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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

VIVEIROS, F., FERREIRA, T., CARDELLINI, C., CALIRO, S., SILVA, C. (2011) - Soil CO2 emission to the atmosphere from Furnas Volcano (São Miguel Island, Azores archipelago). Conference on Global Warning (GCGW-11) (Comunicação Oral).


Carbon dioxide, known as an important “greenhouse gas”, is one of the most emitted gases in volcanic environments. Volcanoes around the world release CO2 to the atmosphere, not only during eruptive events, but also in periods of quiescence. Furnas volcano is a dormant central volcano located in the eastern part of São Miguel Island (Azores archipelago, Portugal). At present, secondary manifestations of volcanism comprise fumarolic fields, thermal and CO2 cold springs and soil diffuse degassing areas. CO2 and 222Rn are the main gases diffusely released through the surface of volcanic edifices. These emissions are continuous and usually imperceptible being the gases detected only by the use of specific instruments. 
2886 soil CO2 flux measurements, based on the accumulation chamber method, were carried out at Furnas volcano between 2005 and 2009 in order to produce CO2 degassing maps that show the spatial distribution of soil gas anomalies. These degassing maps are important to (1) seismo-volcano monitoring, (2) geothermal exploration, (3) land-use planning, (4) public health risks and (5) estimate the amount of volatiles released to the atmosphere.
CO2 flux values oscillated from non detectable to values higher than 25000 g m-2 d-1. On the basis of 100 sequential Gaussian simulations, a mean CO2 emission of ~ 1110 t d-1 was estimated to be released from Furnas volcano (area ~ 6.2 km2). From this total CO2 emitted, more than 80 % is of hydrothermal origin. This estimation represents only the diffusive contribution of the CO2 flux and do not account for other contributions from fumaroles, bubbling pools or Furnas lake, suggesting that the total CO2 emitted from Furnas volcano is larger than our estimate.
CO2 released by Furnas volcano main fumarolic fields is in the same order of magnitude of La Fossa crater (Vulcano Island, Italy) and some degassing areas in Yellowstone volcano (USA). The magnitude of diffuse CO2 degassing at Furnas is also relevant if compared with the annual industrial CO2 emission allocated by the European Commission for Portugal since the CO2 naturally emitted by Furnas volcano results about 1% of the anthropogenic CO2 production. This comparison, together with estimates at global scale of volcanic and non-volcanic natural CO2 emissions, contributes to reinforce the importance of the quantification of natural CO2 diffuse fluxes for a refined global C-budget modelling.