Detection of fresh and thermal waters over an island with extinct volcanism: the island of Salina (Aeolian arc, Italy)

A geochemical prospection of the fluids circulating over a volcanic island highlighted the existence of
reservoirs of both fresh and thermal water although only a few natural manifestation, mainly occurring in
submarine environment, provide clues of their existence. Coupling the information provided by the
diffuse gas bubbling and the low-salinity waters discharged from the sea floor off the Island with those
from the low-salinity and thermal waters collected from in-land wells drilled in recent times we found
that a large amount of fresh and thermal waters are continuously discharged at the sea level. The thermal
waters, collected at a temperature of 32-36°C, show a typical marine recharge with equilibrium
temperatures estimated to be in the range of 120-160°C. As matter of fact, the small island holds
relatively large reservoirs of both fresh and thermal waters. The geochemical features of the circulating
fluids are driven by water-rock and gas-water interaction processes, while the heat supplied to the
geothermal reservoir comes from volcanic rocks that are still cooling down after the end of the last
volcanic activity supposed to be not older than 13ky.

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