Composition Of Thermal Waters Research Articles

Lecznicze wody siarczkowe Ponidzia

THERAPEUTIC SULPHUROUS WATERS OF THE PONIDZIE REGION Abstract. The paper shows the characteristics of sulphurous waters from the Ponidzie area. Physical and chemical properties of waters have been determined on the basis of results of analysis of the archived data from boreholes in Busko-Zdroj, Solec-Zdroj, Las Winiarski, Welnin and Dobrowoda. The treatment profile of these waters is constrained by a high concentration of bivalent sulphur, measured as the amount of free hydrogen sulphide. The waters also contain many iodine, bromine and fluorine compounds. One hydrochemical type – Cl-Na, H 2 S, I – has been distinguished on the basis of the hydrochemical characteristics of the therapeutic waters. They occur in three different rock series: Neogene, Cretaceous and Upper Jurassic. It has been found that all of the waters have total dissolved solids (TDS) from 8.5 to 40.7 g/dm 3 and the hydrogen sulphide content varies from 6.8 to 1064.0 mg/dm3. The research results prove that the variety of rock settings is one of the most important reasons for the water chemistry differentiation. In general, the chemical composition of thermal waters in this region is determined by the interaction between groundwater and different rock environments.

Hydrogeochemistry of thermal and mineralized waters in the Diyadin (Ağri) area, Eastern Turkey

The Diyadin Geothermal area, located in the eastern part of Anatolia (Turkey) where there has been recent volcanic activity, is favorable for the formation of geothermal systems. Indeed, the Diyadin geothermal system is located in an active geodynamic zone, where strike-slip faults and tensional cracks have developed due to N–S regional compression. The area is characterized by closely spaced thermal and mineralized springs, with temperatures in the range 30–64°C, and flowrates 0.5–10L/s. Thermal spring waters are mainly of Ca(Na)-HCO3 and Ca(Mg)-SO4 types, with high salinity, while cold groundwater is mostly of Ca(Na, Mg)-HCO3 type, with lower salinity. High contents of some minor elements in thermal waters, such as F, B, Li, Rb, Sr and Cs probably derive from enhanced water–rock interaction.Thermal water samples collected from Diyadin are far from chemical equilibrium as the waters flow upward from reservoirs towards spring vents and possibly mix with cooler waters. The temperatures of the deep geothermal reservoirs are estimated to be between 92 and 156°C in Diyadin field, based on quartz geothermometry, while slightly lower estimates are obtained using chalcedony geothermometers. The isotopic composition of thermal water (δ18O, δ2H, δ3H) indicates their deep-circulating meteoric origin. The waters are likely to have originated from the percolation of rainwater along fractures and faults to the deep hot reservoir. Subsequent heating by conduction due to the presence of an intrusive cupola associated with the Tendurek volcano, is followed by the ascent of deep waters to the surface along faults and fractures that act as hydrothermal conduits.Modeling of the geothermal fluids indicates that the fluid is oversaturated with calcite, aragonite and dolomite, which matches travertine precipitation in the discharge area. Likewise, the fluid is oversaturated with respect to quartz, and chalcedony indicating the possibility of siliceous precipitation near the discharge areas. A conceptual hydro-geochemical model of the Diyadin thermal waters based on the isotope and chemical analytical results, has been constructed.

Limitation of hardness from thermal water by means of nanofiltration

Geothermal conditions are extremely favourable in Hungary. Thermal water is accessible in 70% of the territory of the country, with a lowest temperature of 30°C. For energetic purposes, it can be utilized in two different ways: for supplying heat or generating electricity. In relation to utilization, one of the most serious problems derives from the chemical composition of thermal water. The present paper investigates the opportunities of preventing scaling by nanofiltration. Experiments were performed on a Thin Film NF DK membrane, thermostated at 50°C and at a pressure of 3.5 MPa with four different samples (from four Hungarian cities - Eger, Mezőkövesd, Bogács, Miskolc-Tapolca) using batch plant. Reproducibility of experiments was also investigated using water samples from Komárom at 50 and 60°C. The results showed that NF DK could achieve high retention of divalent ions. The results of the second phase of the experiments proved that water flux and rejections were very stable. After filtration, the scaling properties of thermal water were simulated with the help of chemical equilibrium modelling software, called Visual MINTEQ 3.0. The results of the permeate samples prove that nanofiltration is a successful process in preventing scaling of thermal water for further use.

Geothermal Water in the San Juan Bautista Londó Aquifer, BCS, Mexico

The San Juan Bautista Londó aquifer, with an extent of 593 km2, is the major source of potable water for the City of Loreto. The San Juan Bautista Londó Basin was an important agricultural area in the seventies but despite over- exploitation, a significant reduction of agriculture activity took place. Previous studies indicated that the composition of thermal water in Concepcion Bay, Guaymas Basin vents, and deep circulation water from Las Tres Virgenes near Santa Rosalia show little variation. Their composition and typical ocean water were compared to water samples from different wells, located in the San Juan B Londó watershed. Based on cluster analyses, five different groups of groundwater were separated which represent seawater, the geothermal end-member, groundwater with a stronger geothermal component, groundwater with a certain geothermal influence, and groundwater without a geothermal influence.

Geochemical patterns and origin of alkaline thermal waters in Central Greece (Platystomo and Smokovo areas)

This study investigates the origin and chemical composition of the thermal waters of Platystomo and Smokovo areas in Central Greece as well as any possible relationships of them to the neighboring geothermal fields located in the south-eastern part of Sperchios basin. The correlations between different dissolved salts and the temperature indicate that the chemical composition of thermal waters are controlled by, the mineral dissolution and the temperature, the reactions due to CO2 that originates possibly by diffusion from the geothermal fields of Sperchios basin and the mixing of thermal waters with fresh groundwater from karst or shallow aquifers. Two major groups of waters are recognized on the basis of their chemistry: thermal waters of Na–HCO3–Cl type and thermal waters mixed with fresh groundwater of Ca–Mg–Na–HCO3 type. All thermal waters of the study area are considered as modified by water–rock interaction rainwater, heated in depth and mixed in some cases with fresh groundwater when arriving to the surface. Trace elements present low concentrations. Lithium content suggests discrimination between the above two groups of waters. Boron geochemistry confirms all the above remarks. Boron concentration ranges from 60 μg L−1 to 10 mg L−1, while all samples’ constant isotopic composition (δ11B ≈ 10 ‰) indicates leaching from rocks. The positive correlation between the chemical elements and the temperature clearly indicates that much of the dissolved salts are derived from water–rock interactions. The application of geothermometers suggests that the reservoir temperature is around 100–110 °C. Chalcedony temperatures are similar to the emergent temperatures and this is typical of convective waters in fault systems in normal thermal gradient areas.

Hydrogeothermal modelling vs. inorganic chemical composition of thermal waters from the area of Carballiño (NW Spain)

Abstract. Hydrothermic features in Galicia (northwest Spain) have been used since ancient times for therapeutic purposes. A characterization of these thermal waters was carried out in order to understand their behaviour based on inorganic pattern and water-rock interaction mechanisms. In this way 15 thermal water samples were collected in the same hydrographical system. The selected thermal water samples were classified using principal component analysis (PCA) and partial least squares (PLS) regression analysis in two groups according to their chemical composition: group I with the young water samples and group II with the samples with longest water-rock contact time. This classification agreed with the results obtained by the use of geothermometers and hydrogeochemical modelling, where the samples were classified into two categories according their residence time in the reservoir and their water-rock interaction.

Origin of components in Chilean thermal waters

Thermal waters of northern (18°–27°S) and southern (37°–45°S) Chile occur in two very different climatic, geologic and hydrologic environments: arid closed basins with abundant evaporites in the north; humid climate and well drained valleys in the south. The origin and behavior of the main components of the two groups of waters are examined and compared to each other. The modeling of the alteration of volcanic rocks leads to water compositions very different from those observed both in the north and south. In addition to hydrothermal alteration and deep emanations, the Cl/Br ratio reveals a major contribution of saline waters to the two groups: infiltrating brines from salt lakes in the north; seawater in the south. In the north, concentrations of Cl, Br, Na, K, Ca, SO4, Li, B, Si result from the mixing of alteration waters with recycled brines. Hydrothermal alteration is obscured by this massive saline input, except for Mg. δ34S values are consistent with an origin of sulfate from salar brines, which are themselves derived from deep Tertiary gypsum. In the south, two processes account for the composition of thermal waters: mixing of alteration waters with seawater and deep magmatic contribution. The mixing process controls the concentration of Cl, Br, Na, Alk, Si, K, Ca, Mg. Magmatic inputs are detectable for SO4, Li and B. δ34S suggests that sulfate stems from the mixing of alteration waters with either marine SO4 in coastal waters or with deep SO2 in inland waters. In both the north and south, the Mg concentration is drastically lowered (<1 μmol/L) by the probable formation of a chlorite-type mineral. In the south, very small amounts of seawater (<1% in volume) are sufficient to imprint a clear signature on thermal waters. Not only coastal springs are affected by seawater mixing, but also remote inland springs, as far as 150 km from the sea. Subduction of marine sediments in the accretive margin could be the source of the marine imprint in thermal waters of southern Chile. Seawater may be expelled from the subducted lithosphere and incorporated into the mantle source.

Hydrological and geochemical change related to volcanic activity of Usu volcano, Japan

Mt. Usu is a stratovolcano located on the southern side of the Toya caldera in Hokkaido, Japan. In historical times it emitted dacitic products associated to remarkable crustal deformations. Usu volcano erupted on March 31st 2000 after 23 yr of dormancy and this eruption was the fourth in the 20th century. Secular variations in water levels, temperature and chemical compositions of thermal water have been observed around Usu volcano. The water levels decreased since October 1999, 6 months prior to the eruption. The decrease in water levels is a precursory change and is probably due to leakage of thermal water from the shallow aquifer hosting it. No variations in temperature and chemical composition of thermal water were evident prior to the eruption. However, in a few wells, the temperature of the thermal water increased by up to 15 °C with respect to the pre-eruptive values. Moreover, the concentration of some solutes (Na, K, Cl and SO 4) became higher after the eruption. These thermal and chemical changes are ascribable to increased input of a deep hydrothermal liquid into the shallow groundwater aquifer.

Geochemical characterization of the Biga Peninsula thermal waters (NW Turkey)

Thermal water chemistry from the Biga Peninsula (NW Turkey) was investigated in order to discriminate among hydrochemical facies, and isotopic groups and identify the major geochemical processes. A systematic hydrogeochemical survey was carried out, incorporating new data as well as results from the previous studies. Results were used to further develop hydrogeological and geochemical models. Thermal water compositions were classified into four groups and the processes affecting evolution of water compositions were interpreted. Types 1, 2 and 3 are representatives of water corresponding to sulfate dominant fluids (mainly NaSO4-type), chloride dominant fluids (mainly NaCl-type), and bicarbonate dominant fluids (Na- or CaHCO3-type), respectively. Group 4 comprises the fluids with compositions that are not dominated by any distinctive anion. Groundwater infiltrates and circulates through the marbles of the Paleozoic basement. The isotopic composition of thermal waters revealed that deep infiltration of meteoric water took place in periods of changed climatic conditions.

Conceptual hydrodynamic model of the Pamukkale hydrothermal field, southwestern Turkey, based on hydrochemical and isotopic data

The results of study on the hydrochemical and isotope characteristics of shallow and deep waters at Pamukkale hydrothermal field Turkey are described in order to obtain a better understanding of the hydrological circulation. The field can be grouped into two groundwater sub-systems; cold water springs of Ca–HCO3 type (10–12 °C), and CO2-rich thermal waters of Ca–HCO3–SO4 type (25–58 °C). The occurrence of these water types is closely related to the morphology of the region, where intense tectonism formed horst and graben structures. Hence, two hydrogeological systems were defined: a deep geothermal system which is related to extensive and deep circulation of meteoric water in the regional flow system, and a shallow system which is related to local groundwater flow through sedimentary strata. The meteoric water falling at higher elevations percolates to the local groundwater system at a shallow level and flows to the deep geothermal system. During a deep convection cycle from a recharge to discharge area, the cold water attains heat from the asthenospheric intrusions, causing it to ascend. Variations of chemical and isotopic composition of thermal waters result from their mixing with cool groundwater in a shallow aquifer during their ascent to the surface.

Seismic‐related variations in the chemical and isotopic composition of thermal springs near Acapulco, Guerrero, Mexico

Chemical and isotopic analyses of waters from 4 thermal springs of the Guerrero Pacific coast, the most seismically active area in Mexico, were performed weekly during a period of 1.5 years (October 2002–March 2004). Within the same time interval more than 200 earthquakes with 3.8 ≤ M ≤ 5.3 occurred in the area. The data display several anomalies in Cl−, SO42−, δD and δ18O, always immediately after an event, with a relaxation time of 3–4 weeks. The responses occurred only to earthquakes with the estimated epicenters very close to the location of a spring. These results indicate that: 1) at least for earthquakes with M &lt; 5.3 within the Guerrero “seismic gap” there were no precursors in the chemical (ionic) and isotopic composition of thermal waters (on a weekly basis); 2) two groups of springs near Acapulco, Dos Arroyos and Paso Real, are sensitive to seismic activity and therefore further monitoring of these springs may help to unravel the mechanisms of the “hydro‐seismo‐interaction” in the area.

Variations in the Cl, SO4, δD and δ18O in Water from Thermal Springs near Acapulco, Guerrero, Mexico, Related to Seismic Activity

Chemical and isotopic analyses of waters from 4 thermal springs of the Guerrero Pacific coast, the most seismically active area in Mexico, were weekly performed during a period of 1.5 years (October 2002-March 2004). Within the same time interval more than 150 earthquakes with 3.5 ＜ M ＜ 5.3 occurred in the area. The data display several anomalies in Cl, SO4, δD and δ^18O, always immediately after an event, with a relaxation time of 3-4 weeks. The responses occurred only with earthquakes having an estimated epicentral site very close or almost coincident with the location of a spring. These results indicate that: 1) at least for earthquakes with M＜5.3 within the Guerrero ”seismic gap” there were no precursors in the chemical (ionic) and isotopic composition of thermal waters (on the weekly basis); 2) two groups of springs near Acapulco, Dos Arroyos and Paso Real, are sensitive to seismic activity and therefore further monitoring of these springs may help to unravel the mechanisms of the ”hydro-seismo-interaction” in the area.

Large-scale hydrothermal fluid discharges in the Norris–Mammoth corridor, Yellowstone National Park, USA

Norris–Mammoth corridor is a complex subsidence structure that extends ∼40km northward from the 0.6Ma Yellowstone caldera, and contains many hydrothermal features with high fluid discharges totaling ∼1000l/s. About 150–250l/s of hydrothermal water, which attains boiling temperature at surface and 360°C at depth, discharge from the Norris Geyser Basin, adjacent to the caldera. The highest thermal water and gas discharges in the corridor are from Mammoth Hot Springs, where 500–600l/s thermal water with surface temperatures of up to 73°C and calculated subsurface temperatures of ∼100°C issue from ∼100 hot springs scattered over a score of step-like travertine terraces that range in age from ∼0.4Ma to recent. All the thermal water is meteoric, likely recharged in the Gallatin Range at 2.5–3.0km elevations. The isotopic and chemical compositions of thermal waters and solutes can be interpreted to indicate a common magmatic source for heat and volatile solutes located near Norris. However, the chemical and isotopic compositions of gases, especially the 3He/4He ratios, provide strong evidence for a separate magmatic source for the Mammoth system.

Water and gas geochemistry of the Euganean and Berician thermal district (Italy)

Between 1987 and 1995 more than 100 chemical and isotopic analyses were carried out on the thermal fluids discharged at surface from wells and springs of the Euganean and Berician thermal district. Results for δD and δ 18O in waters, δ 13C in CO 2 and in C 1–C 4 n-alkanes, δD in CH 4, 3He/ 4He and 40Ar/ 36Ar ratios in natural gases were coupled with chemical analyses in an attempt to determine the main characteristics and evolutionary trends of thermal fluids emerging in the region. The isotopic and chemical composition of thermal waters has led to the postulation of a meteoric origin of discharged thermal fluids and of a “maturation” trend as water moves from the peripheral manifestations of the Berici Hills towards those of the Battaglia, Montegrotto and Abano springs in the inner part of the geothermal field. Numerical simulation suggested that the observed evolutionary path is consistent with differentiation due to processes of water–rock interaction. The results of bulk analyses have shown that the gases are made up mainly of N 2 (65–95 vol%), CO 2 (0.5–20.5 vol%) and CH 4 (up to 10 vol%), with relatively high Ar and He contents (up to 1.5 vol% and 0.16 vol%, respectively) and detectable amounts of C 2–C 6 saturated hydrocarbons. The chemical and isotopic composition of the gases suggests that both the meteoric and crustal contributions to the natural discharges are significant, while any significant magmatic contribution, possibly related to vestiges of the volcanic activity that occurred in the Abano area during the Tertiary age, can be ruled out.

Variation in the total dissolved carbon isotope composition of thermal waters of the Island of Ischia (Italy) and its implications for volcanic surveillance

During surveys conducted in 1997, 30 thermal waters (for a total of 39 analysis) were collected from shallow wells utilised for resort spas on the Island of Ischia. Well temperatures ranged from 25° to 82°C and their depths from 30 to 150 m. Pools with temperatures of 26° to 67°C were also sampled on the northern flank of the Mt. Epomeo. The samples were analysed for bulk chemical composition, as well as H, O and C isotope composition. Isotopic analyses of water samples showed wide variations in both deuterium and oxygen-18, which ranged from −37.4 to +8.1‰ and −6.8 to +1.1‰, respectively. Overall δ 13 C in total dissolved carbon (TDC) ranged from −11.5 to +2.3‰, and computed δ 13 C of CO 2(g) results ranged from −18.5 to −1.72‰. Water samples with CO 2 content of up to about 1 bar partial pressure exhibited δ 13 C ( CO 2) ranging from −4 to −1‰. Water samples varied chemically from low-salinity HCO 3 well waters (1–4 g/l) of essentially meteoric origin, to high-salinity Cl waters (up to 40 g/l). Mixing processes from local groundwater, seawater and evaporated waters have also been identified. Models for the chemical and isotopic data on the thermal manifestations have been developed for low- and high-pressure conditions in order to assess the isotopic composition of deep CO 2, assuming that this component is continuously added to the solutions until degassing occurs at shallow depths or at the surface. Constraints due to the reaction of water with volcanic glass have been taken into account for in the computations in addition to those relative to the carbon components participating in the carbonate equilibria. Results from such simulations indicate that deep CO 2 added to the shallow waters probably has a carbon isotope composition ≥−2‰, which most likely stems from a mixed magmatic–sedimentary origin.

Geochemistry of water and gas discharges from the Mt. Amiata silicic complex and surrounding areas (central Italy)

The Mt. Amiata volcano in central Italy is intimately related to the post-orogenic magmatic activity which started in Pliocene times. Major, trace elements, and isotopic composition of thermal and cold spring waters and gas manifestations indicate the occurrence of three main reservoir of the thermal and cold waters in the Mt. Amiata region. The deepest one is located in an extensive carbonate reservoir buried by thick sequences of low-permeability allochthonous and neo-autochthonous formations. Thermal spring waters discharging from this aquifer have a neutral Ca-SO 4 composition due to the presence of anhydrite layers at the base of the carbonate series and, possibly, to absorption of deep-derived H 2S with subsequent oxidation to SO 4 2− in a system where pH is buffered by the calcite–anhydrite pair ( Marini and Chiodini, 1994). Isotopic signature of these springs and N 2-rich composition of associated gas phases suggest a clear local meteoric origin of the feeding waters, and atmospheric O 2 may be responsible for the oxidation of H 2S. The two shallower aquifers have different chemical features. One is Ca-HCO 3 in composition and located in several sedimentary formations above the Mesozoic carbonates. The other one has a Na-Cl composition and is hosted in marine sediments filling many post-orogenic NW–SE-trending basins. Strontium, Ba, F, and Br contents have been used to group waters associated with each aquifer. Although circulating to some extent in the same carbonate reservoir, the deep geothermal fluids at Latera and Mt. Amiata and thermal springs discharging from their outcropping areas have different composition: Na-Cl and Ca-SO 4 type, respectively. Considering the high permeability of the reservoir rock, the meteoric origin of thermal springs and the two different composition of the thermal waters, self-sealed barriers must be present at the boundaries of the geothermal systems. The complex hydrology of the reservoir rocks greatly affects the reliability of geothermometers in liquid phase, which understimate the real temperatures of the discovered geothermal fields. More reliable temperatures are envisaged by using gas composition-based geothermometers. Bulk composition of the 67 gas samples studied seems to be the result of a continuous mixing between a N 2-rich component of meteoric origin related to the Ca-SO 4 aquifer and a deep CO 2-rich component rising largely along the boundaries of the geothermal systems. Nitrogen-rich gas samples have nearly atmospheric N 2/Ar (=83) and 15 N / 14 N ( δ=0‰) ratios whereas CO 2-rich samples show anomalously high δ 15N values (up to +6.13 ‰), likely related to N 2 from metamorphic schists lying below the carbonate formations. On the basis of average 13 C / 12 C isotopic ratio ( δ 13C around 0‰), CO 2 seems to originate mainly from thermometamorphic reactions in the carbonate reservoir and/or in carbonate layers embedded in the underlying metamorphic basement. Distribution of 3 He / 4 He isotopic ratios indicates a radiogenic origin of helium in a tectonic environment that, in spite of the presence of many post-orogenic basins and mantle-derived magmatics, can presently be considered in a compressive phase.

A tentative correlation between seismic activity and changes in the composition of thermal waters on Vulcano Island, Italy

On Vulcano Island, Italy, the thermal water in the shallow water well W2 is a mixture of reservoir water and shallow steam-heated groundwater of meteoric origin. In the period 1986–1988, the composition of the W2 water changed just before two sequences of tectonic earthquakes, from the almost pure reservoir component to the almost pure steam-heated meteoric component. After the seismic activity, the W2 water returned to its pre-earthquake reservoir composition. These changes in composition could be explained by the dilatancy-fluid diffusion model. According to this model, the observed variations in W2 water composition could be the consequence of stress build-up prior to the seismic events, and stress reduction afterwards.

95/01618 The chemical and isotopic compositions of thermal waters at Waimangu, New Zealand

95/01618 The chemical and isotopic compositions of thermal waters at Waimangu, New Zealand

The chemical and isotopic compositions of thermal waters at Waimangu, New Zealand

The surface expression of the Waimangu Geothermal System comprises hot springs and steaming ground which occur in the vicinity of volcanic craters that formed during the 1886 Tarawera Rift eruption. Boiling chloride spring waters discharge over a 30 m vertical interval from the Steaming Cliffs along the western shore of Lake Rotomahana (∼ 340 m asl) to Inferno Crater (373 m asl) in the upper Waimangu Valley. K-Na and K-Mg ratios, aqueous silica concentrations and Δ 18O (sulfate-water) values of spring waters, indicate deep equilibration temperatures that range from 200 to 280°C, while uniform B/Cl ratios (∼ 0.0075) suggest the chloride waters derive from a single reservoir. Stable isotope data are best explained as the result of boiling and dilution in the upper part (<2 km depth) of the system, with an interpreted parent liquid composition of Cl=585 mg/kg, δ 18 O = −4.75 ‰, and δ D = −37.5 ‰ . This liquid is distinct from the parent inferred for the nearby Waiotapu geothermal system and is positively enriched in both δ 18O and δD compared to local meteoric water ( δ 18 O = −6.85 ‰, δ D = −42 ‰ ). Boiling upflow is interpreted to dominate beneath all surface features except in the vicinity of Lake Rotomahana, where a cold hydrostatic cap (∼ 100 m thick) depresses the temperature gradient of rising fluids discharging at Steaming Cliffs. The effects of ground water dilution generally increase with hot spring elevation in response to a steepening hydraulic gradient and rugged topography associated with the volcanic craters of Waimangu Valley. A minimum chloride flux estimate of 80–100 g/s corresponds to a thermal output of 150 to 190 MW.

Isotopic variation of the hydrothermal system on Vulcano Island, Italy

The isotopic and chemical composition of thermal waters and the isotopic composition of high-temperature fumarolic steam at Vulcano Island indicate an evolution of the hydrothermal system from its magmatic origin through interaction with rocks and mixing with meteoric water. Seawater is not a component in this system. The isotopic values of the fumaroles indicate a local magmatic composition of +7 to +8%. δ 18 O and −5 to +15%. δD. The high δD values of this vapor may reflect contamination of the magma by connate water. The isotopic and chemical composition of water from well W2 indicates the existence of geothermal fluid formed by mixing of HCl and SO 2-bearing condensates of volcanic origin with groundwater, with subsequent evolution via water-rock interaction. The estimated isotopic composition of the geothermal water is δ 18 O = +1%. and δD = −5%. Local shallow seismic events result in a temporary increase in fracture permeability, enabling the mixing of magmatic vapor with groundwater or geothermal water. Tectonic activity associated with deep structures appears to increase the contribution of magmatic vapor to the fumaroles.