Geochemical characteristics of the Yufuin outflow plume, Beppu hydrothermal system, Japan

Thermal water at Yufuin (Kyushu Island, Japan) is tapped through about 820 shallow wells and used mainly for hot-spring bathing purposes. Chemical and isotopic data for fluids from wells and fumaroles in Yufuin and Beppu indicate that the thermal activity at Yufuin represents a dilute, westward-flowing hydrothermal outflow plume from the Beppu hydrothermal system. Two other (eastward-flowing) outflow plumes have long been recognized at Beppu, but the Yufuin outflow plume is first recognized here. The Yufuin outflow plume is apparently a mixture of two end-member fluids: (1) deep high-temperature (250–300°C) fluid from the Beppu system having high chloride concentration (1400–1600 mg/L) and a δ¹⁸O value near −6.0%, and (2) meteoric water having low chloride concentration (≤7 mg/L) and a δ¹⁸O value near −9.2%.A permeable conduit for the vertical and lateral transport of deep fluid from the Beppu system is provided by the Yufuin Fault zone, which extends westward from the southern flank of Mt. Tsurumi volcano to the town of Yufuin. Stable isotope ratios and chloride concentrations for shallow groundwaters near the eastern end of the fault, at an elevation near 700 m, are consistent with those required for the low-chloride meteoric end-member of the Yufuin thermal waters. Recharge of this meteoric water, as well as mixing with the Beppu deep fluid, may occur along the Yufuin Fault. Enthalpy-chloride relations indicate additional conductive heating of the Yufuin waters, in the amount of 350–500 kJ/kg beyond that which can be accounted for by mixing between Beppu deep fluid and meteoric water. This could be a result of conductive heating with convection to a depth of 1–2 km. Estimates of the magnitude of the heat source for the Beppu hydrothermal system should take into account the heat being discharged at Yufuin.     

Preliminary evaluation of soufriere geothermal field, St. Lucia (Lesser antilles)

Geological, geochemical and geophysical studies have been carried out in the Soufrière caldera, St. Lucia, Lesser Antilles. The results are in accordance with the data obtained from previously drilled wells. In particular, these studies have also been used to: (i) determine the extent of the heat anomaly; (ii) indicate the levels containing hot geothermal fluids for high enthalpy exploitation; (iii) estimate the nature and extent of the reservoir; (iv) construct a preliminary model of the geothermal system, with a fluid at 220°C and a deeper one at about 350°C, both originating from a concentrated brine. Heat flux is estimated to be 6–7 times the average terrestrial value (250 – 290 mW/m²); (v) determine the most favourable areas for deep drilling.     

Chilean geothermal resources and their possible utilization

Most of the hot spring areas in Chile are located along the Andean Cordillera, associated with Quaternary volcanism. The volcanic—geothermal activity is mainly controlled by the subduction processes of the Nazca and Antarctic oceanic plates under the South America continental plate, and occurs at three well-defined zones of the Chilean Andes: the northern zone (17°30′–28°S), the central—south zone (33φ–46°S) and the southern-most or Austral zone (48°–56°S).Some tested high temperature geothermal fields, and geological and geochemical surveys of many other hot spring areas, evidence a great potential of geothermal resources in this country. Both electrical and non-electrical applications of this potential are considered in this paper.Taking into account the potentially available geothermal resources, the development of natural resources, the geographic and social—economic conditions existing in the different regions of Chile, it is concluded that power generation, desalination of geothermal waters, recovery of chemicals from evaporite deposits and brines and sulfur-refining are the main possible applications of geothermal energy in northern Chile; in central—south Chile geothermal energy is suitable for agribusiness such as greenhouses, aquaculture and animal husbandry.     

Research and development of geothermal energy production in Hungary

The basement of the Pannonian (Carpathian) basin is represented by Paleozoic metamorphic and Mesozoic dolomite and limestone formations. The Tertiary basin gradually subsided during the Alpine orogeny down to 6000 m and was filled by elastic sediments with several water horizons.A heat flow of 2.0 to 3.4 μcal/cm²s gives temperature gradients between 45 and 70 °C/km in the basin. At 2000 m depth the virgin rock temperature is between 110 and 150°C. 80 geothermal wells about 2000 m deep have shown the great geothermal potential of the basin.The main hot water reservoir is the Upper Pliocene (Pannonian) sandstone formation. Hot water is produced by wells from the blanket or sheet sand and sandstone, intercalated frequently by siltstone. Between a 100–300 m interval, 3 to 8 permeable layers are exploited resulting in 1–3 m³/min hot water at 80–99°C temperature.Wells at present are overflowing with shut-in pressures of 3–5 atm.The Pannonian basin is a conduction-dominated reservoir. Convection systems are negligible, hot igneous systems do not exist. The assessment of geothermal resources revealed that the content of the water-bearing rocks down to 3000 m amounts to 12,600 × 10¹⁸cal. In the Tertiary sediments 10,560 × 10¹⁸cal and in the Upper Pannonian, 1938 × 10¹⁸cal are stored. In the Upper Pannonian geothermal reservoir, below 1000 m, where the virgin rock temperature is between 70 and 140°C, the stored heat is 768 × 10⁸cal. A 10¹⁸ cal is equivalent to the combustion heat of 100 million tons of oil. The amount of recoverable geothermal energy from 768 × 10⁸cal is 7.42 × 10¹⁸cal, i.e. about 10,000 MW century, not considering reinjection.At present the Pannonian geothermal reservoir stores the greatest amount of identified heat which can be mobilized and used. Hungary has 496 geothermal wells with a nominal capacity of 428 m³/min, producing 1342 MW heat. 147 wells have an outflow temperature of more than 60°C producing 190 m³/min, that is, 845 MW. In 1974 290 MWyear of geothermal energy was utilized in agriculture, district heating and industry.     

Isotopic and chemical evidence for water sources and mixing in the Cerro Pando geothermal area, Republic of Panama

The Cerro Pando geothermal area in Chiriqui Province is situated just to the south of the continental divide in western Panama. Three groups of thermal springs are associated with lineations in a complex of late Tertiary and Quaternary extrusives. Spring temperatures reach maximum values of 66°C at Los Pozos, 67°C at Cotito and 41°C at Catalina; flow-rates are low, ranging up to 1.5 l/s. However, total heat output is estimated at around 7 MW from calculations incorporating measured spring discharges with river-bed discharges inferred from stream conductivity anomalies. In all cases the spring hydrochemistries become of a more dominantly Na-Cl character as mineralization increases; the highest salinities are found in samples from test boreholes in which 4500 mg/l Cl⁻ has been measured. ¹⁸O/¹⁶O and ²H/¹H data for all thermal springs are roughly colinear, plotting on the δ-diagram with a slope around 3.6 and intersecting the meteoric water line within the compositional range of local surface water. Moreover, δ¹⁸O data are found to correlate with Cl⁻ concentrations, although separate linear trends represent the Los Pozos/Cotito and the Catalina groups of springs. These data are interpreted as indicating that deep thermal ground water feeds the thermal spring systems, with differing isotopic compositions and/or salinities in the Los Pozos/Cotito and Catalina groups. These end-member compositions have evolved by sub-surface steam loss, possibly without any δ ¹⁴O shift due to water - rock exchange. The observed spring compositions are all mixtures between the deep thermal and shallow cool end-member ground waters. The importance of resolving mixing relationships before applying geothermometric calculations is illustrated.     

Hot springs and geothermal gradients in northern Thailand

Chemical geothermometry of hot springs in northern Thailand indicates that many have reservoir temperatures in excess of 150°C and some in excess of 180°C. Measurements of temperatures in abandoned oil wells in Fang Basin indicate geothermal gradients of 70 – 130 mK/m. The high geothermal gradient may be the result of extensional tectonics in northern Thailand, caused indirectly by sea-floor spreading in the Andaman Sea. Relatively high reservoir temperatures and shallow reservoir depths suggest that hot spring areas in northern Thailand may be potential sources of geothermal energy.     

Geothermal district heating for reno, Nevada, U.S.A.

The City of Reno is one of the most obvious candidates for geothermal district heating in the United States. Lying within a helt of major thermal anomalies, it has within its boundaries the Moana Hot Springs geothermal reservoir and probably other reservoirs, and only 14 km to the south is the major reservoir at Steamboat Hot Springs.This paper discusses the alternative heat sources that can be used, and selects Steamboat as the most conservative choice for a “worst-case” analysis of the details and economics of a model district heating system. A closed 16 km transmission loop between Steamboat and downtown Reno is envisaged, carrying 121°C water in the supply line and 65°C in the return line. This loop is isolated by heat exchangers from both the 176°C geothermal fluids at the Steamboat end of the line, and from the Reno user systems at the other. Detailed analysis of thermal demand densities in different parts of the City led to a model distribution network 48 km long, that serves the optimum grouping of zones of concentrated heat users. A large proportion of existing heating systems are hydronic and retrofitting of the selected buildings to the district heating system is relatively straightforward. Total peak load for the proposed system is 138 MJ s⁻¹ (139 MW_t) and annual consumption is 1.1 × 10¹⁵ J. Capital costs total about $55.4 million, in 1981 dollars. The economic analysis shows this system could provide considerable savings relative to the cost of natural gas, if revenue bond financing at 13% is employed for the construction and startup of the system. Even more favorable economic results could be achieved if a geothermal resource could be developed closer to downtown Reno, eliminating the high cost of the 16 km transmission pipeline. Reducing the service area to the most concentrated area of heat use in downtown Reno produces an even more viable system, about half the size of the full system.     

Comparison of carbon dioxide emissions with fluid upflow, chemistry, and geologic structures at the Rotorua geothermal system, New Zealand

During 2002 and 2003, carbon dioxide fluxes were measured across the Rotorua geothermal system in the Taupo Volcanic Zone (TVZ), New Zealand. The results of a 956-measurement survey and of modeling studies show that CO₂ fluxes could be used to determine the main hot fluid upflow areas in Rotorua, and perhaps in undeveloped geothermal regions. Elevated degassing was observed along inferred fault traces and structures, lending confidence to their existence at depth. Degassing was also observed along lineaments that were consistent with the alignment of basement faulting in the TVZ. Areas where elevated degassing was spatially extensive typically overlapped with known regions of hot ground; however, elevated CO₂ fluxes were also observed in isolated patches of non-thermal ground. The total emission rate calculated from sequential Gaussian simulation modeling of CO₂ fluxes across the geothermal system was 620 t d⁻¹ from an 8.9-km² area. However, because approximately one-third of the geothermal system is known to extend beneath Lake Rotorua, we expect the emissions could be minimally on the order of 1000 t d⁻¹. Comparing the emission rate with geochemical analyses of geothermal fluids and estimated upflows suggests that the majority of deep carbon reaches the surface in the form of carbon dioxide gas, and that less than one tenth of the CO₂ emissions is dissolved in, or released from, the fluids at depth. Thus, the geothermal reservoir exerts very little control on deep degassing of CO₂. Carbon isotopic analyses of soil gases suggest a primarily magmatic source for the origin of the CO₂. The total Rotorua emission rate is comparable to those from active volcanoes such as at White Island, New Zealand, and, when normalized by geothermal area, is comparable to other volcanic and hydrothermal regions worldwide.     

The Iceland Deep Drilling Project: a search for deep unconventional geothermal resources

The Iceland Deep Drilling Project (IDDP) is a long-term program to improve the economics of geothermal energy by producing supercritical hydrous fluids from drillable depths. Producing supercritical fluids will require the drilling of wells and the sampling of fluids and rocks to depths of 3.5–5 km, and at temperatures of 450–600 °C. The IDDP plans to drill and test a series of such deep boreholes in the Krafla, Nesjavellir and Reykjanes geothermal fields in Iceland. Beneath these three developed high-temperature systems frequent seismic activity continues below 5 km, indicating that, even at supercritical temperatures, the rocks are brittle and therefore likely to be permeable, even where the temperature is assumed to exceed 550–650 °C. Temperature gradients are greater and fluid salinities smaller at Nesjavellir and Krafla than at Reykjanes. However, an active drilling program is underway at Reykjanes to expand the existing generating capacity and the field operator has offered to make available one of a number of 2.5 km deep wells to be the first to be deepened to 5 km by the IDDP. In addition to its potential economic significance, drilling deep at this location, on the landward extension of the Mid-Atlantic Ridge, is of great interest to the international science community. This paper examines the prospect of producing geothermal fluids from deep wells drilled into a reservoir at supercritical temperatures and pressures. Since fluids drawn from a depth of 4000–5000 m may prove to be chemically hostile, the wellbore and casing must be protected while the fluid properties are being evaluated. This will be achieved by extracting the fluids through a narrow retrievable liner called the “pipe”. Modelling indicates that if the wellhead enthalpy is to exceed that of conventionally produced geothermal steam, the reservoir temperature must be higher than 450 °C. A deep well producing 0.67 m³/s steam (2400 m³/h) from a reservoir with a temperature significantly above 450 °C could, under favourable conditions, yield enough high-enthalpy steam to generate 40–50 MW of electric power. This exceeds by an order of magnitude the power typically obtained from a conventional geothermal well in Iceland. The aim of the IDDP is to determine whether utilization of heat from such an unconventional geothermal resource at supercritical conditions will lead to increased productivity of wells at a competitive cost. If the IDDP is an economic success, this same approach could be applied in other high-temperature volcanic geothermal systems elsewhere, an important step in enhancing the geothermal industry worldwide.     

Hydrothermal alteration in the Aluto-Langano geothermal field, Ethiopia

The hydrothermal mineral assemblages found in eight wells (with a depth range of 1320–2500 m) of the active geothermal field of Aluto-Langano (Ethiopia) indicate a complex evolution of water-rock interaction processes. The zone of upflow is characterized by high temperatures (up to 335°C) and the presence of a propylitic alteration (epidote, calcite, quartz and chlorite, as major phases) coexisting with calcite and clay minerals. The zone of lateral outflow is characterized by mixing of deep and shallow waters and the occurrence of a calcite-clay alteration that overprints a previous propylitic assemblage. Clay minerals have a mushroom-shaped zonal distribution consistent with the present thermal structure of the field. Microprobe analyses have been carried out on chlorite and illite in order to apply several geothermometers. Most of the chlorite is iron-rich chlorite. It is found that the temperatures calculated from the chlorite geothermometer (159–292°C) after Cathelineau and Nieva [Contrib. Mineral. Petrol. 91, 235–244 (1985)] are in good agreement with in-hole measured temperatures (155–300°C). In the upflow zone, temperatures calculated from this geothermometer (217–292°C), together with fluid inclusion data of Valori et al. [Eur. J. Mineral. 4, 907–919 (1992)], and computed saturation indices of alteration minerals, indicate thermal stability or slight heating. On the other hand, evidence of a significant cooling process (up to 171°C) in the outflow zone is provided by the comparison between fluid inclusion homogenization temperature (240–326°C) and in-hole temperature (155–250°C). The apparent salinities (0.8–2.3 wt% NaCl eq.) of the fluid inclusions are generally higher than the salinity of the present reservoir fluid (0.29–0.36 wt% NaCl eq.). Clay minerals (illite, smectite, Ill/S mixed layers, vermiculite and chloritic intergrades) generally occur at temperatures consistent with their stability fields.     

Measurement and interpretation of terrestrial heat flow in Israel

Sixty-eight new determinations of terrestrial heat flow in Israel have a range of 0.17-11.07 μcal/cm²s. The average value of deep conductive heat flow in the undisturbed complex of the Arabo-Nubian Massif is 0·94 μcal/cm²s; it is least affected by circulation of groundwater. This value is only slightly higher than the heat flow of 0·88 μcal/cm²s in the Levantine Basin of the Mediterranean Sea. Several values that exceed 2·0 μcal/cm²s are due either to (probable) deep hydrothermal activity or to small domal structures of the basement.Within the sedimentary sequence which blankets the crystalline massif, terrestrial heat flow is often redistributed by circulating groundwater. Recharge regions, particularly Judean-Samarian Galilee, where cool meteoric waters percolate into the subsurface have anomalously low heat flow, ranging from 0·17 to about 1·0 μcal/cm²s. Part of the original deep thermal flux in those regions is intercepted at moderate depths by the recharge flow, and is carried into deeper aquifers of the Foothills, Coastal Plain, or the Jordan-Dead Sea Rift. Movement of groundwater occurs mainly along faults.Deep faults associated with the Jordan-Dead Sea Rift system act as conduits for hot waters ascending from deep confined aquifers. The most tangible surface expression of the convective hydrothermal system are the numerous warm to hot springs, emerging along the margins of the Rift. However, the waters emerging on the surface as the warm and hot springs are a minor fraction of the convective system. Most of the ascending thermal waters are absorbed by shallow aquifers with lower hydraulic potential. Such regions are characterized by anomalously high heat flow; several values exceed 2 and one value is 11 μcal/cm²s.     

Fluid-rock interaction processes in the Te Kopia geothermal field (New Zealand) revealed by SEM-CL imaging

Scanning electron microscopy-cathodoluminescence (SEM-CL) imaging of hydrothermal quartz exposed by weathering in the Te Kopia geothermal field (New Zealand) has revealed a history of crystal growth, dissolution, overprinting and fracturing that cannot be detected using other observational techniques (e.g. transmitted or reflected light microscopy, back-scattered electron imaging or secondary electron imaging). The crystals initially grew as CL-dark quartz, at least 350 m below their present location on the Paeroa Fault scarp, in a neutral pH, 215±10 °C liquid reservoir (inferred from the analysis of primary liquid fluid inclusions: mean T_h of 213 °C; 0.2–0.4 wt.% NaCl_eq.). Relict quartz–adularia–illite alteration occurs at the surface, in the vicinity of the quartz crystals, and in drillcores from the nearby TK-1 exploration well. Repeated movement on the Paeroa Fault uplifted pyroclastic rocks hosting the quartz crystals, but also provided pathways for “pulses” of hot fluids to move through the system. Quartz precipitation occurred at the edge of the crystals as the reservoir fluids cooled, as indicated by micron-scale alternating CL-dark/CL-bright quartz growth bands, which contain fluid inclusions with T_h values of 210±40 °C. Pressure fluctuations were the likely cause of dissolution, marked by corroded crystal edges, with subsequent precipitation of quartz into open space. SEM-CL imaging shows that the quartz crystals contain healed fractures, which trapped low salinity fluids with T_h values of 201±6 °C. Low-pH fluids in the near-surface setting also rounded the quartz crystals, and coated them with kaolinite and CL-grey amorphous “silica residue”.     

Geothermal resources of Hachijojima

Hachijojima is a gourd-shaped volcanic island in the Pacific Ocean. Nishiyama and Higashiyama volcanoes consist of basalt lava and associated pyroclastic rocks. A promising geothermal resource was found in south Higashiyama, associated with an uplift of Tertiary rocks consisting of mainly andesite lava and related pyroclastic rocks, overlain by Quaternary volcanic rocks. Steep high-temperature (over 250°C) and high-pressure gradients occur in the deeper portion of the system near the Tertiary–Quaternary contact, indicating the presence of a cap rock. The cap rock formed by deposition of hydrothermal minerals. Geothermal fluid ascends from the deeper portions to shallow depths along vertical fractures through the cap rock. These vertical fractures form the geothermal reservoir in the Tertiary formation. Three wells were drilled into these vertical fractures, and approximately 30 t/h of superheated steam was obtained from each well during flow tests. The geothermal fluid is mainly a mixture of seawater and meteoric water in an approximate ratio of 1 to 2, based on chemical analyses, with a portion of volcanic gas included. At present a 3.3 MW_e, geothermal power plant is being constructed here.     

The Bad Blumau geothermal project: a low temperature, sustainable and environmentally benign power plant

The 250 kW geothermal project at Bad Blumau is the first geothermal project developed in Austria by the private sector following the deregulation of the electricity industry in this country. What makes the project unique besides its private ownership structure is its ability to generate electrical power and district heating for the Rogner Bad Blumau Hotel & Spa by using a low temperature geothermal resource. Installed in the record time of less than a week, the air-cooled ORMAT ® Energy Converter (OEC) CHP module has been in commercial operation since July 2001. With an annual availability exceeding 99%, between October 2001 and December 2002 the plant delivered 1,560,000 kWh to the local grid. The geothermal CHP module utilizes brine at 110 °C, available from a 3000 m deep production well. Exiting the OEC unit at a temperature of 85 °C, the brine is then fed into the district heating system, providing heat for the Rogner Bad Blumau Hotel & Spa. The geothermal brine is returned from the district heating system and injected into a 3000 m depth reinjection well. The system is a pollution-free, unattended operating power generation module, which has avoided more than 1100 kg of CO₂ emissions over its first operating year.     

Hydrogeochemistry and geothermal characteristics of the White Lake basin, South-central British Columbia, Canada

Hydrogeochemistry and geothermal characteristics of the Tertiary White Lake basin are described in order to provide constraints on the hydrogeology and thermal regime of the basin. The basin can be divided into three flow subsystems on the basis of chemical and isotopic variations. The groundwaters evolve chemically from young Ca–Mg–HCO₃ type waters in the shallow surficial sediments to Na-dominated waters in the deeper intermediate system. Surface waters and shallow groundwaters collected from wells completed in overburden have undergone extensive evaporation as evidenced by their enriched δ¹⁸O and δ²H composition. Minor evaporation identified in the isotope composition of groundwater from domestic wells completed in bedrock, as well as from springs, suggests a local to intermediate origin for these waters, and perhaps mixing with shallow evaporative waters. In contrast, the uniform isotope signatures of deep basin waters measured both spatially and vertically suggest recharge at higher elevations, and a much deeper circulation system that is essentially isolated from the shallow subsurface. Chemical geothermometry indicates that spring waters and bedrock well waters have equilibrated at temperatures of less than 20 and 60°C, respectively. Groundwaters encountered by deep diamond drill holes, with equilibration temperatures of less than 80°C, are representative of intermediate flow systems, and may serve to modify the heat flow regime in the basin. Regional groundwater flow within the basin is complex due to numerous faults that exert a strong influence on fluid circulation patterns. Transport of heat in the subsurface, which has resulted in variations in the measured thermal gradients across the basin, occurs either at depths greater than those investigated in this study or has been significantly influenced by the circulation of cooler groundwater in the central part of the basin.     

Takigami geothermal system, northeastern Kyushu, Japan

The Takigami geothermal reservoir is bounded by a system of faults and fractures oriented along two main directions, north to south and east to west. The Noine fault has a large vertical displacement and trends north to south, dividing the subsurface characteristics of resistivity, permeability, temperature and reservoir depth. The Takigami geothermal fluid has a near neutral pH and is of the Na–Cl type, with a chloride content ranging from 400 to 600 ppm. The southwestern part of the area has the highest subsurface temperature, up to 250°C. The deep fluid originates from the southwest, and flow is mainly to the north and partly to the east along faults and fractures, decreasing in temperature with increasing lateral flow.     

Low enthalpy geothermal energy utilisation schemes for greenhouse and district heating at Traianoupolis Evros, Greece

A socio-economic study has been made of the possible use of low enthalpy geothermal resources for district and greenhouse heating in the Traianoupolis Evros region. The thermal energy potential of the Aristino-Traianoupolis geothermal field has been estimated at 10.8 MW_th (discharge temperature of 25 °C). Geothermal wellhead water temperatures range from 53 to 92 °C, from 300 m deep wells yielding over 250 m³/h. Our conclusions show, amongst the different scenarios examined and on the basis of a market study, that utilisation of this geothermal energy capacity for district heating of nearby villages, and/or greenhouse heating directed at serving local vegetable markets, would be an attractive investment.     

Thermophilic microorganisms in the hot springs of Tengchong geothermal area, West Yunnan, China

The distribution of thermophilic microorganisms in the hot springs of the volcanic geothermal area of Tengchong County, Yunnan Province was examined and the following observations made:

1. (1) Large numbers of filamentous and rod-shaped non-photosynthetic bacteria grow in Big Boiling Pot, which is a siliceous, alkaline boiling spring with temperatures ranging from 86 to 91°C. Macroscopic bacteria masses colonized on the surface of the geyserites in the spring pool. The bacteria show distinct ultramicrostructure of the cell wall, which has a striated appearance possibly caused by a number of penetrating micro-channels. Some sections of the bacteria cells also show an unusually thick wall.

2. (2) Typical Synechococcus-Chloroflexus microbial mats grow and cover the substrata of the spring water flows with temperatures ranging from 68 to 72°C.

3. (3) When the spring water cools, the number of species increases progressively. The microbial mats growing at temperatures below 60°C consist mainly of filamentous blue-green algae.

The significance of studies on thermophilic microorganisms and volcanic geothermal environments is discussed.     

Geothermal development in Hungary—country update report 2000–2002

This paper describes the status of geothermal energy utilization—direct use—in Hungary, with emphasis on developments between 2000 and 2002. The level of utilization of geothermal energy in the world increased in this period and geothermal energy was the leading producer, with 70% of the total electricity production, of all the renewable energy sources (wind, solar, geothermal and tidal), followed by wind energy at 28%. The current cost of direct heat use from biomass is 1–5 US¢/kWh, geothermal 0.5–5 US¢/kWh and solar heating 3–20 US¢/kWh. The data relative to direct use in Hungary decreased in this period and the contribution of geothermal energy to the energy balance of Hungary, despite significant proven reserves (with reinjection) of 380 million m³/year, with a heat content of 63.5 PJ/a at ΔT=40 °C, remained very low (0.25%). Despite the fact that geothermal fluids with temperatures at the surface higher than 100 °C are available, no electricity has been generated. As of 31 December 2002, the geothermal capacity utilised in direct applications in Hungary is estimated to be 324.5 MW_t and to produce 2804 TJ/year. Geothermal heat pumps represent about 4.0 MW_t of this installed capacity. The quantity of thermal water produced for direct uses in 2002 was approximately 22 million m³, with an average utilization temperature of 31 °C. The main consumer of geothermal energy is agriculture (68% of the total geothermal heat dedicated to direct uses). The geothermal water is used only in five spas for space heating and sanitary hot water (SHW), although there are 260 spas in the country, and the thermal water produced has an average surface temperature of 68 °C. The total heat capacity installed in the spas is approximately 1250 MW_t; this is not provided by geothermal but could be, i.e., geothermal could provide more than three times the geothermal capacity utilized in direct uses by 31 December 2002 (324.5 MW_t).     

Magmatic fluid input to the Kuju-Iwoyama hydrothermal system prior to the 1995 eruption of the Kuju volcano (Kyushu, Japan)

A schematic model showing the sources of hot waters being discharged at the surface in the Kuju-Iwoyama of the Kuju volcano has been developed. Based on the isotopic characteristics of these fluids it is inferred that deep magmatic fluid mixes with thermal waters derived from rainwater in a shallow geothermal reservoir, and with local groundwaters in a deeper reservoir. These thermal waters feed hot springs that discharge waters with Cl/SO₄ ratios that differ from that of the fumaroles on Kuju-Iwoyama, due to the addition of SO₄²⁻ ions produced by the decomposition of native sulfur and mixing with magmatic fluid of high Cl content.