ALBERT

Description: Methane plays an important role in the Earth’s atmospheric chemistry and radiative balance being the most important greenhouse gas after carbon dioxide. It has recently been established that geogenic gases contribute significantly to the natural CH4 flux to the atmosphere (Etiope et al., 2008). Volcanic/geothermal areas contribute to this flux, being the site of widespread diffuse degassing of endogenous gases (Chiodini et al., 2005). In such an environment soils are a source rather than a sink for atmospheric CH4 (Cardellini et al., 2003; Castaldi and Tedesco, 2005; D’Alessandro et al., 2009; 2011; 2013). Due to the fact that methane soil flux measurements are laboratory intensive, very few data have been collected until now in these areas. Preliminary studies (Etiope et al., 2007) estimated a total CH4 emission from European geothermal and volcanic systems in the range 4-16 kt a-1. This estimate was obtained indirectly from CO2 or H2O output data and from CO2/CH4 or H2O/CH4 values measured in the main gaseous manifestations. Such methods, although acceptable to obtain order-of-magnitude estimates, completely disregard possible methanotrophic activity within the soil. At the global scale, microbial oxidation in soils contributes for about 3-9% to the total removal of methane from the atmosphere. But the importance of methanotrophic organisms is even larger because they oxidise the greatest part of the methane produced in the soil and in the subsoil before its emission to the atmosphere. Environmental conditions in the soils of volcanic/geothermal areas (i.e. low oxygen content, high temperature and proton activity, etc.) have been considered inadequate for methanotrophic microrganisms. But recently, it has been demonstrated that methanotrophic consumption in soils occurs also under such harsh conditions due to the presence of acidophilic and thermophilic Verrucomicrobia. These organisms were found in Italy at the Solfatara di Pozzuoli (Pol et al., 2007), in New Zealand at Hell’s Gate (Dunfield et al., 2007) and in Kamchatka, Russia (Islam et al., 2008). Both the Italian and the Hellenic territories are geodynamically very active with many active volcanic and geothermal areas. Here we report on methane flux measurements made at Pantelleria (Italy) and at Sousaki and Nisyros (Greece). The total methane output of these three systems is about 10, 19 and 1 t a-1, respectively (D’Alessandro et al., 2009; 2011; 2013). The total emissions obtained from methane flux measurements are up to one order of magnitude lower than those obtained through indirect estimations. Clues of methanotrophic activity within the soils of these areas can be found in the CH4/CO2 ratio of the flux measurements which is always lower than that of the respective fumarolic manifestations, indicating a loss of CH4 during the travel of the gases towards earth’s surface. Furthermore laboratory methane consumption experiments made on soils collected at Pantelleria and Sousaki revealed, for most samples, CH4 consumption rates up to 9.50 µg h-1 and 0.52 µg h-1 respectively for each gram of soil (dry weight). Only few soil samples displayed no methane consumption activity. Finally, microbiological and molecular investigations allowed us to identify the presence of methanotrophic bacteria belonging to the Verrucomicrobia and to the Alpha- and Gamma-Proteobacteria in the soils of the geothermal area of Favara Grande at Pantelleria. While the presence of the former was not unexpected due to the fact that they include acidophilic and thermophilic organisms that were previously found in other geothermal environments, the latter are generally considered not adapted to live in harsh geothermal environments. Their presence in the soils of Pantelleria could be explained by the fact that these soils do not have extremely low pH values (〉5). Indeed thermotollerant methanotrophic Gamma-proteobacteria, have been previously found in the sediments of thermal springs in Kamchatka (Kizilova et al., 2012). Such species could find their niches in the shallowest part of the soils of Favara Grande were the temperatures are not so high and they thrive on the abundant upraising hydrothermal methane.

Description: Published

Description: Patras, Greece

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open

Description: Pantelleria is an active volcanic complex, at present in quiescent status, hosting a high enthalpy geothermal system. Explorative geothermal wells tapped exploitable water-dominated reservoirs at 600-800 m depth with maximum measured temperatures of 250°C. Five field campaigns for soil gas measurements were made in the period from July 2005 to October 2006. CO2 flux was measured with the accumulation chamber method at 807 sites, CO2 concentration and Rn activity in soil atmosphere were measured at 50 cm depth at 728 and 358 sites, respectively. The first campaign covered the whole island (about 83 km2) with an approximately sample density of 3.5 points per km2 for CO2 (flux and concentration) measurements and of 1.6 points per km2 for Rn measurements. The distribution of the sampling points was as far as possible evenly distributed. Only few limited areas resulted uncovered due to accessibility problems (inhabited areas, airport, steep or rough topography). In the following four surveys nine areas were studied with greater detail with sample densities of up to 100 points per km2. Flux measurements for the whole surveys gave values in the range 〈 0.1 - 4700 gCO2 m-2 day-1 (Fig. 1). Organic contribution could not be distinguished with statistical methods and in the present study was considered negligible above 30 g m-2 day-1. The sites displaying flux values above this threshold, representing about 32% of the total population, are almost all located within the 50 ka old caldera. The highest values correspond to the areas of Favara Grande and of the lake Specchio di Venere (Fig. 1), which have long been recognized as sites of anomalous degassing with the presence of active fumarolic vents with temperatures of about 100 °C in the former and thermal springs with abundant bubbling gases and a mofette in the latter. A new anomalous degassing area with very high output values has been identified on the southern flank of Mt. Grande (MGS in Fig. 1). In this area the vegetation cover strongly contrasts with that of the neighboring areas, consisting of scrubby low growing plants, mosses and bare land. Indeed, high CO2 flux values are always measured as long as such vegetation cover is found, abruptly decreasing when higher growing plants are present. The contrast is particularly evident in springtime and can be used as a good marker to individuate anomalous degassing areas. Further areas were studied in detail being sites of fumarolic manifestations. All of them are also sites of anomalous CO2 fluxes although of limited areal extension. The area of the last subaerial volcanic activity (Mursia) was also studied but the measurements were all far below the anomaly threshold. The total CO2 output of the anomalous degassing areas was estimated through geostatistical methods considering only values above the anomaly threshold. Results evidence that most of the output (87%) of the island is due to 3 of the anomalous degassing areas (Lake, MGS and Favare), the first of which accounts for more than 50%. Summing up the contribution of all anomalous areas we obtained a total output of about 0.3 kg s-1 (26 t day-1) over an area of about 0.58 km2. Concentrations of CO2 ranged from 0.039 (atmospheric value) up to 95 % (Fig. 1). The distribution of the values on a probability plot evidenced two statistically distinct populations with an inflection point at about 0.8 %. The values below the threshold (65 % of the population) can be considered as derived from organic activity while those above of magmatic/geothermal origin. The spatial distribution of the sites with anomalous concentrations closely resembles those of anomalous CO2 fluxes. Radon222 activity in the soil ranged from 〈 0.1 to 〉1000 kBq m-3 (Fig. 1). The distribution of the values on a probability plot evidenced three statistically distinct populations with inflection points at 40 and 400 kBq m-3. The lower population (74% of the entire population) probably corresponds to close to equilibrium values in soils with different contents of parent isotopes of the 238U decay chain and could be considered as background population. The values of the other two populations have to be considered anomalous and their high activity values have to be related either to sustained fluxes of a carrier gas (CO2) or/and to enhanced release from the soil due to fumarolic alteration. These anomalous values generally correspond to elevated CO2 flux values and are found close to active or fossil fumarolic areas. The close relationship with fumarolic alteration is confirmed by the contrasting behavior of two of the areas displaying the highest CO2 flux values, namely Favare and Lake. In the former area the high soil temperatures, testifying for anomalous fluxes of hydrothermal fluids, are reflected in a high percentage of anomalous values of soil 222Rn activity. On the contrary at the lake area, where the highest CO2 fluxes are measured, soil temperatures are much lower and consequently also soil 222Rn activity. The only high soil 222Rn activity values are measured along the southern shores of the lake where seeps of thermal water with about 60 °C are present. At Mursia, where recent basaltic lavas and scorias crop out, soil 222Rn activity is particularly low due to the low content of parent radioactive elements in these rocks. Finally, the present study evidenced a few areas were the gas hazard due to both CO2 and radon is elevated with either acute or chronic health issues for humans. These are the western shores of the lake and the village of Rekale the only inhabited area close to an anomalous degassing area.

Description: Published

Description: Patras, Greece

Description: 4.5. Studi sul degassamento naturale e sui gas petroliferi

Description: open

Description: Active volcanoes are thought to be important contributors to the atmospheric mercury (Hg) budget, and this chemical element is one of the most harmful atmospheric pollutants, owing to its high toxicity and long residence time in ecosystems. There is, however, considerable uncertainty over the magnitude of the global volcanic Hg flux, since the existing data on volcanogenic Hg emissions are sparse and often ambiguous. In an attempt to extend the currently limited dataset on volcanogenic Hg emissions, we summarize the results of Hg flux measurements at seven active open-conduit volcanoes; Stromboli, Asama, Miyakejima, Montserrat, Ambrym, Yasur, and Nyiragongo.. Data from the domebuilding Soufriere Hills volcano are also reported. Using our determined mercury to SO2 mass ratios in tandem with the simultaneously-determined SO2 emission rates, we estimate that the 7 volcanoes have Hg emission rates ranging from 0.2 to 18 t yr-1 (corresponding to a total Hg flux of ~41 t·yr-1). Based on our dataset and previous work, we propose that a Hg/SO2 plume ratio ~10-5 is bestrepresentative of gas emissions from quiescent degassing volcanoes. Using this ratio, we infer a global volcanic Hg flux from persistent degassing of ~95 t·yr-1

Description: Published

Description: 497-510

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: restricted

Description: During 2007–2008, three CO2 flux surveys were performed on El Chichón volcanic lake, Chiapas, Mexico, with an additional survey in April 2008 covering the entire crater floor (including the lake). The mean CO2 flux calculated by sequential Gaussian simulation from the lake was 1,190 (March 2007), 730 (December 2007) and 1,134 g m−2 day−1 (April 2008) with total emission rates of 164±9.5 (March 2007), 59±2.5 (December 2007) and 109±6.6 t day−1 (April 2008). The mean CO2 flux estimated from the entire crater floor area was 1,102 g m−2 day−1 for April 2008 with a total emission rate of 144±5.9 t day−1. Significant change in CO2 flux was not detected during the period of survey, and the mapping of the CO2 flux highlighted lineaments reflecting the main local and regional tectonic patterns. The 3He/4He ratio (as high as 8.1 RA) for gases in the El Chichón crater is generally higher than those observed at the neighbouring Transmexican Volcanic Belt and the Central American Volcanic Arc. The CO2/3He ratios for the high 3He/4He gases tend to have the MORB-like values (1.41×109), and the CO2/3He ratios for the lower 3He/4He gases fall within the range for the arc-type gases. The high 3He/4He ratios, the MORB-like CO2/3He ratios for the high 3He/4He gases and high proportion of MORB-CO2 (M=25 ±15%) at El Chichón indicate a greater depth for the generation of magma when compared to typical arc volcanoes.

Description: Published

Description: 423-441

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: reserved

Description: Here, we report the first continuous data of geochemical parameters acquired directly from the active summit crater of Vulcano. This approach provides a means to better investigate deep geochemical processes associated with the degassing system of Vulcano Island. In particular, we report on soil CO2 fluxes from the upper part of Vulcano, a closed-conduit volcano, from September 2007 to October 2010. Large variations in the soil CO2 and plume SO2 fluxes (order of magnitude), coinciding with other discontinuous geochemical parameters (CO2 concentrations in fumarole gas) and physical parameters (increase of shallow seismic activity and fumarole temperatures) have been recorded. The results from this work suggest new prospects for strengthening geochemical monitoring of volcanic activity and for improving the constraints in the construction of a “geochemical model”, this being a necessary condition to better understand the functioning of volcanic systems.

Description: Published

Description: 1859-1863

Description: 2V. Dinamiche di unrest e scenari pre-eruttivi

Description: 4V. Vulcani e ambiente

Description: 5V. Sorveglianza vulcanica ed emergenze

Description: 1R. Reti di monitoraggio e Osservazioni

Description: JCR Journal

Description: restricted

Description: On 27 February 2007, a new eruption occurred on Stromboli which lasted until 2 April. It was characterized by effusive activity on the Sciara del Fuoco and by a paroxysmal event (15 March). This crisis represented an opportunity for us to refine the model that had been developed previously (2002-2003 eruption) and to improve our understanding of the relationship between the magmatic dynamics of the volcano and the geochemical variations in the fluids. In particular, the evaluation of the dynamic equilibrium between the volatiles (CO2 and SO2) released from the magma and the corresponding fluids discharged from the summit area allowed us to evaluate the level of criticality of the volcanic activity. One of the major accomplishments of this study is a four-year database of summit soil CO2 flux on the basis of which we define the thresholds (Low-Medium-High) for this parameter that are empirically based on the natural volcanological evolution of Stromboli. The SO2 fluxes of the degassing plume and the CO2 fluxes emitted from the soil at Pizzo Sopra la Fossa are also presented. Noteworthy geochemical signals of volcanic unrest have been clearly identified before, during, and after the effusive activity. These signals were found almost simultaneously in the degassing plume (SO2 flux) and in soil degassing (CO2 flux) at the summit, although the two degassing processes are shown to be clearly different. The interpretation of the results will be useful for future volcanic surveillance at Stromboli.

Description: In press

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: reserved

Description: We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9±0.27‰ and −1.41± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work values of Etna CO2 from~ −4‰, in the 1970’s and the 1980’s, to~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.

Description: Published

Description: 531-542

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: restricted

Description: Seismic activity, ground deformation, and soil and fumarole temperatures acquired during 2004–2007 at Vulcano (Aeolian Islands) are analysed and the time relations among the different time series are discussed. Changes in temperature of fumarolic gases took place during four ‘‘anomalous’’ periods (November 2004–March 2005; October 2005–February 2006; August–October 2006; July–December 2007) at the same time as an increasing number of volcano-seismic events. In particular, the temperatures at high temperature vents and at steam heated soil ranged in time from 180 to 440 C and from 20 to 90 C, respectively. The maximum daily number of volcano-seismic events was 57, reached during the second anomalous period. This seismicity, characterised by focal depth generally lower than 1 km below sea level (b.s.l.) and composed of different kinds of events associated to both resonance and shear failure processes, is related to the shallow dynamics of the hydrothermal system. During the analysed period, very few volcano-tectonic earthquakes took place and tilt recordings showed no sharp or important changes. In light of such observations, the increases in both temperature and volcano-seismic events number were associated to increases in the release of gas from a deep and stable magma body, without magma intrusions within the shallow hydrothermal system. Indeed, a greater release of gas from depth leads to increased fluid circulation, that can promote increases in volcano-seismic events number by both fracturing processes and resonance and vibration in cracks and conduits. The different trends observed in the measured geochemical and geophysical series during the anomalous periods can be due to either time changes in the medium permeability or a changing speed of gas release from a deep magma body. Finally, all the observed variations, together with the changing temporal distribution of the different seismic event kinds, suggest that the hydrothermal system at Vulcano can be considered unsteady and dynamic.

Description: Published

Description: 167–182

Description: 1.5. TTC - Sorveglianza dell'attività eruttiva dei vulcani

Description: JCR Journal

Description: reserved

Description: We describe analytical details and uncertainty evaluation of a simple technique for the measurement of the carbon isotopic composition of CO2 in volcanic plumes. Data collected at Solfatara and Vulcano, where plumes are fed by fumaroles which are accessible for direct sampling, were first used to validate the technique. For both volcanoes, the plume-derived carbon isotopic compositions are in good agreement with the fumarolic compositions, thus providing confidence on the method, and allowing its application at volcanoes where the volcanic component is inaccessible to direct sampling. As a notable example, we applied the same method to Mount Etna where we derived a δ13C of volcanic CO2 between −0.9 ± 0.27‰ and −1.41 ± 0.27‰ (Bocca Nuova and Voragine craters). The comparison of our measurements to data reported in previous work highlights a temporal trend of systematic increase of δ13C values of Etna CO2 from ~ −4‰, in the 1970’s and the 1980’s, to ~ −1‰ at the present time (2009). This shift toward more positive δ13C values matches a concurrent change in magma composition and an increase in the eruption frequency and energy. We discuss such variations in terms of two possible processes: magma carbonate assimilation and carbon isotopic fractionation due to magma degassing along the Etna plumbing system. Finally, our results highlight potential of systematic measurements of the carbon isotopic composition of the CO2 emitted by volcanic plumes for a better understanding of volcanic processes and for improved surveillance of volcanic activity.

Description: In press

Description: 1.2. TTC - Sorveglianza geochimica delle aree vulcaniche attive

Description: 2.4. TTC - Laboratori di geochimica dei fluidi

Description: JCR Journal

Description: reserved