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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

VIVEIROS, F., VIEIRA, J.C., FERREIRA, T., GASPAR, J. L., MARCOS, M. (2004) - Discrimination of the main factors that influence the CO2 flux at Furnas Volcano (São Miguel, Azores). Workshop Bristol (Poster).


The Azores archipelago comprises nine volcanic islands, located where the Eurasian, American and African plate meet. Since its settlement in the 15th century several volcanic eruptions and destructive earthquakes took place in the region.


The islands of São Miguel, Terceira, Graciosa, Faial and Pico present important degassing areas associated with the hydrothermal systems of some active volcanic centres, including fumarolic fields, thermal and CO2 cold springs and soil diffuse degassing.


On October 2001 a CO2 permanent flux station was installed at Furnas Volcano, São Miguel Island, as part of a new continuous geochemical monitoring program. As the gas flux can be influenced by external variables, the station acquires simultaneously barometric pressure, air temperature, air humidity, wind speed and direction, rainfall, soil water content and soil temperature data.


In order to remove the influence of environmental variables on CO2 flux, the data set acquired from March 2002 to March 2003 was statistically processed using multiple regression analysis. The obtained results show that barometric pressure, rainfall, soil water content and soil and air temperature are the variables with statistical meaning on the gas flux fluctuations. According to the adjusted R2 value, these variables account for 30,5% of CO2 flux variation. By this approach, the residuals flux values represent the amount of CO2 flux that cannot be explained by the environmental monitored variables and may provide information in the volcanic system deep processes. In a second step, an ARIMA (Autoregressive Integrated Moving Average) filter was applied to the residuals in order to remove temporal trends from the data.


The model obtained for the analyzed time period was validated using the data series obtained from March 2003 to March 2004. The recognition of a background level behaviour for CO2 soil flux may allow identifying precursory signals of seismic and volcanic activity.