Focused and diffuse effluxes of CO 2 from mud volcanoes and mofettes south of Mt. Etna (Italy) S. Giammanco a, ⁎ , F. Parello b , B. Gambardella c , R. Schifano b , S. Pizzullo b , G. Galante b a Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Catania- Piazza Roma 2, 95123 Catania, Italy b Dipartimento Fisica Chimica della Terra e Applicazioni, Università degli Studi di Palermo, Via Archirafi 33, 90133 Palermo, Italy c Laboratorio di Geochimica, Dip.Ter.Ris., Università degli Studi di Genova, Corso Europa 26, 16132 Genova, Italy Received 13 June 2006; accepted 23 April 2007 Available online 17 May 2007 Abstract Several sites with anomalous emissions of carbon dioxide were investigated in the region south of Mt. Etna volcano in order to assess the types of emission (focused and/or diffuse), their surface extension and the total output of CO 2 . Most of the studied emissions are located on the southwest boundary of Mt. Etna, near the town of Paternò. They consist of three mud volcanoes (known as Salinelle), one spring with bubbling gas (Acqua Grassa) and one area of diffuse degassing (Peschería). Another site (Naftía Lake) with remarkable gas emissions (bubbling gas into a lake as well as adjacent areas of diffuse soil degassing) is located further southwest of Mt. Etna in an area of extinct Quaternary volcanism on the northwest margin of Hyblean Mts. In all of these areas the origin of the highest CO 2 emissions is clearly magmatic, and degassing to the atmosphere occurs mostly through tectonic structures, probably at a regional scale. The magmatic source that feeds anomalous degassing in the above areas is likely to be the same that feeds volcanic activity at Mt. Etna. Focused degassing was measured at each emission vent using devices that measure the air speed, whereas diffuse soil degassing was measured using the accumulation chamber method. In total, 712 measurements were carried out (146 in focused degassing vents, 566 on diffuse degassing areas). Single CO 2 output values ranged from 1.8 10 - 5 to 1.68 kg s - 1 . In the case of diffuse degassing areas, statistical analyses allowed to discriminate between biogenic CO 2 and CO 2 deriving from a magmatic- hydrothermal source. Only the efflux values from the latter source were considered in the output estimates. The total estimated output thus obtained was about 2.61 kg s - 1 , relevant to a total surface of about 146,500 m 2 (which includes only the magmatic CO 2 emissions). This value is comparable with that of most non-volcanic emissions from geothermal and/or faulted areas of central- southern Italy, as well with the CO 2 output from some of the volcanic areas of Italy. © 2007 Elsevier B.V. All rights reserved. Keywords: carbon dioxide; Mt. Etna; mud volcanoes; soil CO 2 effluxes; magmatic degassing 1. Introduction Since the early work of Irwin and Barnes (1980), it has become clear that a close relationship exists between active tectonic areas and anomalous crustal emissions of carbon dioxide. Due to their high crustal permeability, faults act as preferential pathways for the upward migration and eventual release of deep gases to the atmosphere. The central part of eastern Sicily (Italy) is characterized by several sites with remarkable natural emissions of gases. Their occurrence is likely due to Journal of Volcanology and Geothermal Research 165 (2007) 46 – 63 www.elsevier.com/locate/jvolgeores ⁎ Corresponding author. Tel.: +39 095 7165829. E-mail address: giammanco@ct.ingv.it (S. Giammanco). 0377-0273/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jvolgeores.2007.04.010