https://doi.org/10.1140/epjst/e2015-02398-6
Regular Article
Soil radon (222Rn) monitoring at Furnas Volcano (São Miguel, Azores): Applications and challenges
1 Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, Ponta Delgada, Portugal
2 Centro de Informação e Vigilância Sismovulcânica dos Açores, Universidade dos Açores, Ponta Delgada, Portugal
3 Institut de Physique du Globe de Paris, IPGP, Paris, France
a e-mail: Catarina.PP.Silva@azores.gov.pt
Received: 2 March 2015
Revised: 23 April 2015
Published online: 10 June 2015
A soil 222Rn continuous monitoring test was performed in three sampling points inside Furnas Volcano caldera and 222Rn concentration varied between 0 and 153000 Bq/m3. Multivariate regression and spectral analyses were applied to the time series registered in order to understand and filter the influence of external factors on soil 222Rn concentration and to recognise anomalies correlated with deep processes. The regression models show that barometric pressure, soil water content, soil temperature, soil CO2 flux, air temperature, relative air humidity and wind speed are the statistical meaningful variables explaining between 15.8% and 73.6% of 222Rn variations. Spectral analysis allowed to identify seasonal variations and daily variations associated with one cycle per day on winter months only in one of the monitored sites. This diurnal variation is correlated with air temperature, relative air humidity and wind speed cycles. The change in the location of the sampling points was caused by both artificial and natural constrains. On the three monitoring sites, after a period of continuous register, a sudden drop on the 222Rn concentration values was observed and the cause is still under debate. The work performed can be applied for seismovolcanic monitoring and for public health risk assessment.
© EDP Sciences, Springer-Verlag, 2015
