Submarine Geothermal Systems in Southern Tyrrhenian Sea as Future Energy Resource: the Example of Marsili Seamount

Italy has one of the greatest geothermal potential for power production in the world. At the present, the exploitation of geothermal reservoirs for power generation is concentrated in two main areas located in the Tyrrhenian pre-Apennine volcanic district of Southern Tuscany: Larderello- Travale/Radicondoli and Mount Amiata. These two geothermal reservoirs are hosted in Mesozoic carbonatic formations and metamorphic basement, with temperatures of 200–350°C at a depth of 500–3500 m. In the 1970s and 1980s a joint-venture ENEL-AGIP performed an exploration program in Latium, Campania and Sicily regions finding great potential but low exploitability due to high salinity of geothermal fluids. A new target for geothermal exploration and exploitation in Italy is represented by the submarine volcanic district of Southern Tyrrhenian Basin. The latter is a geologically young (Upper Pliocene – Pleistocene) area characterized by tectonic extension with associated magmatism. In this context numerous volcanic centers developed and provide important heat sources; heat flow data of the area show positive anomalies comparable to those of onshore geothermal fields. Fractured basaltic rocks facilitate seawater infiltration and consequent circulation of hot water chemically altered by rock/water interactions, as evidenced by the presence of hydrothermal deposits on Tyrrhenian seamounts, collected during previous oceanographic samplings. A geothermal exploration program of the Marsili seamount, the greatest volcanic edifice in the European area, started in 2006. Preliminary data interpretation suggests the presence of geothermal activity and further research is foreseen to better characterize the whole volcanic-geothermal system. If realistically exploitable geothermal reservoirs are discovered, submarine geothermal systems will be an important – potentially infinite – renewable energy resource in Italy, opening a scenario for a future development of offshore geothermal power generation.