Volcanic Geology of São Miguel Island (Azores Archipelago)

The Azores archipelago in the Atlantic Ocean is composed of nine volcanic islands and São Miguel is the largest and most volcanically active. During the past 5000 years several eruptions have taken place on the three active central volcanoes – Sete Cidades, Fogo and Furnas – and in the basaltic fissure systems of Picos and Congro. There is evidence that Furnas was in eruption when the first settlers arrived some time between 1439 and 1443. In the sixteenth and seventeenth centuries there were two explosive sub-Plinian eruptions, Fogo in 1563 and Furnas in 1630. The last eruption on land occurred in the Picos Fissural Volcanic System in 1652, involving the extrusion of lava domes. In 22 chapters, this volume considers the volcanic geology of the island under the headings of geological setting, volcanic history, geological hazards and risk assessment, volcano monitoring and natural resources.
Diffuse soil emanations of radon and hazard implications at Furnas Volcano, São Miguel Island (Azores) Available to Purchase
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Published:January 01, 2015
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CiteCitation
C. Silva, F. Viveiros, T. Ferreira, J. L. Gaspar, P. Allard, 2015. "Diffuse soil emanations of radon and hazard implications at Furnas Volcano, São Miguel Island (Azores)", Volcanic Geology of São Miguel Island (Azores Archipelago), J. L. Gaspar, J. E. Guest, A. M. Duncan, F. J. A. S. Barriga, D. K. Chester
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Abstract
Furnas Caldera Volcanic Complex, São Miguel Island (Azores), last erupted in 1630 and is famous for its intense hydrothermal activity (i.e. fumarolic fields, thermal springs, cold CO2-rich mineral waters and diffuse CO2 soil emanations), which directly affect the villages of Furnas and Ribeira Quente. Here we report the first systematic investigations and mapping of soil radon (222Rn) emanations in the Furnas Volcanic Complex, and we examine their potential health risks for local inhabitants. 222Rn in volcanic soils (60 cm depth) was repeatedly measured between 2005 and 2010 using a portable solid-state alpha detector (RAD7, Durridge Company Inc.). Results reveal a local background of 8000 Bq m−3 and several areas with anomalously high 222Rn activity (up to c. 400 000 Bq m−3), which coincide with advective or convective gas transport through volcanic structures and active fault zones. High 222Rn radioactivity in Furnas and Ribeira Quente villages represents a risk to the population. Continuous monitoring performed during November and December 2005 in a house in Furnas shows indoor 222Rn reaching 13 273 Bq m−3, two orders of magnitude greater than the reference level (150 Bq m−3), when the ventilation efficiency is reduced.