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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

SOUSA, F., FERREIRA, T., GASPAR, J.L., VIVEIROS, F., FARIA, C., MARCOS, M., SENOS, L. (2004) - CO2 soil degassing mapping: a contribution to the volcanic risk assessment at Furnas Village (S. Miguel Island, Azores). 1st General Assembly da EGU.


In the last few years several CO2 soil diffuse degassing areas have been identified in the Azores archipelago. The most important one is situated at Furnas Volcano, a trachytic central volcano with caldera located in the eastern part of S. Miguel Island.


The first CO2 soil degassing survey in this volcano was conducted during 1993-1994 and revealed the existence of a large anomalous area comprising Furnas Village, with CO2 soil concentrations ranging from 1,5 to nearly 100% vol..


In order to study the spatial evolution of such anomaly a second survey was carried out between 2001 and 2002. It was observed that the shape and intensity of the main anomaly remained unchanged, indicating that any modifications may represent a signal of unrest. Further measurements to the east of Furnas Village allowed to extend the degassing area towards Ribeira dos Tambores fumarolic field. Soil temperatures in the studied area range from 10 to 75°C, being the higher values coincident with the higher CO2 soil concentrations.


The spatial distribution of the geochemical anomalies defines alignments according to the most important tectonic structures mapped at Furnas Volcano.


To assess the public health risk associated with the degassing areas, the obtained results were inserted in a GIS and integrated with vulnerability data for the inhabited zones. It was found that 62% from a total of 900 houses are in areas where the CO2 soil concentration exceeds the background value, being 6% located where the risk of asphyxia is moderate to high.