manifestations take place where there are tectonic peculiarities (faults,
fractures) or structural peculiarities of the subsoil (lava flows
etc.); in other words, where there are areas of relatively higher
permeability. In the communes of Forio and Lacco Ameno the fumarolic
groups of Casa Verde, Roccia della Frana, Montagna Nuova and Portella
Bianca are in correspondence of the crateral edge of Mount Nuovo.
Similarly, in the commune of Lacco Ameno the groups of Mount Vico,
Mount Tabor, Mount Rotaro and Citrunia (Forio Campotese) are in correspondence
of the crateral edges of Mount Vico, Mounts Rotaro, Tabor and Imperatore.
The groups of Bocca, Bellomo, Vagnulo, Schiappa di Montecorvo , in
the Forio territory, are relative to the faults system (non-spontaneous
fractures) determining the western side of the Epomeo massif. The
groups of Cava Fasaniello, Mount Cito, Mount di Mezzo, Fasano, Bianchetto
and Regione Cratica (Casamicciola) are, in turn, relative to the fault
system determining the northern side of the same Epomeo. However,
other groups exist where no tectonic peculiarities are noticed such
as in Lacco Ameno, Cava di Succhivo etc. The subterranean hydrology
of a volcanic region such as Ischia, where formations of various levels
of permeability alternate in all directions and at brief intervals,
is very complex and varies from one area to another.