Displays

Continental rifting has been linked to the thinning and destruction of cratonic lithospheres and to the release of enough CO₂ to impact the global climate [1]. This fundamental plate tectonic process facilitates the infiltration and/or mobilisation of small-volume carbonated melts, which interact with mantle peridotite to form wehrlite through the reaction: enstatite + CO₃^2- (melt) = forsterite + diopside + CO₂ (vapour) [2]. An analysis of the literature reveals that wehrlites are common in shallow mantle lithosphere in disrupted craton settings affected by either extension or subduction, and they have been linked to agents ranging from carbonatites to basanites [e.g. 3,4]. Conversely, the low abundance of wehrlitic diamond and garnet in cratonic mantle xenoliths (as opposed to lherzolitic or harzburgitic) indicate that wehrlitisation is not an important process at depths >~120 km. This may be due to the presence of a dominantly reducing lithosphere, which favours diamond precipitation or dissolution during reaction with carbonated silicate melts, depending on carbon saturation. Based on the relationship between wehrlite and small-volume carbonated melts, we suggest that wehrlite-bearing xenoliths can be used to monitor CO₂ mobility through the shallow continental lithosphere. Assuming a depleted protolith, typically harzburgite at shallow lithospheric depth, the amount of newly-added cpx can be estimated and related to CO₂ in the melt volume based on the above reaction. Considering the proportion of wehrlite in the xenolith population, an estimate of the total CO₂ transported out of the shallow lithosphere can be made. For example, peridotite xenoliths from Liaoyuan in the reactivated northeastern North China craton sample the mantle beneath the mid-Cretaceous Tan Lu Fault Belt (TLFB), which is even vaster in size (5000 x 800-1000 km) than the EAR, the latter linked to degassing of 28 to 34 Mt C/yr over 40 Ma [1]. If wehrlitisation affected only a 10 km depth interval over a similar time, 23 Mt C/yr has passed through the TLFB, possibly contributing to the mid-Cretaceous greenhouse climate. Thus, wehrlites reveal the hidden carbon cycle in lithospheric provinces where CO₂-rich melts are not necessarily observed at the surface.

[1] Foley and Fischer 2017 Nature Geosci 10; [2] Yaxley et al. 1998 J Petrol 39; [3] Aulbach et al. J Petrol 2017 58; [4] Lin et al. subm. J Geophys Res

How to cite: Aulbach, S., Lin, A.-B., Weiss, Y., and Yaxley, G.: Using wehrlites to monitor the passage of CO2-bearing melts in the shallow lithosphere, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8485, https://doi.org/10.5194/egusphere-egu2020-8485, 2020.

Over the last few decades, monitoring of soil CO₂ efflux has been widely used in different scientific disciplines like volcanic and seismic hazard assessment, carbon capture and sequestration, geothermal well integrity, and others. We installed a comprehensive LICOR LI-8150 monitoring system on the Los Humeros normal fault, one of the major structures in the geothermal production field. Over a five-months period, seven accumulation chambers measured CO₂ efflux every hour in combination with an on-site meteorological station recording air temperature, air humidity, barometric pressure, precipitation, wind speed, and wind direction. Seismic activity was recorded simultaneously by a seismic array of 42 stations distributed across the volcanic complex, which identified both, high frequency, volcano tectonic (>10 Hz) and low frequency, long-period events (1-8 Hz). Furthermore, monthly geothermal production and re-injection data are available. Our study aims to (1) characterize significant temporal variations of soil CO₂ efflux, (2) assess the effect of environmental parameters, (3) analyze the possible influence of natural seismicity and geothermal exploitation (production/re-injection) on CO₂ degassing rates. The latter aspect plays an important role to better understand the hydraulic connection and communication between subsurface and surface along structural discontinuities in the volcanic-geothermal system.

How to cite: Jentsch, A., Düsing, W., and Jolie, E.: Continuous monitoring of fault-controlled CO2 degassing in the Los Humeros Volcanic Complex, Mexico, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21937, https://doi.org/10.5194/egusphere-egu2020-21937, 2020.

The Ciomadul volcano is the youngest volcano (32 ka) built by the Neogene volcanism in the Carpathian-Pannonian Region. This volcanic area is characterized by intense gas emissions (Kis et al., 2017) (CO₂, CH₄, H₂S) in the form of bubbling pools, mofettes and mineral water springs. The isotopic compositions of carbon, ¹³C_CO2 up to -3‰ VPDB and helium up to 3.1 Ra suggest magmatic origin of the gas up to 80% (Kis et al., 2019).

Although the volcano seems to be inactive, several features, petrologic and geophysical studies suggest that melt-bearing magmatic body could still exist beneath the volcano (Harangi et al., 2015). Moreover the geodynamic system is characterized by frequent earthquakes with magnitude up to 7 at Vrancea area, close to the CO₂-rich gas emissions of Ciomadul and the neighbouring areas.

In 2015 we started the monitoring of the helium isotopic ratios of Ciomadul to chech the possible relationship with seismicity. Our results show that in several cases the helium isotopic ratios increase at a seismic event with magnitude between 4 and 5.8 suggesting a relationship between the two phenomena.

Harangi, Sz., Lukács, R., Schmitt, A.K., Dunkl, I., Molnár, K., Kiss, B., Seghedi, I., Á. Novothny, Molnár, M. 2015, 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, Journal of Volcanology and Geothermal Research, 301, 66-80

Kis, B.M., Ionescu, A., Cardellini, C., Harangi, Sz., Baciu, C., Caracausi, A; Viveiros, F. 2017, Quantification of carbon dioxide emissions of Ciomadul, the youngest volcano of the Carpathian-Pannonian Region (Eastern-Central Europe, Romania), Journal of Volcanology and Geothermal Research, 341, 119–130

Kis, B.M., Caracausi, A., Palcsu, L., Baciu, C., Ionescu, A., Futó, I., Sciarra, A., Harangi, Sz. 2019, Noble gas and carbon isotope systematic at the seemingly inactive Ciomadul volcano (Eastern-Central Europe, Romania, Geochemistry, Geophysics, Geosystems, 20, 6, 3019–3043

This research belongs to the scientific project supported by the OTKA, K116528 (Hungarian National Research Fund), the EU and Hungary, co-financed by the European Regional Development Fund in the project GINOP-2.3.2-15-2016-00009 ‘ICER’ and the Deep Carbon Observatory.

How to cite: Kis, B.-M., Harangi, S., Palcsu, L., and Hegyeli, B.: Noble gas monitoring at the seemingly inactive Ciomadul volcano, Eastern Carpathians, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-869, https://doi.org/10.5194/egusphere-egu2020-869, 2020.

Tenerife (2034 km²), the largest island of the Canarian archipelago, is characterized by three volcanic rifts oriented NW-SE, NE-SW and N-S with a central volcanic complex, Las Cañadas Caldera, hosting Teide-Pico Viejo volcanoes. The North West volcanic Rift Zone (NWRZ, 72 km²) of Tenerife is one of the youngest and most active volcanic systems of the island, where two historical eruptions have occurred: Arenas Negras in 1706 and Chinyero in 1909. Diffuse degassing studies has become an important volcanic surveillance tool at those volcanic areas where visible manifestations of volcanic gases are absent, as in the case of NWRZ. Mapping soil gas emission along volcanic structures can provide a better understanding of the processes occurring at depth and allows monitoring the spatial distribution, magnitude and temporal evolution of the surface gas emissions. The geochemical properties of He, minimize the interaction of this noble gas on its movement toward the earth’s surface, and make this gas an almost ideal geochemical indicator of changes occurring in the magmatic plumbing system of the volcano (Padrón et al., 2013, Geology 41(5):539–542). Since 2014, surface He emission surveys have been performed once a year as an additional geochemical tool to monitor the volcanic activity of NWRZ. At 345 sampling sites soil gas samples were collected at 40 cm depth and analyzed for He concentration within 24 hours by means of QMS, model Pfeiffer Omnistar 422. The soil helium concentration data were used to estimate the diffusive helium flux at each point, to construct spatial distribution maps by sequential Gaussian simulation and then to estimate the total helium emission in the NWRZ. Helium emission ranged between non-detected values up to 7.2 mgm^-2d^-1, and the emission rate of the entire area was in the range ~1 – 45 kg d^-1. An increasing trend was observed in the period 2016-2018, showing a good temporal coincidence with a significant increase in seismic activity recorded in Tenerife. The promising results observed in the NWRZ and in other volcanic systems (Padrón et al., 2013) indicate that soil helium emission monitoring could be an excellent early warning geochemical precursory signal for future volcanic unrest.

How to cite: Recio, G., Dunn, E., McInally, Y., Pérez, N. M., Amonte, C., Alonso, M., Padrón, E., Asensio-Ramos, M., and Morales, F. A.: Diffuse He degassing monitoring of the Tenerife North-western Rift Zone (NWRZ) volcano, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11646, https://doi.org/10.5194/egusphere-egu2020-11646, 2020.

Some active volcanoes host thermal springs with ultra- (1<pH<2) and even hyper- (pH < 1) acidic waters with composition corresponding to a mixture of HCl and H2SO4 acids and with cations where Al and Fe are often the major components. Such springs sometimes are known as inferred drainages from active crater lakes (e.g., Rios Agrio at Poas and Copahue volcanoes). However, there are a number of acidic volcano-hydrothermal systems of Cl-SO4 composition at volcanoes without crater lakes.  At least ten groups of manifestation of this type are known for Kuril Islands. Several groups of acid volcanic springs including the famous Tamagawa springs are described in Japan.  Most of the acid Cl-SO4 volcano-hydrothermal systems are characteristic for island volcanoes, probably due to specific hydrological conditions of small volcanic islands. Maybe most known are coastal acid springs at Satsuma Iwojima volcano, Ryukyu arc, Japan. The accepted idea about the origin of such systems is scrubbing (dissolution) of magmatic HCl, HF and SO2 by groundwaters above magmatic conduits.  If so, the composition of acid springs must reflect the state of activity of a volcano. This review describes case histories that are known from the literature and from authors’ studies. Most of the volcanoes hosting acid systems show frequent phreatic activity. We show that  in contrast to crater lakes (Poas, Ruapehu, Copahue, White Island), acid springs on slopes of active volcanoes generally do not response on the preparing or ongoing volcanic eruptions. The aquifers and flow paths of the acid waters in volcanic edifices can be not associated with active conduits but with other degassing magmatic bodies and/or with deeper aquifers. One of the examples of such a complicated system is Ebeko volcano with Yuryevskye springs in Kuril Islands. These springs have a hydrochemical record since 1950s, and during this period Ebeko volcano had at least 10 strong phreatic eruptions.

How to cite: Taran, Y. and Kalacheva, E.: Ultra-acid volcanic waters: origin and response on volcanic activity. A review, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12242, https://doi.org/10.5194/egusphere-egu2020-12242, 2020.

Magma transfer in an open-conduit volcano is a complex process that is still open to debate and not entirely understood. For this reason, a multidisciplinary monitoring of active volcanoes is not only welcome, but also necessary for a correct comprehension of how volcanoes work. Mt. Etna is probably one of the best test sites for doing this, because of the large multidisciplinary monitoring network setup by the Osservatorio Etneo of Istituto Nazionale di Geofisica e Vulcanologia (INGV-OE), the high frequency of eruptions and the relatively easy access to most of its surface.
We present new data on integrated monitoring of volcanic tremor, plume sulphur dioxide (SO₂) flux and soil hydrogen (H₂) and carbon dioxide (CO₂) concentration from Mt. Etna. The RMS amplitude of volcanic tremor was measured by seismic stations at various distances from the summit craters, plume SO₂ flux was measured from nine stations around the volcano and soil gases were measured in a station located in a low-temperature (T ∼ 85 °C) fumarole field on the upper north side of the volcano.
During our monitoring period, we observed clear and marked anomalous changes in all parameters, with a nice temporal sequence that started with a soil CO₂ and SO₂ flux increase, followed a few days later by a soil H₂ spike-like increase and finally with sharp spike-like increases in RMS amplitude (about 24 h after the onset of the anomaly in H₂) at all seismic stations.
After the initial spikes, all parameters returned more or less slowly to their background levels. Geochemical data, however, showed persistence of slight anomalous degassing for some more weeks, even in the apparent absence of RMS amplitude triggers. This suggests that the conditions of slight instability in the degassing magma column inside the volcano conduits lasted for a long period, probably until return to some sort of balance with the “normal” pressure conditions.
The RMS amplitude increase accompanied the onset of strong Strombolian activity at the Northeast Crater, one of the four summit craters of Mt. Etna, which continued during the following period of moderate geochemical anomalies. This suggests a cause-effect relationship between the anomalies observed in all parameters and magma migration inside the central conduits of the volcano. Volcanic tremor is a well-established key parameter in the assessment of the probability of eruptive activity at Etna and it is actually used as a basis for a multistation system for detection of volcanic anomalies that has been developed by INGV-OE at Etna. Adding the information provided by our geochemical parameters gave us more solid support to this system, helping us understand better the mechanisms of magma migration inside of an active, open-conduit basaltic volcano.

How to cite: Falsaperla, S., Caltabiano, T., Donatucci, A., Giammanco, S., Langer, H., Messina, A., Salerno, G., Sortino, F., Spampinato, S., and Ferlito, C.: Integrated monitoring of soil gases, plume SO2 and volcanic tremor to detect impulsive magma transfer at Mt. Etna volcano (Italy), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14698, https://doi.org/10.5194/egusphere-egu2020-14698, 2020.

Taal Volcano produces powerful eruptions and is the largest volcanic threat to the Phillipines. Six of the 24 known eruptions since 1572 have resulted in fatalities, and today several million people live with a 20-km radius. Since 2008, our volcano research group has conducted a collaborative research program with Phillipine scientists on applied geochemistry for volcano monitoring. One of the outcomes of this collaborative research was to observed precursor signals to the January 2020 eruptive activity.

Significant temporal variations in diffuse CO₂ emission at the Taal Crater Lake (TLC) was observed across the ~12 years. Two periods are especially noteworthy. From March 2010 to March 2011 the diffuse CO₂ emission rate increased from 763 ± 18  to 4.670 ± 159 tons per day. This anomalous increase coincided with the occurrence of a volcano-seismic unrest characterized mainly by a significant increase in the frequency of volcanic earthquakes, which was interpreted as indicating a new magma intrusion (Arpa et al., 2013; Hernández et al., 2017). A second anomalous diffuse CO₂ degassing at the TCL, from 860 ± 42 to 3.858 ± 584 tons per day during the period October 2016 to November 2017, was observed.

In addition to the geochemical surveys of diffuse CO₂ emission from the TCL, an automatic geochemical station for continuous monitoring of soil CO₂ efflux at the northern sector of the Taal Volcano Island crater rim was installed on January 2016. Although short-temp fluctuations in the diffuse CO₂ emission time series have been partially driven by meteorological parameters, the major CO₂ efflux changes were not driven by such external fluctuations. The major long-term variation of the CO₂ emission was an increase trend of the moving average of soil CO₂ efflux measurements (168 values) in 2017. Since 14 March, 2017, the station measured a sharp increase of CO₂ emission from ~0.1 up to 1.1 kg m^-2 d^-1 in 9 hours and continued to show a sustained increase in time up to 2.9 kg m^-2 d^-1 in November 2017. These combined geochemical and geophysical observations are most simply explained by magma recharge to the system, and represent precursor signals to the January 2020 eruptive activity.

Taal Volcano Background
Taal Volcano is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Located on the southwestern part of Luzon Island, Taal consists of a 15-22-km prehistoric caldera, occupied by the Taal Lake and the active vent complex of Taal Volcano Island with its Crater Lake (TCL).

Arpa M. C. et al (2013). Geochemical evidence of magma intrusion inferred from diffuse CO₂ emissions and fumarole plume chemistry: the 2010–2011 volcanic unrest at Taal Volcano, Philippines. Bulletin of Volcanology,  DOI: 10.1007/s00445-013-0747-9.

Hernández P. A. et al (2017). The acid crater lake of Taal Volcano, Philippines: hydrogeochemical and hydroacoustic data related to the 2010–11 volcanic unrest. Geological Society, London, Special Publications, 437, DOI:10.1144/SP437.17

How to cite: Pérez, N. M., Melián, G. V., Hernández, P. A., Padrón, E., Padilla, G. D., Baldago, Ma. C., Barrancos, J., Rodríguez, F., Asensio-Ramos, M., Alonso, M., Arcilla, C., Lagmay, A. M., Rodríguez-Pérez, C., Amonte, C., Pankhurst, M. J., Calvo, D., and Solidum, R. U.: Diffuse CO2 degassing precursors of the January 2020 eruption of Taal volcano, Philippines, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19374, https://doi.org/10.5194/egusphere-egu2020-19374, 2020.

The southern margin of the Siberian craton, which experienced severe tectonic deformations in the Neoproterozoic-Cambrian and Jurassic, is currently a part of the Baikal seismic belt. In groundwater budget of the area, the main contribution is provided by the homogeneous South Baikal reservoir (SBR) with ²³⁴U/²³⁸U activity ratio (AR) 1.95–1.99 and U concentration 0.44–0.46 µg/L. Lateral penetration of the SBR water from the hydrostatically loaded deeper part of the lake (1000 m and more) to the adjacent Siberian craton area is promoted by gentle ruptures of the Angara thrust fault and sub-vertical shear fissures of the Main Sayan suture zone. In order to predict the time and place of a strong earthquake, AR are determined in groundwater from craton basement and sedimentary cover in an area from Lake Baikal to Irkutsk. AR values associated with deformational (Cherdyntsev–Chalov) effect vary from 1.0 to 3.5. Chemical impacts in evaporates result in AR values as high as 16. Data of a 7-year monitoring show key points in AR variations that might be used for prediction of a future strong earthquake.

This work is supported by the RSF grant 18-77-10027.

How to cite: Rasskazov, S., Chebykin, E., Ilyasova, A., and Chuvashova, I.: Hydro-isotopic (234U/238U) zoning of groundwaters in the seismically active southern margin of the Siberian craton, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12963, https://doi.org/10.5194/egusphere-egu2020-12963, 2020.

The 2017 M_W 5.5 Pohang earthquakes, which were known as triggered by enhanced geothermal system (EGS) stimulations, had significant effects on the groundwater system. This study aimed to identify the hydrogeochemical anomalies and to understand the response mechanisms of groundwater system to the earthquake. For this, the environmental isotopes (²²²Rn, Sr, ²H, and ¹⁸O), major ions, and time-series data (groundwater level, temperature, and electrical conductivity) were analyzed. Principal component analysis (PCA) was also employed. The results from time-series data showed the anomalies in the groundwater wells located near the epicenter. The hydrochemical parameters including stable isotopes data of ²H and ¹⁸O showed the different change patterns among groundwater wells before/after the earthquakes, which were related to the distance from epicenter, faults, and seawater. The environmental isotopes, radon and strontium, suggested the possible mechanisms underlying the effects of earthquakes by spatial distributions, such as seawater intrusion, water-rock interactions, shallow and deep aquifer mixing, deep fluid upwelling, and bedrock fracture opening. With this, the main cluster of PCA results was also distributed along these isotope concentration gradients.

Our findings proved the usefulness of environmental isotopes and hydrogeochemical parameters to understand the earthquake-related changes in groundwater system. These studied parameters and the adopted methods would be positively applied for other earthquake zones.

How to cite: Kim, J. and Lee, K.-K.: Hydrogeochemical anomalies associated with the 2017 MW 5.5 Pohang earthquake in South Korea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2786, https://doi.org/10.5194/egusphere-egu2020-2786, 2020.

The Dilatancy Diffusion model of Scholz et al (1973) is a model describing saturated rocks behaviour under differential tectonic stress in time domain, and one of the first trial of earthquake precursory phenomena listing and explanation. After around 50 years, improvements, outline and structure of this however successful model are still a reference point of many researcher. The role of water has been explained only as a pressure transducer, acting on host rocks, during the various stages of dilatancy diffusion, acting as a pressure cycle.

Theme of present model is the water active chemical role in DD.

A temperature pressure diagram of water aggregation state could be drawn as a section of the earth crust. Assuming that the brittle ductile transition line could be localised even close to 500 °C isotherm, most hypocentre are surely localised in liquid phase area, while some main shock localisation may fall even in water supercritical region.

I modelled the water isothermal behaviour in relation of most relevant variable acting on water in dilatancy diffusion: pressure. Pressure acting on water could drop drastically as soon as microcraks open. Then, water flow into newly created fractures, and, since tectonic load continues, pressure rise again, before main shock. In this pressure cycle, water chemical response, could be splitted into two diverse fields: liquid and supercritical, resulting however in a rock weakening.

• 1) Liquid. The entity of depressurisation makes the difference. According to Scholz et al (1973), and Brace et al (1966), the entity is high. It is a matter of water quantities and of volumetric geometry of microcracks. Ionic solubility depends slightly from pressure. Going into vapour phase is equal to a distillation process: when pressures rise again, this kind of water is extremely aggressive toward newly opened rock surfaces. If not, water could maintain most, not all, solute in. In every case, molecules like CO₂ and H₂ migrates away from water and, thanks to their characteristics (radius and electrostatic field), following the path of extremely little fissurations, normally secluded to water. Resulting water changes its chemical content.
• 2) Supercritical. Molecular structure of this aggregation state makes this fluid compressible. That is, its density varies highly with pressure. Solvent capability varies highly with density: supercritical water acquires polar solvent power with growing density. Solubility depends highly from pressure, with all consequences.

Subcritical crack growth. It is a common point of 1) and 2), and it could be a function of dissociation grade of water too. In an environment, with freshly created surfaces, quartz and silicates are subjected to a further weakening due to high dissociated water.

The integration of water chemistry in dilatation diffusion model is a needed upgrade and depict a situation in which, as soon as new crack creates, the chemical action of water can trigger a near irreversible process of rock weakening accelerating the main shock, since rock resistance could be lowered well below original breaking load.

How to cite: Calcara, M.: The Chemistry of Earthquakes: Chemical role of Water in Dilatancy Diffusion model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5482, https://doi.org/10.5194/egusphere-egu2020-5482, 2020.

Earthquakes are the main natural processes which are able to cause the strongest crustal perturbations in the world. Seismic events change crustal stress, both static and dynamic, in the co-seismic and post-seismic phases. In particular, hydrogeological and hydrogeochemical responses include: changes in water level, temperature, chemical composition, stream flow, and gas geochemistry. Among these parameters water level changes is the most recorded signal because of its fast acquisition and easy instrumentation. Depending on the involved mechanism, groundwater level variation is different. In particular, previous studies have highlighted permanent and transient signals which are characterized by step and spike changes both upward and/or downward. Only few studies have reported groundwater level variations induced by earthquakes that are very far away from the observation point and they are known as “teleseism”. In order to investigate relationship between groundwater properties and seismic cycle, since July 2014 we installed a multiparameter probe in a 100 m deep groundwater well (PF60.3) in Central Apennines (Central Italy). This monitoring well is part of a more complex monitored test site developed for this aim and it has recorded already hydrogeochemical anomalies related to Amatrice-Norcia 2016-2017 seismic sequence. The occurrence of the strongest earthquakes in the world (≈M_w>7.5), from the well probe installation (July 2014) until January 2020, has caused significant changes in groundwater level data. We analysed groundwater level behaviour in relationship to the occurrence of all 218 seismic events with M_w>6.5. We identified 16 interactions, where groundwater level is characterized by an anomalous spike change both upward and/or downward. In particular, we observed a significant interaction between signals for all the strongest seismic events with a M_w≥7.6, except for those happened in Papua Nuova Guinea and for those with ipocenter depth greater than 150 kilometers. We also found some interactions for less strong seismic events (6.5<M_w<7.5) but closer to the monitoring site. Among the observed correlations, 5 are characterized by a M_w between 8 and 8.2 meanwhile the others have a M_w between 6.5 and 7.9. The ipocenter depths of the considered 16 events are within 100 km, except two events that are deeper. We calculated the maximum amplitude of the perturbation and its duration. In this study we present our results with the main aim of expanding our understanding about perturbations due to distant earthquakes in the upper crust and in particular the relative fluid migration.

How to cite: Barberio, M. D., Gori, F., Barbieri, M., Billi, A., Franchini, S., Petitta, M., and Doglioni, C.: First observation of multi-groundwater level responses to the strongest worldwide seismicity in Central Apennines (Central Italy)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5659, https://doi.org/10.5194/egusphere-egu2020-5659, 2020.

The Anninghe fault (ANHF) and the Zemuhe fault (ZMHF) with high level of seismic hazards in the China Seismic Experimental Site, located in southeastern of Tibet, are some of the most active faults in China. Measurement of the soil gas CO₂ has been conducted in three sites along the ANHF and the ZMHF for the first time. Totally, 394 sampling points along 15 profiles were measured. The fault locking degree of different segments of the ANHF and the ZMHF were inverted by the negative dislocation model using GPS velocity data  since 2013 to 2017. The measurements results show that the average and maximum value of CO₂ in the ZMHF is significantly higher than that in the ANHF. Soil gas CO₂ geochemistry yielded different spatial anomalous features, indicating the different properties and permeability of the faults. The inversion results reveal that the level of coupling including the locking depth and intensity along the southern segment of the ANHF was significantly larger than the northern segment of the ZMHF. Combining the CO₂ emission results, we concluded that the intensive locking of the segments reduced their permeability due to the self-sealing process, results in less gas to escape from the deep. Correspondingly, the creeping fault with low level of coupling can maintain high permeability which is more favorable to gas CO₂ migration.

How to cite: Li, Y., Yang, Y., and Chen, Z.: Soil gas CO2 emissions and fault locking along the Anninghe fault and the Zemuhe fault, in China Seismic Experimental Site, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7589, https://doi.org/10.5194/egusphere-egu2020-7589, 2020.

The aim of this study was to identify changes of trace element concentration in groundwater and test for coupling with seismic and volcanic activity in Iceland. Samples used in this study were collected between September 2010 and June 2018 from the HA-01 groundwater well in Hafralækur (Northern Iceland), south of the Tjörnes Fracture Zone (oblique transform zone), and near the Laxá and Skálfandafljót river valleys. The temperature of the groundwater from the HA-01 well is 71–76 °C, pH is ca. 10.2 (at ~ 25ºC), and the dissolved solid content is about 240 ppm, which is typical of low temperature geothermal groundwaters in inland areas of Iceland. The HA-01 well groundwater is also influenced by mixing between old ice age aquifer and younger aquifer groundwater. The same samples were previously analyzed for major element concentrations and isotopic ratios, with results - changes prior to seismic activity - being published in recent papers. The 495 earthquakes (Mw≥4.0, September 2010 to June 2018) considered in this study are from the USGS database. Twenty-two of these earthquakes occurred in the Tjörnes Fracture Zone with M_w between 4.1 and 5.5 whereas the remaining ones with M_w between 4 and 5.5 were related to the Bárðarbunga eruption in central Iceland, which began on 29 August 2014 and ended on 27 February 2015. Results of trace element analysis highlight characteristic variations in the temporal series related to the Bárðarbunga eruption (onset in August 2014) and to the 2018 seismic swarm that occurred in the Tjörnes Fracture Zone. In particular, a marked increase of Li, B, Ga, Mo and Rb and a slight increase of Sr and V were observed prior to and in connection with the onset of the Bárðarbunga eruption. Moreover, our results show a pre-seismic (2018 seismic swarm in the Tjörnes Fracture Zone) hydrogeochemical variability greater than the background variability. Despite the distance to the Bárðarbunga eruption site, GPS data from northern Iceland show a clear strain changes that are associated with the large dike intrusion that fed the eruption and are possibly correlated with the hydrogeochemical time series. Results from this study in Iceland show that the hydrogeochemical monitoring of volcanic and seismic areas is a promising method in the science of seismic and volcanic precursors.

How to cite: Franchini, S., Barberio, M. D., Barbieri, M., Billi, A., Boschetti, T., Jónsson, S., Petitta, M., Skelton, A., and Stockmann, G.: Hydrogeochemical changes in trace element concentrations in connection with earthquakes and a volcanic eruption in Iceland, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9403, https://doi.org/10.5194/egusphere-egu2020-9403, 2020.

The involvement of fluids in the earthquake cycle is a still open debate in the scientific community (e.g. Gratier et al., 2002). In the last years, new data from laboratory experiments and on-field discrete and continuous monitoring of soil gas, springs and gas vents were gathered worldwide (e.g. Martinelli, 2015; Nielsen et al., 2016). The aim of these studies was to better define the role of the observed fluid changes either as a trigger of earthquakes or as the co and post-seismic response to the transient (dynamic) and permanent (static) stress changes. This subject is particularly attractive in central and southern Apennines (Italy), where both huge water and CO₂ circulation at depth, occur (e.g Frondini et al., 2018). In this respect, the three long-lasting earthquake sequences that hit central Apennine in the last decades (1997, 2009 and 2016-2017, M_w up to 6.5) were accompanied by hydrological (increase or decrease in the spring discharges) and hydrochemical (variations in chemical composition, physico-chemical parameters) anomalies (e.g. Carro et al., 2005; Barberio et al., 2017; Petitta et al., 2018). Changes were observed mainly in the co and post-seismic phase and only a few pre-seismic signals were recorded. Temporal monitoring ranged from weeks to months, but higher sampling rates are needed to study crustal deformation processes (stress and volumetric strain) during the earthquake cycle. For example, since 2015 De Luca et al. (2016, 2018) are been performing high frequency (up to 20 samples/second) continuous monitoring of temperature, hydraulic pressure, and electrical conductivity in the Gran Sasso aquifer. They recorded unambiguous long-term (days to months) pre-Amatrice earthquake anomalies in both hydraulic pressure and electrical conductivity, related to its preparation stage.

In the light of the above, we decided to duplicate the equipment presently working in the Gran Sasso aquifer in a site with similar hydrological setting: the Venafro carbonate hydrostructure (Molise, Saroli et al., 2019). The site we chose is located in one of the most seismically active sectors of central-southern Apenninic belt, repeatedly hit in the past by large magnitude earthquakes and crossed by up to 20 km-long extensional fault systems (e.g. Galli & Naso, 2009). The main goals of our research are: i) measuring and understanding the dynamics of the carbonate aquifer, also through the analysis of rainfall, ii) deepening the relationships between aquifer behavior and earthquakes as well as to iii) widen the monitored areas.

Our experimental equipment includes a 3-channels 24-bit ADC set up for continuous local recording in groundwater (De Luca et al., 2016, 2018) in a horizontal borehole located in the drainage gallery “San Bartolomeo”, managed by Campania Aqueduct company. We started data acquisition in May 2019 by high-frequency continuous sampling (20 Hz for each channel) of physical parameters such as groundwater hydraulic pressure, temperature and electrical conductivity. We present some preliminary results (elaborated through a statistical approach) and possible explanations regarding the hydraulic pressure signals recorded before and during nearby (Mw 4.4, distance ~ 45 km) and regional (Albania, Mw 6.2, distance ~ 400 km) earthquakes, both occurred in November 2019.

How to cite: De Luca, G., Di Carlo, G., Frepoli, A., Moro, M., Pizzino, L., Saroli, M., Tallini, M., and Trionfera, B.: Continuous monitoring of physical parameters (temperature, electrical conductivity, water pressure) in a karst aquifer of central Italy (Venafro Mts., Molise): first results in a seismically active region, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11644, https://doi.org/10.5194/egusphere-egu2020-11644, 2020.

Geochemical features of the geothermal and mineral waters from Apuseni Mountains, Romania

Alin-Marius Nicula¹, Artur Ionescu^1,2, Cristian-Ioan Pop¹, Carmen Roba¹, Walter D’Alessandro³, Ferenc Lazar Forray⁴, Iancu Oraseanu⁵, Calin Baciu¹

¹Babes-Bolyai University, Faculty of Environmental Science and Engineering, Str. Fantanele nr. 30, 400294, Cluj-Napoca, Romania (marius_alin92@yahoo.com)

²University of Perugia, Department of Physics and Geology, Via A. Pascoli 06123, Perugia, Italy

³Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, Via Ugo la Malfa, 153,

90146 Palermo, Italy

⁴Department of Geology, Babes-Bolyai University, Kogalniceanu 1, 400084 Cluj-Napoca, Romania

⁵Romanian Association of Hydrogeologists, Bucuresti, Romania

The Apuseni Mountains are located in the western part of Romania and separate the Pannonian Basin from the Transylvanian Basin. These mountains are famous and intensely studied for their important non-ferrous metal resources. Few data were published about the geothermal potential of this area. More works have been dedicated to mineral waters, while the geothermal waters are only briefly described, without sufficient emphasis on them. The current research is focusing on the two categories, cold mineral and geothermal water in the Apuseni Mountains, compared to the surrounding areas, in order to better understand their genesis and the general context of the geothermalism in the study region. A preliminary survey of these waters was done in 2019 taking water and gas samples from 41 sources.

The pH varies between 6.00 and 9.02 and, the lowest values have been measured in the CO₂-rich waters of the Southern Apuseni Mountains. Water temperatures vary between 11.1 ^â—‹C and 81 ^â—‹C. In the southern part of the Apuseni Mountains, the geothermal waters are of the calcium bicarbonate type (Ca-HCO₃), while in the north-western part, the sodium bicarbonate type (Na-HCO₃) is more common. The water sources from the north-western part are close to the Pannonian Basin and show features comparable to the thermal waters of this basin. Conductivity values show significant variations between 142 and 2040 µS/cm, but regional homogeneities were observed. The highest concentration of bicarbonate was measured in one of the localities of the northern study area (BeiuÅŸ Depression - 3318.4 mg/L). The dissolved heavy metal concentrations (Zn, Pb, Cd, Cr, Ni, Cu, Fe) in the water samples were also measured. For all the investigated waters, the heavy metal content was low. The highest concentrations were recorded for Fe 342.90 µg/L and Zn 86.14 µg/L. The isotopic data (δ¹⁸O and δ²H) demonstrate the meteoric origin of the thermal waters.

Some springs and wells release free gases. The gas chromatographic analyses show the prevalence of N₂ and CO₂, with minor amounts of CH₄ in the water sources close to the Pannonian Basin. The isotope composition of Helium shows values between 0.9 and 2.18 R/Ra indicating a prevailing crustal source with a significant mantle component. In the case of δ¹³C-CO₂ the values range between -12.7 and -6.1 ‰ vs.V-PDB, indicating that the CO₂ originates possibly from a limestone source.

How to cite: Nicula, A.-M., Ionescu, A., Pop, C.-I., Roba, C., D’Alessandro, W., Forray, F. L., Orașeanu, I., and Baciu, C.: Geochemical features of the geothermal and mineral waters from Apuseni Mountains, Romania, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-583, https://doi.org/10.5194/egusphere-egu2020-583, 2020.

The Carpathian-Pannonian region was dominated by diverse volcanic activity for the last 20 million years, and even 1 million years ago there was precedent for active zones.  Although volcanic eruptions are very uncommon in the region today, however the frequent earthquakes in the Carpathian-bend, the numerous appearance and intense manifestation of gas-emissions in the southeastern areas of the region and many petrochemical and geochemical volcanologic studies as well, indicate that the area is likely not completely inactive. The gas emissions investigated by us may be directly related to these geodynamic processes [1].

In Romania, the Eastern Carpathian Neogene-Quaternary volcanic chain and it’s neighbouring zones contain most of the carbon dioxide rich gas emissions, which also occur in the form of natural mofettes, bubbling pools and springs. They can appear in frequently populated settlements more often in cellars, which puts the inhabitants in direct danger due the lack of information in the public knowledge.

The motivation of our work is to gather real time and in-situ information with the help of Multi-Gas instrument about the composition of the gas-emissions across the Eastern Carpathians and to create a high resolution geological map from the measured sites in the mentioned area above. Furthermore, we would like to clarify if there is any relation between the tectonic characteristics of the study area and the manifestation, concentration of gas-emissions.

In total, 205 gas emissions were investigated for their CO₂ (0-100%), CH₄ (0-7%) and H₂S (0-200 ppm) concentrations. The composition of the different gas-species varied according to the geological context. The CO₂ concentrations varied between 0.96 and 98.08 %. The highest values were measured in the the Quaternary volcanic area of Ciomad, and also in the neighbouring thrusted and folded area of the Carpathian Flysch which suggests a tectonic control over the appearance of the gas emissions.

The CH₄ concentrations ranged between 0.21 and 6.76% and were higher at hydrocarbon-prone areas, such as the sedimentary deposits of the Transylvanian Basin and Carpathian Flysch. In these cases the CO₂ concentrations were low (up to 4.6%).

The H₂S concentrations varied between 0.21 and 200 ppm, according to our knowledge, these are the first H₂S in-situ measurements in the gas emissions of the study area. The concentrations of H₂S were higher at the volcanic area of Ciomad, reaching values above the detection limit (~200 ppm) which are related to volcanic degassing.

In conclusion, based on the investigated sites, there is a spatial correlation between the appearance of mineral water springs, gas emissions on surface and the neighbouring tectonic structures. The Multi-Gas proved to be a useful tool in the in-situ investigation of gas emissions of the Eastern Carpathians, being efficient especially for the measurement of the H₂S concentrations that are very sensitive for oxidation processes.

Bibliography:

1.Kis B.M., Caracusi, A., Palcsu, L., Baciu, C., Ionescu, A., Futó, I., Sciarra, A., Harangi, Sz., Noble Gas and Carbon Isotope Systematics at the Seemingly Inactive Ciomadul Volcano (Eastern‐Central Europe, Romania): Evidence for Volcanic Degassing, Geochemistry, Geophysics, Geosystems, vol.20, issue 6, 2019, 3019-3043.

How to cite: Szalay, R., Kis, B.-M., Harangi, S., Palcsu, L., Bitetto, M., Aiuppa, A., and Imecs, Z.: Real time and in-situ analysis of the gas-emissions of the Eastern Carpathians: results and perspectives, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-849, https://doi.org/10.5194/egusphere-egu2020-849, 2020.

The South Sandwich Islands (SSI) are a chain of active volcanoes in the Southern Ocean and remain one of the most remote and enigmatic island arcs on Earth. The relatively recent development of the SSI over the past 20 million years has been closely linked with the formation of the Drake Passage, making this one of the youngest known volcanic arcs and therefore one of the most critical for understanding the early stages of arc geochemical evolution. Recent volcanic eruptions in the SSI have had significant impacts on local terrestrial and marine ecosystems, including some of the largest penguin colonies ever observed, through tephra deposition and from sustained volcanic degassing. Rare cloud-free satellite images over the last two decades have indicated that the summit of Mt Michael (Saunders) hosts a sustained lava lake, but until now these observations have not been ground-truthed by in-situ measurements. Long-term persistent passive outgassing at many of these volcanoes, even between eruptive phases, suggests that the SSI volcanic arc could be a significant source of volatiles to our atmosphere, and yet we lack any constraints on the degassing budgets of this volcanic arc. Here, we present novel measurements of gas chemistry, aerosol composition, and carbon isotope signature from along the South Sandwich Island arc. By combining ground-based measurements of SO₂ flux with in-situ samples of plume composition using Unoccupied Aerial Systems (UAS), we present multi-species volatile fluxes for the major along-arc degassing sources. Further, by evaluating the carbon to sulfur ratio (C/S_T) and carbon isotope composition in emitted gases together with petrological constraints from erupted tephra, we aim to test the hypothesis that carbon is supplied to the SSI by subduction of oceanic carbonated serpentinite, and thus contribute to our understanding of carbon recycling at subduction zones.

How to cite: Liu, E., Wood, K., Aiuppa, A., Giudice, G., Bitetto, M., Pering, T., Wilkes, T., McGonigle, A., McCormick Kilbride, B., Fischer, T., Nowicki, S., Mason, E., Richardson, T., and Hart, T.: Volcanic degassing along the enigmatic South Sandwich volcanic arc, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1682, https://doi.org/10.5194/egusphere-egu2020-1682, 2020.

In order to study groundwater anomaly related to the 2018 Hokkaido Eastern earthquake (Mw6.6) occurred on 6^th September, we have measured δD and δ¹⁸O values of commercial bottled mineral water at two sites in Iburi region, Hokkaido, Northern Japan from June 2015 to May 2019. At the Uenae site, 21km west of the epicenter, both δD and δ¹⁸O values are constant from June 2015 to February 2018. Then these values have decreased substantially from April 2018 to December 2018 with significant fluctuations. These variations may be attributable to a mixing of groundwater with light δD and δ¹⁸O values. At the Eniwa site 34km northwest of the epicenter, δD values have decreased slightly and monotonically, while δ¹⁸O values are constant from June 2016 to October 2018. Observed isotopic variations of the Uenae site are different from those found at the 2016 Tottori earthquake where the δ¹⁸O value of groundwater increased a couple of months before the seismic event, while the δD value was constant. These data were attributable to water-rock interaction in the aquifer. Thus, the mechanism of groundwater isotopic anomaly may be different between Tottori and Hokkaido earthquakes. In addition to the M6.7 earthquake, CO₂ injection by CCS project at Tomakomai, 13km southwest of the Uene site may be another factor to induce such variations. In order to evaluate the environmental impact of CO₂ injection, we should measure total carbonate concentration and δ¹³C value of carbonate at both sites. Then we will discuss mechanism of groundwater anomaly.

How to cite: Sano, Y., Kagoshima, T., Takahata, N., Shirai, K., Park, J.-O., Shibata, T., Yamamoto, J., Nishio, Y., Xu, S., Chen, A.-T., and Daniele, P.: Groundwater anomaly related to the 2018 Hokkaido Eastern Iburi earthquake in Northern Japan , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2287, https://doi.org/10.5194/egusphere-egu2020-2287, 2020.

The Duvalo locality is located in the SW of the Republic of North Macedonia, in the Ohrid region, near the village of Kosel. It is an area of strong soil degassing, called “volcano” by the local people despite volcanic activity has never been documented in the recent geologic history of the area [1]. A large area (thousands of sqm) shows signs of strong alteration and is devoid of vegetation. Until the 19^thcentury sulphur was mined from this area [1].

In August 2019, a campaign of soil CO₂ flux measurements and soil gas sampling was made. Duvalo is sometimes referred to as an active geothermal feature but no signs of enhanced geothermal gradient were found and the soil temperatures at 50 cm depth in this campaign were always within the range of local mean air temperatures. Soil CO₂ flux values ranged from 1.3 to 59,000 g/m²/d and can be modelled with the overlapping of 3 or 4 flux populations. A possible biological background is estimated in 6.8±1.8 g/m²/d while the other populations are characterized by an anomalous average flux ranging from 180 to 33,000 g/m²/d. The CO₂ total emission, estimated both with a statistical and geostatistical approach, provided similar values in the order of 50 t/d. This has to be considered as a minimum value because only areas with evident signs of alteration have been investigated. Nevertheless, the estimated output is quite high for an area unrelated with recent volcanism or geothermal activity.

The chemical composition of soil gases shows: CO₂ (96.6%), N₂ (1.8%), H₂S (0.6%) and CH₄ (0.3%) as the main gases. The present composition is almost indistinguishable from previous analyses made in 1957 and 1977 [1] pointing to a stability of the system in last decades. The isotope compositions indicate for CO₂ (δ¹³C -0.2 ‰) a pure carbonate rock origin, for CH₄ (δ¹³C -34.4 ‰ and δ²H -166 ‰) a thermogenic origin and for He (R/R_A 0.10) a pure crustal origin.

The H₂S released at Duvalo may be produced by either microbial or thermochemical sulphate reduction favoured by hydrocarbons whose presence can be inferred by the uprise of thermogenic methane. Partial oxidation of H₂S during its upflow, producing sulphuric acid, may be responsible of the production of abundant CO₂ through dissolution of carbonate rocks. Similar processes have been evidenced also in other parts of North Macedonia [2]. These gases rise up through the N–S trending normal faults bordering the seismically active Ohrid basin graben [3] being released to the atmosphere through the soils of Duvalo “volcano”.

This research was funded by: DCO Grant n. 10881-TDB “Improving the estimation of tectonic carbon flux”; GINOP-2.3.2-15-2016-00009 ‘ICER’ project and PO-FSE Sicilia 2014–2020 (CUP: G77B17000200009).

References

[1] Markovski B. et al., 2018. Duvalo a geological phenomenon near Ohrid. DOI: 10.18509/AGB.2020.05

[2] Temovski M., 2017. Hypogene Karst in Macedonia. In: Klimchouk et al. (eds.), Hypogene Karst Regions and Caves of the World, Springer

[3] Hoffmann N. et al., 2010. Biogeosciences, 7, 3377–3386

How to cite: Li Vigni, L., Ionescu, A., Molnár, K., Temovski, M., Palcsu, L., Cardellini, C., Gagliano, A. L., and D'Alessandro, W.: Duvalo (North Macedonia): A “volcano” without volcanic activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2449, https://doi.org/10.5194/egusphere-egu2020-2449, 2020.

Like most of the Balkan Peninsula, North Macedonia is a geodynamically active area. As such it has many hydrothermal features and gas manifestations. Until now, no systematic study about the geochemical characterization of the geogenic gases was made before in this country. In August 2019, 24 gas samples were collected in the study area. All, except one collected at Duvalo (soil gas), are gases bubbling or dissolved in thermomineral waters (temperatures from 12 to 66 °C). They were analysed in the laboratory for their chemical (He, Ne, Ar, O₂ , N₂ , H₂ , H₂S, CH₄ and CO₂) and isotopic composition (δ¹³C-CO₂, δ¹³C-CH₄, δ²H-CH₄ and R/R_A). Most of the gases have CO₂ as the main component (400-998,000 ppm) while the remaining are enriched in N₂ (1300-950,000 ppm). Helium ranges from 0.3 to 2560 ppm while CH₄ from 1.6 to 20,200 ppm. R/R_A and ⁴He/²⁰Ne ratios indicate a generally low atmospheric contamination, a prevailing crustal contribution and mantle contributions between 1 and 20% considering a MORB endmember. The highest mantle contributions are found in the SE part of the country very close to the sites that show the highest R/R_A values in continental Greece [1]. This area is characterised by extensional tectonics and Plio-Pleistocene volcanism. A quite high mantle contribution (about 15%) is also found in two manifestations in the NW part of the country along a main normal fault system. With the exception of the sample of Smokvica, which has very low CO₂ (1400 ppm) and δ¹³C-CO₂ (-15.7 ‰ V-PDB), all free gases show a relatively narrow range in δ¹³C-CO₂ values (-4.6 to +1.0 ‰ V-PDB) indicating the mixing between a mantle and a carbonate rock source. The isotope composition allows us to assign the CH₄ origin to three sources. The largest group can be attributed to a hydrothermal origin (δ¹³C-CH₄ around -20 ‰ V-PDB and δ²H-CH₄ around -100‰). Three samples collected in the SW part of the country have a thermogenic origin (δ¹³C-CH₄ around -35 ‰ V-PDB and δ²H-CH₄ around -160‰ V-SMOW). Finally, one sample (Smokvica) with the highest values (δ¹³C-CH₄ -7.2 ‰ V-PDB and δ²H-CH₄ -80‰ V-SMOW) may be attributed to abiotic processes in a continental serpentinization environment or to methane oxidation.

This research was funded by the DCO Grant n. 10881-TDB “Improving the estimation of tectonic carbon flux”, GINOP-2.3.2-15-2016-00009 ‘ICER’ project and PO FSE Sicilia 2014 – 2020 (CUP: G77B17000200009).

References:

[1] Daskalopoulou et al., 2018 – Chemical Geology, 479, 286-301

How to cite: Temovski, M., D’Alessandro, W., Ionescu, A., Li Vigni, L., Molnár, K., Palcsu, L., and Cardellini, C.: Preliminary geochemical characterization of gas manifestations in North Macedonia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2763, https://doi.org/10.5194/egusphere-egu2020-2763, 2020.

The Ebeko volcano (50°41′N, 156°01′E) is located at the northern part of Paramushir Island and composed of several Quaternary volcanic cones. The Neogene volcano-clastic basement occurs below ~200 m asl. The post-glacial cone of Ebeko is composed by lava flows and pyroclastics of andesitic composition. The summit is represented by three craters (Northern, Middle and Southern). The modern phreatic and fumarolic activity of Ebeko started after a strong explosive phreatic–magmatic eruption from the Middle crater in 1934–1935 which ejected about 10⁶ t of andesitic ash and bombs. Last eruptive activity of Ebeko volcano began in October 2016 and continues to the present. 

Main feature of the hydrothermal activity of Ebeko is the existence of two thermal fields separated in the space. The summit field consists ~ 10 thermal grounds, low-temperature fumaroles (<120 °C) and near-boiling pools with no or weak outflowrates. The second thermal field, Yurievskie springs, is locatedat low elevations, ~550 m asl down to 280 m asl, on the western slope of Ebeko volcano in the canyon of Yurieva River. Gases from different parts of the summit thermal field are all water-rich (97–99 mol%) and show varying contents of HCl and total sulfur and ratios of C/S and H₂S/SO₂. All waters from the Yurievskie springs and Ebeko pools are ultra-acidic, with pH < 2. The Yurievskie waters are of the SO₄–Cl type (SO₄/Cl ratios are ~1:1molar and 3:1 by weight), whereas the SO₄/Cl ratio in Ebeko pools show low (<1) and varying SO₄/Cl ratios. Major and trace element composition of Ebeko-Yurievskie acidic waters is suggesting congruent dissolution of volcanic rocks. Oxygen and hydrogen isotopic composition of water and Cl concentration for Yurieva springs show an excellent positive correlation, indicating a mixing between meteoric water and magmatic vapor. In contrast, volcanic gas condensates of Ebeko fumaroles do not show a simple mixing trend but rather a complicated data suggesting evaporation of the acidic brine. Temperatures calculated from gas compositions and isotope data are similar, ranging from 150 to 250 °C, which is consistent with the presence of a liquid aquifer below the Ebeko fumarolic fields.

Thermal grounds and pools of the summit field are closely associated with the volcano activity. Each period of volcano excitation causes changes in the locations of major fumarole vents, crater lakes, and affects the chemical composition of water and gas. The Ebeko volcano eruption (from 2016 to the present) also triggered changes in the isotope and chemical composition of the Yuryevskie springs.

In this paper we report data on water and gas compositions of samples obtained during the 2016-2019 field seasons and compare partially published data from 2005-2014 field campaigns. This work was supported by the RFBR grant #20-05-00517.

How to cite: Kalacheva, E., Kotenko, T., and Voloshina, E.: Geochemistry of fluid manifistations of the Ebeko Volcano, Paramushir Island (Kurile Islands, Russia)., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3395, https://doi.org/10.5194/egusphere-egu2020-3395, 2020.

Bagana volcano, Papua New Guinea, is among Earth’s youngest and most active volcanoes. Bagana typically exhibits multi-year episodes of lava extrusion, interspersed with pause periods characterised by strong passive degassing. Based on satellite-based observations, Bagana is the third ranked global source of volcanic sulfur dioxide over the past 15 years. Recent work based on global correlations between volcanic gas composition and magma trace element chemistry has predicted that it may be the fifth ranked global volcanic deep carbon source. However, this indirect estimate of Bagana’s potential carbon budget has yet to be ground-truthed by in-situ sampling.

We visited Bagana in September 2019 and made the first measurements of the chemical composition of the volcano’s summit gas plume. We placed a miniaturized MultiGAS sensor array on board an unoccupied aerial system (UAS, or drone) and flew the sensors through the plume. Our aircraft flew beyond visual line of sight, reaching the gas plume from around 7 km horizontal distance and 2 km altitude below the summit. Such long-range UAS flights offer immense potential for studying gas emissions from such steep, active or remote volcanoes.

Our MultiGAS flights found relatively low concentrations of both sulfur dioxide and carbon dioxide in the Bagana plume. Moreover, we made coincident remote sensing measurements of sulfur dioxide emissions using ground- and UAS-based ultraviolet spectroscopy and calculated SO2 fluxes of only ~400 tonnes per day. These are an order of magnitude below the typical fluxes inferred from satellite observations. Combining MultiGAS plume composition (CO2/SO2 molar ratio, mean ~3.4) and SO2 fluxes allow us to estimate Bagana’s CO2 flux into the atmosphere as only ~1360 t/d.

Our interpretation of these results is that the volcano is presently in a low state of activity. From satellite observations, we note the cessation of the most recent extrusive episode several weeks prior to our field campaign. The lack of the anticipated strong passive degassing often observed by spaceborne UV sensors is likely a result of “scrubbing” in the volcanic edifice, where rising gases interact with groundwater, resulting in dissolution of sulfur species into the groundwater and perhaps precipitation of sulfur-bearing minerals into edifice fractures. As the volcano moves towards a future extrusive episode, we might anticipate the gradual drying out of the hydrothermal system and a shift towards more truly magmatic gas compositions. Our results show that short campaign measurements may not provide data which are representative of a volcano’s longterm behaviour and we suggest that caution is needed in using such data to calculate or extrapolate regional and global volatile emissions inventories.

How to cite: McCormick Kilbride, B., Liu, E., Wood, K., Wilkes, T., Schipper, I., Mulina, K., Richardson, T., Werner, C., McGonigle, A., Pering, T., Aiuppa, A., Bitetto, M., Giudice, G., and Itikarai, I.: First measurements of volcanic gas composition at Bagana volcano, Papua New Guinea, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10712, https://doi.org/10.5194/egusphere-egu2020-10712, 2020.

La Palma Island is the north-westernmost and one of the youngest of the Canarian Archipelago. In the last 123ka, volcanic activity has taken place exclusively at Cumbre Vieja volcano which is located at the southern part of the island. Cumbre Vieja is characterized by a main north–south rift zone 20km long and 1950m in elevation covering an area of 220km² with volcanic vents located northwest and northeast. Cumbre Vieja is the most active basaltic volcano in the Canaries with 7 historical eruptions, being Teneguía (1971) the most recent one. The most relevant volcanic activity episodes occurred since Teneguía eruption, are two intense seismic swarms occurred beneath Cumbre Vieja on 7-9 and 13-14 of October 2017. Since visible volcanic gas emissions do not occur at the surface of Cumbre Vieja, the geochemical surveillance program has been focused mainly on diffuse degassing studies. In the last 18 years diffuse CO₂ emission surveys have been yearly performed in summer periods to minimize the influence of meteorological variations. Measurements have been performed following the accumulation chamber method in about 600 sites and spatial distribution maps have been constructed following the sequential Gaussian simulation (sGs) procedure to quantify the diffuse CO₂ emission. Herein we summarize the diffuse CO₂ emission time series during this period and describe the results obtained in the last 2019 survey. The soil CO₂ efflux values measured in 2019 survey ranged from non-detectable to 72.7gm⁻²d⁻¹. Diffuse CO₂ output was estimated in 1,064 ± 35td^-1, a value within the background +1s range (1,254 td^-1) (Padrón et al., 2015, Bull. Volcanol. 77:28). In the period 2001-2017, the diffuse CO₂ output released to the atmosphere from Cumbre Vieja volcano ranged between 320 to 1,544td^-1. Enhanced endogenous contributions of deep seated CO₂ might have been responsible for the higher CO₂ emission values measured in 2011 and 2013. After the October 2017 seismic swarms, diffuse CO₂ output showed an increasing trend from 788 to 3,251td^-1 in March 2018, to decrease gradually until 852td^-1 in September of that same year, and begin to gradually increase again to 2,371td^-1 in November 2018. These changes were possibly caused by an upward magma migration. Our results demonstrate that periodic surveys of diffuse CO₂ emission are extremely important for the detection of early warning signals of future volcanic unrest episodes at Cumbre Vieja.

How to cite: Di Nardo, D., Redfern, E.-M., Zummo, F., Martín-Lorenzo, A., Rodríguez-Pérez, C., Padrón, E., Melián, G. V., Sáez-Gabarrón, L., Alonso, M., Asensio-Ramos, M., Pérez, N. M., Hernández, P. A., Morales-González, F. A., and Pitti-Pimienta, L.: Geochemical monitoring of Cumbre Vieja volcano (Canary Islands) by summer diffuse CO2 degassing surveys, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11386, https://doi.org/10.5194/egusphere-egu2020-11386, 2020.

Tenerife (2,034 km²) is the central and largest island of the Canarian archipelago, located about 100 km west of the African coast between 27º37’ and 29º25’N and between 13º20’ and 18º10’W. The structure of Tenerife is controlled by a volcano-tectonic rift-system with NW, NE and NS directions with Teide volcano located in the intersection of the three rifts. Teide is the highest stratovolcano in the Atlantic Ocean reaching 3,718 m.a.s.l. with its last eruption occurred in 1798 through an adventive cone of Teide-Pico Viejo volcanic complex. Persistent degassing activity, both visible and diffuse, takes place at the summit cone of the volcano, being the diffuse degassing the principle degassing mechanism of Teide (Mori et. al., 2001; Pérez et. al., 2013). As part of the volcanic monitoring program of INVOLCAN in Tenerife, 8 surveys were performed during summer 2019 in order to evaluate the short term variations of diffuse CO₂ and H₂S emissions in the summit crater. The emissions were calculated using data from 38 sampling sites homogeneously distributed inside the crater covering an area of 6,972 m² by means of a portable CO₂ and H₂S fluxmeter using the accumulation chamber method (Parkinson 1981). During the study period, CO₂ and H₂S emissions ranged from 33 ± 5 to 93 ± 25 t/d and from 0.6 ± 0.2 to 4 ± 0.1 kg/d, respectively. Despite the small changes observed in the temporal evolution, values are considered normal for a quiescence period in Teide volcanic system. Short term variations in CO₂ and H₂S emissions indicate changes in the activity of the system and can be useful to understand the behaviour of the volcanic system and as forecast of future volcanic activity.

References
Mori T. et al. (2001). Chemical Geology, 177, 85–99.
Parkinson K. J. (1981). Journal of Applied Ecology, 18, 221–228.
Pérez N. M. et al. (2013). Journal of the Geological Society, 170, 585–592.

How to cite: Alonso, M., Hoffman, H. T. A., Smith, J. G., Thompson, E., Rodríguez, F., Amonte, C., Asensio-Ramos, M., Pitti, L., Padrón, E., and Pérez, N. M.: Short-term variations of diffuse CO2 and H2S at the summit crater of Teide volcano, Tenerife, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11710, https://doi.org/10.5194/egusphere-egu2020-11710, 2020.

The occurrence of hydrothermal emissions implies the existence of heat sources related to magma reservoirs both in convergent margins (Bransfield-South Shetland) and in mid-ocean ridge and intra-plate settings (Azores). The importance of these systems lies in (a) producing important mineralizations,  (b) favouring extremophilic ecosystems, (c) being precursors of underwater volcanic eruptions, (d) playing a major role they play in the matter and energy exchange between the geosphere and the hydrosphere and (d) their impact on the geochemistry of the oceans. In subduction margins, rifts, transforming faults or volcanic buildings in hot spots, emissions of hot fluids related to magmas and/or circulation in hydrothermal systems can occur. The fluids associated with magmas are fundamentally gases (CO₂, H₂O, H₂, SO₂, H₂S, He, etc.). Hydrothermal fluids constitute a complex system where seawater percolates through fissures and fractures in sediments and rocks at different depths and heats up upon contact with magmas and hot volcanic rocks, leaching a large amount of chemical elements. The identification of acoustic plumes in the water column is the first step in the exploration of unknown underwater emissions. The new acoustic detection technologies, which operate with a wide frequency range, are one of the most innovative tools for detecting gas plumes and other fluids in the water column, especially in deep waters. Once detected, physical-chemical parameters (temperature, salinity, turbidity, cations, anions, dissolved gases, isotopic signature, etc.) that allow their characterization and classification will be determined. This type of studies is particularly useful when it is not possible to collect free gases, fumarolic and/or bubbling gases, as in the case of submarine activity. In this work, we show the results obtained regarding the chemical composition of dissolved gases (He, H₂, CO₂ (aq), O₂, N₂, CH₄ and He) and isotopic signature of the dissolved CO₂ (δ¹³C-CO₂) in sea water sampled in sites of hydrothermal interest. With this purpose, we carried out two oceanographic surveys (EXPLOSEA1 and EXPLOSEA2) in 2019: the first in Antarctica aboard the Spanish Research Vessel (RV) Hespérides and the second in North Atlantic Ocean aboard the Spanish RV Sarmiento de Gamboa. To do so, 13 and 10 water vertical profiles were studied in the RV Hespérides and the RV Sarmiento de Gamboa, respectively, using a SBE 911plus CTD system where there was evidence of acoustic plumes or where appropriate, emission buildings of fluids were present. Water samples were kept in glass bottles for subsequent analysis. The establishment of the physicochemical characteristics of volcanic hydrothermal fluids and the characterization of the nature and origin of the different types of fluid emissions will help to classify the hydrothermal fluids in order to understand the phenomena that take place in them and their surroundings.

How to cite: Asensio-Ramos, M., Amonte, C., Santofimia, E., Melián, G. V., López, E., Padrón, E., Somoza, L., Hernández, P. A., Medialdea, T., González, F. J., and Pérez, N. M.: Seawater dissolved gases associated with hydrothermal fluids in convergent margins (Brandsfield-South Shetland, Antarctica) and mid-ocean ridge and intraplate settings (Azores, Portugal), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11991, https://doi.org/10.5194/egusphere-egu2020-11991, 2020.

Fluid migration along faults can be highly complex and spatially variable, with channelled flow along karstified structures of the vadose zone. One such example is Vapor cave, near the urban area of Alhama de Murcia, situated along a tectonically active, NE-SW trending master fault as results of the convergence between Africa and the microplate of Iberia. Vapor cave represents an outstanding gases-blowout site from the upper vadose zone, developed in a favourably fissured carbonate-cemented conglomerate host rock under hypogene speleogenesis by the upwelling of hydrothermal (>33°C, and 100% relative humidity) and CO₂-rich air, in or from the zone of fluid-geodynamic influence.

In this study, we investigate the gaseous composition and, specifically, the geochemical fingerprint of deep-origin greenhouse gases (CO₂, CH₄) of both cave and soil air at Vapor cave. Detailed surveys were conducted to monitor the deep-origin gases exhaled by the cave, by using high precision field-deployable CRDS and FTIR spectrometers to in situ and real time measure the concentration and δ¹³C of both carbon-GHGs. Inert gases like radon were also measured in parallel by a pulse-counting ionization chamber (alpha spectroscopy). The collected data provide new insights into the control exerted by active fault segments on deep-seated gas migration toward the surface.

The C species of the deep-origin fluids are dominated by CO₂ (concentration higher than 1% and δ¹³C-CO₂ ranging from −4.5 to −7.5‰) with the abundance of CH₄ below the atmospheric background. It is estimated that the exhaled  air  represents  between  1 to 3%  of  this  pure‐theoretical  CO₂  added  from  the  deep  endogenous source feeding the cave atmosphere and linked to the fault activity. Anomalous radon concentrations recorded at this site also confirm the contribution of this geogenic gas in the cave atmosphere (²²²Rn ranges 40-60 kBq/m³ at -30 m depth) and its accumulation in the overlying soil (exceeding 10K kBq/m³).

In contrast to the release of large volumes of deep endogenous CO₂, Vapor cave constitutes an effective sink of methane (CH₄). The deep-sourced CH₄ is continuously depleted and ¹³C-enriched along the vertical migration pathway into the cave (CH₄<1 ppm and δ¹³C close to −30‰). Some anomalous concentrations of deep endogenous methane have been already registered in the cave air, e.g. during march 2016, with CH₄ ranging 2.3 to 3.4 ppm and δ¹³C-CH₄ lighter than that found in the local background atmosphere. These anomalous CH₄ data could be related to the occurrence of contemporary earthquakes, characterized by a total amount of seismic energy released of 4.9 x 10⁹ J and epicenter locations southwest of the cave and within a radius of 20 km.

The continuous depletion of CH₄ in the cave air constitutes itself a very valuable property in terms of using as potential earthquake precursor in combination with other geochemical indicators. Hence, any anomalous concentration and isotopic deviation of this gas in the cave atmosphere with reference to the background level in the cave atmosphere could denote a more intense migration of endogenous fluids through the upper vadose zone, which could be related with an increase of the regional seismotectonic activity.

How to cite: Fernandez-Cortes, A., Perez-Lopez, R., Martin-Pozas, T., Cuezva, S., Calaforra, J. M., and Sanchez-Moral, S.: Geochemical monitoring of mantle-derived gases migration along active faults: case of Vapor cave (southern Spain) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17591, https://doi.org/10.5194/egusphere-egu2020-17591, 2020.

The Latronico thermal area is located in the southern sector of the Apennines chains, in proximity to the south boundary of the Mt. Alpi. This area is a seismically active region and it is located between Val d’Agri basin and Pollino area, two of the highest seismic risk zones in Italy. It is well documented that tectonic discontinuities act as preferential channels for the uprise of deep fluids trough the continental crust towards the surface (e.g., Caracausi et al. 2013). Hence in seismically areas, these fluids can move across the volume of rocks characterized by an active field of stress and their fluids can take a memory of the occurring rock-water-gas interactions. Taking this into account, we sampled waters and dissolved gases released in the Latronico hydrothermal basin in order to define: i) water-rock interaction processes; ii) thermalism origin; iii) the geochemical model of fluid circulation in a seismic area.  In details, we analysed the chemical and isotopic (C and noble gases) composition both groundwater and dissolved gases. The acquired knowledge will allow us to plan long-term geochemical monitoring useful for identification of the possible relationship between fluid circulation and regional-scale seismicity. We sampled 24 springs, of which 9 belonging to thermal set (Latronico Spa springs) and 15 to cold one. Thermal waters have an average temperature of 21°C, these are slightly alkaline (7.12 <pH< 7.54), show negative Eh values up to −93 mV and are calcium bicarbonate-sulphate water type. The cold springs have temperature values from 7.7 to 14.8 °C, pH from 7.05 to 8.15, with positive Eh values up to 200 mV. These waters are calcium-bicarbonate water type. The oxygen and hydrogen isotopes clearly indicate their meteoric origin. Regarding the gas geochemistry, He and C isotopes have been used as the key tracer for recognizing the contribution of crustal and mantle components and possibly the source of heat. Thermal waters have CO₂ and He contents of 1 and 2 order of magnitude higher than cold water, respectively. The dissolved gases show an atmospheric component, being Air Saturated Water (ASW). ³He/⁴He ratios in the gases dissolved are 0.12 Ra ±0.2 (Ra is the He isotopic signature in the atmosphere, 1.39x10^-6). Assuming that He isotopic signature in typical crustal fluids is < 0.05 Ra, the measured He data show traces of mantle-derived helium, to the mixing between atmospheric and radiogenic end-members (0.02 Ra). Coupling Total Dissolved Inorganic Carbon (TDIC) and δ¹³C_TDIC data, 2 water sub-sets have been identified: (i) infiltrating waters, with low δ¹³C_TDIC, and (ii) thermal waters with positive δ¹³C_TDIC and high TDIC values, indicative of outgassing of deeply sourced CO₂. This study for the first time proposes a model of fluids origin in the Latronico hydrothermal basin and the main processes that control their chemistry during their circulation through the crust. Hence, geochemical monitoring of the fluids in the region can provide if these fluids are sensitive to chemical variation due to a modification of the field of stress in the preparatory phases of an earthquake

How to cite: Paternoster, M., Apollaro, C., Caracausi, A., Randazzo, P., Aiuppa, A., De Rosa, R., Fuoco, I., Mongelli, G., Muto, F., Vanni, E., and Vespasiano, G.: Fluid geochemistry in the Latronico thermal area (south Italy): new preliminary data for upcoming monitoring of a seismically active area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18296, https://doi.org/10.5194/egusphere-egu2020-18296, 2020.

La Palma Island (708.3 km²) is located at the north-western end of the Canarian Archipelago and is one of the youngest island (~2.0My). During the last 123 ka, volcanic activity has taken place exclusively at the southern part of the island, where Cumbre Vieja volcano, the most active basaltic volcano in the Canaries, has been constructed. Seven historical eruptions have occurred at Cumbre Vieja, been Teneguía the last one (1971). On 7-14 of October 2017 and 10-15 November 2018, two intense seismic swarms occurred beneath Cumbre Vieja. In order to monitor the volcanic activity at Cumbre Vieja, main efforts have been focused on diffuse degassing studies since visible volcanic emissions are absent at the surface environment of this volcano. Diffuse CO₂ emissions have been monitored at Cumbre Vieja since 1997 in a yearly basis, with a higher frequency since the start of intense seismic swarms until August, 2019. At each survey, 600 sampling sites are selected for soil CO₂ efflux measurements performed in situ following the accumulation chamber method. Spatial distribution maps are constructed following the sequential Gaussian simulation (sGs) procedure and, to quantify the CO₂ emission from the studied area, 100 simulations are performed for each survey. At each sampling site, soil gas samples were collected at 40cm depth. Isotopic analysis of C in the CO₂ of selected soil gas samples (10% of the total) was performed to discriminate the origin of the CO₂. Between 2001 and 2017, the estimated diffuse CO₂ emission rate released to the atmosphere from Cumbre Vieja volcano has ranged between 320 to 1,544 td^-1. After October 2017 seismic swarms, diffuse CO₂ emission rates were estimated on a nearly daily basis, showing three increasing trends from 800td^-1 up to 3,251td^-1, 2,850td^-1 and 1,904td^-1, respectively. With the aim to filter out the effects of rainfall on the measured CO₂ efflux time series, a decorrelation pluviometric data analysis was performed. We found that a moving average of sixty days of the averaged rainfalls of six pluviometers on the studied area explained 49.4% of variability of diffuse CO₂ emission. The first peak on diffuse CO₂ emission remained after filtering, with a highest value of 2,020td^-1, when the time series had a non linear behaviour and the two seismic swarms occurred. Highest value of the second peak was 1,495td^-1 whereas the third peak practically disappears after filtering, due to the high influence with rainfall. Isotopic analysis of soil C-CO₂ showed enrichments in volcanic-hydrothermal CO₂ before the two mean peaks of filtered soil CO₂ emission time series. We found seismological and geochemical evidences that these swarms were linked to a deep-seated magmatic intrusion. We hypothesize that the October 2017 seismic swarms were produced by an upward magma migration from an ephemeral magmatic reservoir located in the upper mantle (about 25 km depth), toward another reservoir located close to the Moho beneath Cumbre Vieja (12-15 km). The consequent depressurization of the magma batch was the source of the volatiles observed at the surface, with a delay of few weeks for CO₂.

How to cite: Leal, V., Padilla, G. D., Melián, G. V., Martin-Lorenzo, A., Rodríguez, F., Padrón, E., Asensio-Ramos, M., Hernández, P. A., and Pérez, N. M.: Environmental factors controlling diffuse CO2 emission rates from Cumbre Vieja Volcano, La Palma, Canary Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19479, https://doi.org/10.5194/egusphere-egu2020-19479, 2020.

Thermal waters from natural hot springs and boreholes are clear geothermal features of the city of Ourense (Galicia, Spain). The urban area of Ourense is located in the Miño River’s valley which is characterized by two fault systems (NW–SE and NE–SW) that determine the groundwater circulation in the region. The low permeability of the granite and granodiorite only allows fluid circulation throughout faults and fractures transporting the fluid and transferring the heat to the lower elevations in the valley (Araujo 2008; Fernández Portal et al. 2007). During July to August 2019, an intensive soil gas geochemical survey was carried out at urban area of Ourense in order to identify the presence of vertical permeable structures and possible upflow of deep-seated gases. A total of 539 soil gas samples were taken with an average distance of ≈100 m between sampling sites and covering an area about 13Km². In-situ soil CO₂ efflux and soil gas ²²²Rn activity measurements were performed at each sampling site. In addition, soil gas samples at 40 cm depth were collected for chemical (He, Ne, H₂, O₂, N₂, CH₄ and CO₂) and isotope (d¹³C-CO₂ vs. VPDB) analysis by micro-gas chromatography and IRMS, respectively. Soil CO₂ efflux and ²²²Rn activity values ranged from 0.7 to 92 g·m^-2·d^-1 (mean value of 16 g·m^-2·d^-1) and from 2.7 to 743 Bq·m^-³ (mean value of 73 Bq·m^-³), respectively. Regarding soil gas He and H₂ concentration, the values ranged from 5.2 to 25.0 ppmV (mean value of 6.2 ppmV) and from 0.5 to 24.9 ppmV (mean value of 1.9 ppmV), respectively. Soil CO₂ concentrations showed a range between 355 and 53,766 ppmV (mean value of 7,824 ppmV) with a range of isotopic ratios from -14.1 to -28.5‰ vs. VPDB (mean value of -22.1 ‰). The binary plot of d¹³C-CO₂ vs 1/CO₂ concentration suggest the presence of small fractions of CO₂ deep-seated in the soil gas atmosphere (mainly an atmospheric and biogenic gas mixture) of the city of Ourense. Soil CO₂ efflux, soil gas Rn-222 activity and soil gas He, H₂ and CO₂ concentration contour maps were constructed using the sequential Gaussian simulation (sGs) interpolation method. Estimated diffuse CO₂ emission from the study area is about 201 tons per day and about 8 tons per day could be considered deep-seated degassing. Spatial distribution analysis of the soil gas geochemical data show relatively high values of soil CO₂ efflux and soil gas H₂ concentration at the Chavasqueira-Tinteiro urban sector, while As Burgas and Outariz-Muiño urban sectors showed relatively high values of soil ²²²Rn activity. These results show the usefulness of the soil gas geochemistry to identify permeable zones and possible upflow of deep-seated gases at the city of Ourense.

How to cite: Melián, G. V., Pérez, N., Sáez -Gabarrón, L., Rodríguez, F., Hernández, P. A., Padrón, E., Asensio-Ramos, M., Cid, J. A., Araujo, P. A., González Castro, R., and Pumar Tesouro, J.: Urban soil gas geochemistry to identify permeable zones and possible upflow of deep-seated gases at the city of Ourense, Galicia, Spain, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19805, https://doi.org/10.5194/egusphere-egu2020-19805, 2020.

The aim of this work is to provide a methodology for the investigation of seismic precursors starting from hydrogeological, hydrogeochemical, and seismic study of the territory. Hydrological effects originated during the seismic cycle (particularly prior to and during strong earthquakes) have long been observed and documented, as they are among the most outstanding coseismic phenomena that can be even observed over great distances. Moreover, since a few decades, geochemical changes of groundwater prior to intermediate and/or strong (Mw ≥ 5.0) earthquakes have started to be a concrete hope and, at the same time, a big scientific and technological challenge for geoscientists working in the field of seismic precursors. Deformation and stress perturbation during the seismic cycle can cause changes in deep fluid migration eventually leading to changes in shallower groundwater circulation and geochemistry. As monitoring sites, we identified the Sulmona and Matese areas in the central-southern Apennines. These two areas were affected in the past by Mw > 5.5 earthquakes. Each study area includes 5-6 monitored springs and boreholes. Groundwaters are mainly calcium-bicarbonate type or secondarily sulphate-calcium-bicarbonate type. Continuous monitoring and monthly sampling of the two study areas started in December 2017, although in the Sulmona area they had already started in 2014 for a previous project, whose results have been published in previous papers. In an attempt to identify potential seismic precursors, we carried out, for each monitored spring, analyses of major and trace elements and analyses of isotopes of the water molecule, boron, and strontium. During these years of monitoring (2018-2019), there were no high magnitude earthquakes. The three seismic events with the highest magnitude were indeed the 2019 Collelongo (Mw 4.1, January 1^st), Balsorano (Mw 4.4, November 7^th), and San Leucio del Sannio (Mw 3.9, December 16^th) earthquakes. The most interesting result is that these earthquakes (except Collelongo) were not substantially preceded by hydrogeochemical anomalies. This evidence suggests that this type of pre-seismic anomalies could arise substantially only with intermediate and strong earthquakes (Mw≥5.0); however, it is also true that the Collelongo earthquake, which occurred on a very large Apennine normal fault (the fault that generated the great Avezzano earthquake of 1915, Mw 7.0) at great depths - about 16-17 km -, was preceded by very weak hydrogeochemical anomalies of Li, B, and Sr in most monitored springs. These weak anomalies could be related to pre-seismic breakages at great crustal depths along a very large fault. We also describe the monitoring stations as well as the used instrumentations, procedures, and analyses. We propose some preliminary results that emphasize the importance of collecting data from a widespread network of monitoring stations over a seismic territory and for long time. HydroQuakes provides new evidence for the importance of building a national hydrogeochemical network for the identification of seismic precursors. Future possible implementations as well as further societal uses for such a network are also addressed. The HydroQuakes Project is funded by Fondazione ANIA to CNR-IGAG.

How to cite: Billi, A., Franchini, S., Barberio, M. D., Barbieri, M., Boschetti, T., and Petitta, M.: HydroQuakes: a pilot study in the central-southern Apennines for the realization of a hydrogeochemical monitoring network for seismic precursors and other societal applications, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13365, https://doi.org/10.5194/egusphere-egu2020-13365, 2020.