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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Referência Bibliográfica

VIVEIROS, F.; FERREIRA, T.; SILVA, C.; OSKARSSON, N., HIPÓLITO, A. (2009) - Natural and anthropogenic influences on the gas geochemical monitoring at Fogo Volcano (São Miguel Island, Azores). In: VOLUME project, EU PF6 (No. 018471). Editado por : C. J. Bean, A. K. Braiden, I. Lokmer, F. Martini, G. S. O’Brien. ISBN 978-1-905254-39-2. VOLUME Project Consortium, Dublin, 299-308.


​Since the end of 2002, several seismic swarms have occurred on São Miguel Island, (Azores archipelago), at Fogo Volcano and at the Congro Volcanic System on its eastern side. The maximum peak of activity was in September 2005, when thousands of low magnitude earthquakes were recorded. A gas geochemical monitoring programme began at Fogo Volcano in February 2002 with the installation of a permanent soil CO2 flux station in the northern flank of the volcano. A second permanent station was set up inside Fogo Volcano caldera during the 2005 increase in the seismic activity. The main fumaroles have been sampled every three months since 2002, with the sampling frequency increased to once or twice per month during 2005. Meteorological parameters and anthropogenic activities have a significant influence on the soil gas flux variations. It is therefore crucial to know, and understand, the controls of these influences to establish any definite correlation between gas variations and deep processes of the volcano. Soil CO2 flux variations and monitoring of fumarole discharge during the recent seismic crisis gave no clear precursor of volcanic unrest. However, fumarole discharge compositions showed slight changes in some gas ratios (H2/CH4 and CO2/CH4) that may be interpreted as resulting from increased pressure at depth.