of the same.

Group C (transition facies)
The waters ascribable to transition facies represent about 1/3 of the examined samples. Part of these waters is located along a probable blending line between the abovementioned bicarbonate-alkaline and sulphate-chlorate-alkaline waters. Due to the relation between chlorides and alkaline ions as well as for other reasons, the same waters may be considered to be an intermediate chemism limit between those in groups B and D.
As far as the temperature trend and the conductibility of this group is concerned, a decrease in temperature is observed as one moves closer to the coastline, in the area of the Ischia Graben, in the north-western sector of the island; conductibility (varying from 10000 to 20000 mS/cm) assumes generally higher values to those of bicarbonate-alkaline waters and lower values with respect to those typical of sulphate- chlorate-alkaline waters. The waters that can be traced back to these facies were generally sampled from wells in the basic table of the marginal area of the island; in the depressed area of Ischia they were sampled up to a considerable distance from the coastline.

Group D (Sulphate-chloride-alkaline facies)
The water samples examined belong to the sulphate-chloride-alkaline group and their composition is similar to that of seawater. However, they do not derive from the blending of marine and phreatic waters.
These waters can be distinguished for their high level of conductibility, which often exceeds 40000 mS/cm. Temperatures vary according to the acquiferous portion considered: in the north-eastern sector of the island, which coincides with the Ischia Graben, the temperatures are relatively low and limited to a relatively restricted interval (from 20 to 40?C); whereas, in the marginal sector of Mount Epomeo, the temperatures are generally higher and do not always decrease as one moves towards the coastline. On the contrary, in some cases they actually exceed 80?C. These waters generally characterise the wells near the coastline, including both superficial wells and the deeper ones that go beyond the water interface of the marine ingression water table. Obviously, the latter reveal higher levels of salinity and chloride.