ISOR Iceland GeoSurvey

Akureyri, Iceland

ISOR Iceland GeoSurvey

Akureyri, Iceland
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Lichoro C.M.,Geothermal Development Company | Lichoro C.M.,University of Iceland | Arnason K.,ISOR Iceland GeoSurvey | Cumming W.,Cumming Geoscience
Geothermics | Year: 2017

An extensive electromagnetic (EM) survey comprising over 400 sites on the Korosi, Paka and Silali volcanoes in the northern volcanic province in Kenya was conducted in order to assess the occurrence of geothermal resources in the context of the geophysics of the major volcanic centers of the north Kenyan East African Rift System (EARS). This area lies within the (EARS) where active extension is currently taking place. A joint inversion of magnetotelluric (MT) and co-located Transient electromagnetic (TEM) has revealed a resistivity pattern consistent with the existence of several geothermal systems within the study area. Each geothermal system is characterized by a relatively resistive 100 Ω m surficial layer overlying a ∼ 10 Ω m low resistivity zone interpreted as the hydrothermally altered clay cap of the system. The cap overlies a higher resistivity zone of about 60 Ω m with a top at about 1000 m depth, interpreted as a potential high temperature alteration zone. The trend of moderate high resistivity at the depth of the potential reservoir corresponds to the zone of intense faulting and fracturing as imaged on the surface. Similarly the moderate high resistivity at sea level mimics the trend of the rift with a break in between Paka and Silali volcanoes where the resistivity trend is offset to the west. This break and the accompanying offset maps a possible westward shift of the axis of the rift in the rift alignment between Paka and Silali volcanoes. Although the 1000–2000 m thick low resistivity zones imaged on the flanks of the Korosi, Paka and Silali volcanoes have been tentatively interpreted as volcanoclastic sediments, elsewhere in the Kenyan EARS, low resistivity zones adjacent to volcanoes have been interpreted differently. To address this ambiguity, these thick low resistivity zones will be further investigated, principally using gravity surveys. © 2017 Elsevier Ltd

Asmundsson R.,ISOR Iceland GeoSurvey | Pezard P.,Montpellier University | Sanjuan B.,Bureau de Recherches Géologiques et Minières | Henninges J.,German Research Center for Geosciences | And 15 more authors.
Geothermics | Year: 2014

During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical geothermal reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300. °C and 400. °C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions. © 2013 Elsevier Ltd.

Sanjuan B.,Bureau de Recherches Géologiques et Minières | Millot R.,Bureau de Recherches Géologiques et Minières | Asmundsson R.,ISOR Iceland GeoSurvey | Brach M.,Bureau de Recherches Géologiques et Minières | Giroud N.,National Cooperative for the Disposal of Radioactive Waste
Chemical Geology | Year: 2014

This work has made it possible to obtain two new Na/Li geothermometric relationships in addition to the three already known (Fouillac and Michard, 1981; Kharaka et al., 1982) and confirms that the Na/Li geothermometer, unlike the Na/K, Na/K/Ca, K/Mg and silica geothermometers, or the isotope δ18O (H2O-SO4) geothermometer, also depends on the fluid salinity and the nature of the reservoir rocks reacting with the geothermal water. One of the relationships concerns the fluids derived from seawater-basalt interaction processes existing in emerged rifts such as those of Iceland (Reykjanes, Svartsengi, and Seltjarnarnes geothermal fields) and Djibouti (Asal-Ghoubbet and Obock geothermal areas), or in numerous oceanic ridges and rises (Mid-Atlantic and Middle-Valley ridges, East Pacific rise, etc.). The best adapted Na/Li relationship for geothermal fluids discharged from emerged rifts between 0 and 365°C is:TK=920/[log(Na/Li)-1.105] (r2=0.994, n=27) where Na and Li are the aqueous concentrations of these elements given in mol/L. The other Na/Li relationship was determined using dilute waters collected from wells located in different high-temperature (200-325°C) volcanic geothermal areas of Iceland (Krafla, Námafjall, Nesjavellir and Hveragerdi). This relationship can be expressed as follows:T(K)=2002/ [log(Na/Li)+1.322] (r2=0.967, n=17).These two relationships give estimations of temperature with an uncertainty close to ±. 20. °C. The second Na/Li relationship was also successfully applied to HT dilute geothermal waters from the East African Rift (Ethiopia, Kenya).Some case studies in the literature and thermodynamic considerations suggest that the Na/Li ratios for this type of fluids could be controlled by full equilibrium reactions involving a mineral assemblage constituting at least albite, K-feldspar, quartz and clay minerals such as kaolinite, illite (or muscovite) and Li-micas. Unlike the Na/Li ratios, no thermometric relationship using Li isotopes could be determined for this type of water. However, it was noticed that δ7Li values higher than 16% are always associated with low- to medium-temperature waters. © 2014 Elsevier B.V.

Gasperikova E.,Lawrence Berkeley National Laboratory | Newman G.,Lawrence Berkeley National Laboratory | Feucht D.,Lawrence Berkeley National Laboratory | Arnason K.,ISOR Iceland GeoSurvey
Transactions - Geothermal Resources Council | Year: 2011

Three-dimensional (3D) magnetotelluric (MT) inversions leading to the characterization of the electrical structure of geothermal reservoirs in a single self-consistent manner and presumably optimal accuracy and resolution are now feasible. Our work focused on two large geothermal fields - the Hengill and Krafla volcanic complexes, 200 km apart, and both known as high-temperature systems located within neo-volcanic zones of Iceland. This is the first full 3D MT inversion of Krafla MT dataset. The inverted model of electrical resistivity reveals the presence of highly resistive near surface layer, identified as unaltered porous basalt, which covers a low resistivity cap corresponding to the smectite-zeolite zone. Below this cap a more resistive zone is identified as the epidote-chlorite zone or also called the resistive core. Resistivity in the upper 1-2 km does not to correlate with lifhology but with alteration mineralogy. At the site of the IDDP well, which encountered magma at 2.1 km depth, the resistivity image shows high resistivity most likely due to epidote-chlorite geology. Just to the northwest of the well, however, an intrusive electrically conductive feature has been imaged rising from depth, and has been interpreted as a magma reservoir. A possible explanation for the magma encounter at the IDDP well is the existence of pathways or fissures connecting the magma chamber to the well. The MT response to magma pathways is not to be discernible in the data. Hengill geothermal area can be divided into two major complexes, one in the southwest and one in the northeast. The inverted model identified two low-resistivity layers. The nature of the uppermost low-resistivity layer and the increasing resistivity below is due to hydrothermal mineral alteration while the nature of the deep low-resistivity layer is not yet well understood. 3D MT inversions of Krafla and Hengill data sets showed that this approach is very promising in imaging geothermal reservoirs and that knowledge of the subsurface electrical resistivity can contribute to a better understanding of complex geothermal systems.

Galeczka I.,ISOR Iceland Geosurvey | Galeczka I.,University of Iceland | Sigurdsson G.,IMO Icelandic Meteorological Office | Eiriksdottir E.S.,University of Iceland | And 2 more authors.
Journal of Volcanology and Geothermal Research | Year: 2016

The 2014/15 Bárdarbunga volcanic eruption was the largest in Iceland for more than 200 years. This eruption released into the atmosphere on average 60,000 tonnes/day of SO2, 30,000 tonnes/day of CO2, and 500 tonnes/day of HCl affecting the chemical composition of rain, snow, and surface water. The interaction of these volcanic gases with natural waters, decreases fluid pH and accelerates rock dissolution. This leads to the enhanced release of elements, including toxic metals such as aluminium, to these waters. River monitoring, including spot and continuous osmotic sampling, shows that although the water conductivity was relatively stable during the volcanic unrest, the dissolution of volcanic gases increased the SO4, F, and Cl concentrations of local surface waters by up to two orders of magnitude decreasing the carbon alkalinity. In addition the concentration of SiO2, Ca, Mg, Na and trace metals rose considerably due to the water-molten lava and hot solid lava interaction. The presence of pristine lava and acidic gases increased the average chemical denudation rate, calculated based on Na flux, within Jökulsá á Fjöllum catchment by a factor of two compared to the background flux.Melted snow samples collected at the eruption site were characterised by a strong dependence of the pH on SO4, F and Cl and metal concentrations, indicating that volcanic gases and aerosols acidified the snow. Protons balanced about half of the negatively charged anions; the rest was balanced by water-soluble salts and aerosols containing a variety of metals including Al, Fe, Na, Ca, and Mg. The concentrations of F, Al, Fe, Mn, Cd, Cu, and Pb in the snowmelt water surpassed drinking- and surface water standards. Snowmelt-river water mixing calculations indicate that low alkalinity surface waters, such as numerous salmon rivers in East Iceland, will be more affected by polluted snowmelt waters than high alkalinity spring and glacier fed rivers. © 2016 Elsevier B.V.

Frioleifsson G.O.,HS Orka hf | Armannsson H.,ISOR Iceland GeoSurvey | Guomundsson T.,Landsvirkjun | Arnason K.,ISOR Iceland GeoSurvey | And 3 more authors.
Geothermics | Year: 2014

This paper describes the site selection for the IDDP-1 well within the Krafla volcano in 2008. In a feasibility study in 2003, 12 potential well sites within three geothermal areas were suggested and prioritized to meet the goal of finding supercritical temperatures and pressures together with high permeability. In 2006 one of these priority sites was selected within the Krafla field, but in autumn 2007 due to its proximity to the Krafla power plant a new location had to be selected only a few months before drilling. Choice of that new site was justified by new MT-resistivity survey data, seismic data and information from an earlier nearby production well, K-36. © 2013 Elsevier Ltd.

Gasperikova E.,Lawrence Berkeley National Laboratory | Rosenkjaer G.K.,ISOR Iceland GeoSurvey | Rosenkjaer G.K.,University of British Columbia | Arnason K.,ISOR Iceland GeoSurvey | And 2 more authors.
Geothermics | Year: 2015

Krafla and Hengill volcanic complexes, located 300. km apart, are both known as high-temperature geothermal systems located within neo-volcanic zones of Iceland. This paper demonstrates the utilization of three-dimensional (3D) magnetotelluric (MT) inversions from three different inverse modeling algorithms, which leads to characterizing the electrical resistivity structure of geothermal reservoirs with a much greater level of confidence in accuracy and resolution than if a single algorithm was employed in the data interpretation. These are the first 3D MT inversions of a Krafla MT dataset. The inverted model of electrical resistivity is a classic example of a high-temperature hydrothermal system, with a highly resistive near-surface layer, identified as unaltered porous basalt, overlying a low resistivity cap corresponding to the smectite-zeolite zone. This layer is in turn underlain by a more resistive zone, identified as the epidote-chlorite zone, also called the resistive core, which is often associated with production of geothermal fluids. The electrical structure in the upper 1-2. km does not correlate with lithology but with alteration mineralogy. At the location of the IDDP-1 well, which encountered magma at 2.1. km depth, the resistivity image shows high resistivity, most likely due to the epidote-chlorite geology and the presence of deeper superheated or supercritical fluids. Two km northwest of the well, however, an intrusive low-resistivity feature is imaged rising from depth, and a plausible interpretation is that of a magma intrusion. One possible explanation for the magma encounter at the IDDP-1 well is the existence of pathways or fissures connected to the magma chamber and intersected by the well. The MT response to these magma pathways is not discernible in the existing data, perhaps because this magma volume is below the threshold of resolvability. The electrical resistivity structure of the Hengill geothermal area also reveals characteristic features of a high temperature geothermal system with two low-resistivity layers. The nature of the uppermost low-resistivity layer and the increasing resistivity below it is attributed to hydrothermal mineral alteration, while the nature of the deep low-resistivity layer, centered over the northeast, is not yet well understood. The geothermal system in the northeast area appears to be shallower than the system manifested in the southwest. 3D MT inversions of Krafla and Hengill data sets show that knowledge of the subsurface electrical resistivity contributes substantially to a better understanding of complex geothermal systems. © 2015 Elsevier Ltd.

Armannsson H.,ISOR Iceland GeoSurvey
Applied Geochemistry | Year: 2016

Icelandic high temperature geothermal systems are considered to number thirty three, thereof three are submarine and seven subglacial. All are briefly described but the chemistry of fluids from twenty four of them is considered. The fluid in the three submarine areas and those four on land that are closest to the sea are relatively saline but to a differing extent mixed with groundwater. The rest contain dilute fluids. The fluids of the central highland systems are mostly locally derived but may in some instances be quite old whereas those in the northerly Krafla area which is inland and the Öxarfjördur area which is close to the sea appear to be a mixture of local and central highland water, but those in the inland Hengill, Geysir, Námafjall and Theistareykir areas appear to have travelled relatively long distances from the central highlands. The gas observed is magmatic except in the northerly Öxarfjördur area close to the sea where it is apparently derived from organic sediments. © 2015 Elsevier Ltd.

Arnason K.,ISOR Iceland GeoSurvey | Eysteinsson H.,ISOR Iceland GeoSurvey | Hersir G.P.,ISOR Iceland GeoSurvey
Geothermics | Year: 2010

An extensive study of the resistivity structure of the Hengill area in SW Iceland was carried out by the combined use of TEM and MT soundings. Joint inversion of the collected data can correct for static shifts in the MT data, which can be severe due to large near-surface resistivity contrasts. Joint 1D inversion of 148 TEM/MT sounding pairs and a 3D inversion of a 60 sounding subset of the MT data were performed. The 3D inversion was based on full MT impedance tensors previously corrected for static shift. Both inversion approaches gave qualitatively similar results, and revealed a shallow resistivity layer reflecting conductive alteration minerals at temperatures of 100-240 °C. They also delineated a deep conductor at 3-10 km depth. The reason for this deep-seated high conductivity is not fully understood. The distribution of the deep conductors correlates with a positive residual Bouguer gravity anomaly, and with transform tectonics inferred from seismicity. One model of the Hengill that is consistent with the well temperature data and the deep conductor that does not attenuate S-waves, is a group of hot, solidified, but still ductile magmatic intrusions that are closely associated with the heat source for the geothermal system. © 2010 Elsevier Ltd. All rights reserved.

Gunnarsdottir M.J.,University of Iceland | Gardarsson S.M.,University of Iceland | Armannsson H.,ISOR Iceland Geosurvey | Bartram J.,University of North Carolina at Chapel Hill
Hydrology Research | Year: 2015

Information about natural background levels (NBLs) of chemicals in source waters allows water utilities to identify trends in drinking water contamination. We estimate NBLs for chemicals in source waters for Icelandic water utilities at both national levels with all data pooled, and according to geological regime. NBLs were derived by collecting samples from 79 aquifers considered largely unimpacted by human activities. The aquifers were categorized into four geological settings that are representative of the geology of Iceland. NBLs were calculated as 90%iles of all aquifers in each setting and in all pooled. There was a statistical difference between the geological settings in 11 parameters of 37 tested. The 90%ile for nitrate for all aquifers pooled was 1.36 mg/l, indicating little anthropogenic influence on water used for public water supply in Iceland. The results were compared to the chemical status of 60 European aquifers, collected for the European Union's Sixth Framework Program Background Criteria for the Identification of Groundwater Thresholds project, revealing lower dissolved solids concentration for Icelandic groundwater than that from other parts of Europe. The explanation is likely due to high permeability of young geology settings and low population density in Iceland whereas there is a long history of agriculture and industry in most European countries. © IWA Publishing 2015.

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