Fátima Viveiros

Soil CO2 emissions at Furnas volcano, São Miguel Island, Azores archipelago: Volcano monitoring perspectives, geomorphologic studies, and land use planning application

Accepted for publication in Journal of Geophysical Research. Copyright (2010) American Geophysical Union.

Meteorological factors controlling soil gases and indoor CO2 concentration: a permanent risk in degassing areas.

Furnas volcano is one of the three quiescent central volcanoes of São Miguel Island (Azores Archipelago, Portugal). Its present activity is marked by several degassing manifestations, including fumarolic fields, thermal and cold CO2 springs and soil diffuse degassing areas. One of the most important soil diffuse degassing areas extends below Furnas village, located inside the volcano caldera. A continuous gas geochemistry programme was started at Furnas volcano in October 2001 with the installation of a permanent soil CO2 efflux station that has coupled meteorological sensors to measure barometric pressure, rain, air and soil temperature, air humidity, soil water content and wind speed and direction. Spike-like oscillations are observed on the soil CO2 efflux time series and are correlated with low barometric pressure and heavy rainfall periods. Stepwise multiple regression analysis, applied to the time series obtained, verified that the meteorological variables explain 43.3% of the gas efflux variations. To assess the impact of these influences in inhabited zones a monitoring test was conducted in a Furnas village dwelling placed where soil CO2 concentration is higher than 25 vol.%. Indoor CO2 air concentration measurements at the floor level reached values as higher as 20.8 vol.% during stormy weather periods. A similar test was performed in another degassing area, Mosteiros village, located on the flank of Sete Cidades volcano (S. Miguel Island), showing the same kind of relation between indoor CO2 concentrations and barometric pressure. This work shows that meteorological conditions alone increase the gas exposure risk for populations living in degassing areas.

Periodic behavior of soil CO2 emissions in diffuse degassing areas of the Azores archipelago: Application to seismovolcanic monitoring

Time series of soil CO2 efflux recorded in the Azores archipelago volcanic-hydrothermal areas feature daily and seasonal variations. The recorded CO2 efflux values were lower during summer than in the winter season. The diurnal CO2 efflux values were higher at dawn and lower in the early afternoon, contrary to that observed in biogenic environments. CO2 efflux cycles correlated well with the environmental variables, such as air temperature, wind speed, and barometric pressure, which also showed low- and high-frequency periodicities. Several simulations were performed here using the Transport of Unsaturated Groundwater and Heat 2 (TOUGH2) geothermal simulator to complement the study of Rinaldi et al. (2012). The effects of the water table depth, air temperature perturbation amplitude, and soil thermal gradient contributed to an explanation of the contrasts observed in the diurnal (S1) and semidiurnal (S2) soil CO2 efflux peaks for the different monitoring sites and seasons. Filtering techniques (multivariate regression analysis and fast Fourier transform filters) were also applied to the recorded time series to remove effects of external variables on the soil CO2 efflux. The resulting time series (the residuals) correspond to the best approach to the deep-seated (volcanic/hydrothermal) CO2 emissions and thus should be used in seismovolcanic monitoring programs. Even if no evident correlation can be established yet between the soil CO2 residuals and seismicity over the monitored time, a seismic swarm that occurred around the end of 2008 might have triggered some deviations from the observed daily cycles.

Contribution of CO 2 emitted to the atmosphere by diffuse degassing from volcanoes: The Furnas Volcano case study

Furnas Volcano is a dormant central volcano located in the eastern part of Sao Miguel Island (Azores archipelago, Portugal). The last volcanic eruption in this volcanic system took place in 1630 causing about 200 victims. Present-day activity comprises fumarolic fields, thermal and cold CO 2 -rich springs and soil diffuse degassing areas. CO 2 diffusely released from the volcano soils was estimated at ~ 0.4 Mt y –1 . Only about 14% of this emission has a biogenic origin, the highest amount of the CO 2 emitted being mantle derived. Hydrothermal CO 2 released from Furnas Volcano is in the same order of magnitude as emissions from other volcanic geothermal areas of the world. This work highlights the need to account for the natural CO 2 emitted from quiescent volcanoes to refine the global carbon budget modelling.

Chapter 15 Diffuse soil emanations of radon and hazard implications at Furnas Volcano, São Miguel Island (Azores)

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.

Chapter 14 Mapping of soil CO2 diffuse degassing at São Miguel Island and its public health implications

Abstract Soil CO2 diffuse degassing constitutes a permanent risk in quiescent volcanic–hydrothermal areas, as is the case in the Azores archipelago. Since the early 1990s geochemical studies carried out in São Miguel Island showed that some villages are placed in anomalous high degassing areas, and indoor measurements performed in various dwellings highlight the risk to the population. These high indoor CO2 concentrations are not only measured in areas classified as high degassing areas, but lethal CO2 concentrations are also registered in buildings located in areas previously defined as low- and medium-risk zones. These lethal values are measured in non-ventilated environments and basements in areas with soil CO2 concentration above 1.5 vol%. Hazardous CO2 concentrations are also commonly measured in buildings located in zones where soil CO2 is higher than 5 vol%. Considering the dangerous values registered and the fact that indoor gas concentration can increase several orders of magnitude owing to peculiar meteorological conditions, updated values are suggested for the correlation between soil gas concentration and CO2 exposure. This study highlights that both the use of soil degassing maps by land-use planners and appropriate construction rules for buildings placed in degassing areas are necessary.

Chapter 20 Permanent monitoring of soil CO2 degassing at Furnas and Fogo volcanoes (São Miguel Island, Azores)

Abstract Eight years of permanent soil CO2 diffuse degassing monitoring at Furnas and Fogo volcanoes shows that several environmental variables may influence soil CO2 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 CO2 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 CO2 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.

Air Pollution by Hydrothermal Volcanism and Human Pulmonary Function.

The aim of this study was to assess whether chronic exposure to volcanogenic air pollution by hydrothermal soil diffuse degassing is associated with respiratory defects in humans. This study was carried in the archipelago of the Azores, an area with active volcanism located in the Atlantic Ocean where Eurasian, African, and American lithospheric plates meet. A cross-sectional study was performed on a study group of 146 individuals inhabiting an area where volcanic activity is marked by active fumarolic fields and soil degassing (hydrothermal area) and a reference group of 359 individuals inhabiting an area without these secondary manifestations of volcanism (nonhydrothermal area). Odds ratio (OR) and 95% confidence intervals (CIs) were adjusted for age, gender, fatigue, asthma, and smoking. The OR for restrictive defects and for exacerbation of obstructive defects (COPD) in the hydrothermal area was 4.4 (95% CI 1.78–10.69) and 3.2 (95% CI 1.82–5.58), respectively. Increased prevalence of restrictions and all COPD severity ranks (mild, moderate, and severe) was observed in the population from the hydrothermal area. These findings may assist health officials in advising and keeping up with these populations to prevent and minimize the risk of respiratory diseases.

Soil CO2 Degassing Path along Volcano-Tectonic Structures in the Pico-Faial-São Jorge Islands (Azores Archipelago, Portugal)

The Azores archipelago is composed of nine volcanic islands located at the triple junction between the North American, Eurasian and Nubian plates. Nowadays the volcanic activity in the archipelago is characterized by the presence of secondary manifestations of volcanism, such as hydrothermal fumaroles, thermal and cold CO2-rich springs as well as soil diffuse degassing areas, and low magnitude seismicity. Soil CO2 degassing (concentration and flux) surveys have been performed at Pico, Faial and Sao Jorge islands to identify possible diffuse degassing structures. Since the settlement of the Azores in the 15th Century these three islands were affected by seven onshore volcanic eruptions and at least six destructive earthquakes. These islands are crossed by numerous active tectonic structures with dominant WNW-ESE direction, and less abundant conjugate NNW-SSE trending faults. A total of 2855 soil CO2 concentration measurements have been carried out with values varying from 0 to 20.7 vol.%. Soil CO2 flux measurements, using the accumulation chamber method, have also been performed at Pico and Faial islands in the summer of 2011 and values varied from absence of CO2 to 339 g m-2 d-1. The highest CO2 emissions were recorded at Faial Island and were associated with the Pedro Miguel graben faults, which seem to control the CO2 diffuse degassing and were interpreted as the pathways for the CO2 ascending from deep reservoirs to the surface. At Sao Jorge Island, four main degassing zones have been identified at the intersection of faults or associated to WNW-ESE tectonic structures. Four diffuse degassing structures were identified at Pico Island essentially where different faults intersect. Pico geomorphology is dominated by a 2351 m high central volcano that presents several steam emissions at its summit. These emissions are located along a NW-SE fault and the highest measured soil CO2 concentration reached 7.6 vol.% with a maximum temperature of 77 oC. The diffuse degassing maps show that anomalous CO2 degassing areas are controlled essentially by the tectonic structures and the lithology of the sites since the youngest volcanic systems are characterized by very low CO2 emissions.

New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop

Recent geophysical evidence for large-scale regional crustal inflation and localized crustal magma intrusion has made Lastarria volcano (northern Chile) the target of numerous geological, geophysical, and geochemical studies. The chemical composition of volcanic gases sampled during discrete campaigns from Lastarria volcano indicated a well-developed hydrothermal system from direct fumarole samples in A.D. 2006, 2008, and 2009, and shallow magma degassing using measurements from in situ plume sampling techniques in 2012. It is unclear if the differences in measured gas compositions and resulting interpretations were due to artifacts of the different sampling methods employed, short-term excursions from baseline due to localized changes in stress, or a systematic change in Lastarria’s magmatic-hydrothermal system between 2009 and 2012. Integrated results from a two-day volcanic gas sampling and measurement campaign during the 2014 International Association of Volcanology and Chemistry of the Earth’s Interior (IAVCEI) Commission on the Chemistry of Volcanic Gases (CCVG) 12th Gas Workshop are used here to compare and evaluate current gas sampling and measurement techniques, refine the existing subsurface models for Lastarria volcano, and provide new constraints on its magmatic-hydrothermal system and total degassing budget. While compositional differences among sampling methods are present, distinct compositional changes are observed, which if representative of longterm trends, indicate a change in Lastarria’s overall magmatic-hydrothermal system. The composition of volcanic gases measured in 2014 contained high proportions of relatively magmaand water-soluble gases consistent with degassing of shallow magma, and in agreement with the 2012 gas composition. When compared with gas compositions measured in 2006–2009, higher relative H2O/CO2 ratios combined with lower relative CO2/St and H2O/St and stable HCl/St ratios (where St is total S [SO2 + H2S]) are observed in 2012 and 2014. These compositional changes suggest variations in the magmatichydrothermal system between 2009 and 2012, with possible scenarios to explain these trends including: (1) decompression-induced degassing due to magma ascent within the shallow crust; (2) crystallization-induced degassing of a stalled magma body; (3) depletion of the hydrothermal system GEOSPHERE GEOSPHERE; v. 14, no. 3 doi:10.1130/GES01495.1 12 figures; 6 tables; 2 supplemental files CORRESPONDENCE: tmlopez@ alaska .edu CITATION: Lopez, T., Aguilera, F., Tassi, F., de Moor, J.M., Bobrowski, N., Aiuppa, A., Tamburello, G., Rizzo, A.L., Liuzzo, M., Viveiros, F., Cardellini, C., Silva, C., Fischer, T., Jean-Baptiste, P., Kazayaha, R., Hidalgo, S., Malowany, K., Lucic, G., Bagnato, E., Bergsson, B., Reath, K., Liotta, M., Carn, S., and Chio dini, G., 2018, New insights into the magmatic-hydrothermal system and volatile budget of Lastarria volcano, Chile: Integrated results from the 2014 IAVCEI CCVG 12th Volcanic Gas Workshop: Geosphere, v. 14, no. 3, p. 983–1007, doi:10.1130/GES01495.1. Science Editor: Raymond M. Russo Guest Associate Editor: Shanaka de Silva Received 12 January 2017 Revision received 4 December 2017 Accepted 21 March 2018 Published online 7 May 2018