Chapter 20 Permanent monitoring of soil CO ₂ degassing at Furnas and Fogo volcanoes (São Miguel Island, Azores)

Abstract

Eight years of permanent soil CO 2 diffuse degassing monitoring at Furnas and Fogo volcanoes shows that several environmental variables may influence soil CO 2 flux to a different extent depending on the location. Stepwise multivariate regression analysis applied to the data acquired by the permanent flux stations installed on São Miguel showed that the monitored environmental variables may influence the gas flux in a proportion between 18 and 51%. The external variables that most significantly correlate with the soil CO 2 flux values for Fogo and Furnas volcanoes monitoring sites are the rainfall/soil water content with its effect on permeability; the barometric pressure pumping effect; the wind speed owing to the atmospheric air intrusion and the air temperature through the action of atmospheric tides. These variables are responsible not only for spike-like oscillations in CO 2 emission, but also for the long-term oscillations with higher and lower values registered usually during winter and summer months, respectively. Residual time-series, calculated using regression models, are compared with other geophysical and geochemical monitoring data in order to recognize changes that may be correlated with the volcanic/hydrothermal systems.

Heat flux-based strategies for the thermal monitoring of sub-fumarolic areas: Examples from Vulcano and La Soufrière de Guadeloupe

“…The second limitation of the ETH method is the difficulty to estimate the effect of effective precipitations (note that this limitation applies to any geochemical flux monitoring (Viveiros et al, 2015)). The proportion of precipitation percolating in the soil might decrease with the intensity of the rainfall event, due to soil pores saturation.…”

“…While numerous techniques have been used to monitor the gas flux of volcanoes in particular UV spectroscopy for the monitoring of SO 2 fluxes (Edmonds et al, 2003;Aiuppa et al, 2005;Salerno et al, 2009;Vita et al, 2012), soil stations for the monitoring of CO 2 degassing (Inguaggiato et al, 2011(Inguaggiato et al, , 2012a(Inguaggiato et al, , 2012b(Inguaggiato et al, , 2013Viveiros et al, 2014Viveiros et al, , 2015, and MultiGAS for the bulk composition of fumaroles and plumes (Aiuppa et al, 2007a(Aiuppa et al, , 2007bAllard et al, 2014) , the observation of heat fluxes is much less developed. Thermal infrared images have been used with partial success to map the heat fluxes of sub fumarolic zones (Yuhara et al, 1978;Harris et al, 2009;Gaudin et al, 2013Gaudin et al, , 2016Vilardo et al, 2015), but quantitative estimations are usually asso ciated to large uncertainties.…”

Automatic Filtering of Soil CO2 Flux Data; Different Statistical Approaches Applied to Long Time Series

“…Studies of these permanent and silent gas emissions started to be performed in the early nineties in Italian volcanoes (Baubron et al, 1990;Allard et al, 1991). The permanent soil CO 2 flux networks that have been set up in various volcanic areas of the world since then (Mori et al, 2002;Salazar et al, 2002;Granieri et al, 2003Granieri et al, , 2010Gurrieri et al, 2008;Padrón et al, 2008;Viveiros et al, 2008Viveiros et al, , 2015aHernández et al, 2012;Liuzzo et al, 2013;Laiolo et al, 2016) already contributed to identify geochemical signs that represent changes on the volcanic activity, namely by recognizing volcanic unrest episodes (Granieri et al, 2003(Granieri et al, , 2010Salazar et al, 2004;Pérez et al, 2006) or as precursors of eruptive periods (Brusca et al, 2004;Carapezza et al, 2004;Aiuppa et al, 2010;Pérez et al, 2012;Liuzzo et al, 2013;Inguaggiato et al, 2017). Some gas flux anomalies were also associated with seismic activity (Salazar et al, 2002) and the stations installed have also been used as proxy for indoor environments and showed to be useful for risk assessment in diffuse degassing areas (Viveiros et al, 2009(Viveiros et al, , 2015b.…”

“…Despite all the useful information obtained with these stations for the seismo-volcanic monitoring, the recorded soil CO 2 flux values have showed that gas fluxes are highly influenced by environmental factors, such as meteorological changes, which can be responsible for more than 50% of the gas flux variations (Granieri et al, 2003(Granieri et al, , 2010Viveiros et al, 2009Viveiros et al, , 2015a. Different statistical methodologies have been applied to filter the recorded CO 2 time series in order to remove the external influences and produce a gas flux sign that may represent deep changes (e.g., Granieri et al, 2003;Viveiros et al, 2008Viveiros et al, , 2015aCannata et al, 2010;Liuzzo et al, 2013;Lelli and Raco, 2017).…”

Chapter 1 Volcanic geology of São Miguel Island (Azores Archipelago): introduction

“…Ground deformation is an important tool for monitoring geothermal and magmatic systems and Okada et al (2015) provide an interpretation of recent data. Cruz et al (2015) investigate variation in the hydro-geochemistry of mineral waters on São Miguel, while the systems in place to monitor soil degassing of CO 2 on Fogo and Furnas are described by Viveiros et al (2015b).…”