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(searched for: doi:10.1016/j.jvolgeores.2016.02.004)
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Journal of Volcanology and Geothermal Research, Volume 418; https://doi.org/10.1016/j.jvolgeores.2021.107347

Abstract:
Diffuse emission of magmatic CO2 is one of the main indicators of volcanic unrest at Mammoth Mountain, but the presence of deep seasonal snowpack at the site has hindered year-round CO2 flux observations. A permanent eddy covariance station was established at the largest area of diffuse CO2 degassing on Mammoth Mountain (Horseshoe Lake tree kill) that measured CO2 fluxes (Fc) and meteorological parameters on a half-hourly basis. From July 22, 2014 to May 24, 2020, Fc ranged from −35 to 10,546 g m−2 d−1. Fc decreased on average by 53% over the study period, tracking the long-term decline in CO2 emissions following the last major increase that occurred at the Horseshoe Lake tree kill area from 2009 to 2011. Statistical and spectral analyses were applied to the Fc and ancillary meteorological parameter time series to understand (1) relationships between these parameters, (2) their dominant periodicities, and (3) changes in Fc that may be unexplained by meteorological forcing. Variations in detrended Fc (Fcdt) were most strongly correlated with wind direction and atmospheric temperature, followed by atmospheric pressure on diurnal to annual time scales, but wind direction likely exerted the most direct control on Fcdt. Comparison of the smoothed (180-d span) Fcdt time series to the time series of average-daily snow water equivalent measured ~1 km away suggested that snowpack may have suppressed CO2 emissions. No evidence of a change in CO2 emissions related to the last major seismic swarm beneath Mammoth Mountain on February 2–18, 2014 was observed.
, F. Ambrosino, G. Chiodini, F. Giudicepietro, G. Macedonio, S. Caliro, W. De Cesare, F. Bianco, M. Pugliese, V. Roca
Published: 12 June 2020
Scientific Reports, Volume 10, pp 1-10; https://doi.org/10.1038/s41598-020-66590-w

Abstract:
This is a seven-year study (1/7/2011-31/12/2017) of radon monitoring at two sites of Campi Flegrei caldera (Neaples, Southern Italy) that in the last 70 years experienced repeated phases of volcanic unrest. The sites are equipped with devices for radon detection, based on the spectrometry analysis of the α-particles of radon daughters. A hybrid method, as combination of three known methods, is applied for the identification of residuals (anomalies) and trends of the time series of Radon. The results are compared with the following indicators of current caldera unrest: the tremor caused by the major fumarolic vent registered by a seismic station; the cumulative of background seismicity; the maximum vertical deformation acquired by GPS networks during the current phase of uplift; the temperature-pressure of the hydrothermal system estimated based on gas geo-indicators. The comparisons show strong correlation among independent signals and suggest that the extension of the area affected by current Campi Flegrei crisis is larger than the area of seismicity and of intense hydrothermal activity from which the radon stations are 1–4 km away. These results represent an absolute novelty in the study of a such calderic area and mark a significant step forward in the use and interpretation of the radon signal.
M. Içhedef, , , R. Catalano, G. Immé, D. Morelli, F. Muré, N. Giudice
Journal of Environmental Radioactivity, Volume 218; https://doi.org/10.1016/j.jenvrad.2020.106267

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F. Barberi, , , M. Ranaldi, , A. Gattuso
Published: 3 December 2019
GeoHealth, Volume 3, pp 407-422; https://doi.org/10.1029/2019gh000211

Abstract:
The Rome region contains several sites where endogenous gas is brought to the surface through deep reaching faults, creating locally hazardous conditions for people and animals. Lavinio is a touristic borough of Anzio (Rome Capital Metropolitan City) that hosts a Country Club with a swimming pool and an adjacent basement balance tank. In early September 2011, the pool and the tank had been emptied for cleaning. On 5 September, four men descended into the tank and immediately lost consciousness. On 12 August 2012, after a long coma the first person died, the second one reported permanent damage to his central nervous system, the other two men recovered completely. Detailed geochemical investigations show that the site is affected by a huge release of endogenous gas (CO2≈96 vol.%, H2S≈ 4 vol.%). High soil CO2 and H2S flux values were measured near the pool (up to 898 and 7.155 g*m‐2day‐1 respectively) and a high CO2 concentration (23‐25 vol.%) was found at 50‐70 cm depth in the soil. We were able to demonstrate that gas had been transported into the balance tank from the swimming pool through two hubs connected to the lateral overflow channels of the pool. We show also that the time before the accident (60 hours), during which the balance tank had remained closed to external air, had been largely sufficient to reach indoor nearly lethal conditions (oxygen deficiency and high concentration of both CO2 and H2S).
Marco Camarda, , Giorgio Capasso, , Sergio Gurrieri, Vincenzo Prano
Published: 21 August 2019
Earth-Science Reviews, Volume 198; https://doi.org/10.1016/j.earscirev.2019.102928

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Nury Morales-Simfors, Ramon A. Wyss,
Critical Reviews in Environmental Science and Technology, Volume 50, pp 979-1012; https://doi.org/10.1080/10643389.2019.1642833

Abstract:
Prediction of earthquakes and volcanic eruptions has concerned researchers for many decades. Several precursors (e.g. seismic, geodetic, geochemical, geological, atmospheric/ionospheric, geomagnetic, electrical) have been observed shortly before an earthquake or volcanic event. However, no precursor, that can accurately be used for forecasting, has yet been discovered due to the involvement of several complex overlapping and interacting physical and chemical processes. In particular, the non-linearity of actual eruptions or quakes implies a high statistical uncertainty about location of measurement devices. Among geochemical precursors, radon gas in groundwater and soil is considered a notable precursor, used to detect chemical and physical changes during the generation of earthquakes and volcanic events. This article critically reviews progress in radon-based monitoring from the year 2000 onwards and catalogs anomalous radon variations found in groundwater and soils. A future deployment of large sensor networks of 1000–10,000 detectors for radon and also thoron detection would bring a shift in paradigm with respect to long-term earthquake and volcanic monitoring. Such a dense network would enable rapid and precise measurements of radon over large areas resulting in establishing significant and relevant statistical data. Graphical Abstract
, , Natividad Luengo-Oroz, , Ilazkiñe Iribarren, M. José Blanco, Vicente Soler, Ana Jiménez-Abizanda,
Journal of Volcanology and Geothermal Research, Volume 381, pp 32-43; https://doi.org/10.1016/j.jvolgeores.2019.05.018

The publisher has not yet granted permission to display this abstract.
, Toshiya Mori, Akihiko Yokoo, Takahiro Ohkura, Yuichi Morita
Published: 7 January 2019
Earth, Planets and Space, Volume 71; https://doi.org/10.1186/s40623-018-0980-8

Abstract:
Continuous measurements of soil CO2 flux are useful for understanding degassing processes and for monitoring volcanic activities. Recent studies at many volcanoes have revealed that soil CO2 flux variations are significantly influenced by environmental parameters as well as volcanic processes. In this study, we conducted continuous monitoring of soil CO2 flux in the flank of Nakadake cone, Aso volcano, Japan, from January 2016 to November 2017. The results of our observations during an active period before and after a large phreatomagmatic eruption on 8 October 2016 and during a calm period from 2017 showed variations in soil CO2 flux due to oscillations in environmental parameters. Excluding these variations from the raw time series by multivariate linear regression analysis, the time series of soil CO2 flux presented some anomalous peaks in both the active and calm periods. Careful comparison of the anomalous peaks with the environmental parameters revealed that most of the anomalous peaks were likely due to an increase in wind speed and/or a decrease in barometric pressure. However, the anomaly after the 8 October 2016 eruption was not completely explicable by the variations in the environmental parameters and coincided with increases in seismic amplitude and plume SO2 flux. This anomaly was possibly attributed to an increase in magmatic CO2 flux. These findings emphasized the importance of careful statistical treatment of the soil CO2 flux data after excluding the influences of the environmental parameters at each measurement site. These statistical treatments will contribute to a better understanding of the degassing processes and monitoring of volcanic activities, including phreatic or phreatomagmatic eruptions.
Sérgio Oliveira, , , Joana E. Pacheco
Published: 20 November 2018
Frontiers in Earth Science, Volume 6; https://doi.org/10.3389/feart.2018.00208

Abstract:
Monitoring soil CO2 diffuse degassing areas has become more relevant in the last decades to understand seismic and/or volcanic activity. These studies are specially valuable for volcanic areas without visible manifestations of volcanism, such as fumaroles or thermal springs. The development and installation of permanent soil CO2 flux instruments has allowed to acquire long time series in different volcanic environments, and the results obtained highlight the influence of environmental variables on the gas flux variations. Filtering the influence of these external variables on the gas flux is crucial to understand deep processes on the volcanic system. This study focuses on the discussion of different statistical approaches applied to the long time series recorded in a diffuse degassing area of the Azores archipelago, mainly on the application of stepwise multivariate regression analysis, wavelets and Fast Fourier transforms to understand the CO2 flux variations and to detect eventual anomalous periods that can represent deep changes in the volcano feeding reservoirs. A permanent soil CO2 flux station is installed at Caldeiras da Ribeira Grande area since June 2010. This degassing site is located at Fogo Volcano, a polygenetic volcano at S. Miguel Island. The station performs measurements based on the accumulation chamber method and has coupled several environmental sensors. Average soil CO2 flux and soil temperature values around 1,165 gm−2 d−1 and 33°C, respectively, were measured in this site between June 2010 and June 2017. Multivariate regression analysis shows that about 47% of the soil CO2 flux variations are explained by the effect of the soil and air temperature, wind speed, and soil water content. Spectral analysis highlights the existence of 24 h cycles in the soil CO2 flux time series, mainly during the summer period. The filtered time series showed some anomalous periods and a correlation with the geophysical data recorded on the area was carried out. The models proposed have been applied on a near real-time automatic monitoring system and implementation of these approaches will be profitable in any volcano observatory of the world since it allows a fast understanding of the degassing processes and contribute to recognize unrest periods.
C. Cigolini, , D. Coppola, C. Trovato, G. Borgogno
Geological Society, London, Special Publications, Volume 451, pp 183-208; https://doi.org/10.1144/sp451.1

Abstract:
Understanding the behaviour of fluids in hydrothermal systems is a key factor in volcano monitoring. Measuring gas emissions in volcanic areas is strategic for detecting and interpreting precursory signals of variations in volcanic activity. The role of radon as a potential precursor of earthquakes has been extensively debated. However, radon anomalies appear to be better suited to forecast eruptive episodes as we know the loci of volcanic eruptions and we can follow the evolution of volcanic activity. Radon mapping is an effective tool in assessing diffuse and concentrated degassing at the surface. We hereby summarize the in-soil radon emissions collected worldwide and further discuss a collection of data on our key targets. These are closed-conduit and open-conduit volcanoes: Vesuvius (Italy) and La Soufrière (Guadeloupe, Lesser Antilles), Stromboli (Italy) and Villarrica (Chile), respectively. In all the above volcanoes, faults and fracture systems control radon degassing. Automatic and real-time measurements help us to detect major changes in volcanic activity. We present and discuss the radon time series associated with the last effusive eruption at Stromboli. Spectral analyses reveal diurnal and semi-diurnal cycles being probably modulated by atmospheric variations. Multiple linear regression (MLR) analyses have been performed by filtering the radon signals from the effects of local environmental parameters. The residuals do not show particular variations or precursory peaks as the gases have been released from this open-conduit volcano before the onset of the effusive phase (7 August 2014). It is finally emphasized that radon is not the sole precursor, and we should also rely on other geochemical and geophysical parameters. In this perspective, we propose a methodological procedure that can contribute to improving volcano surveillance in an attempt to mitigate volcanic risk.
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