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Papadakis, G.
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- PublicationRestrictedHydrogen sulphide as a natural air contaminant in volcanic/geothermal areas: the case of Sousaki, Corinthia (Greece)(2009)
; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment; ; ; ; Volcanic and geothermal areas are one of the major natural sources of H2S to the atmosphere. Its environmental impact is often the main cause of the opposition to the development of geothermal energy exploitation programs. In this paper we analyze the air concentrations and dispersion pattern of naturally emitted H2S at the geothermal area of Sousaki (Corinthia, Greece). Measurements, made with a network of passive samplers, evidence a rapid decrease of concentration values away from the emission points. The fact that the decrease is more pronounced in the summer with respect to the winter indicates that it is not only due to a dilution effect, but also to redox reactions favoured by higher temperatures and intense sunlight typical of the summer period.175 28 - PublicationRestrictedMethana, the westernmost active volcanic system of the south Aegean arc (Greece): insight from fluids geochemistry(2008)
; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment; ; ; ; An extensive geochemical survey of the fluids released by the volcanic/geothermal system of Methana was undertaken. Gases were characterized based on the chemical and isotopic [helium (He) and carbon (C)] analysis of 27 samples. Carbon dioxide soil gas concentration and fluxes were measured at 179 sampling sites throughout the peninsula. Forty samples of thermal and cold groundwaters were also sampled and analysed to characterize the geochemistry of the aquifers. Gases of hydrothermal origin gave a preliminary geothermometric estimate of about 210 °C. The He-isotope composition indicated mantle contributions of up to 40%, and the C-isotope composition of CO2 indicated that it predominantly (>90%) originated from limestone decomposition. The groundwater composition was suggestive of mixing between meteoric and hydrothermally modified sea-water endmembers and water–rock interaction processes limited to simple rock dissolution driven by an increased endogenous CO2 content. All of the thermal manifestations and anomalous degassing areas, although of limited extent, were spatially correlated with the main active tectonic system of the area. The total CO2 output of the volcanic system has been preliminary estimated to be less than 0.05 kg s–1. Although this value is very low compared to those of other volcanic systems, anomalous CO2 degassing at Methana – which is currently restricted to limited areas and at present is the only volcanic risk of the peninsula – is a potential gas hazard that warrants further assessment in future studies.157 26 - PublicationRestrictedDiffuse and focused carbon dioxide and methane emissions from the Sousaki geothermal system, Greece(2006)
; ; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; Department of Geology, University of Athens, Athens, Greece. ;Rotolo, S.; Dipartimento di Chimica e Fisica della Terra ed Applicazioni (CFTA), University of Palermo, Palermo, Italy. ;Michas, G.; Department of Geology, University of Athens, Athens, Greece. ;Minio, M.; Dipartimento di Chimica e Fisica della Terra ed Applicazioni (CFTA), University of Palermo, Palermo, Italy. ;Papadakis, G.; Department of Geology, University of Athens, Athens, Greece.; ; ; ; ; ; We report first data on chemical composition of the gas emitted by the geothermal system of Sousaki, Greece. Gas manifestations display typical geothermal gas composition with CO2 as the main component and CH4 and H2S as minor species. Soil gas composition derives from the mixing of two end-members (atmospheric air and geothermal gas). Soil CO2 fluxes range from<2 to 33,400 g m 2 d 1. The estimated diffuse output of hydrothermal CO2, estimated for an area of 0.015 km2, is about 630 g s 1, while a tentative estimation of CH4 diffuse output gave a value of about 1.15 g s 1. Point sources accounted for lower flux values of 26 g s 1 of CO2, 0.1 g s 1 of CH4 and 0.02 g s 1 of H2S.248 35 - PublicationOpen AccessGEOCHEMICAL CHARACTERIZATION OF THERMAL AND COLD GROUNDWATERS OF METHANA PENINSULA (PELOPONNESUS, GREECE)(2008-10-08)
; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment ;Bellomo, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment; ; ; ; ; ; ; ; ; ;Migiros, G.; Agricultural University of Athens, Dept: Sciences ;Stamatis, G.; Agricultural University of Athens, Dept: Sciences ;Stournaras, G.; University of Athens, Dept. of Geology and Geoenvironment; ; A comprehensive hydrogeochemical study of the cold and thermal groundwaters of the presently quiescent volcanic system of Methana was undertaken collecting 59 natural water samples during the period 2004-2007. Methana is a peninsula whose climatology and hydrology can be compared to the nearby small islands of the Aegean Sea. Similarly the chemical and isotopic composition of its water is dominated by the mixing of seawater with meteoric water. But the simple mixing trend is modified by water-rock interaction processes, enhanced by the dissolution of endogenous CO2, leading to strong enrichments in Alkalinity, Calcium, Barium, Iron and Manganese.161 256 - PublicationOpen AccessStatic chamber methane flux measurements in volcanic/geothermal areas: preliminary data from Sousaki and Nisyros (Greece)(2010-05-02)
; ; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Fiebig, J.; University of Frankfurt a.M., Inst. für Geowissenschaften, Germany ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Maneta, V.; University of Athens, Dept. Geology and Geoenvironment, Greecey ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment, Greece; ; ; ; ; ; Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the second most important greenhouse gas after carbon dioxide. Methane is released to the atmosphere by a wide number of sources, both natural and anthropogenic, with the latter being twice as large as the former (IPCC, 2007). It has recently been established that significant amounts of geological methane, produced within the Earth’s crust, are currently released naturally into the atmosphere (Etiope, 2004). Active or recent volcanic/geothermal areas represent one of these sources of geological methane. But due to the fact that methane flux measurements are laboratory intensive, very few data have been collected until now and the contribution of this source has been generally indirectly estimated (Etiope et al., 2007). The Greek territory is geodynamically very active and has many volcanic and geothermal areas. Here we report on methane flux measurements made at two volcanic/geothermal systems along the South Aegean volcanic arc: Sousaki and Nisyros. The former is an extinct volcanic area of Plio-Pleistocene age hosting nowadays a low enthalpy geothermal field. The latter is a currently quiescent active volcanic system with strong fumarolic activity due to the presence of a high enthalpy geothermal system. Both systems have gas manifestations that emit significant amounts of hydrothermal methane and display important diffuse carbon dioxide emissions from the soils. New data on methane isotopic composition and higher hydrocarbon contents point to an abiogenic origin of the hydrothermal methane in the studied systems. Measured methane flux values range from –48 to 29,000 (38 sites) and from –20 to 1100 mg/mˆ2/d (35 sites) at Sousaki and Nisyros respectively. At Sousaki measurement sites covered almost all the degassing area and the diffuse methane output can be estimated in about 20 t/a from a surface of about 10,000 mˆ2. At Nisyros measurements covered the Stephanos and Kaminakia areas, which represent only a part of the entire degassing area. The two areas show very different methane degassing pattern with latter showing much higher flux values. Methane output can be estimated in about 0.25 t/a from an area of about 30,000 mˆ2 at Stephanos and about 1 t/a from an area of about 20,000 mˆ2 at Kaminakia. The total output from the entire geothermal system of Nisyros probably should not exceed 2 t/a.465 361 - PublicationRestrictedDiffuse hydrothermal methane output and evidence of methanotrophic activity within the soils at Sousaki (Greece)(2011-01)
; ; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Martelli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Salerno, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; Methane soil flux measurements have been made in 38 sites at the geothermal system of Sousaki (Greece) with the closed chamber method. Fluxes range from –47.6 to 29,150 mg m-2 d-1 and the diffuse CH4 output of the system has been estimated at 19 t a-1. Contemporaneous CO2 flux measurements showed a moderate positive correlation between CO2 and CH4 fluxes. Comparison of the CO2/CH4 soil flux ratios with the CO2/CH4 ratio of the gases of the main gas manifestations provided evidence for methanotrophic activity within the soil. Laboratory CH4 consumption experiments confirmed the presence of methanotrophic microorganisms in soil samples collected at Sousaki. Consumption was generally in the range from –4.9 to –38.9 pmolCH4 h-1 g-1 but could sometimes reach extremely high values (–33,000 pmolCH4 h-1 g-1.). These results are consistent with recent studies on other geothermal systems that revealed the existence of thermoacidophilic bacteria exerting methanotrophic activity in hot, acid soils, thereby reducing methane emissions to the atmosphere.284 33 - PublicationOpen AccessFluid geochemistry investigations on the volcanic system of methana(2007-05)
; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens ;Margaritopoulos, M.; University of Athens ;Michas, G.; University of Athens ;Papadakis, G.; University of Athens; ; ; ; ; An extensive geochemical survey on the fluids released by the volcanic/geothermal system of Methana was undertaken. Characterization of the gases was made on the basis of the chemical and isotopic (He and C) analysis of 14 samples. CO2 soil gas concentration and fluxes were measured on the whole peninsula at more than 100 sampling sites. 31 samples of thermal and cold groundwaters were also sampled and analysed to characterize the geochemistry of aquifers. Anomalies referable to the geothermal system, besides at known thermal manifesta-tions, were also recognized at some anomalous degassing soil site and in some cold groundwater. These anomalies were always spatially correlated to the main active tectonic system of the area. The total CO2 output of the volcanic system has been preliminary estimated in about 0.2 kg s-1. Although this value is low compared to other volcanic systems, anomalous CO2 degassing at Methana may pose gas hazard problems. Such volcanic risk, although restricted to limited areas, cannot be neglected and further studies have to be undertaken for its better assessment239 217 - PublicationOpen AccessHYDROTHERMAL METHANE FLUXES FROM THE SOIL AT SOUSAKI (GREECE)(2010-09-23)
; ; ; ; ; ; ; ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Kyriakopoulos, K.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Martelli, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Michas, G.; University of Athens, Dept. Geology and Geoenvironment, Greecey ;Papadakis, G.; University of Athens, Dept. Geology and Geoenvironment, Greece ;Salerno, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; ; ; ; ; ; ;Christofolides, G.; School of Geology, Aristotle University of Thessaloniki, Greece ;Kantiranis, N.; School of Geology, Aristotle University of Thessaloniki, Greece ;Kostopoulos, D.S.; School of Geology, Aristotle University of Thessaloniki, Greece ;Chatzipetros, A.A.; School of Geology, Aristotle University of Thessaloniki, Greece; ; ; Methane soil flux measurements have been made in 38 sites at the geothermal system of Sousaki (Greece) with the closed chamber method. Fluxes range from –47.6 to 29,150 mg m-2 d-1 and the diffuse CH4 output of the system has been estimated in 19 t/a. Contemporaneous CO2 flux measurements showed a fair positive correlation between CO2 and CH4 fluxes but the flux ratio evidenced methanotrophic activity within the soil. Laboratory CH4 consumption experiments confirmed the presence of methanotrophic microorganisms in soil samples collected at Sousaki. These results further confirm recent studies on other geothermal systems that revealed the existence of thermophilic and acidophilic bacteria exerting methanotrophic activity also in hot and acid soils thereby reducing methane emissions to the atmosphere.207 176