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Giannini, Luciano
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- PublicationOpen AccessSeafloor doming driven by degassing processes unveils sprouting volcanism in coastal areas(2016-03-01)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;; ; ;; We report evidences of active seabed doming and gas discharge few kilometers offshore from the Naples harbor (Italy). Pockmarks, mounds, and craters characterize the seabed. These morphologies represent the top of shallow crustal structures including pagodas, faults and folds affecting the present-day seabed. They record upraise, pressurization, and release of He and CO2 from mantle melts and decarbonation reactions of crustal rocks. These gases are likely similar to those that feed the hydrothermal systems of the Ischia, Campi Flegrei and Somma-Vesuvius active volcanoes, suggesting the occurrence of a mantle source variously mixed to crustal fluids beneath the Gulf of Naples. The seafloor swelling and breaching by gas upraising and pressurization processes require overpressures in the order of 2-3 MPa. Seabed doming, faulting, and gas discharge are manifestations of non-volcanic unrests potentially preluding submarine eruptions and/or hydrothermal explosions.142 29 - PublicationRestrictedGeochemical and isotopic changes in the fumarolic and submerged gas discharges during the 2011–2012 unrest at Santorini caldera (Greece)(2013)
; ; ; ; ; ; ; ; ; ;Tassi, F.; Department of Earth Sciences, University of Florence,Italy ;Vaselli, O.; Department of Earth Sciences, University of Florence,Italy ;Papazachos, C. B.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Giannini, L.; Department of Earth Sciences, University of Florence,Italy ;Chiodini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Vougioukalakis, G. E.; IGME—Institute for Geology and Mineral Exploration, ;Karagianni, E.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Vamvakaris, D.; Geophysical Laboratory, Aristotle University of Thessaloniki, ;Panagiotopoulos, D.; Geophysical Laboratory, Aristotle University of Thessaloniki,; ; ; ; ; ; ; ; Abstract A geochemical survey of fumarolic and submerged gases from fluid discharges located in the Nea Kameni and Palea Kameni islets (Santorini Island, Greece) was carried out before, during, and after the unrest related to the anomalously high seismic and ground deformation activity that affected this volcanic system since January 2011. Our data show that from May 2011 to February 2012, the Nea Kameni fumaroles showed a significant increase of H2 concentrations. After this period, an abrupt decrease in the H2 contents, accompanied by decreasing seismic events, was recorded. A similar temporal pattern was shown by the F−, Cl−, SO4 2−, and NH4 + concentrations in the fumarolic condensates. During the sharp increase of H2 concentrations, when values up to 158 mmol/ mol were measured, the δ13C–CO2 values, which prior to January 2011 were consistent with a dominant CO2 thermometamorphic source, have shown a significant decrease, suggesting an increase of mantle CO2 contribution. Light hydrocarbons, including CH4, which are controlled by chemical reactions kinetically slower than H2 production from H2O dissociation, displayed a sharp increase in March 2012, under enhanced reducing conditions caused by the high H2 concentrations of May 2011–February 2012. The general increase in light hydrocarbons continued up to July 2012, notwithstanding the contemporaneous H2 decrease. The temporal patterns of CO2 concentrations and N2/Ar ratios increased similarly to that of H2, possibly due to sealing processes in the fumarolic conduits that diminished the contamination related to the entrance of atmospheric gases in the fumarolic conduits. The compositional evolution of the Nea Kameni fumaroles can be explained by a convective heat pulse from depth associated with the seismic activation of the NE–SW-oriented Kameni tectonic lineament, possibly triggered by either injection of new magma below Nea Kameni island, as apparently suggested by the evolution of the seismic and ground deformation activity, or increased permeability of the volcanic plumbing system resulting from the tectonic movements affecting the area. The results of the present study demonstrate that the geophysical and geochemical signals at Santorini are interrelated and may be precursory signals of renewed volcanic activity and encourage the development of interdisciplinary monitoring program to mitigate the volcanic risk in the most tourist-visited island of the Mediterranean Sea.462 66