Quantification of carbon dioxide emissions of ...

Journal of Volcanology and Geothermal Research 341 (2017) 119–130

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Quantification of carbon dioxide emissions of Ciomadul, the youngest volcano of the Carpathian-Pannonian Region (Eastern-Central Europe, Romania) Boglárka-Mercédesz Kis a, Artur Ionescu a,b,⁎, Carlo Cardellini c, Szabolcs Harangi a,d, Călin Baciu b, Antonio Caracausi e, Fátima Viveiros f a

MTA-ELTE Volcanology Research Group, H-1117 Budapest, Pázmány sétány 1/C, Hungary Babes-Bolyai University, Faculty of Environmental Science and Engineering, RO-400294 Cluj-Napoca, Fântânele nr. 30, Romania c University of Perugia, Department of Physics and Geology, IT-06123 Perugia, Via A.Pascoli, Italy d Department of Petrology and Geochemistry, Eötvös Loránd University, Budapest, Hungary e Istituto Nazionale di Geofisica e Vulcanologia, Via Ugo La Malfa 153, 90146 Palermo, Italy f Research Institute of Volcanology and Risk Assessment (IVAR), University of the Azores, Ponta Delgada, Azores, Portugal b

a r t i c l e

i n f o

Article history: Received 31 December 2016 Received in revised form 20 May 2017 Accepted 21 May 2017 Available online 22 May 2017 Keywords: Ciomadul Dormant volcano CO2 flux Total emission

a b s t r a c t We provide the first high-resolution CO2 flux data for the Neogene to Quaternary volcanic regions of the entire Carpathian-Pannonian Region, Eastern-Central Europe, and estimate the CO2 emission of the seemingly inactive Ciomadul volcanic complex, the youngest volcano of this area. Our estimate includes data from focused and diffuse CO2 emissions from soil. The CO2 fluxes of focused emissions range between 277 and 8172 g d−1, corresponding to a CO2 output into the atmosphere between 0.1 and 2.98 t per year. The investigated areas for diffuse soil gas emissions were characterized by wide range of CO2 flux values, at Apor Baths, ranging from 1.7 × 101 to 8.2 × 104 g m−2 d−1, while at Lăzărești ranging between 1.43 and 3.8 × 104 g m−2 d−1. The highest CO2 focused gas fluxes at Ciomadul were found at the periphery of the youngest volcanic complex, which could be explained either by tectonic control across the brittle older volcanic edifices or by degassing from a deeper crustal zone resulting in CO2 flux at the periphery of the supposed melt-bearing magma body beneath Ciomadul. The estimate of the total CO2 output in the area is 8.70 × 103 t y−1, and it is consistent with other long (N10 kyr) dormant volcanoes with similar age worldwide, such as in Italy and USA. Taking into account the isotopic composition of the gases that indicate deep origin of the CO2 emissions, this yields further support that Ciomadul may be considered indeed a dormant, or PAMS volcano (volcano with potentially active magma storage) rather than an inactive one. Furthermore, hazard of CO2 outpourings has to be taken into account and it has to be communicated to the visitors. Finally, we suggest that CO2 output of dormant volcanic systems has to be also accounted in the estimation of the global volcanic CO2 budget. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Monitoring the activity of volcanoes involves various methods, such as the assessment of gas yield, either by remote sensing techniques or by in situ measurements. The gas flux, together with the gas composition, provide important information about the nature of the volcanic plumbing system and can be used in forecasting potential eruption.

⁎ Corresponding author at: Babes-Bolyai University, Faculty of Environmental Science and Engineering, ISUMADECIP, Fântânele nr. 30, RO-400294 Cluj-Napoca, Cluj, Romania. E-mail addresses: [email protected] (B.-M. Kis), [email protected] (A. Ionescu), [email protected] (C. Cardellini), [email protected] (S. Harangi), [email protected] (C. Baciu), [email protected] (A. Caracausi), [email protected] (F. Viveiros).

http://dx.doi.org/10.1016/j.jvolgeores.2017.05.025 0377-0273/© 2017 Elsevier B.V. All rights reserved.

On the other hand, there has been a major effort to achieve a better estimation of contribution of volcanoes to the global CO2 budget, which has been estimated mostly from the data coming from active volcanic systems (e.g., Marty and Tolstikhin, 1998; Burton et al., 2013; Shinohara, 2013; Chiodini et al., 2015; Giammanco et al., 2016). Knowledge on the total CO2 emitted into the atmosphere by volcanoes is important to have a better understating about their role and their relations to the anthropogenic emission (Gerlach, 2011). However, there has been increasing evidence suggesting that significant amount of gases including CO2 is released also by dormant/quiescent volcanoes, (Notsu et al., 2006; Werner et al., 2008; Viveiros et al., 2010; Carapezza et al., 2003, 2012; Carapezza and Tarchini, 2007; Caracausi et al., 2015 and references therein; Goepel et al., 2015), which are much less studied, although their gas emissions has to be also considered and

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quantified. These data demonstrate that volcanic plumbing systems could be still active in spite of the relative calmness of the volcano on the surface and this has to be taken into account during evaluation the nature of the volcanic system. Monitoring of gas release in such areas could help constraining any changes in the deep magmatic and hydrothermal systems and forecasting re-awakening of the volcano or threat of sudden degassing (Chiodini et al., 2001; Pizzino et al., 2002; Carapezza et al., 2003, 2012; Carapezza and Tarchini, 2007; Issa et al., 2014; Sano et al., 2015). Furthermore, the significant CO2 emission in seemingly inactive volcanic areas could yield threat to society, since there is much less attention to the potential hazards. People and animals may be exposed directly to the gases, therefore knowledge of the emitted quantities and composition of the gases, as well as the gas dispersion in air are important to involve the public health risk assessment (Costa et al., 2008; Granieri et al., 2013; Viveiros et al., 2016). Such gas emissions could occasionally reach even the orders of magnitude of that of active volcanoes (Chiodini et al., 1998, 2004a; Rogie et al., 2001; Hernandez et al., 2006; Carapezza et al., 2003, 2012; Carapezza and Tarchini, 2007; Viveiros et al., 2010; Nisi et al., 2014; Caracausi et al., 2015; Paz et al., 2016). Non-volcanic, tectonically active areas also contribute to the total budget of deep CO2 release, sometimes associating with earthquakes due to accumulation of over-pressurized gas in the crust (Lewicki and Brantley, 2000; Rogie et al., 2000; Mörner and Etiope, 2002; Chiodini et al., 2004b, 2011; Kämpf et al., 2013; Lewicki et al., 2013; Weinlich, 2014). Here, we provide the first high-resolution CO2 flux data for the Neogene to Quaternary volcanic regions of the entire Carpathian-Pannonian Region, Eastern-Central Europe. Quantifying the CO2 gas release on focused gas emissions and diffused soil degassing in selected parts of

Ciomadul, the youngest volcano of this area, we emphasize the role of dormant volcanoes to the global CO2 gas emission and point to a potential hazard in this seemingly inactive volcano. The new CO2 gas flux data along with their composition indicate that significant magma degassing could take place in the depth. This is consistent with the results of the geophysical studies (Popa et al., 2012; Harangi et al., 2015a) suggesting melt-bearing magma body in the crust. 2. Geological setting 2.1. The Ciomadul volcano The Ciomadul volcano is located at the southeastern end of the Calimani-Gurghiu-Harghita volcanic chain, the eastern segment of the Carpathian-Pannonian Region, which has been active since 11.3 Ma (Szakács et al., 1993; Szakács and Seghedi, 1995; Pécskay et al., 2006) (Fig. 1). The andesitic to dacitic volcanism is regarded as being post-collisional, since it has occurred following the convergence and collision of the Tisza-Dacia microplate with the western margin of the Eurasian plate (Mațenco, 2000; Mațenco et al., 2007; Seghedi et al., 2011). The volcanic edifices gradually changed from NW to SE from large-volume stratovolcanoes to smaller composite volcanoes, dome complexes and monogenetic fields. Ciomadul is a lava dome complex composed of about 8–14 km3 high-K dacitic volcanic product (Karátson and Timár, 2005; Szakács et al., 2015). The volcanic structure of Ciomadul consists of a central cluster of lava domes hosting the Mohos and St. Ana explosive craters and it is surrounded by older isolated peripheral lava domes (Haramul Mic, Bálványos, Büdös-Puturosul and Dealul Mare). Most of the lava domes have preserved well their original morphology, while some of them (e.g. Bálványos and Büdös/Puturosul domes) show

Fig. 1. Geological sketch map of the study area, including the main focused emissions and strong diffuse soil degassing areas (modified after Ianovici et al., 1968). The numbers of the focused emissions as well as the letters of the diffuse soil emissions are the same as in Table 1.


intensive erosional and fumarolic alteration features (Szakács and Seghedi, 1995; Karátson et al., 2013; Szakács et al., 2015). Volcanism at Ciomadul lava dome field has started around 1 Ma before present, while the Ciomadul volcano itself has been built up since ca. 200 ka with initial lava extrusion followed by a relatively long quiescence period from about 100 ka to 57 ka (Harangi et al., 2015b). The youngest active stage (from 57 to 32 ka) of the volcanic activity was more explosive and involved several collapse events of the extruded lava domes accompanied by vulcanian and sub-plinian eruptions (Harangi et al., 2015b; Karátson et al., 2016). The latest eruptions occurred at 32 ka (Vinkler et al., 2007; Harangi et al., 2010, 2015b), since then the volcano has been in quiescence state. Nevertheless, in spite of this relatively long dormancy, collective evidences from geology, petrology and geophysics (Demetrescu and Andreescu, 1994; Szakács et al., 2002; Harangi and Lenkey, 2007; Popa et al., 2012; Szakács and Seghedi, 2013; Harangi et al., 2015a, 2015b) indicate that there could be still a melt-bearing magma body beneath it. Petrogenetic interpretation of the pre-eruptive magma chamber processes as well as new zircon U-Th and U-Pb dating studies indicate the existence of longlasting (up to 350 kyr), low-temperature (700–750 °C) silicic crystal mush body beneath the volcano, which was periodically remobilized by injection of hot basaltic magmas rapidly triggering volcanic eruptions (Kiss et al., 2014; Harangi et al., 2015a, 2015b). This suggests that there is still a potential for reawakening of the magmatic system. Based on these observations, Harangi et al. (2015a, 2015b) introduced a new term for such long-dormant volcanoes: PAMS volcanoes, i.e. volcanoes with potentially active magma storage. This involves volcanoes (e.g., Yellowstone, Uturuncu, Albani Hills, among others), which erupted N10 ka ago, but the presence of melt-bearing magma body beneath them provides a potential for fast reactivation and volcanic eruption in the future. The Ciomadul developed on clastic flysch sedimentary suite forming the outer belt along the Carpathians. The Eastern segment of the Carpathian chain is an arcuate orogenic mountain, formed as a result of the continental collision of Tisza-Dacia microplates with the Eurasian plate during Cretaceous and Tertiary (Csontos et al., 1992). The outer flysch belt consists of several nappes. The Lower Cretaceous units are represented by thick flysch deposits of the Ceahlău nappe, consisting of alternation of sandstones, calcareous sandstones and clays/marls (Ianovici et al., 1968; Solcanu, 2015). The Ciomadul volcano is located close (~50 km) to the Vrancea region, which has the largest present-day strain concentration and poses a persistent regional seismic hazard in continental Europe (Wenzel et al., 1999; Ismail-Zadeh et al., 2012) at the arc bend of the Southern Carpathians. The frequent earthquakes with deep hypocentres (70–170 km, magnitude up to 7), concentrated in a narrow, vertical slice, and are related to a well-defined body of high velocity lithospheric slab, descending in the asthenospheric mantle. In addition to the Vrancea area crustal and subcrustal earthquakes (with magnitude b 4) occur in the vicinity of the Perșani Mountains and South Harghita Mountains beneath Ciomadul volcano. Recent seismic tomographic data identified almost vertical low-velocity areas for the P and S waves beneath Ciomadul (Popa et al., 2012). These can be viewed as columns of rocks that are hotter and more ductile than the neighboring ones, thus related to the presence of a still hot magma transport path in connection with the most recent volcanic activity, or a crustal magma chamber beneath Ciomadul. A melt-bearing crustal magma body was suggested also by Harangi et al. (2015a) based on a combined magnetotelluric and petrologic study. 2.2. Gas emission in the Ciomadul volcano Gas compositional data on few sites (Bálványos, Büdös–Puturosul– Stinky Cave) at Ciomadul were first reported by Althaus et al. (2000) and Vaselli et al. (2002) and this represents the present-day knowledge on the geochemistry of volatiles from Ciomadul volcano. These studies describe the presence of a CO2 dominated (up to 98%, Althaus et al.,

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2000) gas in the study area. The 13CCO2 composition of the gases in the Eastern Carpathians is between −2.1 to − 4.7‰ (Vaselli et al., 2002), which overlaps the fields of mantle-derived gases, and CO2 related to metamorphic processes suggested that the emitted CO2 could be a mixture of magmatic gases and a source derived from the alteration and hydrothermal metamorphism of marine carbonates, while in the Ciomadul the gases are inferred predominantly magmatic. Noble gas compositions, with R/Ra up to 3.19 (at Stinky Cave, Althaus et al., 2000) and 4.48 (at Balvanyos, Vaselli et al., 2002) suggest considerable amount of mantle-derived 3He (estimates up to 50% of the total He flux, Vaselli et al., 2002). This implies release of deep fluids that rise directly from the mantle, or are linked to a deep-seated magma reservoir beneath Ciomadul volcano that is undergoing by cooling and degassing through tectonic lineaments. The study area is characterized by the largest thermal anomaly in Romania, such as relatively high heat-flow, up to 85–120 mW/m2, in comparison with the surrounding areas (Demetrescu and Andreescu, 1994). High temperature Na-HCO3 type water of 63 °C was recorded in a hydrogeological well at Băile Tușnad (Mitrofan, 2000) while some springs have surface temperatures up to 23 °C, significantly higher than air temperature (Jánosi et al., 2013). The gas emission from soil or water in confined spaces represents a potential threat for people and animals, especially in popular tourist places visited by people, who are not fully aware of the danger they are exposed to. A particular case is represented by some unsupervised caverns with strong gas emission, with CO2 concentrations up to 98% (Althaus et al., 2000). In addition, CO2 gas occurs very often also in the cellars of the houses in inhabited areas that potentially could cause lethal consequences (asphyxia). On the related hazard there are some monographic descriptions (Orbán, 1868), local news and few scientific data (Barti, 1999; Barti and Varga, 2004) that report events of lethal events for human beings and animals entering the mofettes and these caverns. Other clues suggesting the hazard related to these gas emissions is given by the etymology of the local names, e.g. the name of the caves, “Peștera Puturosul” in Romanian or “Büdös-barlang” in Hungarian, meaning the “Stinky cave”, the “Peștera Ucigașă” in Romanian or “Gyilkos-barlang” in Hungarian meaning the “Killer Cave” or “Cimitirul Păsărilor” or “Madártemető” meaning the „graveyard of the birds”, suggesting that many small animals have found their death by approaching these degassing places (Orbán, 1868). 3. Materials and methods Carbon dioxide flux measurements in the Ciomadul volcanic area were performed at 19 sites representing focused gas emissions, such as gas vents and bubbling pools. The fluxes of CO2 for the focused emissions were measured using the accumulation chamber method. Instead of the chamber an inverted funnel with known volume (0.0016 m3 with footprint area of 0.03 m2.) was used in the case of bubbling pools. The bubbles were trapped into the funnel, which was directly connected to the flux meter. The fluxes were automatically calculated through a linear regression of the gas concentration build-up in the funnel. The total emissions were calculated by summing the measured fluxes within a pool or vent (Etiope et al., 2011, Etiope, 2015). The CO2 flux of the Stinky Cave (Site #22, Table 1) was measured and calculated using the method and Eq. (1) given by Rogie et al., 2000. The high gas flux from the Stinky Cave forms a stream of dense CO2, which was trapped into a channel. Red colored smoke bombs were used to color the path of the CO2 stream. After measuring the channel dimensions, the gas velocity was determined using an anemometer. The flux was determined using the equation: ΦCO2 ¼

A∙V∙C∙P R∙T

ð1Þ

where, A: cross-sectional area of the hose; V: gas velocity in the exit hose; C: CO2 concentration (gas-chromatography data); P: pressure of

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Table 1 CO2 flux of the focused emissions and diffuse soil degassing of Ciomadul volcanic area. No Site 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

Várpad-Ibolya pool Várpad-Ibolya pool 2 Bálványos pool Csiszárfürdő - Iker pool white Csiszárfürdő - Hammas pool Csiszárfürdő - Hammas collector pool Csiszárfürdő -Timsós pool Csiszárfürdő - Csokoládés pool Csiszárfürdő - Szemvizek Mikesfürdő - Vallató pool Mikesfürdő - Vallató mofetta Mikesfürdő - Hammas pool Mikesfürdő - Bükkös pool Gyógyvizek Bálványosfürdő Sósmező drilling 1 Bálványosfürdő Sósmező drilling 2 St Ana crater rim Jajdon pool Bixad Antalkáék feredeje Tusnad Tiszas Nadas Stinky Cave

N 46.1134 46.1134 46.1095 46.1063 46.1065 46.1065 46.1063 46.1059 46.1065 46.1170 46.1180 46.1168 46.1161 46.1133 46.1159 46.1159 46.1310 46.0701 46.1146 46.1551 46.1776 46.1198

E

CO2 g d−1

25.9600 25.9600 25.9590 25.9514 25.9504 25.9504 25.9504 25.9508 25.9514 25.9281 25.9283 25.9340 25.9349 25.9504 25.9424 25.9424 25.8936 25.9538 25.8526 25.8750 25.9131 25.9487

1453.59 741.92 291.42 313.07 2029.26 453.97 1012.72 277.25 1020.89 1682.78 4988.64 2167.43 3928.32 6339.99 3391.35 8172.11 638.25 442.63 658.84 328.77 7671.23 5,270,162

St Anna crater diffuse soil flux A B

Băile Balvanyos Apor Baths diffuse soil flux Lăzăresti-Nyír Baths diffuse soil flux

see Supplementary Dataset 1 see Supplementary Dataset 2

see Supplementary Dataset 1 see Supplementary Dataset 2

SUMM

the gas in the exit hose; R: universal gas constant (0.082057 L mol−1 K−1), T temperature of the gas in the exit hose (°C). For CO2 diffuse soil surveys, the two most important emission areas of the region, Băile Bálványos–Apor Baths and Lăzărești–Nyír Baths were considered, located at the south-eastern and northern margin of Ciomadul volcanic complex, respectively (Fig. 1). Băile Bálványos– Apor Baths is renowned as a popular tourist place, while Lăzărești– Nyír Baths is located within an inhabited area. In both cases the gas emissions are indicated by lack of vegetation and sulphur deposition. The survey of diffuse CO2 soil flux covered an area of 2200 m2, with 44 transects and 400 measuring points at Băile Bálványos-Apor-Baths, and 2650 m2, with 13 transects and 175 measuring points at Lăzărești-Nyír-Baths. The transects were set perpendicular to the axis of the area. The distance between transects was approximately 2 m at Apor and 4 m at Nyír-Lăzărești, while distance between measuring points varied between 1 and 4 m. Additional measuring points were added when anomalies were detected in the field (ex. sulphur deposition between two points and/or sizzling noise suggesting gas-emission). The fluxes of CO2 were measured using the accumulation chamber method (Chiodini et al., 1998; Cardellini et al., 2003) in meteorologically stable conditions. Measurements were performed in springtime, in five days at Apor Baths and in three days at Lăzărești. The instrumental package (West System, Pontedera, Italy) was equipped with a CO2 sensor and wireless data communication to a palm-top computer. The CO2 detector is a double beam infrared sensor (LI-COR, with a range of 0–20,000 ppmv, accuracy of 2% and a repeatability of ±5ppmv). The accumulation chamber was equipped with a Nafion drying tube (Perma Pure, USA) for humidity removal. In the case of bubbling pools an inverted funnel was used instead of the accumulation chamber. Humidity is removed using silica-gel and a Drierite drying unit. The CO2 soil flux data were elaborated by both statistical and geostatistical methods to characterize the soil diffuse degassing, to discriminate the CO2 origin, to map its spatial distribution and to compute

t y−1 0.53 0.27 0.11 0.11 0.74 0.17 0.37 0.10 0.37 0.62 1.82 0.79 1.43 2.53 1.24 2.98 0.23 0.16 0.24 0.12 2.80 1.92 × 103 6.50 5.29 × 103 1.46 × 103 8.70 × 103

Nr. of measurements

Reference

4 5 1 2 3 1 5 2 2 4 5 7 9 13 5 2 1 3 1 unknown unknown 5

This work This work This work This work This work This work This work This work This work This work This work This work This work This work This work This work This work This work This work Frunzeti (2013) Frunzeti (2013) This work

91 400

Frunzeti and Baciu (2012) This work

175

This work

the total release of CO2. Soil gas anomalous degassing areas are generally characterized by complex statistical distributions, which may reflect the coexistence of different gas sources, such as biogenic and endogenous, or different flux regimes, e.g. diffusive or advective (Cardellini et al., 2003), which results in datasets representative of the combination of different statistical populations. In a logarithmic probability plot, where a straight line describes a single log-normal population, these complex distributions form a curve with n inflection points describing the overlapping of n + 1 lognormal populations. The partition of these complex distributions into the individual log-normal populations and the estimations of their proportion (fi), mean value and standard deviation can be performed according to the graphical procedure proposed by Sinclair (1974). Since the statistical parameters (i.e. mean and standard deviation) of the populations computed by Sinclair procedure refer to the logarithm of values, the mean value of CO2 fluxes and the standard deviation were estimated by means of a Montecarlo simulation starting from the parameters estimated by the by Sinclair procedure. In order to obtain maps of CO2 flux spatial distribution and to estimate the amount of gas released by the diffuse degassing, the measured values were elaborated using the approach proposed by Cardellini et al. (2003) and Lewicki et al. (2005), based on sequential Gaussian simulations (sGs). The sGs method consists of the production of numerous realizations of the spatial distribution of an attribute (CO2 flux, this study), here performed using the sGsim algorithm described by Deutsch and Journel (1998). In this work the simulations of CO2 flux were performed considering an area of about 2200 m2 and 2650 m2 for Apor and Lăzărești, respectively. Simulation grid cells of 0.25 m2 were used. For each dataset 100 realizations were produced and then post-processed obtaining the “expected” value at any location, through a pointwise linear average of all the realizations (Cardellini et al., 2003). The expected flux values were used to draw the CO2 maps reported in Figs. 4 and 5. The total release of CO2 derived from soil degassing was estimated by summing the


contribution of each cell, computed by multiplying the average flux value obtained for each cell by the area of the cell. For the statistical and geostatistical analysis the WinGslib 1.5 (Statios Software and Services), Acque and Surfer 13 software (Golden Software Ltd.) were used. The location of the study area together with the geographical position of the sampling sites is available in Fig. 1. The site, sample IDs, geographical locations according to their GPS coordinates (WGS84, geographical coordinates) of the focused emissions, together with the total CO2 output of the area, represented by the sum of the flux of focused emissions and diffuse soil gas measurements are listed in Table 1. The statistical results of the population partition for the Apor and Lăzărești data sets are reported in Table 2. Detailed data on diffuse soil flux measurements together with the coordinates of measuring points (WGS84, UTM coordinates) for the two selected sites are reported in Supplementary Dataset 1 for Apor Baths, and Supplementary Dataset 2 for Lăzărești. 4. Results The CO2 fluxes for focused emissions range between 277 and 8172 g d− 1, corresponding to a CO2 output into the atmosphere between 0.1 and 2.98 t per year (Table 1, Fig. 2). Higher emissions were identified at sites #16 (2.95 t y−1), #14 (2.53 t y−1), #11 (1.82 t y−1), #13 (1.43 t y−1) and #15 (1.24 t y−1), located at the proximity of the oldest volcanic domes Puturosul and Bálványos (500–600 ka). The largest emission was measured at the Stinky Cave (#22), with a CO2 output of 1.92 × 103 t y−1. In addition to the focused emissions, we report data on diffuse soil flux measurements at two sites considered as representative for the region, due to the visible gas emissions (Fig. 1, data available in Supplementary Datasets 1 and 2). The investigated areas for diffuse gas emissions were characterized by a wide range of CO2 flux values, varying up to three orders of magnitude at Apor Baths, ranging from 1.7 × 101 to 8.2 × 104 g m−2 d−1. At Lăzărești the soil flux ranged between 1.43 and 3.8 × 104 g m−2 d−1. Each data set is reported in the logarithmic probability plots of Fig. 3A and B for Apor and Lăzărești sites, and shows the presence of more than one statistical population. In particular Lăzărești dataset shows a combination of 2 populations, while Apor dataset suggests 3 populations, of which main statistical parameters are reported in Table 2. Based on the mean flux values characterizing the different populations, we can attempt to constrain the main source of the CO2 gases. Apor population C and Lăzărești Population B are characterized by mean CO2 flux values compatible with fluxes produced by biogenic sources in the soil (i.e., root respiration and organic matter decomposition). The values of the biogenic sources which approximately range in various ecosystems from 0.2 to 21 g m− 2 d−1 (e.g., Raich and Schlesinger, 1992; Raich and Tufekcioglu, 2000) with maximum flux values for grassland of ~ 50 g m− 2 d− 1 (e.g., Norman et al., 1992; Bajracharya et al., 2000; Nakadai et al., 2002). On the contrary, Apor populations A and B and Lăzărești Population A are characterized by high mean CO2 flux values, from 102 to 105 g m− 2 d− 1, hence much higher than those produced by biogenic sources in the soil. Such high values are representative of the degassing of deeply produced CO2. Evidence for deep CO2 is provided by isotopic composition of carbon (δ13C), measured in the gases emitted in the area, from − 2.1 and − 4.7 (‰) Table 2 Estimated parameters and partitioned populations for CO2 fluxes. Site name

Population Mean log flux

Lăzăresti A B Apor A B C

3.74 1.46 4.01 2.75 1.37

Log flux st.dev.

Fraction Mean flux g % m−2 d−1

Flux dev.st. g m−2 d−1

0.65 0.51 0.5 0.43 0.14

14 86 42 54.2 3.8

10,806 7.94 2570 80.0 2.1

17,106 54.1 19,825 919 24.7

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(Vaselli et al., 2002; Kis et al., 2016), which overlie the range of the mantle carbon isotopic signature and carbon derived from the thermal alteration of carbonates (Hoefs, 2009), but at Ciomadul infer a predominantly magmatic origin. In the Apor area, the presence of more than one anomalous population possibly reflects the differences in soil permeability and/or of areas where advective (concentrated fluxes on one spot) flux prevails on diffusive one. Using the sGs method, for the Apor site we calculated a total output of 14.5 t d−1 of CO2 corresponding to 5.29 × 103 t y−1 of CO2. In the case of Lăzărești area we calculated 4 t d−1, meaning 1.46 × 103 t y−1 emission of CO2. 5. Discussion The main path for gas release in the case of dormant volcanoes and tectonically active areas is diffuse soil degassing, focused emissions (vents and small areas of strong degassing) and/or gas dissolution in groundwater (e.g. Chiodini et al., 1998, 2000; Rogie et al., 2000; Cardellini et al., 2003; Tassi et al., 2013; Oppenheimer et al., 2014; Pedone et al., 2015; Lee et al., 2016). Determination of diffuse soil CO2 fluxes and the observation of their spatial variation provide important tools for identification of a relationship between degassing and volcanic activity (Carapezza et al., 2003, Carapezza and Tarchini, 2007; Lewicki et al. 2003; Aiuppa et al., 2010; Chiodini et al., 2015; Giammanco et al., 2016; Wen et al., 2016), geothermal exploration (Brombach et al., 2001; Bloomberg et al., 2012; Fridrikson et al., 2016) and seismogenesis (Lewicki and Brantley, 2000; Weinlich, 2014). The highest CO2 focused gas fluxes at Ciomadul were found at the periphery of the youngest volcanic complex, at the intersection of the older (500–600 ka) lava domes, Puturosul and Bálványos (Fig. 3). They are emitted along creeks, having a NW–SE striking direction. Thus a tectonic control of the gas emission is assumed where fractures in the basement rocks could enhance gas transport by creating major migration pathways to the surface. Some of the CO2-rich gases may reach the surface without major interaction with the shallow aquifer and occur as dry mofettes, whereas others dissolve in groundwater and are transported to the surface by CO2-rich springs. At some places, swamps could have formed over fracture lines and the surface water dissolves the uprising deep gas and contributes to their transport (Newell et al., 2005; Macpherson, 2009; Keating et al., 2010; Chiodini et al., 2011). Dissolution and exsolution processes of CO2 in the aquifers are demonstrated by the presence of bubbling mineral water springs in the area. Most of the focused emissions (mofettes and bubbling pools) with high fluxes are localized at the oldest part of Ciomadul volcanic area, around the Puturosul and Bálványos lava domes, most probably because these are more fractured than the youngest volcanic edifices, around the explosive craters of St. Ana and Mohoș. Deep gas emissions at the main craters have been suggested recently by Túri et al. (2016), who pointed out their upwelling and dissolution into the water on the bottom of St. Ana Lake. The CO2 flux map for the Apor site (Fig. 4) shows an increase of CO2 fluxes towards the southern part. The higher emission can be attributed to a change in the soil permeability, possibly in the presence of shallow groundwater (emergence of the springs) that enhances the gas migration. In the middle of the measured area we presume the presence of a fracture-zone that channels the deep gas, described also as DDS (Diffuse Degassing Structures, Chiodini et al., 2001). Significant soil CO2 degassing can help to detect active tectonic features as shown by Lewicki and Brantley (2000), Kämpf et al. (2013), Weinlich (2014) and Giammanco et al. (2016), among others. Tectonically active areas in non-volcanic regions contribute also to the total budget of deep CO2 release, sometimes associating with earthquakes due to accumulation of over-pressurized gas in the crust (Lewicki and Brantley, 2000; Rogie et al., 2000; Mörner and Etiope, 2002; Chiodini et al., 2004b, Chiodini et al., 2011; Kämpf et al., 2013; Lewicki et al., 2013; Weinlich, 2014). The Cheb Basin in the western Eger rift at central Europe is such a

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Fig. 2. Dot plot of the CO2 flux of individual vents (number of samples as in Table 1). The yellow star represents the flux of the Stinky Cave. The red, yellow and blue dots denotes the intensity of the CO2 degassing.

Fig. 3. Probability plots of log CO2 flux for A) Apor and B) Lăzărești sites. The figure shows the original data (dots), the theoretical partitioned populations following the procedure of Sinclair (1974) (colored dashed lines), and the theoretical statistical distribution resulting from the combination of the partitioned populations (red lines).


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Fig. 4. Diffuse soil degassing at Apor site. A. General view of the degassing area. B. Small bubbling pool. C. Map of geographical location of Apor site with respect to Băile Bálványos, D. Variogram model based on the measurement data. E. Grid of the measuring points F. Map of diffuse soil degassing. Data reported in Supplementary Dataset 1.

region, where Kämpf et al. (2013) pointed out significant CO2 emission. Although, this area seems to be presently a nonvolcanic region, Quaternary volcanism at 300–500 ka (Wagner et al., 2002) indicates that this could be just a quiescence period. Furthermore, elevated 3He/4He ratios suggest mantle-derived origin of the gases. Bräuer et al. (2005) interpreted this as a sign of ascending mantle-derived melts into the lower crust that trigger the occasional earthquake swarms as well as occurrences of mofettes in this area. The other studied area at Ciomadul, at Lăzărești (Fig. 5), the highest emission is observed near the locations of the main degassing features (dry mofettes and bubbling pools) suggesting the strong influence of advective emissions upon diffuse degassing. Like in the case of Apor site, we presume a tectonic control also here that enhances migration of gases towards the surface.

The total output of CO2 derived from soil degassing in the study area is determined, taking in consideration the total flux from Apor and Lăzărești sites and emissions from St. Ana crater (Frunzeti and Baciu, 2012), together with the focused emissions (Table 1). Considering all of these data, the total CO2 emission is quantified as 8.70 × 103 t y−1. However, this is still a minimum value, since the investigated area is very limited with respect to the whole Ciomadul volcanic system, and the possible contribution from dissolved gas has not been investigated yet. This result for the total CO2 emission is two to three orders of magnitude lower than that observed at active volcanoes, like at Etna or Stromboli. Nevertheless the output is still significant and is akin to the published data for other volcanic areas, where the last eruptions occurred N 10′s ka before, but in some cases there are indications for the

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Fig. 5. Diffuse soil degassing at Lăzărești site. A.Map of geographical location of Lăzărești site B. Variogram model based on the measurement data. C. Grid of the measuring points D. Map of diffuse soil degassing. Data reported in Supplementary Dataset 2.

presence of melt-bearing magma body beneath them (Table 3 and Figs. 6 and 7). Thus, significant amount of deep-sourced gas could be emitted long after the last volcanic eruption (Caracausi et al., 2015; Fig. 7). The significant CO2 emission at Ciomadul with inferred magmatic origin (Vaselli et al., 2002; Kis et al., 2016) could be consistent also with the proposed existence of a melt-bearing crystal mush magmatic body at the depth beneath the volcano (Popa et al., 2012; Harangi et al., 2015a). Nevertheless, the locations of the strongest outgassing do not coincide with the youngest eruption centers of Ciomadul, but are in a peripheral occurrence. The reason of this requires further studies, although we can provisionally assume two explanations. The first one is that brittle fractures were formed preferentially at the margins of the lava dome complex, where diffuse degassing of the assumed shallow magma storage is more efficient. On the other hand, the source of the CO2 gases could be deeper, coming from a more mafic magma reservoir residing at lower crustal hot zone (Annen et al., 2006). The gases find the way up to the surface through the melt-bearing magma body less effectively and thus they occur mostly at its periphery (Allard et al., 1991; Edmonds, 2008). The Ciomadul is located close (~50 km) to an active geotectonic setting, which is one of the most seismically active areas of Europe. (Vrancea zone; Wenzel et al., 1999). Earthquakes at crustal and subcrustal depths have been also detected beneath Ciomadul (Popa et al., 2012). Relationship between the seismicity and CO2 degassing would be important to constrain, however, this requires more precise data about the crustal seismic activity around Ciomadul. The relatively high CO2 output at Ciomadul warns that this has to be incorporated into the risk assessment of the area. This seemingly inactive volcanic area is a popular tourist destination, although visitors

know little about the potential hazards. Our results could promote to involve this issue into the local risk assessment and to perform continuous monitoring of the gas flux in order to understand better the seasonal variation as well as any connections to the seismic events. Furthermore, this new result provides additional emphasize that gas emissions at long-dormant and seemingly inactive volcanic areas could significantly contribute to the global CO2 emission budget and therefore additional gas flux research would be required in this regions. 6. Conclusions Ciomadul is the youngest volcano of the Carpathian-Pannonian region, with the last eruption at 32 ka (Vinkler et al., 2007; Harangi et al., 2010; Harangi et al., 2015b). In spite of the relatively long inactivity since the last eruption, there are several features that may indicate that volcanic activity may not be completely ceased within the region. In particular the high heat flow (85–120 mW/m2, Demetrescu and Andreescu, 1994); the occurrence of a low-velocity seismic anomaly just beneath the volcano at mid to lower crustal level as shown by seismic tomography model (Popa et al., 2012); the existence of a melt-bearing crystal mush at 5 to 20 km depth as demonstrated by combined petrologic and magnetotelluric studies (Harangi et al., 2015a); and the active tectonic setting at Vrancea zone (Wenzel et al., 1999; Popa et al., 2012) are all evidences for the potential of future reawakening. These are in a good agreement with our data that highlight an active release of deep origin CO2. However, more detailed investigations are necessary to recognize if such high CO2 emissions are due to release of magmatic gas from crustal reservoirs or it is due to magma degassing at greater depth.


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Table 3 Total CO2 output of active, long-dormant and inactive volcanic areas vs. the time elapsed since the last eruption. The total output in ascending order from no. 1 to 30. No Volcano

Country

Total output mol y−1 Total output t y−1 Years from last eruption

Reference

1 2 3 4 5 6 7 8 9 10 11

Kozhuh Showa-Shinzan Amiata Nea Kameni Ciomadul Jefferson Roccamonfina Panarea Vulture Cuicocha White Island

2.69E + 07 8.55E + 07 8.80E + 07 1.28E + 08 1.54E + 08 1.80E + 08 1.70E + 08 3.90E + 08 4.85E + 08 8.80E + 08 9.62E + 08

1.18E + 03 3.76E + 03 3.87E + 03 5.62E + 03 6.78E + 03 7.92E + 03 7.48E + 03 1.72E + 04 2.13E + 04 3.87E + 04 4.23E + 04

12,200,000 71 200,000 66 32,000 70,000 50,000 20,000 141,000 1300 15

Nisi et al. (2013) Hernandez et al. (2006) Gambardella et al. (2004), Nisi et al. (2014) Chiodini et al. (1998) This work James et al. (1999) Gambardella et al. (2004) Schipek et al. (2013) Caracausi et al. (2015) Padrón et al. (2008) Bloomberg et al. (2012)

12 13 14 15 16 17 18 19 20

Miyakejima Satsuma-Iwo-Jima Copahue-Cavihue Pululahua Latera Caldera Iwo Jima Hengill Vulcano Albani Hills

Bulgaria Japan Italy Greece Romania USA Italy Italy Italy Ecuador New Zeeland Japan Japan Argentina Ecuador Italy Japan Iceland Italy Italy

1.04E + 09 1.50E + 09 1.92E + 09 2.20E + 09 2.40E + 09 3.70E + 09 3.80E + 09 4.00E + 09 4.20E + 09

4.56E + 04 6.60E + 04 8.45E + 04 9.68E + 04 1.06E + 05 1.63E + 05 1.67E + 05 1.76E + 05 1.85E + 05

10 1200 16 1700 156,000 13 2000 126 22,900

21 22

M.Mountain Teide (Las Canadas) Vesuvius Furnas Pantelleria Ischia Campi Flegrei Stromboli Ol Doinyo Lengai Etna

USA Spain

4.60E + 09 5.10E + 09

2.02E + 05 2.24E + 05

754 105

Hernández et al. (2001) Shimoike et al. (2002) Chiodini et al. (2015) Padrón et al. (2008) Chiodini et al. (2007) Notsu et al. (2005) Hernández et al. (2012) Inguaggiato et al. (2012) Chiodini and Frondini (2001), Soligo et al. (2003) Sorey et al. (1998) Marrero et al. (2008)

Italy Portugal Italy Italy Italy Italy Tanzania Italy

5.80E + 09 8.85E + 09 9.00E + 09 1.10E + 10 1.30E + 10 1.80E + 10 5.6E + 10 1.6E + 11

2.55E + 05 3.89E + 05 3.96E + 05 4.84E + 05 5.72E + 05 7.92E + 05 2.46E + 06 7.04E + 06

70 384 123 712 476 1 1 1

Frondini et al. (2004) Viveiros et al. (2010), Pedone et al. (2015), Andrade et al. (2016) Favara et al. (2001) Pecoraino et al. (2005) Chiodini et al. (2001) Carapezza and Federico (2000) Koepenick et al. (1996) Burton et al. (2013)

23 24 25 26 27 28 29 30

In this study, the CO2 emission has been quantified in this area of Europe at first time and it turned out that significant amount of CO2 is continuously emitted around Ciomadul. The measured fluxes for focused vents together with the diffuse degassing outputs of the area indicate a total CO2 output in the area of 8.70 × 103 t y−1, which is consistent with other long-dormant volcanoes of similar age, worldwide. Our results on the CO2 output are an additional support that Ciomadul may be considered as a PAMS volcano, i.e. a volcano, which seems to be inactive but with potential of fast magma storage reactivation, rather than an inactive one and also constitutes a contribution to the estimation of

the global CO2 budget attributed to volcanoes. Furthermore, this new result could enhance to develop risk assessment and awareness in this popular touristic area. Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.jvolgeores.2017.05.025. Acknowledgments This research was performed with financial support from OTKA (Hungarian National Research Fund) project number K116528, the

Fig. 6. Total CO2 output and soil CO2 output of different volcanoes. In the case of Ciomadul volcano, the total CO2 output is marked in red, while the soil CO2 output is marked in yellow. The data are reported in Table 3.

128


Fig. 7. Total CO2 output of active, long-dormant and inactive volcanic areas vs. the time elapsed since the last eruption. Ciomadul volcano is marked with red diamond. The data are reported in Table 3.

Romanian National Authority for Scientific Research (CNCS - UEFISCDI), project number PN-II-ID-PCE-2011-3-0537, the European Regional Development Fund in the project of GINOP-2.3.2-15-2016-00009 ‘ICER’, and the MTA Postdoctoral Program, Hungary. Special thanks to Giovanni Chiodini, for helping us with the use of Acque Software. The comments and suggestions received from anonymous reviewers helped us to greatly improve the manuscript. References Aiuppa, A., Burton, M., Caltabiano, T., Giudice, G., Guerrieri, S., Liuzzo, M., Mure, F., Salerno, G., 2010. Unusually large magmatic CO2 gas emissions prior to basaltic paroxysm. Geophys. Res. Lett. 37, LI7303. http://dx.doi.org/10.1029/2010GL043837. Allard, P., Carbonelle, J., Dajlevic, D., Le Bronec, J., Morel, P., Robe, M.C., Maurenas, J.M., FaivrePierret, R., Martin, D., Sabroux, J.C., Zettwoog, P., 1991. Eruptive and diffuse emissions of CO2 from Mount Etna. Nature 351:387–391. http://dx.doi.org/10.1038/351387a0. Althaus, T., Niedermann, S., Erzinger, J., 2000. Noble gas studies of fluids and gas exhalations in the East Carpathians, Romania. Chem. Erde 60, 189–207. Andrade, C., Viveiros, F., Cruz, J.V., Coutinho, R., Silva, C., 2016. Estimation of the CO2 flux from Furnas volcanic Lake (Sao Miguel, Azores). J. Volcanol. Geotherm. Res. 315: 51–64. http://dx.doi.org/10.1016/j.jvolgeores.2016.02.005. Annen, C., Blundy, J.D., Sparks, R.S.J., 2006. The genesis of intermediate and silicic magmas in deep crustal hot zones. J. Petrol. 47:505–539. http://dx.doi.org/10.1093/petrology/ egi084. Bajracharya, R.M., Lal, R., Kimble, J.M., 2000. Diurnal and seasonal CO2-C flux from soil as related to erosion phases in central Ohio. Soil Sci. Soc. Am. J. 64, 286–293. Barti, L., 1999. T, the bat victims of the natural gas break-offs a the Büdöshegy, Torja-Turia, Covasna County. Acta Siculica 1999 (23), 103–114 (In Hungarian). Barti, L., Varga, A., 2004. The bat victims caused by carbon dioxide intoxication in come caves in Transylvanian part of Eastern Carpathians, especially in BüdöshegyCiomadul-Puturosul Mountains, Covasna County. Acta Siculica 2003 (1), 65–73. Bloomberg, S., Rissmann, C., Mazot, A., Oze, C., Horton, T., Gravley, D., Kennedy, B., Werner, C., Christenson, B., Pawson, J., 2012. Soil Gas Flux Exploration at the Rotokawa Geothermal Field and White Island, New Zealand, Proceedings, Thirty-Sixth Workshop on Geothermal Reservoir Engineering. Stanford University, Stanford, California. Bräuer, K., Kämpf, H., Niedermann, S., Strauch, G., 2005. Evidence for ascending upper mantle-derived melt beneath the Cheb basin, central Europe. Geophys. Res. Lett. 32. http://dx.doi.org/10.1929/2004GL022205. Brombach, T., Hunziker, C.J., Chiodini, G., Cardellini, C., 2001. Soil diffuse degassing and thermal energy fluxes from the southern Lakki plain, Nisyros (Greece). Geophys. Res. Lett. 28 (1), 69–72. Burton, M.R., Sawyer, G.M., Granieri, D., 2013. Deep carbon emissions from volcanoes. Rev. Mineral. Geochem. 75, 323–354. Caracausi, A., Paternoster, M., Nuccio, P.M., 2015. Mantle CO2 degassing at Mt. Vulture volcano (Italy): relationship between CO2 outgassing of volcanoes and the time of their last eruption. Earth Planet. Sci. Lett. 411, 268–280. Carapezza, M.L., Badalamenti, B., Cavarra, L., Scalzo, A., 2003. Gas hazard assessment in a densely inhabited area of Colli Albani Volcano (Cava dei Selci, Roma). J. Volcanol. Geotherm. Res. 123, 81–94.

Carapezza, M.L., Tarchini, L., 2007. Accidental gas emission from shallow pressurized aquifers at Alban Hills volcano (Rome, Italy): geochemical evidence of magmatic degassing? J. Volcanol. Geotherm. Res. 165, 5–16. Carapezza, M.L., Federico, C., 2000. The contribution of fluid geochemistry to the volcano monitoring of Stromboli. J. Volcanol. Geotherm. Res. 95 (1–4), 227–245. Carapezza, M.L., Barbieri, F., Ranaldi, M., Ricci, T., Tarchini, L., Barrancos, J., Fischer, C., Granieri, D., Lucchetti, C., Melian, G., Perez, N., Tuccimei, P., Vogel, A., Weber, K., 2012. Hazardous gas emissions from the flanks of the quiescent Colli Albani volcano (Rome, Italy). Appl. Geochem. 27, 1767–1782. Cardellini, C., Chiodini, G., Frondini, F., 2003. Application of stochastic simulation to CO2 flux from soil: mapping and quantification of gas release. J. Geophys. Res. 108 (B9): 2425. http://dx.doi.org/10.1029/2002JB002165. Chiodini, G., Cioni, R., Guidi, M., Raco, B., Marini, L., 1998. Soil CO2 flux measurements in volcanic and geothermal areas. Appl. Geochem. 13 (5), 543–552. Chiodini, G., Frondini, F., Cardellini, C., Parello, F., Peruzzi, L., 2000. Rate of diffuse carbon dioxide Earth degassing estimated from carbon balance of regional aquifers: the case study of central Apennine, Italy. J. Geophys. Res. 105, 8423–8434. Chiodini, G., Frondini, F., Cardellini, C., Granieri, D., Marini, L., Ventura, G., 2001. CO2 degassing and energy release at Solfatara volcano, Campi Flegrei, Italy. J. Geophys. Res. 106 (B8), 16213–16221. Chiodini, G., Frondini, F., 2001. Carbon dioxide degassing from the Albani Hills volcanic region, Central Italy. Chem. Geol. 177 (1–2):67–83. http://dx.doi.org/10.1016/S00092541(00)00382-X. Chiodini, G., Avino, R., Brombach, T., Caliro, S., Cardellini, C., De Vita, S., Frondini, F., Granieri, D., Marotta, E., Ventura, G., 2004a. Fumarolic and diffuse soil degassing west of Mount Epomea, Ischia, Italy. J. Volcanol. Geotherm. Res. 133, 291–309. Chiodini, G., Cardellini, C., Amato, A., Boschi, E., Caliro, S., Frondini, F., Ventura, G., 2004b. Carbon dioxide Earth degassing and seismogenesis in central and southern Italy. Geophys. Res. Lett. 31, L07615. http://dx.doi.org/10.1029/2004GL019480. Chiodini, G., Baldini, A., Barberi, F., Carapezza, M.L., Cardellini, C., Frondini, F., Granieri, D., Ranaldi, M., 2007. Carbon dioxide degassing at Latera caldera (Italy): evidence of geothermal reservoir and evaluation of its potential energy. J. Geophys. Res. Solid Earth 112 (12), B12204. Chiodini, G., Caliro, S., Cardellini, C., Frondini, F., Inguaggiato, S., Matteucci, F., 2011. Geochemical evidence for and characterization of CO2 rich gas sources on the epicentral area of Abruzzo 2009 earthquakes. Earth Planet. Sci. Lett. 304, 389–398. Chiodini, G., Cardellini, C., Lamberti, M.C., Agusto, M., Caselli, A., Liccioli, C., Tamburello, G., Tassi, F., Vaselli, O., Caliro, S., 2015. Carbon dioxide diffuse emission and thermal energy release from hydrothermal systems at Copahue-Caviahue volcanic complex (Argentina). J. Volcanol. Geotherm. Res. 304, 294–303. Costa, A., Chiodini, G., Granieri, D., Folch, A., Hankin, R.K.S., Caliro, S., Avino, R., Cardellini, C., 2008. A shallow-layer model for heavy gas dispersion from natural sources: application and hazard assessment at Caldara di Manziana, Italy. Geochem. Geophys. Geosyst. 9:3. http://dx.doi.org/10.1029/2007GC001762. Csontos, L., Nagymarosy, A., Horváth, D., Kovác, M., 1992. Tertiary evolution of the intraCarpathian area: a model. Tectonophysics 208, 221–241. Demetrescu, C., Andreescu, M., 1994. On the thermal regime of some tectonic units in a continental collision environment in Romania. Tectonophysics 230, 265–276. Deutsch, C.V., Journel, A.G., 1998. Geostatistical Software Library and User's Guide. second ed. Oxford University Press, New York. Edmonds, M., 2008. New geochemical insights into volcanic degassing. Phil. Trans. R. Soc. A 366:4559–4579. http://dx.doi.org/10.1098/rsta.20080185. Etiope, G., Nakada, R., Tanaka, K., Yoshida, N., 2011. Gas seepage from Tokamachi mud volcanoes, onshore Niigata Basin (Japan): origin, post-genetic alterations and CH4CO2 fluxes. Appl. Geochem. 26, 348–359. Etiope, G., 2015. Natural Gas Seepage. The Earth's Hydrocarbon Degassing. 200. Springer International Publisher, Switzerland. Favara, R., Giammanco, S., Inguaggiato, S., Pecoraino, G., 2001. Preliminary estimate of CO2 output from Pantelleria Island volcano (Sicily, Italy): evidence of active mantle degassing. Appl. Geochem. 16, 883–894. Frondini, F., Chiodini, G., Caliro, S., Cardellini, C., Granieri, D., Ventura, G., 2004. Diffuse CO2 degassing at Vesuvio, Italy. Bull. Volcanol. 66 (7):642–651. http://dx.doi.org/10.1007/ s00445-004-0346-x. Fridrikson, T., Padron, E., Oskarsson, F., Perez, N.M., 2016. Application of diffuse gas flux measurements and soil gas analysis to geothermal exploration and environmental monitoring: example from the Reykjanes geothermal field, SW Iceland. Renew. Energy 86, 1295–1307. Frunzeti, N., 2013. Geogenic emissions of greenhouse gases in the southern part of the Eastern Carpathians. Romanian, PhD Thesis. 117. Frunzeti, N., Baciu, C., 2012. Diffuse CO2 emission at Sfanta Ana lake-filled crater (Eastern Carpathians, Romania). Procedia Environ. Sci. 14, 188–194. Gambardella, B., Cardellini, C., Chiodini, G., Frondini, F., Marini, L., Ottonello, G., Vetuschi Zuccolini, M., 2004. Fluxes of deep CO2 in the volcanic areas of central southern Italy. J. Volcanol. Geotherm. Res. 136, 31–52. Gerlach, T., 2011. Volcanic versus anthropogenic carbon dioxide. Eos vol. 92 (24), 201–202. Giammanco, S., Melian, G., Neri, M., Hernandez, P.A., Sortino, F., Barrancos, J., Lopez, M., Pecoraino, G., Perez, N.M., 2016. Active tectonic features and structural dynamics of the summit area of Mt. Etna (Italy) revealed by soil CO2 and soil temperature surveying. J. Volcanol. Geotherm. Res. 311, 79–98. Granieri, D., Costa, A., Macedonio, G., Bisson, M., Chiodini, G., 2013. Carbon dioxide in the urban area of Naples: contribution and effects of the volcanic source. J. Volcanol. Geotherm. Res. 260, 52–61. Goepel, A., Lonschinski, M., Viereck, L., Büchel, G., Kukowski, N., 2015. Volcano-tectonic structures and CO2-degassing patterns in the Laacher See basin, Germany. Int. J. Earth Sci. 104:1483–1495. http://dx.doi.org/10.1007/s00531-014-1133-3 (Geol Rundsch).

B.-M. Kis et al. / Journal of Volcanology and Geothermal Research 341 (2017) 119–130 Harangi, S.z., Lenkey, L., 2007. Genesis of the Neogene to Quaternary volcanism in the Carpathian-Pannonian region: role of subduction, extension and mantle plume. Geol. Soc. Am. Spec. Pap. 418, 67–92. Harangi, S.z., Molnár, M., Vinkler, A.P., Kiss, B., Jull, A.J.T., Leonard, A.G., 2010. Radiocarbon dating of the last volcanic eruption of Ciomadul Volcano, Southeast Carpathians, Eastern-Central Europe. Radiocarbon 52, 1498–1507. Harangi, S.z., Novák, A., Kiss, B., Seghedi, I., Lukács, R., Szarka, L., Wesztergom, V., Metwaly, M., Gribovszki, K., 2015a. Combined magnetotelluric and petrologic constrains for the nature of the magma storage system beneath the Late Pleistocene Ciomadul volcano (SE Carpathians). J. Volcanol. Geotherm. Res. 290, 82–96. Harangi, S.z., Lukács, R., Schmitt, A.K., Dunkl, I., Molnár, K., Kiss, B., Seghedi, I., Novothny, A., Molnár, M., 2015b. Constraints on the timing of Quaternary volcanism and duration of magma residence at Ciomadul volcano, east-central Europe, from combined U-Th/He and U-Th zircon geochronology. J. Volcanol. Geotherm. Res. 301, 66–80. Hernandez, P.A., Notsu, K., Okada, H., Mori, T., Sato, M., Barahona, F., Perez, N., 2006. Diffuse emission of CO2 from Showa-Shinza, Hokkaido, Japan: a sign of volcanic dome degassing. Pure Appl. Geophys. 163:869–881. http://dx.doi.org/10.1007/s00024006-0098-x. Hernández, P.A., Pérez, N.M., Fridriksson, T., Egbert, J., Ilyinskaya, E., Thárhallsson, A., Ívarsson, G., Gíslason, G., Gunnarsson, I., Jónsson, B., Padrón, E., Melián, G., Mori, T., Notsu, K., 2012. Diffuse volcanic degassing and thermal energy release from Hengill volcanic system, Iceland. Bull. Volcanol. 74:2435–2448. http://dx.doi.org/10.1007/ s00445-012-0673-2. Hernández, P.A., Salazar, J.M., Shimoike, Y., Mori, T., Notsu, K., Pérez, N.M., 2001. Diffuse emission of CO2 from Miyakejima volcano, Japan. Chem. Geol. 177, 175–185. Hoefs, J., 2009. Stable Isotope Geochemistry. Springer. Ianovici, V., Rădulescu, D., Vasilescu, A., 1968. Harta geologică 1:200.000, Foaia Odorhei, Comitetul de Stat al Geologiei, București. Inguaggiato, S., Mazot, A., Diliberto, I., Inguaggiato, C., Madonia, P., Rouwet, D., Vita, F., 2012. Total CO2 output from Vulcano island (Aeolian Islands, Italy). Geochem. Geophys. Geosyst. 13, Q02012. http://dx.doi.org/10.1029/2011GC003920. Ismail-Zadeh, A., Matenco, L., Radulian, M., Cloetingh, S., Panza, S., 2012. Geodynamics and intermediate-depth seismicity in Vrancea (the south-eastern Carpathians): current state-of-the art. Tectonophysics 530–531:50–79. http://dx.doi.org/10.1016/j.tecto. 2012.01.016. Issa, T., Ohba, B., Tchamabé, C., Padron, E., Hernandez, P., Takem Eneke, E.G., Barrancos, J., Sighomnoun, D., Ooki, S., Nmamdjou, S., Kusakabe, M., Yoshida, Y., Dionis, S., 2014. Gas emission from diffuse degassing structures (DDS) of the Cameroon volcanic line (CVL): implications for the prevention of CO2 related hazards. J. Volcanol. Geotherm. Res. 283, 82–93. James, E.R., Manga, M., Rose, T.P., 1999. CO2 degassing in the Oregon cascades. Geology 27 (9):823–826. http://dx.doi.org/10.1130/0091-7613. Jánosi, C.s., Berszán, J., Péter, E., 2013. The Mineral Baths of Szeklerland, Tipographic, Miercurea Ciuc. 215. Karátson, D., Timár, G., 2005. Comparative volumetric calculations of two segments of the Carpathian Neogene/Quaternary volcanic chain using SRTM elevation data: implications for erosion and magma output rates. Z. Geomorphol. 140, 19–35 (Suppementary Issues). Karátson, D., Telbisz, T., Sz, Harangi, Magyari, E., Dunkl, I., Kiss, B., Cs, Jánosi, Veres, D., Braun, M., Fodor, E., Bíró, T., Kósik, S., Von Eynatten, H., Lin, D., 2013. Morphomentrical and geochronological constraints on the youngest eruptive activity in East-Central Europe at the Ciomadul (Csomád) lava dome complex, East Carpathians. J. Volcanol. Geotherm. Res. 255, 43–56. Karátson, D., Wulf, S., Veres, D., Magyari, E., Gertisser, R., Timár-Gabor, A., Novothny, A., Telbisz, T., Szalai, Z., Anechitei-Deacu, V., Appelt, O., Bormann, M., Cs, Jánosi, Hubay, K., Schabitz, F., 2016. The latest explosive eruptions of Ciomadul (Csomád) volcano, East Carpathians - a tephrostratigrapic approach for the 51–29 ka BP time interval. J. Volcanol. Geotherm. Res. 319, 29–51. Kämpf, H., Brauer, K., Schumann, J., Hahne, K., Strauch, G., 2013. CO2 discharge in an active, non-volcanic continental rift area (Czech Republic): characterization (δ13C, 3He/4He) and quantification of diffuse and vent CO2 emissions. Chem. Geol. 339, 71–83. Keating, E.H., Fessenden, J., Kanjorski, N., Koning, D.J., Pawar, R., 2010. The impact of CO2 on shallow groundwater chemistry: observations at a natural analog site and implications for carbon sequestration. Environ. Earth Sci. 60, 521–536. Kis, B.M., Ionescu, A., Harangi, S.z., Palcsu, P., Etiope, G., Baciu, C., 2016. Gas geochemical survey of long dormant Ciomadul volcano (South Harghita Mts., Romania): constraints on the flux and origin of fluids. Geophys. Res. Abstr. 18 (EGU2016–9576). Kiss, B., Harangi, Sz, Ntaflos, T., Mason, P., Pál-Molnár, E., 2014. Amphibole perspective to unravel pre-eruptive processes and conditions in volcanic plumbing systems beneath intermediate arc volcanoes: a case study from Ciomadul volcano (SE Carpathians). Contrib. Mineral. Petrol. 167:986. http://dx.doi.org/10.1007/s00410-014-0986-6. Koepenick, K.W., Brantley, S.L., Thompson, J.M., Rowe, G.L., Nyblade, A.A., Moshy, C., 1996. Volatile emissions from the crater and flank of Oldoinyo Lengai volcano, Tanzania. J. Geophys. Res. Solid Earth 101 (6), 13819–13830. Lee, H., Muirhead, J., Fischer, T.P., Ebinger, C.J., Kattenhorn, S.A., Sharp, Z.D., Kianji, G., 2016. Massive and prolonged deep carbon emissions associated with continental rifting. Nat. Geosci. 9:145–149. http://dx.doi.org/10.1038/ngeo2622. Lewicki, J.L., Brantley, S.L., 2000. CO2 degassing along the San Andreas fault, Parkfield. California. Geophys. Res. Lett. 27 (1), 5–8. Lewicki, J.L., Bergfeld, D., Cardellini, C., Chiodini, G., Granieri, D., Varley, N., Werner, C., 2005. Comparative soil CO2 flux and geostatistical estimation methods on Masaya volcano, Nicaragua. Bull. Volcanol. 68:79–90. http://dx.doi.org/10.1007/s00445-0050423-9. Lewicki, J.L., Connor, C., St-Amand, K., Stix, J., Spinner, W., 2003. Self-potential, soil CO2 and temperature on Masaya volcano, Nicaragua. Geophys. Res. Lett. 30:15–1817. http://dx.doi.org/10.1029/2003GL017731.

129

Lewicki, J.L., Hilley, G.E., Dobeck, L., McLing, T.L., Kennedy, B.M., Bill, M., Marino, B.D.V., 2013. Geologic CO2 input into groundwater and the atmosphere, Soda Springs, ID, USA. Chem. Geol. 339, 61–70. Marty, B., Tolstikhin, I.N., 1998. CO2 fluxes from mid-ocean ridges, arcs and plumes. Chem. Geol. 145, 233–248. Macpherson, G.L., 2009. CO2 distribution in groundwater and the impact of groundwater extraction on the global C cycle. Chem. Geol. 264, 328–336. Marrero, R., López, D.L., Hernández, P.A., Pérez, N.M., 2008. Carbon dioxide dis-charged through the Las Cañadas Aquifer, Tenerife, Canary Islands. Pure Appl. Geophys. 165: 147–172. http://dx.doi.org/10.1007/s00024-007-0287-3. Mațenco, L., Bertotti, G., 2000. Tertiary tectonic evolution of the external East Carpthians (Romania). Tectonophysics 316, 255–286. Mațenco, L., Bertotti, G., Leever, K., Cloething, S., Schmidt, S.M., Tărăpoancă, M., Dinu, C., 2007. Large-scale deformation in a locked collisional boundary: interplay between subsidence and uplift, intraphase stress, and inherited litospheric structure in the large stage of the SE Carpathian evolution. Tectonics 26. http://dx.doi.org/10.1029/ 2006TC001951 (Art. No TC4011). Mitrofan, H., 2000. Tusnad-Bai - a geothermal system associated with the most recent volcanic eruption in Romania. Proceedings Worlds Geothermal Congress, KyushuTohoku, Japan, pp. 1147–1452. Mörner, N.A., Etiope, G., 2002. Carbon degassing from the litosphere. Glob. Planet. Chang. 33, 185–203. Nakadai, T., Yokozawa, M., Ikeda, H., Koizumi, H., 2002. Diurnal changes of carbon dioxide flux from bare soil in agricultural field in Japan. Appl. Soil Ecol. 19, 161–171. Newell, D.L., Crossey, L.J., Karlstrom, K.E., Fischer, T.P., Hilton, D.R., 2005. Continental-scale links between the mantle and groundwater systems of the western United States: Evidence from travertinte springs and regional He isotope data. GSA Today 15 (12): 4–10. http://dx.doi.org/10.1130/1052-5173(2005)015. Nisi, B., Vaselli, O., Tassi, F., de Elio, J., Ortega, M., Caballero, J., Rappuoli, D., Mazadiego, L.F., 2014. Origin of the gases released from the Aqua Passante and Ermeta wells (Mt. Amiata, central Italy) and pissible environmental implications for their closure. Ann. Geophys. 57 (4), S0438. http://dx.doi.org/10.4401/ag-6584. Nisi, B., Vaselli, O., Marchev, P., Tassi, F., 2013. Diffuse CO2 Soil Flux Measurements at the Youngest Volcanic System in Bulgaria: The 12.2 Ma old Kozhuh Cryptodome. 25, 1–2 pp. 169–177. Norman, J.M., Garcia, R., Verma, S.B., 1992. Soil surface CO2 fluxes and the carbon budget of grassland. J. Geophys. Res. 97 (D17), 18,845–18,853. Notsu, K., Mori, T., Do Vale, S.C., Kagi, H., Ito, T., 2006. Monitoring quiescent volcanoes by diffuse CO2 degassing: case study of Mt. Fuji, Japan. Pure Appl. Geophys. 163: 825–835. http://dx.doi.org/10.1007/s00024-006-0051-0. Notsu, K., Sugiyama, K., Hosoe, M., Uemura, A., Shimoike, Y., Tsunomori, F., Sum-ino, H., Yamamoto, J., Mori, T., Hernández, P.A., 2005. Diffuse CO2 efflux from Iwojima volcano, Izu–Ogasawara arc, Japan. J. Volcanol. Geotherm. Res. 139, 147–161. Oppenheimer, C., Fischer, T., Scaillet, B., 2014. Volcanic degassing: process and impact. In: Holland, H.D., Turekian, K.K. (Eds.), Treatise on Geochemistry, second ed. 4. Elsevier, pp. 111–179. Orbán, B., 1868. A Székelyföld leírása, Budapest. Padrón, E., Hernández, P.A., Toulkeridis, T., Pérez, N.M., Marrero, R., Melián, G., Vir-gili, G., Notsu, K., 2008. Diffuse CO2 emission rate from Pululahua and the lake-filled Cuicochacalderas, Ecuador. J. Volcanol. Geotherm. Res. 176, 163–169. Paz, J.M., Inguaggiato, S., Taran, Y., Vita, F., Pecoraino, G., 2016. Carbon dioxide emissions from Specchio di Venere, Pantelleria, Italy. Bull. Volcanol. 78:29. http://dx.doi.org/10. 1007/s0045-016-1023-6. Pecoraino, G., Brusca, L., D'Alessandro, W., Giammanco, S., Inguaggiato, S., Longo, M., 2005. Total CO2 output from Ischia Island volcano (Italy). Geochem. J. 39, 451–458. Pécskay, Z., Lexa, J., Szakács, A., Seghedi, I., Balogh, K., Konecny, V., Zelenka, T., Kovacs, M., Póka, T., Fülöp, A., Márton, E., Panaiotu, C., Cvetkovic, V., 2006. Geochronology of Neogene magmatism in the Carpathian arc and intra-Carpathian area. Geol. Carpath. 57 (6), 511–530. Pedone, M., Viveiros, F., Aiuppa, A., Giudice, G., Grassa, F., Gagliano, A.L., Francofonte, V., Ferreira, T., 2015. Total (fumarolic+diffuse soil) CO2 output from Furnas volcano. Earth Planets Space 67:174. http://dx.doi.org/10.1186/s40623-015-0345-5. Pizzino, L., Galli, G., Mancini, C., Quattrocchi, F., Scarlato, P., 2002. Natural gas hazard (CO2, 222Rn) within a quiescent volcanic region and its relations with tectonics: the case of the Ciampino-Marino Area, Alban Hills volcano, Italy. Nat. Hazards 27, 257–281. Popa, M., Radulian, M., Szakács, A., Seghedi, I., Zaharia, B., 2012. New seismic and tomography data inthe southern part of the Harghita Mountains (Romania, southeastern Carpathians): connection with recent volcanic activity. Pure Appl. Geophys. 169, 1557–1573. Raich, J.W., Schlesinger, W.H., 1992. The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus 44B, 81–99. Raich, J.W., Tufekcioglu, A., 2000. Vegetation and soil respiration: correlations and controls. Biogeochemistry 48 (1), 71–90. Rogie, J.D., Kerrick, D.M., Chiodini, G., Frondini, F., 2000. Flux measurements on nonvolcanic CO2 emissions from some vents in central Italy. J. Geophys. Res. 105 (B4), 8435–8445. Rogie, J.D., Kerrick, D.M., Sorey, M.L., Chiodini, G., Galloway, D.L., 2001. Dynamics of carbon dioxide emission at Mammoth Mountain, California. Earth Planet. Sci. Lett. 188, 535–541. Sano, Y., Kagoshima, T., Takahata, N., Nishio, Y., Roulleau, E., Pinti, D., Fischer, T.P., 2015. Ten-year helium anomaly prior to the 2014 Mt. Ontake eruption. Sci. Rep. 5:13069. http://dx.doi.org/10.1038/srep13069. Schipek, M., Sieland, D., Steinbruckner, D., Ponepal, K., Bauer, K., Merkel, B., 2013. CO2 fluxes in the submarine hydrothermal system of Panarea. Goldschmidt abstracts 2013. Mineral. Mag. 77:2154. http://dx.doi.org/10.1180/minmag.2013.077.5.19.

130


Shimoike, Y., Kazahaya, K., Shinohara, H., 2002. Soil gas emission of volcanic CO2 at Satsuma–Iwojima volcano, Japan. Earth Planets Space 54, 239–247. Shinohara, H., 2013. Volatile flux from subduction zone volcanoes: insights from a detailed evaluation of the fluxes from volcanoes in Japan. J. Volcanol. Geotherm. Res. 268, 46–63. Sinclair, A.J., 1974. Selection of threshold values in geochemical data using probability graphs. J. Geochem. Explor. 3, 129–149. Solcanu, M., 2015. Stratigraphic and tectonic data on the Cretaceous Flysch in the Northern Ciuc Mountains (Eastern Carpathians, Romania). Acta Palaeontol. Romaniae 11 (1), 9–24. Soligo, M., Tuccimei, P., Giordano, G., Funicello, R., De Rita, D., 2003. New U-series dating of a carbonate level underlying the Peperino Albano phreatomagmatic ignimbrite (Colli Albani, Italy). Il Quaternario-Special Volume INQUA. Italian J. Quaternary Sci. 16, 115–120. Sorey, M.L., Evans, W.C., Kennedy, B.M., Farrar, C.D., Hainsworth, L.J., Hausback, B., 1998. Carbon dioxide and helium emissions from a reservoir of magmatic gas beneath Mammoth Mountain, California. J. Geophys. Res. Solid Earth 103 (7):15303–15323. http://dx.doi.org/10.1029/98JB01389. Szakács, A., Seghedi, I., Pécskay, Z., 1993. Pecularities of South Harghita Mts. as terminal segment of the Carpathian Neogene to Quaternary volcanic chain. Rev. Roum. Géol 37, 21–36. Szakács, A., Seghedi, I., 1995. The Călimani-Gurghiu-Harghita volcanic chain, East Carpathians, Romania: volcanological features. Acta Volcanol. 7, 145–153. Seghedi, I., Matenco, L., Downes, H., Mason, P., Szakács, A., Pécskay, Z., 2011. Tectonic significance of changes in post-subduction Pliocene-Quaternary magmatism in the south east part of the Caprathian-Pannonian Region. Tectonophysics 502, 146–157. Szakács, A., Seghedi, I., 2013. The relevance of volcanic hazard in Romania: is there any? Enviroon. Eng. Manag. J. 12, 125–135. Szakács, A., Seghedi, I., Pécskay, Z., 2002. The most recent volcanism in the Carpathian Pannonian Region. Is there any volcanic hazard? Geol. Carpath. 193–194. Szakács, A., Seghedi, I., Pécskay, Z., Mirea, V., 2015. Eruptive history of a low-frequency and low-output rate Pleistocene volcano, Ciomadul, South Harghita Mts., Romania. Bull. Volcanol. 77:12. http://dx.doi.org/10.1007/s00445-014-0894-7. Tassi, F., Nisi, B., Cardellini, C., Capecchiacci, F., Donnini, M., Vaselli, O., Avino, R., Chiodini, G., 2013. Diffuse soil emission of hydrothermal gases (CO2, CH4 and C6H6) at Solfatara crater (Campi Flegrei, southern Italy). Appl. Geochem. 35, 142–153.

Túri, M., Palcsu, L., Papp, L., Horvath, A., Futó, I., Molnár, M., Rinyu, L., Janovics, R., Braun, M., Hubay, K., Kis, B.M., Koltai, G., 2016. Isotope characteristics of the water and sediment in volcanic lake Saint Ana, East-Carpathians, Romania, Carpathian. J. Earth Environ. Sci. 11 (2), 475–484. Vaselli, O., Minissale, A., Tassi, F., Magro, G., Seghedi, I., Ioane, D., Szakács, A., 2002. A geochemical traverse across the Eastern Carpathians (Romania): constraints on the origin and evolution of the mineral waters and gas discharge. Chem. Geol. 182, 637–654. Vinkler, A.P., Sz, Harangi, Ntaflos, T., Szakács, A., 2007. Petrology and geochemistry of pumices from the Ciomadul volcano (Eastern Carpathians)-implications for petrogenetic processes (in Hungarian with an English abstract). Földtani Közlöny 137 (1), 103–128. Viveiros, F., Gaspar, J.L., Ferreira, T., Silva, C., 2016. Hazardous indoor CO2 concentrations in volcanic environments. Environ. Pollut. 214, 776–786. Viveiros, F., Cardellini, C., Ferreira, T., Caliro, S., Chiodini, G., Silva, C., 2010. Soil CO2 emissions at Furnas volcano, Sao Miguel Islands, Azores archipelago: volcano monitoring perspectives, geomorphologic studies and land use planning application. J. Geophys. Res. 115, B12208. http://dx.doi.org/10.1029/2010JB007555. Wagner, G.A., Gögen, K., Jonckhere, R., Wagner, I., Woda, C., 2002. Dating of Quaternary volcanoes Komorní hůrka (Kammerbühl) and Železná hůrka (Eisenbühl), Czech Republic, by TL, ESR, alpha-recoil and fission track chronomertry. Z. Geol. Wiss. 30, 191–200. Weinlich, F.H., 2014. Carbon dioxide controlled earthquake distribution pattern in the NW Bohemian swarm earthquake region, western Eger Rift, Czech Republic-gas migration in the crystalline basement. Geofluids 14, 143–159. Wen, H., Yang, T.F., Lan, T.F., Lee, H., Lin, C., Sano, Y., Chen, C., 2016. Soil CO2 flux in hydrothermal areas of the Tatun Volcano Group, Northern Taiwan. J. Volcanol. Geotherm. Res. 321, 114–124. Wenzel, F., Lorenz, F.P., Sperner, B., Oncescu, M.C., 1999. Seismotectonics of the Romanian Vrancea Area. In: Wenzel, F., Lungu, D., Novak, O. (Eds.), Vrancea Earthquakes: Tectonics, Hazard and Risk Mitigation. 15-25. Springer Netherlands. Werner, C., Hurwitz, S., Evans, W.C., Lowenstern, J.B., Bergfeld, D., Heasler, H., Jaworowski, C., Hunt, A., 2008. Volatile emissions and gas geochemistry of Hot Spring Basin, Yellowstone National Park, USA. J. Volcanol. Geotherm. Res. 178, 751–762.