SILVA, C., VIVEIROS, F., FERREIRA, T., GASPAR, J.L., ALLARD, P. (2015) – Diffuse soil emanations of radon and hazard implications at Furnas Volcano, São Miguel Island (Azores). In: Gaspar, J.L., Guest, J.E., Duncan, A.M., Barriga, F.J.A.S., Chester, D.K. (eds.) Volcanic Geology of São Miguel Island (Azores Archipelago), Geological Society of London Memoir, 44: 197-211, doi: 10.1144/M44.15.​

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.