Journal of Volcanology and Geothermal Research 165 (2007) 1–4www.elsevier.com/locate/jvolgeores

Editorial

Gas geochemistry as a tool to investigate the Earth's degassingthrough volcanic and seismic areas: The soul of the 8th International

Conference on Gas Geochemistry

The ICGGs are the only international conferencesfully dedicated to the gas geochemistry, where scientistscoming from many different countries with differentcultures have the opportunity to exchange experienceson the multiple aspects of gas geochemistry. The maingoal of the conference is always to keep together the gas-geochemistry people, to share their most recent experi-ences, advances and upgrading in analytical techniquesand in theoretical modelling, in a friendly and construc-tive environment where everybody feels free to ask anyquestion and to discuss about past and future cooperationwith all of the colleagues. In many cases the advance ingas geochemistry researches has already been applied byseveral colleagues for practical applications in the fieldsof environmental, volcanic and seismic monitoring.

The development in gas-geochemistry knowledgeprovides new insights into volatile release from the interiorof the Earth, a continuous and fundamental activity in theevolution of our planet that has determined the currentcomposition of the atmosphere and of the Earth itself.Considering the history of the Earth, the term “release”should be substituted by “exchange” given that the atmos-phere, formed by Earth degassing, is in continuous inter-action with the lithosphere and the hydrosphere. Volatileexchange between the atmosphere and the Earth's surfaceconstitutes an important aspect of global geochemicalcycles of major gas components (H2O, CO2, N2, CH4, S,halogens) but also of trace metals or noble gas.

It is of common knowledge that Earth degassingdoes not occur homogeneously over the Earth's surface,being rather concentrated along the plate boundaries,where the dynamics of the lithosphere is more intenseand gas from the Earth's interior can be more easilytransported toward the surface. The connection betweenthe volcanic and seismic activities, mainly located along

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the plate boundaries, and the Earth's degassing istherefore obvious. As a well-known example, on a globalscale the seismically active regions are those mostinvolved in CO2 degassing (Irwin and Barnes, 1980).Also on a local scale, the relationship between degassingand seismicity may be direct: recent studies havehighlighted that CO2 can accumulate in natural traps,generating overpressurized reservoir and triggering earth-quakes (Chiodini et al., 2004; Miller at al., 2004). Gasgeochemistry has also been used in the search of reliableprecursors of seismic activity and a lot of anomaloussignals have been recognised a posteriori. For acomprehensive review we refer to the articles of King(1986) and Toutain and Baubron (1999).

Although the most spectacular and concentratedmanifestations of Earth's degassing are from volcanicplumes, many other degassing ways (soil emanation,mofettes, mud volcanoes, bubbling waters, etc.), some ofwhich important for the global geochemical cycles, occur.An example: mud volcanoes present both on and off-shorein tectonically active regions release to the atmospherelarge amounts of CH4 quantitatively important for the geo-chemical cycle of this compound (Milkov et al., 2003),besides significant amounts of carbon dioxide. Moreover,natural emissions of CO2 and CH4 are sources of green-house gases and take part in the climate change models.

Despite the various ways of outcropping at the Earth'ssurface, the chemical compounds that constitute themajor volatiles and thus act as carrier for minor and tracespecies are restricted to H2O (in the form of water vapourin volcanic environments), CO2 and CH4. Rarely areN2-dominated gas phases found. The origin of such gasspecies is much debated, and in this sense the isotopiccompositions of C, H, O as well as of minor or tracespecies (S, He, Ne, Ar) are usually studied in detail. The

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origin of CO2 is attributed to a direct provenance fromthe mantle through degassing of magmas or to CO2

production in response to thermal and/or chemical decom-position of carbonate horizons in the crust (e.g. Marty,2001). Although the CO2 produced by organic matterdecay usually represents a small part of the total in areas ofhigh-flux emissions, it could sometimes be the onlysource also along important active tectonic structures likethe San Andreas fault in California (Lewicki et al., 2003).Recent studies show how CO2 can be generated in theabsence of heat as the primary energy source and thatmechanical energy, as primary source (that obviouslyproduces heat as a consequence of the Joule effect), is ableto induce a total dissociation of calcite by “milling” effect(Martinelli and Plescia, 2004; Italiano et al., 2005 andreferences therein). This mechanism may account for theexistence of large CO2 reservoirs where the isotopic ratioof helium as low as 0.01–0.02 Ra reveals the absence ofmantle-derived fluids.

Talking about CH4, two main generation processesare possible: the thermogenic and the biogenic (micro-bial) alteration of kerogene (Schoell, 1983).

Air or air-saturated water infiltrated in the crust andrecycled in degassing areas is the most common sourceof N2 (Giggenbach, 1991). At convergent plate boun-daries, the main process responsible for the contributionof non-atmospheric nitrogen seems to be the recyclingof sedimentary material from the subducting litho-sphere, although upper mantle degassing could some-times contribute (Sano et al., 2001).

During the transport of volatile phases toward thesurface, the interaction with aquifers plays a fundamen-tal role in determining the final gas composition, giventhat the different solubility of the various gas speciesmodifies both the absolute and relative amounts of gasreaching the surface. As a consequence of gas–waterinteraction, the most soluble gas species (SO2 and theacid species like H2S, HCl and HF present in volcanicenvironments) will be enriched in the aqueous phasegiving birth to new equilibria in water, while the lesssoluble species (like light noble gases) will as a result beenriched in the gas phase. Carbon dioxide has inter-mediate behaviour and being less soluble than sulphurand halogen species it becomes highly enriched in gasesreleased by geothermal systems (Symonds et al., 2001).Also, during gas–water interaction isotopic equilibriawill take place between the free and dissolved species,the most studied system in this sense being the CO2–H2O–CaCO3 (see Hoefs, 1987).

Volcanoes continuously emit gases to the atmosphere,both during and between eruptions, carrying importantinformation about underground magmatic and hydro-

thermal conditions, with application in eruption fore-casting. Their study is also important because of theirstrong impacts upon the atmosphere, climate and humanhealth (Graf et al., 1997; Robock, 2000; Delmelle, 2003).Volcanoes, in fact, sometimes rival with anthropogenicsources in emission strength, becoming global or atleast regional scale “pollution” sources. For example,Mt. Etna (Italy) is considered as the greatest HF pointsource to the atmosphere (Francis et al., 1998) whiledaily SO2 emission of Miyakejima volcano (Japan)during the climactic stages of its recent eruptive crisis(2000–2001) was comparable to the anthropogenicemissions of the whole Asia (Kazahaya et al., 2004).

Due to the importance of volcanic gas geochemistry,measuring techniques have evolved very rapidly in therecent period. The traditional and sometimes very haz-ardous direct sampling techniques were associated to alarge variety of remote sensing techniques both ground-(McGonigle, 2005) and satellite-based (Carn et al.,2003; Gu et al., 2005).

Gases from the Earth's interior may also appear in theform of small inclusions (usually b1 mm) in glasses orminerals that during their growth trapped portions of thefluid present in their environment (e.g. Roedder, 1984).Volcanic eruption, tectonic movements and/or erosioncan take such minerals to or near the surface, where theycan be sampled. Fluid inclusions are of great value forscientists as they help in reconstruct the history of fluidsand minerals before any possible contamination at sur-face with atmospheric gas.

Another aspect of the direct effect of Earth's de-gassing on human life is represented by focused or dif-fuse cold gas emissions, usually CO2-dominated andpresent in both volcanic and non-volcanic areas. Despitebeing apparently harmless, such gas emissions havesometimes caused both sudden human death due to thetoxicity of many compounds (CO2, sulphur gases likeSO2 and H2S, volatile As compounds) and long-termdiseases due to high concentration of radon, a radioactivenoble gas.

The 8th International Conference on Gas Geochem-istry (ICGG 8) was held in Sicily (Italy) in two differentsites: Palermo, the capital, and Milazzo, a small town inNE Sicily. The latter town falls in an area affected (un-fortunately) by all of the above-mentioned Earth's de-gassing conditions. The NE Sicily area is surrounded bythe volcanic arc of the Eolian Islands, made up of activeand quiescent volcanoes, to the north; the active volcanoof Mt. Etna to the south; the seismic area of the MessinaStrait (90,000 dead in M7.2, 1908 earthquake) to theeast; and the seismic area of Patti Gulf (last destructiveearthquake M6.4 in 1978) to the west.

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The 8th International Conference on Gas Geochem-istry (ICGG 8, 2nd–8th October, 2005) was part of aseries of meetings that were held in Mons, Belgium in1990, Besançon, France in 1993, Amristar, India in1995, Rome, Italy in 1997, Debrecen, Hungary in 1999,Cuernavaca, Mexico in 2001 and Freiberg, Germany in2003. The next conference is due to be held in Taipei,Taiwan in October 2007.

A total of 82 participants coming from 14 countriesattended the ICGG 8, and 93 papers were presented in theconference which covered a variety of important re-search topics regarding gas geochemistry in geosciences:from the advances in researches on mechanochemicalgas production to practical applications to evaluate theimpact of volcanic emissions on the environment; fromthe most advanced estimations on Earth's degassingdevoted to a better evaluation of climate changes toadvanced contributions for gas hazard managementin populated seismic and volcanic areas; from geneticevaluations of the gases released through tectonic lines tomodifications induced by seismic activity.

Eight representative contributions have been includ-ed in this special issue of Journal of Volcanology andGeothermal Research. The first one (Carapezza andTarchini) shows that gas geochemistry offers importantclues on the probable activity of the Alban Hills, avolcanic system close to Rome previously consideredextinct. The following three papers highlight the im-portance of carbon dioxide efflux measurements. In thefirst case (Barberi et al.) this technique is applied forthe definition and mitigation of gas hazard, an oftenneglected natural risk. Carbon dioxide efflux measure-ments were used by Lan et al. and Giammanco et al.,together with chemical and isotopic analyses of gasmanifestations, for the study of active degassing areasat geothermal and volcanic systems. In both cases theresults concur in the quantification of the total carbondioxide release of the systems and in the definition ofthe gas sources. The paper of D'Alessandro et al.evidences the possibility of studying paleodegassing ofan area through the analysis of travertine deposits.Brogna et al. focus their paper on public health issuesraised by Radon release by active tectonic structures ina volcanic area. Estimates of methane emissions fromgeothermal and volcanic sources in Europe made byEtiope et al. are important for the greenhouse-gasatmospheric budget calculations and add constraintsfor the modelling of future scenarios of climate change.Passive degassing activity of volcanoes represents animportant contribution to atmospheric burden of manyelements with strong environmental impacts, at least atlocal scale. Bellomo et al. in their paper discuss the

effects of volcanic-derived fluorine in the area aroundMt. Etna.

Acknowledgements

The conference was supported by INGV funds andreceived a special support from GV Instruments. Wewould like to express our gratitude to the authors whohave contributed to this special issue. We are alsograteful to all the reviewers who gave their critical andconstructive comments and suggestions, thereby im-proving the manuscripts.

Special thanks to Dr. Francesca Leone who dealt withall of the abstracts and manuscripts before, during andafter the conference. Without her efforts the publicationof this special issue would not be possible. Thanks aredue to all of the colleagues from INGV-Section ofPalermo who cooperated with the organizer to carry outthe conference.

References

Carn, S.A., Krueger, A.J., Bluth, G.J.S., Schaefer, S.J., Krotkov, N.A.,Watson, I.M., Datta, S., 2003. Volcanic eruption detection by theTotal Ozone Mapping Spectrometer (TOMS) instruments: A22-year record of sulphur dioxide and ash emissions. In: Oppenhei-mer, C., Pyle, D.M., Barclay, J. (Eds.), Volcanic Degassing. Spec.Publ. Geol. Soc. Lon., vol. 213, pp. 177–202.

Chiodini, G., Cardellini, C., Amato, A., Boschi, E., Caliro, S.,Frondini, F., Ventura, G., 2004. Carbon dioxide Earth degassingand seismogenesis in central and southern Italy. Geophys. Res.Lett. 31. doi:10.1029/2004GL019480.

Delmelle, P., 2003. Environmental impacts of tropospheric volcanic gasplumes. In: Oppenheimer, C., Pyle, D.M., Barclay, J. (Eds.), VolcanicDegassing. Spec. Publ. Geol. Soc. Lon., vol. 213, pp. 381–399.

Francis, P., Burton, M., Oppenheimer, C., 1998. Remote measure-ments of volcanic gas compositions by solar FTIR spectroscopy.Nature 396, 567–570.

Giggenbach, W.F., 1991. Chemical techniques in geothermal explo-ration. In: D'Amore, F. (Ed.), Application of geochemistry ingeothermal reservoir development. UNITAR, Rome, pp. 119–144.

Graf, H.F., Feichter, J., Langmann, B., 1997. Volcanic sulfur emissions:estimates of source strength and its contribution to the globalsulphate distribution. J. Geophys. Res. 102, 10727–10738.

Gu, Y., Rose, W.I., Schneider, D.J., Bluth, G.J.S., Watson, I.M., 2005.Advantageous GOES IR results for ash mapping at high latitudes:Cleveland eruptions 2001. Geophys. Res. Lett. 32, L02305.

Hoefs, J., 1987. Stable isotope geochemistry. Springer-Verlag, Berlin.241 pp.

Irwin, W.P., Barnes, I., 1980. Tectonic relations of carbon dioxidedischarges and earthquakes. J. Geophys. Res. 85, 3115–3121.

Italiano, F., Martinelli, G., Plescia, P., 2005. Mechanochemical CarbonDioxide and Methane generation by laboratory simulated faultfriction conditions. 8th International Conference on Gas Geo-chemistry, ICGG8, Palermo & Milazzo, Italy 2–8 October 2005oral comm., abstr. Book pg 34.

Kazahaya, K., Shinohara, H., Uto, K., Odai, M., Nakahori, Y., Mori, H.,Iino,H.,Miyashita,M., Hirabayashi, J., 2004.Gigantic SO2 emission

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from Miyakejima volcano, Japan, caused by caldera collapse.Geology 32, 425–428.

King, C.Y., 1986. Gas geochemistry applied to earthquake prediction.An overview. J. Geophys. Res. 91, 12269–12281.

Lewicki, J.L., Evans, W.C., Hilley, G.E., Sorey, M.L., Rogie, J.D.,Brantley, S.L., 2003. Shallow soil CO2 flow along the San Andreasand Calaveras Faults, California. J. Geophys. Res. 108 (B4), 2187.doi:10.1029/2002JB002141.

Martinelli, G., Plescia, P., 2004. Mechanochemical dissociation ofcalcium carbonate: laboratory data and relation to naturalemissions of CO2. Phys. Earth Planet. Inter. 142 (3–4), 205–214.

Marty, 2001. New prospects for old gas. Nature 409, 293–295.McGonigle, A.J.S., 2005. Volcano remote sensing with ground-based

spectroscopy. Philos. Trans. R. Soc. Lond., A 363, 2915–2929.Milkov, A.V., Sassen, R., Apanasovich, T.V, Dadashev, F.G., 2003.

Global gas flux from mud volcanoes: a significant source of fossilmethane in the atmosphere and the ocean. Geophys. Res. Lett. 30.doi:10.1029/2002GL016358.

Miller, S.A., Collettini, C., Chiaraluce, L., Cocco, M., Barchi, M.,Kaus, B.J.P., 2004. Aftershocks driven by a high-pressure CO2

source at depth. Nature 427, 724–727.Robock, A., 2000. Volcanic eruptions and climate. Rev. Geophys. 38,

191–219.Roedder, E., 1984. Fluid inclusions. In: Ribbe, P.E. (Ed.), Reviews in

Mineralogy, vol. 12. Mineralogical Society of America. 644 pp.

Sano, Y., Takahata, N., Nishio, Y., Fischer, T.P., Williams, S.N., 2001.Volcanic flux of nitrogen from the earth. Chem. Geol. 171, 263–271.

Schoell, 1983. Genetic characterization of natural gases. AAPG Bull.67, 2225–2238.

Symonds, R.B., Gerlach, T.W., Reed, M.H., 2001. Magmatic gasscrubbing: implications for volcanomonitoring. J. Volcanol.Geotherm.Res. 108, 303–341.

Toutain, J.P., Baubron, J.C., 1999. Gas geochemistry and seismotec-tonics: a review. Tectonophys 304, 1–27.

F. Italiano*

W. D'AlessandroM. Martelli

Istituto Nazionale di Geofisica e Vulcanologia,Sezione di Palermo, via U. La Malfa 153,

Palermo, Italy⁎Corresponding author. Tel.: +39 0916809411;

fax: +39 0916809449.E-mail address: italiano@pa.ingv.it (F. Italiano).

9 May 2007