Papers by Magnús Ólafsson
Procedia Earth and Planetary Science, 2013
Drilling commenced in the Bjarnarflag field of the Námafjall high temperature area in 1963. The f... more Drilling commenced in the Bjarnarflag field of the Námafjall high temperature area in 1963. The first wells were shallow and some were destroyed in the Krafla Fires (1975 to 1984). At present six production wells are available in the area for a proposed 45 MWe power plant, and more wells will be drilled in the near future. The well fluid has low mineral and gas contents and is well suited for a power plant.
Sampling and analysis provide the data for all geochemical interpretation and thus it is imperati... more Sampling and analysis provide the data for all geochemical interpretation and thus it is imperative that these tasks be performed by trained personnel with insight into possible errors. Different types of containers (glass, or plastic, amber or transparent) and different pre-treatment (filtering, freezing, addition of chemicals) is needed for the various constituents determined. Some constituents need analysis shortly after collection either on the spot or in a nearby laboratory which may be a field laboratory. The most common analytical techniques employed for geothermal fluid samples that are likely to be available in most laboratories are titrimetry, UV-Vis spectrophotometry, atomic absorption spectrophotometry (AAS), ion chromatography (IC), electrometry and gas-solid chromatography (GSC). In recent years inductively coupled plasma has become widely used both with atomic emission spectrometry (ICP/AES) and mass spectrometry (ICP/MS) but this requires expensive equipment and these instruments tend to be run by large commercial laboratories on a commercial basis and it is quite common that samples are sent there for analysis, especially for major cations and trace elements. Stable isotopes are analysed for by mass spectrometry (MS) and radioactive isotopes by radiometry. These techniques are not available to all laboratories and are frequently carried out on a commercial basis. From the returns in the inter-laboratory comparison of analytical techniques carried out by the International Atomic Energy Agency in 2002 involving 31 laboratories working with geothermal samples it is clear that AAS is the most used technique for cation analysis but titrimetry and UV-Vis spectrophotometry for anion analysis.
Open Journal of geology, 2018
This paper presents a multidisciplinary structural analysis of a 165 km 2 area in the Northern Ri... more This paper presents a multidisciplinary structural analysis of a 165 km 2 area in the Northern Rift Zone and the Tjörnes Fracture Zone of Iceland, and unravels the tectonic control of the Theistareykir geothermal field and its surroundings. About 10729 fracture segments (faults, open fractures, joints) are identified in the upper Tertiary to Holocene igneous series. The segments were extracted from aerial images and hillshade, and then analyzed in terms of number of sets, geometry, motions, frequency, and relative age. The correlation with surface geothermal manifestations, resistivity, earthquakes, and occasional well data reveals the critical regional and local fractures at the surface, reservoir level and greater depth. The main conclusions of this study are: 1) The structural pattern consists of N-S rift-parallel extensional fractures and the Riedel shears of the transform zone striking NNE, ENE, E-W, WNW and NW, which compartmentalize together the blocks at any scale. 2) The en échelon segmentation shows strike and oblique slips on the Riedel shears, with a dextral component on the WNW and NW planes and a sinistral component on the NNE to ENE faults. 3) Fractures form under the influence of the transform mechanism and the effect of rifting becomes significant only with time. 4) The WNW dextral oblique-slip Stórihver Fault of the transform zone has a horsetail splay that extends eastwards into the geothermal field. There, this structure, along with few NW, ENE, NNE and N-S fractures, controls the alteration, alignment of fumaroles, emanating deep gases. These fractures also rupture during natural or induced earthquakes. 5) The resistivity anomalies present en échelon geometries controlled by the six fracture sets. These anomalies display clockwise and anticlockwise rotations within the upper 8 km crustal depth, but at 8 km depth, only three sets
Earth and Planetary Science Letters, Aug 1, 1983
The subsolidus mineralogy and the isobarically-invariant solidus of peridotite in the presence of... more The subsolidus mineralogy and the isobarically-invariant solidus of peridotite in the presence of small amounts of H20 and CO 2 have been determined from 13.5 to 26 kbar pressure. The composition of fluid buffered by amphibole peridotite, below 17.5 kbar, is CO2-rich; amphibole melts completely, although incongruently, near the solidus, contributing materially to the nephelinitic character of the liquids. Fluid-absent amphibole peridotite also melts to nephelinitic liquid. Between 17.5 kbar and 22 kbar, amphibole-carbonate peridotite, without fluid, melts to alkalic, very silica-undersaturated liquid. Above 22 kbar, fluid buffered by carbonate peridotite, with accessory phlogopite, is H20-rich. Quenched liquids could not be analyzed, but they are inferred to be carbonate-rich by analogy with synthetic systems. Buffering offo 2 by graphite-carbonate-silicates maintains these phase relations if graphite is present. The subsolidus change of peridotite carbonate mineralogy from low-pressure dolomite to high-pressure magnesite has been bracketed at 975°C, 28 kbar. Suboceanic thermal models are consistent with the existence of a relatively deep, partially-molten asthenosphere even beneath old (180 m.y.) lithosphere, but melts should be exclusively carbonate-rich. Beneath younger lithosphere, a shallower zone should change, with increasing depth, from nephelinitic to carbonate-rich. Amounts of liquid are proportional to amounts of volatiles present, because amphibole, phlogopite, and carbonates melt quantitatively at or close to the solidus; in particular, 0.1% water in amphibole peridotite represents about 5% nephelinitic melt.
The low-temperature geothermal waters that feed the district heating system in Stykkishólmur, W-I... more The low-temperature geothermal waters that feed the district heating system in Stykkishólmur, W-Iceland, are found in volcanic rocks. The main production aquifer is related to a fracture in a gabbroic intrusion. The high degree of alteration of the reservoir rocks indicates much higher temperatures than presently observed (87°C). Geological investigations reveal that the well is situated within an extinct central volcano. The chemical and isotopic composition of the hot water from the production well in Stykkishólmur differs significantly from that of other lowtemperature areas in Iceland. The geothermal water is brackish, calcium is the dominant cation, and the water type is Cl-Ca-Na. The isotopic composition of the thermal water indicates that it is not strictly a mixture of seawater and present-day freshwater. The results from geothermometry equations indicate that chalcedony controls the silica concentration in the reservoir. Chemical equilibrium calculations for geothermal water in Stykkishólmur were performed with the speciation programs SOLVEQ, WATCH, and PHREEQCI. They show the distribution of aqueous species in the water, as well as saturation indices for minerals occurring in the reservoir. Graphs of log (Q/K) vs. temperature indicate that some alteration minerals found in the well are close to equilibrium with the water at the measured temperature. Chalcedony and anhydrite, in particular, seem to be in full equilibrium.
Biogeosciences, 2015
Colonization of life on Surtsey has been observed systematically since the formation of the islan... more Colonization of life on Surtsey has been observed systematically since the formation of the island 50 years ago. Although the first colonisers were prokaryotes, such as bacteria and blue-green algae, most studies have been focused on the settlement of plants and animals but less on microbial succession. To explore microbial colonization in diverse soils and the influence of associated vegetation and birds on numbers of environmental bacteria, we collected 45 samples from different soil types on the surface of the island. Total viable bacterial counts were performed with the plate count method at 22, 30 and 37 • C for all soil samples, and the amount of organic matter and nitrogen (N) was measured. Selected samples were also tested for coliforms, faecal coliforms and aerobic and anaerobic bacteria. The subsurface biosphere was investigated by collecting liquid subsurface samples from a 181 m borehole with a special sampler. Diversity analysis of uncultivated biota in samples was performed by 16S rRNA gene sequences analysis and cultivation. Correlation was observed between nutrient deficits and the number of microorganisms in surface soil samples. The lowest number of bacteria (1 × 10 4 − 1 × 10 5 cells g −1) was detected in almost pure pumice but the count was significantly higher (1 × 10 6 − 1 × 10 9 cells g −1) in vegetated soil or pumice with bird droppings. The number of faecal bacteria correlated also to the total number of bacteria and type of soil. Bacteria belonging to Enterobacteriaceae were only detected in vegetated samples and samples containing bird droppings. The human pathogens Salmonella, Campylobacter and Listeria were not in any sample. Both thermophilic bacteria and archaea 16S rDNA sequences were found in the subsurface samples collected at 145 and 172 m depth at 80 and 54 • C, respectively, but no growth was observed in enrichments. The microbiota sequences generally showed low affiliation to any known 16S rRNA gene sequences.
Biogeosciences Discussions, 2014
Colonisation of life on Surtsey has been observed systematically since the formation of the islan... more Colonisation of life on Surtsey has been observed systematically since the formation of the island 50 years ago. Although the first colonisers were prokaryotes, such as bacteria and blue-green algae, most studies have been focusing on settlement of plants and animals but less on microbial succession. To explore microbial colonization in diverse BGD
Geothermics, Dec 1, 2010
... (2005b) review the associated research and experience. ... A large geothermal area 17 km east... more ... (2005b) review the associated research and experience. ... A large geothermal area 17 km east of Reykjavík, the Reykir/Reykjahlíd (Mosfellssveit) field, was considered to be ideal because of its proximity and its capability to produce large quantities of geothermal water. ...
The paper describes in a general way what kind of surface studies are carried out in Iceland in e... more The paper describes in a general way what kind of surface studies are carried out in Iceland in exploration of our geothermal high temperature fields. It is outlined what is required to engage in a complete exploration work in a new greenfield geothermal resource area. At present, this is usually what is needed to fulfil the requirements to apply for, or receive, exploitation rights in a geothermal area. The aim of the work is based on three main components. • The recognition of possible geothermal resources to develop. • The geo-scientific work needed to estimate its size and potential. • The project development work needed to be able to carry out the exploration, plan for the exploitation and estimate it’s feasibility.
iNTRoDUCTioN Surtsey island is a part of the Vestmannaeyjar archipelago. it was constructed from ... more iNTRoDUCTioN Surtsey island is a part of the Vestmannaeyjar archipelago. it was constructed from the sea floor in a volcanic eruption that lasted from 1963 to 1967 (Thórarinsson 1966, 1969, Thórarinsson et al. 1964). During the hydromagmatic explosive submarine phase of the eruption, from November 1963 to April 1964, basalt tephra was produced. The tephra layers formed two crescent-shaped cones which merged. The Surtsey eruption evolved from an explosive phase into an effusive phase at the western crater in April 1964. Altogether, seven craters and crater fissures emitted lava between April 1964 and june 1967. The first major effusive phase (1964–1965) produced a lava shield reaching 100 m above sea level, while the second phase (1966–1967) produced a 70 m high lava shield. Together they form a lava field that slopes gently to the south and east. in addition there are five small lava flows on the slopes of Austurbunki (Fig. 1). Apart from Surtsey, eruptions occurred on the sea floor...
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Papers by Magnús Ólafsson