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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Artigos em livros de actas ► Internacionais


Referência Bibliográfica

MARCOS, M., FERREIRA, T., VIVEIROS, F., GASPAR, J.L., QUEIROZ, G., GOMES, A., GERTISSER, R., PIMENTEL, A., SOUSA, F., TROTA, A.N., RODRIGUES, R. (2004) - Geological and geochemical characterisation of Furnas do Enxofre degassing (Terceira Island, Azores). Abstract book of the International Symposium on “Reducing Volcanic Risk in Islands”, p. 51.


The Azores archipelago is located in a complex geological setting dominated by the American, African and Eurasian plates boundaries interplay. Terceira island lies in the central part of the so-called Terceira Rift, a NW-SE structural line that extends from the Mid-Atlantic Ridge into the E-W Azores-Gibraltar Fault.


The active volcanic systems at Terceira Island include the central volcanoes of Santa Barbara and Pico Alto and a basaltic ridge that crosses the island along a general NW-SE trend. Since its settlement in the 15th century only one volcanic eruption took place on land in 1761. Submarine eruptive activity occurred in 1867 and 1998-2001 along the Serreta Submarine Ridge, a volcanotectonic structure that extends W of the island (Gaspar et al., 2003).


Furnas do Enxofre is the unique fumarolic field known at Terceira Island. It is located at Pico do Galhardo, a trachytic dome emplaced where the NW-SE basaltic ridge intersects Pico Alto Volcano.


CO2 is the main component of the fumarolic gas compositions, representing more than 94% of the total gas. H2S, H2, N2 and CH4 appear in minor amounts.


In order to define the entire degassing area two surveys for CO2 soil concentration and soil temperature measurements were carried out in March and August 2002. In July 2003 a network of 60 georeferenced points was set up and a CO2 soil flux survey was performed. It was concluded that gas emissions occur in an area of approximately 7000 m2. Soil CO2 concentration and temperature reach values up to 100 % vol. and 98,1 ºC, respectively. CO2 flux measurements showed a maximum value of 2348,16 g/m2/d.


In the scope of the Terceira Island volcano monitoring programme a continuous CO2 soil flux station was installed in the area on December 2002. The equipment comprises sensors to measure meteorological and environmental parameters that will be used to study the influence of external factors in the CO2 flux.