Hrefna Kristmannsdóttir

High temperature alteration minerals and thermal brines, Reykjanes, Iceland

The geothermal area on Reykjanes, Iceland has been investigated mineralogically. The temperature within the studied area is very variable from 30–300° C. Mineral zones corresponding to the temperature conditions in the area are found. Accidental changes in the geothermal system are also reflected in the mineralogy by formation of anhydrite. Changes in temperature conditions in the field are indicated by epidote occurrence at 40° C and retrograd formation of montmorillonite.

Environmental aspects of geothermal energy utilization

Geothermal energy is a clean and sustainable energy source, but its development still has some impact on the environment. The positive and negative aspects of this environmental impact have to be considered prior to any decision to develop a geothermal field, as well as possible mitigation measures. The main environmental effects of geothermal development are related to surface disturbances, the physical effects of fluid withdrawal, heat effects and discharge of chemicals. All these factors will affect the biological environment as well. As with all industrial activities, there are also some social and economic effects. In Iceland an enforcement program was launched in the early 1990s to study the environmental impact of developing geothermal resources. Work began on tackling the environmental issues relative to the high-temperature geothermal fields under development in Iceland. Research was conducted on microearthquake activity in geothermal areas and a methodology developed for mapping steam caps. The foundations were laid of networks for monitoring land elevation and gravity changes. Baseline values were defined for the concentrations of mercury and sulfur gases. Groundwater monitoring studies were enforced. Atmospheric dispersion and reaction of geothermally-emitted sulfur gases and mercury were studied. Aerial thermographic survey methods were refined and tested and their capacity to detect and map changes in surface manifestations with time was demonstrated. To further the use of geothermal energy worldwide the International Energy Association set up a Geothermal Implement Agreement (GIA) in 1997; its environmental Annex has been actively implemented, with several projects still under way.

Discovery and Description of Giant Submarine Smectite Cones on the Seafloor in Eyjafjordur, Northern Iceland, and a Novel Thermal Microbial Habitat

ABSTRACT With the submersible JAGO and by scuba diving we discovered three remarkable geothermal cones, rising 33, 25, and 45 m from the seafloor at a depth of 65 m in Eyjafjordur, northern Iceland. The greatest geothermal activity was on the highest cone, which discharged up to 50 liters of freshwater per s at 72°C and pH 10.0. The cones were built up from precipitated smectite, formed by mixing of the hot SiO2-rich geothermal fluid with the cold Mg-rich seawater. By connecting a rubber hose to one outflow, about 240 liters of pure geothermal fluids was concentrated through a 0.2-μm-pore-size filter. Among 50 thermophilic isolates, we found members of Bacillus and Thermonema and a new unidentified low-G+C gram-positive member of theBacteria as well as one member of theArchaea, Desulfurococcus mobilis. Analysis of small-subunit rRNA genes PCR amplified and cloned directly from environmental DNA showed that 41 out of 45Bacteria sequences belonged to members of theAquificales, whereas all of the 10Archaea sequences belonged to theKorarchaeota. The physiological characteristics of isolates from different parts of the cones indicate a completely freshwater habitat, supporting the possibility of subterranean transmittance of terrestrial organisms.

Geothermal environmental impact

Abstract Geothermal utilization can cause surface disturbances, physical effects due to fluid withdrawal, noise, thermal effects and emission of chemicals as well as affect the communities concerned socially and economically. The environmental impact can be minimized by multiple use of the energy source and the reinjection of spent fluids. The emission of greenhouse gases to the atmosphere can be substantially reduced by substituting geothermal energy for fossil fuels as an industrial energy source wherever possible.

Effects of volcanic eruptions on the CO2 content of the atmosphere and the oceans: the 1996 eruption and flood within the Vatnajökull Glacier, Iceland

Abstract The October 1996 eruption within the Vatnajokull Glacier, Iceland, provides a unique opportunity to study the net effect of volcanic eruptions on atmospheric and oceanic CO 2 . Volatile elements dissolved in the meltwater that enclosed the eruption site were eventually discharged into the ocean in a dramatic flood 35 days after the beginning of the eruption, enabling measurement of 50 dissolved element fluxes. The minimum concentration of exsolved CO 2 in the 1×10 12 kg of erupted magma was 516 mg/kg, S was 98 mg/kg, Cl was 14 mg/kg, and F was 2 mg/kg. The pH of the meltwater at the eruption site ranged from about 3 to 8. Volatile and dissolved element release to the meltwater in less than 35 days amounted to more than one million tonnes, equal to 0.1% of the mass of erupted magma. The total dissolved solid concentration in the floodwater was close to 500 mg/kg, pH ranged from 6.88 to 7.95, and suspended solid concentration ranged from 1% to 10%. According to H, O, C and S isotopes, most of the water was meteoric whereas the C and S were of magmatic origin. Both C and S went through isotopic fractionation due to precipitation at the eruption site, creating “short cuts” in their global cycles. The dissolved fluxes of C, Ca, Na, Si, S and Mg were greatest ranging from 1.4×10 10 to 1.4×10 9 mol. The dissolved C flux equaled 0.6 million tonnes of CO 2 . The heavy metals Ni, Mn, Cu, Pb and Zn were relatively mobile during condensation and water–rock interactions at the eruption site. About half of the measured total carbon flood flux from the 1996 Vatnajokull eruption will be added to the long-term CO 2 budget of the oceans and the atmosphere. The other half will eventually precipitate with the Ca and Mg released. Thus, for eruptions on the ocean floor, one can expect a net long-term C release to the ocean of less than half that of the exsolved gas. This is a considerably higher net C release than suggested for the oceanic crust by Staudigel et al. [Geochim. Cosmochim. Acta, 53 (1989) 3091]. In fact, they suggested a net loss of C. Therefore, magma degassed at the ocean floor contributes more C to the oceans and the atmosphere than magma degassed deep in the oceanic crust. The results of this study show that subglacial eruptions affecting the surface layer of the ocean where either Mn, Fe, Si or Cu are rate-determining for the growth of oceanic biomass have a potential for a transient net CO 2 removal from the ocean and the atmosphere. For eruptions at high latitudes, timing is crucial for the effect of oceanic biota. Eruptions occurring in the wintertime when light is rate-determining for the growth of biota have much less potential for bringing about a transient net negative CO 2 flux from the ocean atmosphere reservoir.

BIOGENIC SAPONITE FROM AN ACTIVE SUBMARINE HOT SPRING, ICELAND

A study of the mineralogy, chemical composition and structure of poorly-crystalline saponite precipitated from a submarine hot spring in Eyjafjordur, northern Iceland is reported. Special emphasis was placed on the microstructures of the minerals and a possible connection with biological activity during their precipitation. The microstructures of the minerals were found to be very similar to specific clay minerals precipitated from geothermal vents in oceanic rift zones. The composition of the minerals was, however, found to be similar to magnesium silicate scales formed in geothermal installations in Iceland where geothermal waters were mixed with cold fresh waters. High contents of organic substances were found in the clay mineral samples as compared to geothermal precipitates from other localities. Microstructural features of the layer silicates in one of the samples suggest that a gelatinous substance was a precursor of the saponite clay. The organic matter content appears to be greater when the precipitates are more crystalline.

Chemical Evidence from Icelandic Geothermal Systems as Compared to Submarine Geothermal Systems

The Reykjanes geothermal system is the most interesting of the Icelandic geothermal areas for chemical comparison with submarine geothermal systems. The geothermal water at Reykjanes is seawater. Base temperatures in the Reykjanes geothermal system is considerably lower than the estimated temperatures of the submarine systems. In the Krafla geothermal system the base temperatures are almost as high as in the submarine geothermal systems but the geothermal water is of meteoric origin with low content of dissolved solids. Magmatic activity has strongly influenced the chemistry of the Krafla geothermal system.

Groundwater in the Lake Myvatn area, northern Iceland: Chemistry, origin and interaction

Lake Myvatn, northern Iceland is unique in that almost all the inflow is supplied through the groundwater by artesian springs. Hardly any surface water is encountered in the area which is covered by young and porous lava fields and transected by faults. The inflow of water and its chemical composition is, therefore, very stable. Geothermal and volcanic activities affect the groundwater system in the Lake Myvatn area and greatly influence the lakes chemistry and thus the biological conditions especially by providing continuous and ample sources of silica and sulphate. Groundwater studies have been intensified in the area during the last years for further developing the Námafjall geothermal field in the area and the Krafla geothermal field about 10 km from Námafjall. Groundwater chemistry was monitored regularly for 2 years at 22 sampling sites and for determining selected indicator constituents in the samples. Concurrently, several tracer tests were performed in the area, the rate of groundwater flow measured, a reservoir model of the groundwater system established. These studies enabled us to divide cold groundwater and geothermal effluent in the Lake Myvatn area into six distinct groups, based on stable isotope ratios, chemical composition and geographical position. The groundwater has separate origins in the local high ground north of Lake Myvatn and the highlands far to the south, possibly as far south as the glacier Vatnajökull. The waters are to a different extent affected by geothermal activity, and effects of volcanic activity were noted during the Krafla fires in 1975–1984. Although these have diminished, they have not completely disappeared. The effluent from Krafla seems to travel to the east of Lake Myvatn and traces of it have not been found to enter the lake. The Námafjall effluent on the other hand travels along fissures to the lake. Attempts made to simulate the evolution of the geothermal water of Krafla and by theoretically titrating local groundwater with rock at elevated temperatures and adding volcanic gas seem promising and result in a composition close to the natural one.

Magnesium silicate scaling in district heating systems in Iceland

Abstract Scaling of magnesium silicates has been a problem in some of the Icelandic district heating systems. This kind of scaling is not encountered in heating systems utilizing geothermal weater directly but occurs by heating and deaeratmg freshwater. The properties and causes of the scaling have been examined and the results are reported in the paper. Possible remedies for the problems have been tested and their effectiveness is discussed It is concluded that even though there appears not to be any definite solution to the problem, it can be kept at a minimum by a design based on pilot plant tests.

Trace element composition of anorthosite plagioclase

Abstract Plagioclases from massif anorthosites are strongly depleted in Rb and Cs relative to those from anorthosites associated with volcanic rocks, but are enriched in K and REE. Anorthosite plagioclases generally show strong enrichment of the lighter REE. The inclusions in Icelandic basalts are unique in having low K and K/Rb and relatively less-fractionated REE patterns; they may be the closest terrestrial analogues to the lunar highlands anorthosites. Regular variations in the trace element concentrations of terrestrial plagioclases are produced by the systematic relations between bulk composition and trace element composition of magma, on the one hand, and between plagioclase composition and element partitioning on the other. The failure of lunar plagioclases to follow these regular trends reflects differences in the relative abundances of K, Ca, Ba and Sr between terrestrial and lunar magmas of similar bulk composition.