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Numrering	Referens	Omslagsbild	Hitta
1.	Mattsson, Hannes, et al. (författare) Geology of the Heimaey volcanic centre, south Iceland: early evolution of a central volcano in a propagating rift? 2005 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273 .- 1872-6097. ; 127, s. 55-71 Tidskriftsartikel (refereegranskat)
2.	Andersson, Tommy, et al. (författare) Bottom characterization of Lagoa das Furnas on Sao Miguel, Azores archipelago 2016 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 321, s. 196-207 Tidskriftsartikel (refereegranskat)abstract Lagoa das Furnas is a crater lake located in an area exposed to geohazards from earthquakes and volcanic activity on the island of sao Miguel in the Azores Archipelago. Geophysical mapping of Lagoa das Furnas reveals a previously undiscovered volcanic dome. This dome is comprised largely of subaquatic pyroclastic debris of trachytic composition. Sedimentological, petrological, geochemical and geochronological studies of pyroclastic deposits from the dome link it to the historically documented Furnas 1630 eruption. The chemistry of glass and crystal fragments sampled from the dome suggests that it is comprised of more evolved magma than that of the main Furnas 1630 dome located 1400 m away. This suggests that the dome was formed during a final phase of the 1630 eruption in the Lagoa das Furnas area.
3.	Arellano, Santiago, 1981, et al. (författare) Degassing patterns of Tungurahua volcano (Ecuador) during the 1999–2006 eruptive period, inferred from remote spectroscopic measurements of SO2 emissions 2008 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 176, s. 151-162 Tidskriftsartikel (refereegranskat)abstract This paper presents the results of 7 years (Aug. 1999–Oct. 2006) of SO2 gas measurements during the ongoingeruption of Tungurahua volcano, Ecuador. From 2004 onwards, the operation of scanning spectrometers hasfurnished high temporal resolution measurements of SO2 flux, enabling this dataset to be correlated with otherdatasets, including seismicity. The emission rate of SO2 during this period ranges from less than 100 to35000 tonnes/day (t/d) with a mean daily emission rate of 1458 t/d and a standard deviation of ±2026 t/d.Average daily emissions during inferred explosive phases are about 1.75 times greater than during passivedegassing intervals. The total amount of sulfur emitted since 1999 is estimated as at least 1.91 Mt, mostlyinjected into the troposphere and carried westwards from the volcano. Our observations suggest that the rateof passive degassing at Tungurahua requires SO2 exsolution of an andesitic magma volume that is two orders ofmagnitude larger than expected for the amount of erupted magma. Two possible, and not mutually exclusive,mechanisms are considered here to explain this excess degassing: gas flow through a permeable stagnant magma-filled conduit and gas escape from convective magma overturning in the conduit.We have found thatreal-time gas monitoring contributes significantly to better eruption forecasting at Tungurahua, because it hasprovided improved understanding of underlying physical mechanisms of magma ascent and eruption.
4.	bazargan, mohsen, et al. (författare) Dike-induced stresses and displacements in layered volcanic zones 2019 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. Tidskriftsartikel (refereegranskat)abstract During a volcanic unrest period with dike injection, one of the main scientific tasks is to assess the geometry and the propagation path of the dike and, in particular, the likelihood of the dike reaching the surface to erupt. Currently, the dike path and geometry (including depth and opening/aperture) are both partly determined from geodetic surface data using mostly dislocation models that assume the volcanic zone/volcano to be an elastic half-space of uniform mechanical properties. By contrast, field observations of volcanic zones/volcanoes (active and extinct) show that they are composed of numerous layers whose mechanical properties (primarily Young's modulus) vary widely and whose contacts commonly arrest dikes. Here we provide field observations and numerical models on the effects of a typical variation in Young's modulus in an active volcanic zone on the internal and surface stresses and displacements induced by a dike whose tip is arrested at 0.5 km depth below the surface of the volcanic zone. Above the layer or unit hosting the dike are four layers of equal thickness. We vary Young's modulus or stiffness of the fourth layer (the one adjacent to the layer or unit hosting the dike) from 10 GPa to 0.01 GPa, while all the other layers/units maintain their Young's moduli in the model runs. The results show that as the fourth layer becomes more compliant or soft (0.1–0.01 GPa) dike-induced stresses and displacements (lateral and vertical) above the layer, including those at the surface, become suppressed but the stresses and displacements of the layer/unit hosting the dike increase and their peaks do not coincide in location or magnitude with those of the other layers. Thus, the dike-induced internal deformation of the volcanic zone increases as the fourth layer becomes softer. Also, the tensile-and-shear stress peaks at the surface occur at locations widely different from those of maximum surface uplift. More specifically, for a comparatively stiff fourth layer (1–10 GPa), the surface tensile and shear stresses peak at lateral distances of 0.5–0.7 km from the projection of the dike to the surface. (Essentially no tensile/shear stresses reach the surface when the fourth layer is as soft as 0.1–0.01 GPa so that there are no stress peaks). By contrast the maximum surface displacements (uplift) peak at lateral distances of 2.8–3.3 km from the dike projection to the surface. If tension fractures or faults – in particular the boundary faults of a graben – are induced by the dike, they should form at the tensile/shear stress peaks and not, as is commonly suggested, at the location of the surface displacement peaks. Our results thus suggest that any dike-induced graben is likely to be of width about twice the depth to the tip/top of the arrested dike. The results demonstrate that elastic half-space models overestimate the dike-induced surface stresses, and thus the depth to the tip/top of the associated dike. In particular, the models presented here indicate that for typical dikes little or no dike-induced surface deformation would be expected until the dike tip propagates to depths below the surface of less than a kilometre.
5.	bazargan, mohsen, et al. (författare) Stresses and displacements in layered rocks induced by inclined (cone) sheets 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; :106965 Tidskriftsartikel (refereegranskat)abstract Currently, the sheet-intrusion paths and geometries, including the sheet opening/thickness as well as the depth to sheet tip, are commonly determined from geodetic surface data using elastic dislocation models. These models assume the volcanic zone/central volcano to be an elastic half-space of uniform mechanical properties. Field observations, however, show that volcanic zones/volcanoes are composed of numerous layers whose mechanical properties (primarily Young's modulus) vary widely. Here we provide new numerical models on the effects of a typical variation in Young's modulus in an active volcanic zone/central volcano on the internal and surface stresses and displacements induced by a sheet-intrusion whose tip is arrested at a depth below the surface of 100 m. The sheet has a dip dimension (height) of 2 km. It's opening (thickness) depends on the magmatic overpressure, sheet dimension and host-rock Young's modulus. For the values used here, sheet thickness would be in the range of 0.5–1.4 m, similar to commonly measured sheet thicknesses in the field. The only loading is internal magmatic overpressure in the sheet of 5 MPa. The modelled crustal segment/volcano consists of 5 layers, all with the same Poisson's ratio (0.25). Each of the 4 uppermost layers is 10 m thick. Layer 1 (the top or surface layer) has Young's modulus of 3 GPa, layer 2 a modulus of 20 GPa, layer 3 a modulus of 30 GPa, and layer or unit 5 a modulus of 40 GPa. We vary Young's modulus or stiffness of the fourth layer from 10 GPa to 0.01 GPa, while the dip of the sheet takes the following values: 30°, 45°, 60° (for an inclined sheet) and 90° (for a dike). The resulting displacement and stresses are highly asymmetric across the sheet tip (except for the dike), with the main surface stresses and displacements being above the dipping sheet and highest for the 30°-dipping sheet. For comparison, three elastic half-space models of the same sheet configuration and loading but uniform Young's modulus in each model (40GPa, 20GPa, and 10 GPa) all yield much higher surface stresses and displacements than any of the layered models. As the stiffness of layer 4 decreases the surface stresses gradually decrease while changes in vertical displacements are comparatively small but greater in horizontal displacements. In particular, as the stiffness of layer 4 decreases from 10 GPa to 0.01 GPa, for the 30°-dipping sheet, the maximum surface shear stress decreases from about 6.6 MPa to 2.2 MPa and the maximum tensile stress from about 6.9 MPa to about 2.3 MPa. Thus, even a single comparatively thin (10 m) soft layer close to the surface of a central volcano/volcanic zone (where such layers are almost universal) may cause a great change in the maximum sheet-induced stresses at the surface and, thereby, in any sheet-induced fracture pattern. Furthermore, the stress peaks in the layered models do not coincide with the displacement peaks; fracture formation is most likely at the location of the stress peaks. The results have important implications for the correct interpretation of geodetic data and fracturing during unrest periods with magma-chamber rupture and sheet injection.
6.	Benediktsdottir, Asdis, et al. (författare) Ambient noise tomography of Eyjafjallajokull volcano, Iceland 2017 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 347, s. 250-263 Tidskriftsartikel (refereegranskat)abstract We present a shear-velocity model for the Eyjafjallajokull stratovolcano, based on ambient seismic noise tomography applied to seven months of data from six permanent stations and -10 temporary seismic stations, deployed during and after the 2010 volcanic unrest. Vertical components of noise were cross correlated resulting in 30 robust phase-velocity dispersion curves between 1.6 and 6.5 s in period, displaying a +/- 20% variation in phase velocity beneath the volcano. The uneven distribution of noise sources, evaluated using signal-to-noise ratios, was estimated to cause less than 2% error in most curves. Sensitivity kernels showed resolution down to 10 km and the lateral resolution of the resulting phase-velocity maps was about 5 km. The model reveals east-west oriented high-velocity anomalies due east and west of the caldera. Between these a zone of lower velocity is identified, coinciding with the location of earthquakes that occurred during the summit eruption in April 2010. A shallow, southwest elongated low-velocity anomaly is located 5 km southwest of the caldera. The limited depth resolution of the shear-velocity model precludes detection of melt within the volcano.
7.	Berghuijs, Jaap F., et al. (författare) Magma ascent, fragmentation and depositional characteristics of “dry” maar volcanoes : Similarities with vent-facies kimberlite deposits 2013 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 252, s. 53-72 Tidskriftsartikel (refereegranskat)abstract Several maar craters within the Lake Natron-Engaruka monogenetic volcanic field (LNE-MVF) of northern Tanzania show compelling evidence for magmatic fragmentation and dry deposition. This is in contradiction of the common belief that most maars are formed through the explosive interaction between ascending magma and ground- or surface water. We here present a detailed study on the eruptive and depositional characteristics of the Loolmurwak and Eledoi maar volcanoes, two of the largest craters in the LNE-MVF, focusing on high-resolution stratigraphy, sedimentology, grain size distribution, pyroclast textures and morphologies, bulk geochemistry and mineral chemistry. At both maars, ejected material has been emplaced by a combination of pyroclastic surges and fallout. Indicators of phreatomagmatic fragmentation and wet deposition, such as impact sags, accretionary lapilli, vesiculated tuffs and plastering against obstacles, are absent in the deposits. juvenile material predominantly occurs as fluidal-shaped vesicular melt droplets and contains no glass shards produced by the breakage of bubble walls. The Eledoi deposits comprise a large amount of inversely graded beds and lenses, which result from grain flow in a dry depositional environment. Preferential deposition of fine material toward the northern side of its crater can be related to effective wind winnowing in a dry eruption plume. This large variety of observations testifies to the dominance of magmatic fragmentation as well as dry deposition at the Loolmurwak and Eledoi maars, which is in line with what has been found for other structures in the LNE-MVF but contrasts with current ideas on maar formation. We infer that a volatile-rich, olivine melilitic magma was formed by small amounts of partial melting at upper mantle depths. With minimum average ascent rates of 5.3 m s(-1) for Loolmurwak and 26.2 m s(-1) for Eledoi, this magma rapidly moved toward the surface and exsolved a substantial amount of volatiles, sufficiently large to drive magmatic fragmentation. Both eruptions were pulsating in intensity and relatively short-lived, with estimated durations of 23 and 10 h for Loolmurwak and Eledoi, respectively. The depositional characteristics of these maars, including the abundant occurrence of mantle xenoliths in the deposits, as well as their envisaged mode of emplacement show a strong similarity to the often poorly preserved vent-facies of kimberlitic diatremes. Therefore, future research on well-preserved melilititic maar-diatreme deposits may provide valuable insights into kimberlite emplacement processes. (C) 2012 Elsevier B.V. All rights reserved.
8.	Bosshard-Stadlin, Sonja A., et al. (författare) Leaching of lava and tephra from the Oldoinyo Lengai volcano (Tanzania) : Remobilization of fluorine and other potentially toxic elements into surface waters of the Gregory Rift 2017 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 332, s. 14-25 Tidskriftsartikel (refereegranskat)abstract Volcanic ash leachate studies have been conducted on various volcanoes on Earth, but few have been done on African volcanoes until now. Tephra emissions may affect the environment and the health of people living in this area, and therefore we conducted a first tephra (ash and lapilli sized) leachate study on the Oldoinyo Lengai volcano, situated in northern Tanzania. The recent explosive eruption in 2007-2008 provided us with fresh samples from the first three weeks of the eruption which were used for this study. In addition, we also used a natrocarbonatitic sample from the activity prior to the explosive eruption, as the major activity at Oldoinyo Lengai is natrocarbonatitic. To compare the leaching process affecting the natrocarbonatitic lavas and the tephras from Oldoinyo Lengai, the 2006 natrocarbonatitic lava flow was resampled 5 years after the emplacement and compared to the initial, unaltered composition. Special interest was given to the element fluorine (F), since it is potentially toxic to both humans and animals. A daily intake of fluoride (F-) in drinking water of >1.5 mg/l can lead to dental fluorosis, and higher concentrations lead to skeletal fluorosis. For this reason, a guideline value for fluoride in drinking water was set by the WHO (2011) to 1.5 mg/l. However, surface waters and groundwaters in the Gregory Rift have elevated fluoride levels of up to 9.12 mg/l, and as a consequence, an interim guideline value for Tanzania has been set at 8 mg/l. The total concentration of fluorine in the samples from the natrocarbonatitic lava flow is high (3.2 wt%), whereas we observed a significant decrease of the fluorine concentration (between 1.7 and 0.5 wt%) in the samples collected three days and three weeks after the onset of the explosive 2007-08 eruption. However, the total amount of water-extractable fluoride is lower in the natrocarbonatitic lavas (319 mg/l) than in the nephelinitic tephra (573-895 mg/l). This is due to the solubility of the different F-bearing minerals. In the natrocarbonatites, fluorine exists predominantly in fluorite (CaF2), and in the early tephra as Na-Mg bearing salts such as neighborite (NaMgF3) and sellaite (MgF2). All these three minerals have very low solubility in water (16-130 mg/l). The later nephelinitic tephras contain surface coating of villiaumite (NaF), which is highly soluble (42,200 mg/l) in water and can thus release the fluoride more readily upon contact with water. Although there is still the need for further data and a more precise study on this topic in Tanzania, we can already draw a first conclusion that the intake of water during or directly following the deposition of the tephra is not advisable and should be avoided, whereas the release of fluoride from the lava flow has less influence on the river waters. 2017 Elsevier B.V. All rights reserved.
9.	Bosshard-Stadlin, Sonja A., et al. (författare) Magma mixing and forced exsolution of CO2 during the explosive 2007-2008 eruption of Oldoinyo Lengai (Tanzania) 2014 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 285, s. 229-246 Tidskriftsartikel (refereegranskat)abstract Oldoinyo Lengai is probably most famous for being the only active volcano on Earth which is erupting natrocarbonatitic magma. However, the mildly explosive natrocarbonatitic activity is alternating with highly explosive, nephelinitic eruptions of which the most recent episode occurred in September 2007 (and lasted until April 2008). Here we present petrographic observations, mineral chemistry as well as major- and trace element analyses of samples covering the evolution of the eruption with time. In the early phases of the eruption, the phenocryst assemblages are dominated by the carbonate minerals nyerereite and gregoryite, but as the eruption progresses the mineralogy becomes dominated by silicate minerals like nepheline, pyroxene, garnet, alumoakermanite, combeite and wollastonite. The observed major- and trace element variations during the 2007-2008 eruption indicate mixing between a natrocarbonatitic magma and a combeite-wollastonite-bearing nephelinitic magma (CWN), with higher portions of natrocarbonatite in the early stages of the eruption. Euhedral and uncorroded clinopyroxene crystals are abundant in the late 2007 deposits but quickly start to break-down and corrode as the eruption continues, indicating that the natrocarbonatite and the CWN are not in fact conjugate magmas derived from a single magma reservoir, but must have evolved separately in the crust from the point of immiscibility. When these magmas interact beneath the volcano, a hybrid silicate magma forms (where clinopyroxene is no longer stable) and the composition of this hybrid causes the overall solubility of CO2 in the system to decrease drastically. This results in rapid exsolution of CO2 (g) which is allowed to expand during ascent, and we conclude that this is most likely the reason behind the unexpected vigor in the explosive eruptions of Oldoinyo Lengai. This massive release of CO2 during ascent may also explain the petrographic features of the pyroclasts as these are dominated by near-spherical droplets with moderate vesicularities, indicative of being transported in a hot gas-stream/jet in the upper conduit and forming an aerosol-type spray. (C) 2014 Elsevier B.V. All rights reserved.
10.	Burchardt, Steffi, 1982- (författare) New insights in the mechanics of sill emplacement provided by field observations of the Njardvik Sill, Northeast Iceland 2008 Ingår i: Journal of Volcanology and Geothermal Research. - Amsterdam : Elsevier. - 0377-0273 .- 1872-6097. ; 173:3-4, s. 280-288 Tidskriftsartikel (refereegranskat)abstract Sills are concordant sheet-like bodies of magma. Their mechanics of emplacement is an important but still not fully understood topic. The well-exposed basaltic Njardvik Sill in the extinct Tertiary Dyrfjöll Volcano in Northeast Iceland offers exceptionally clear insights into the mechanism of sill emplacement. The sill is multiple and consists of at least 7 units (sills) all of which were emplaced along a sharp contact between a rhyolitic intrusion and adjacent basaltic lava flows. Each sill unit was supplied with magma from an inclined sheet. The contacts between the sheets and the sill units are very clear and show that the sill units are much thicker than their feeder sheets. Since the Njardvik Sill consists of separate units, it obviously did not evolve into a homogeneous magma body. Nevertheless, the abrupt change in dip and thickness from inclined sheets to horizontal sills at this particular locality indicates that the earlier sills were influencing the stress field in their vicinity during the subsequent sheet injections. The local stresses around the newly formed sill units forced each of the subsequently injected sheets to change into sills. The Njardvik Sill can be followed laterally in a coastal section for 140 m until it ends abruptly at a fault that cuts the sill. Using these field observations as a basis, a numerical model shows how an inclined sheet opens up the contact between the felsic intrusion and the basaltic lava pile, along which the sill emplacement takes place. The results suggest that sill emplacement is primarily the result of stress rotation at contacts between layers of contrasting mechanical properties. There, the orientation of the maximum principal compressive stress σ1 is horizontal. Hence, such contacts can represent interfaces along which sill emplacement is encouraged. Once a sill has been emplaced, it extends the stress field with a horizontal orientation of σ1. Consequently, inclined sheets and dykes injected near the sill will be deflected into sills. The injection frequency of further sill units controls if the sill can grow into a larger magma body by mixing of the newly supplied with the initially injected magma. In case of the Njardvik Sill, the injection frequency was low, so subsequently emplaced sill units can be distinguished.
11.	Carn, Simon, et al. (författare) Daily monitoring of Ecuadorian volcanic degassing from space 2008 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 176:1, s. 141-150 Tidskriftsartikel (refereegranskat)abstract We present daily measurements of sulfur dioxide (SO2) emissions from active volcanoes in Ecuador and southern Colombia between September 2004 and September 2006, derived from the Ozone Monitoring Instrument (OMI) on NASA's EOS/Aura satellite. OMI is an ultraviolet/visible spectrometer with an unprecedented combination of spatial and spectral resolution, and global coverage, that permits daily measurements of passive volcanic degassing from space. We use non-interactive processing methods to automatically extract daily SO2 burdens and information on SO2 sources from the OMI datastream. Maps of monthly average SO2 vertical columns retrieved by OMI over Ecuador and S. Colombia are also used to illustrate variations in regional SO2 loading and to pinpoint sources. The dense concentration of active volcanoes in Ecuador provides a stringent test of OMI's ability to distinguish SO2 from multiple emitting sources. Our analysis reveals that Tungurahua, Reventador and Galeras were responsible for the bulk of the SO2 emissions in the region in the timeframe of our study, with no significant SO2 discharge detected from Sangay. At Galeras and Reventador, we conclude that OMI can detect variations in SO2 release related to cycles of conduit sealing and degassing, which are a critical factor in hazard assessment. The OMI SO2 data for Reventador are the most extensive sequence of degassing measurements available for this remote volcano, which dominated regional SO2 production in June–August 2005. At Tungurahua, the OMI measurements span the waning stage of one eruptive cycle and the beginning of another, and we observe increasing SO2 burdens in the months prior to explosive eruptions of the volcano in July and August 2006. Cumulative SO2 loadings measured by OMI yield a total of ~ 1.16 Tg SO2 emitted by volcanoes on mainland Ecuador/S. Colombia between September 2004 and September 2006; as much as 95% of this SO2 may originate from non-eruptive degassing. Approximate apportionment of the total SO2 loading indicates that ~ 40% originated from Tungurahua, with ~ 30% supplied by both Reventador and Galeras. These measurements of volcanic SO2 degassing in Ecuador confirm OMI's potential as an effective, economical and risk-free tool for daily monitoring of SO2 emissions from hazardous volcanoes.
12.	Clarke, H., et al. (författare) Phreatomagmatic to strombolian eruptive activity of basaltic cinder cones: Montana Los Erales, Tenerife, Canary Islands 2009 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 180, s. 225-245 Tidskriftsartikel (refereegranskat)
13.	Dingwell, Adam, et al. (författare) Estimating volcanic ash hazard in European airspace 2014 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 286, s. 55-66 Tidskriftsartikel (refereegranskat)abstract The widespread disruption of European air trafﬁc in late April 2010, during the eruption of Eyjafjallajökull,showed the importance of early assessment of volcanic hazard from explosive eruptions. In this study, wefocus on the short-term hazard of airborne ash from a climatological perspective, focusing on eruptions onIceland. By studying eruptions of different intensity and frequency, we estimate the overall probability that ashconcentration levels considered hazardous to aviation are exceeded over different parts of Europe.The method involves setting up a range of eruption scenarios based on the eruptive history of Icelandic volcanoes,and repeated simulation of these scenarios for 2 years' worth of meteorological data. Simulations are conducted using meteorological data from the ERA-Interim reanalysis set, which is downscaled using the Weather Researchand Forecasting (WRF) model. The weather data are then used to drive the Lagrangian particle dispersion model FLEXPART-WRF for each of the eruption scenarios. A set of threshold values, commonly used in Volcanic Ash Advisories, are used to analyze concentration data from the dispersion model.We see that the dispersion of ash is highly dominated by the mid-latitude westerlies and mainly affect northern UK and the Scandinavian peninsula. The occurrence of high ash levels from Icelandic volcanoes is lower over con-tinental Europe but should not be neglected for eruptions when the release rate of ﬁne ash (<16 μm) is in theorder of 107 kg s−1 or higher.There is a clear seasonal variation in the ash hazard. During the summer months, the dominating dispersiondirection is less distinct with some plumes extending to the northwest and Greenland. In contrast, during thewinter months, the strong westerly winds tend to transport most of the emissions eastwards. The affected area of a winter-time eruption is likely to be larger as high concentrations can be found at a further distance downwind from the volcano, effectively increasing the probability of hazardous levels of ash reaching the European continent.The concentration thresholds for aviation, which were adopted after the Eyjafjallajökull eruption in 2010, havestrong inﬂuence on the hazard estimates for weaker eruptions but is less important for larger eruptions; thusash forecasts for weaker eruptions are likely more uncertain in comparison to larger eruptions.
14.	Donoghue, E., et al. (författare) Low-temperature hydrothermal alteration of intra-caldera tuffs, Tejeda caldera, Gran Canaria: mineralogical and isotopic changes. 2008 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 176, s. 551-564 Tidskriftsartikel (refereegranskat)
15.	Eriksson, Per, et al. (författare) Magma flow directions inferred from field evidence and magnetic fabric studies of the Streitishvarf composite dike in east Iceland 2011 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 206:1-2, s. 30-45 Tidskriftsartikel (refereegranskat)abstract Anisotropy of magnetic susceptibility (AMS) and rock magnetic studies have been made on three outcrops separated by 12 km along strike (NNE–SSW) on the Streitishvarf composite dike in east Iceland. Samples for this study have been collected from the inner quartz-porphyry part of the dike, which show clear field evidence of a lateral flow component from north to south at one of the sites. This flow component is consistent with margin AMS results from all three sites. The quartz-porphyry has a substantial bulk magnetic susceptibility (10-2 SI) mainly carried by magnetically soft titanium-poor titanomagnetite (MDF 15 mT). The ferrimagnetic grains yield a characteristic remanent magnetization in all three sites which gives a virtual geomagnetic pole at latitude 52:6°S and longitude 319:6°E. The degree of anisotropy is low (PJ = 1:033) and the magnetic fabrics shifts from oblate to prolate shapes depending on dike margin and outcrop. The magnetic fabric has been interpreted according to the imbrication model, using the minor susceptibility axis as shear plane indicator. The absolute directions given by the minor susceptibility are then quantified using vector algebra. The magma flow is indicated as an upward directed flow, flowing from north to south with an inclination between 30° – 64°, with a 95% confidence ellipse of 3° – 9°. A model for the intrusion of the Streitishvarf dike has been constructed where a magma pocket with felsic magma is punctured by a mafic dike, enabling the felsic magma to rise and extend to the south within the pathway created. The results of this study confirm the applicability of AMS in studies of magma flow directions in igneous dikes of felsic composition.
16.	Galeczka, Iwona, et al. (författare) The effect of the 2002 glacial flood on dissolved and suspended chemical fluxes in the Skafta river, Iceland 2015 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 301, s. 253-276 Tidskriftsartikel (refereegranskat)abstract This study describes the chemical composition of dissolved, degased and suspended fluxes of the 2002 Skafta glacial flood, which emerged from one of the Skafta subglacial lake due to geothermal activity beneath the Icelandic Vatnajokull glacier. The dissolved and suspended fluxes during the flood are compared with those normally observed in the Skafta river to determine the effect of such floods on the annual fluxes of material delivered to the coastal waters. Concentrations of most dissolved elements during the flood were significantly higher than those normally observed in the Skafta river. In addition, dissolved concentrations of nutrients such as SiO2, Fe, and V, increased more than an order of magnitude during the flood. These will affect biological processes on a local scale. The delta S-34 composition in the flood water suggests that the dissolved SO4 was derived from the oxidation of H2S and the geothermal fluid. The total suspended particulate load measured in the Skafta river during the 8-day 2002 flood was approximately half of the non-flood total annual Skafta suspended load. As particles carry the bulk of limiting nutrients to the oceans, this demonstrates the importance of glacial floods for primary production of coastal waters. The composition of the flood water and the Skafta subglacial lake, together with reaction path modelling suggest that substantial degasing of CO2 and H2S occurred at the glacial outlet during the flood. This degasing may have released as much as 262,000 and 7,980 tonnes of CO2 and H2S, respectively, to the atmosphere having a considerable impact on the local carbon and sulphur cycles during the flood event.
17.	Geirsson, H., et al. (författare) Multidisciplinary observations of the 2011 explosive eruption of Telica volcano, Nicaragua: Implications for the dynamics of low-explosivity ash eruptions 2014 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 271, s. 55-69 Tidskriftsartikel (refereegranskat)abstract We present multidisciplinary observations of the March-June 2011 VEI 2 eruptive episode of the basalticandesite Telica volcano, Nicaragua, which allow for a comprehensive study of the eruption mechanics of low-explosivity eruptions at persistently active volcanoes. The observations are from a dense network of seismic and GPS instrumentation augmented by visual observations of the eruptive episode, geochemical and petrologic analysis of eruptive products, plume SO2 measurements, and temperature measurements of fumaroles inside and outside the active vent. The 2011 eruptive episode was Telica's most explosive since 1999 and consisted of numerous vulcanian explosions, with maximum column heights of 1.5-2 km above the crater rim, depositing a low volume of dominantly hydrothermally altered ash. Based on observed variations in seismicity, temperature, and SO2 flux, the lack of deformation of the edifice, the non-juvenile origin of and predominance of accretionary lapilli in the ash, we propose that temporary sealing of the hydrothermal system between similar to 0.5 and 2 km depth, allowed pressure to build up prior to vulcanian explosions, making this a phreatic eruptive episode.
18.	Gilichinsky, Michael (författare) Morphometric and morphological development of Holocene cinder cones: A field and remote sensing study in the Tolbachik volcanic field, Kamchatka 2011 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 201, s. 301-311 Tidskriftsartikel (refereegranskat)abstract The evolution of landscape over time is a central aspect of geological, paleogeographical and geomorphological studies. Volcanic features like cinder cones offer the opportunity to monitor the processes and development of the landscape. Cinder cones are perhaps the simplest and most common volcanic landforms in the world. Morphological and morphometric study of cinder cones has proven an efficient tool for determining their relative dates, and the erosional processes affecting them. The extensive Kamchatka volcanic province (Russian Far East), with its large Tolbachik cinder cone field, is an excellent case study for spatial and temporal classification and calibration of changes in morphometric values with time.We show how the morphological and morphometric values of the monogenetic cinder cones, measured in the field and by digital elevation models, can be used to validate their age and erosional processes.Field data were GPS measurements of cinder cones formed at the Tolbachik 1975-1976 eruption and of Holocene cinder cones; erosion processes on the cinder cones and lava flows were identified and evaluated. For every studied cinder cone morphometric parameters were assessed on the basis of remotely sensed data and digital elevation model. Morphometric measurements were taken of cone height and slope and average axis diameter and the height-width ratio was obtained.The comparison of morphometric parameters calculated from ASTER DEM and topographic map clearly supports the concept of relative morphometric dating as the most recent cinder cones are always associated with the highest slopes and h/W ratio. The measured morphometric values of the recent Tolbachik cinder cones are valuable benchmark data for determining erosion rates, such as the measured values for the Paricutin cone in Mexico after the 1943 eruption. The variability of the morphometric values of the recent cinder cones is due to their lithological coarse composition. A comparison with the older cinder cones in the area shows that the climatic conditions of the Kamchatka peninsula and the slow development of vegetation cover determine a high rate of erosion and rapid change in the morphometric values, as compared to published values for other volcanic fields. (C) 2010 Elsevier B.V. All rights reserved.
19.	Grahn, Håkan, et al. (författare) What's that smell? Hydrogen sulphide transport from Bardarbunga to Scandinavia 2015 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 303, s. 187-192 Tidskriftsartikel (refereegranskat)abstract On Sep 9 2014 several incidences of foul smell (rotten eggs) were reported on the coast of Norway (in particular in the vicinity of Molde) and then on Sep 10 in the interior parts of county Vasterbotten, Sweden. One of the theories that were put forward was that the foul smell was due to degassing of the Bardarbunga volcano on Iceland. Using satellite images (GOME-1,-2) of the sulphur dioxide, SO2, contents in the atmosphere surrounding Iceland to estimate flux of SO2 from the volcano and an atmospheric transport model, PELLO, we vindicate this theory: we argue that the cause for the foul smell was hydrogen sulphide originating from Bardarbunga. The model concentrations are also compared to SO2 concentration measurements from Muonio, Finland.
20.	Greiner, Sonja H. M., et al. (författare) Interaction between propagating basaltic dikes and pre-existing fractures : A case study in hyaloclastite from Dyrfjoll, Iceland 2023 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 442 Tidskriftsartikel (refereegranskat)abstract Magma in the Earth's crust is commonly transported through dikes. Fractures and faults, which are common in the shallow crust, form structural weaknesses that can act as energy-efficient propagation pathways. Although examples of this are known from active and extinct volcanoes in varying host rocks, the conditions and mechanisms of how and when dikes are influenced by these structures are not yet fully understood. This study investigates how basaltic dikes propagating through hyaloclastite in the shallow crust interact with pre-existing fractures. Using virtual 3D-models from drone-based photogrammetry, we mapped basaltic dikes exposed in a caldera-filling hyaloclastite in the extinct Dyrfjoll volcano, NE-Iceland, to measure the orientations of fractures and dikes, and quantify their interactions. We observe 39 changes in strike among 45 dikes and found a strong control of the governing stress field on orientations and interactions. Three types of dike-fracture interaction were identified: (1) Dikes propagating along pre-existing fractures. This is most frequently observed for dikes following the tectonic stress field. (2) Dikes with an abrupt change in strike occurring near or at a crosscutting fracture, but without magma flow into the fracture. (3) Dikes arrested at a crosscutting fracture. Such dikes may develop offshoots near the dike tip, which may approach the fracture at different angles and be able to cut across. Understanding how dikes interact with pre-existing fractures in moderately fractured host rock such as hyalo-clastite is relevant for hazard assessment and monitoring of volcanically active areas.
21.	Gudmundsson, Olafur, 1958- (författare) Jeddi, Zeinab, Gudmundsson, Olafur, Tryggvason, Ari, 2017. Ambient-noise tomography of Katla volcano, south Iceland, J. Volc. Geoth. Res. 347, 264-277. 2017 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273 .- 1872-6097. ; 347, s. 264-277 Tidskriftsartikel (refereegranskat)
22.	Gudmundsson, Olafur, 1958- (författare) Sgattoni, Giulia, Gudmundsson, Olafur, Einarsson, Pall, Lucchi, Federico, Li, Ka Lok, Sadeghisorkhani, Hamzeh, Roberts, Roland, Tryggvason, A, 2017. The 2011 unrest at Katla volcano: characterization and interpretation of the tremor sources, J. Volc. Geoth. Res. 338, 63-78. 2017 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273 .- 1872-6097. ; 338, s. 63-78 Tidskriftsartikel (refereegranskat)
23.	Gunnarsson-Robin, Jóhann, et al. (författare) Sulfur isotopes in Icelandic thermal fluids 2017 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 346, s. 161-179 Tidskriftsartikel (refereegranskat)abstract Multiple sulfur isotope compositions of thermal fluids from Iceland were measured in order to evaluate the sources and reactions of sulfur and sulfur isotope fractionation in geothermal systems at Icelandic divergent plate boundaries, characterized by MORB-like basalts. The geothermal systems studied had a wide range of reservoir temperatures of 56-296 degrees C and Cl concentrations of 18-21,000 ppm. Dissolved sulfide (Sigma S-II) and SO4 concentrations in liquid water measured <0.01-165 ppm and 1.3-300 ppm, respectively, and H2S(g) concentrations in the vapor 4.9-2000 ppm. The delta S-34 and Delta S-33 values for different phases and oxidation states were highly variable: delta S-34 Sigma s(-II) = -11.6 to 10.5 parts per thousand (n = 99), Delta S-33 Sigma s(-II) = -0.12 to 0.00 parts per thousand (n = 45), delta(34)Sso(4) = -1.0 to 24.9 parts per thousand (n = 125), Delta(33)Sso(4) = -0.04 to 0.02 parts per thousand (n = 50), delta(34)SH(2)s(g) = -2.6 to 5.9 parts per thousand (n = 112) and Delta(33)SH(2)s(g) = -0.03 to 0.00 parts per thousand (n = 56). The multiple sulfur isotope values of the thermal fluids are interpreted to reflect various sources of sulfur in the fluids, as well as isotope fractionation occurring within the geothermal systems associated with fluid-rock interaction, boiling and oxidation and reduction reactions. The results of isotope geochemical modeling demonstrate that the sources of S-II in the thermal fluid are leaching of basalt (MORB) and seawater SO4 reduction for saline systems with insignificant magma gas input, and that the observed ranges of delta S-34 and Delta S-33 for Sigma S-II and H2S(g) reflect isotope fractionation between minerals and aqueous and gaseous species upon fluid -rock interaction and boiling. The sources of SO4 are taken to be multiple, including oxidation of S-II originating from basalt, leaching of S-VI from the basalts and the seawater itself in the case of saline systems. In low-temperature fluids, the delta S-34 and Delta S-33 values reflect the various sources of sulfur. For high-temperature fluids, fluid -rock interaction, Sigma S-II oxidation and SO4 reduction and sulfide and sulfate mineral formation result in a large range of delta S-34 and Delta S-33 values for Sigma S-II and SO4 in the fluids, highlighting the importance and effects of chemical reactions on the isotope systematics of reactive elements like sulfur. Such effects needed to be quantified in order to reveal the various sources of an element.
24.	Heap, Michael J., et al. (författare) Imaging strain localisation in porous andesite using digital volume correlation 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 404 Tidskriftsartikel (refereegranskat)abstract Strain localisation structures, such as shear fractures and compaction bands, are of importance due to their influence on permeability and therefore outgassing, a factor thought to influence eruptive style. In this study, we aim to develop a better understanding of strain localisation in porous volcanic rocks using X-ray tomographic images of samples of porous andesite (porosity = 0.26) acquired before and after deformation in the brittle and ductile regimes. These 3D images have been first analysed to provide 3D images of the porosity structure within the undeformed andesite, which consists of a large, well-connected porosity backbone alongside many smaller pores that are either isolated or connected to the porosity backbone by thin microstructural elements (e.g., microcracks). Following deformation, porosity profiles of the samples show localised dilation (porosity increase) and compaction (porosity reduction) within the samples deformed in the brittle and ductile regimes, respectively. Digital volume correlation (DVC) of the images before and after triaxial deformation was used to quantify the tensor strain fields, and the incremental divergence (volumetric strain) and curl (used as an indicator of shear strain) of the displacement fields were calculated from the DVC. These fields show that strain localisation in the sample deformed in the brittle regime manifested as a ~ 1 mm-wide, dilatational shear fracture oriented at an angle of 40–45° to the maximum principal stress. Pre- and post-deformation permeability measurements show that permeability of the sample deformed in the brittle regime increased from 3.9 × 10−12 to 4.9 × 10−12 m2, which is presumed to be related to the shear fracture. For the sample deformed in the ductile regime, strain localised into ~1 mm-thick, undulating compaction bands orientated sub-perpendicular to the maximum principal stress with little evidence of shear. Taken together, our data suggest that these bands formed during large stress drops seen in the mechanical data, within high-porosity zones within the sample, and within the large, well-connected porosity backbone. Pre- and post-deformation permeability measurements indicate that inelastic compaction decreased the permeability of the sample by a factor of ~3. The data of this study assist in the understanding of strain localisation in porous volcanic rocks, its influence on permeability (and therefore volcanic outgassing), and highlight an important role for DVC in studying strain localisation in volcanic materials.
25.	Heap, Michael J., et al. (författare) The tensile strength of hydrothermally altered volcanic rocks 2022 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 428 Tidskriftsartikel (refereegranskat)abstract The tensile strength of volcanic rocks is an important parameter for understanding and modelling a wide range of volcanic processes, and in the development of strategies designed to optimise energy production in volcanic geothermal reservoirs. However, despite the near-ubiquity of hydrothermal alteration at volcanic and geothermal systems, values of tensile strength for hydrothermally altered volcanic rocks are sparse. Here, we present an experimental study in which we measured the tensile strength of variably altered volcanic rocks. The alteration of these rocks, quantified as the weight percentage of secondary (alteration) minerals, varied from 6 to 62.8 wt%. Our data show that tensile strength decreases as a function of porosity, in agreement with previous studies, and as a function of alteration. We fit existing theoretical constitutive models to our data so that tensile strength can be estimated for a given porosity, and we provide a transformation of these models such that they are a function of alteration. However, because porosity and alteration influence each other, it is challenging to untangle their individual contributions to the measured reduction in tensile strength. Our new data and previously published data suggest that porosity exerts a first-order role on the tensile strength of volcanic rocks. Based on our data and observations, we also suggest that (1) alteration likely decreases tensile strength if associated with mineral dissolution, weak secondary minerals (such as clays), and an increase in microstructural heterogeneity and (2) alteration likely increases tensile strength if associated with pore- and crack-filling mineral precipitation. Therefore, we conclude that both alteration intensity and alteration type likely influence tensile strength. To highlight the implications of our findings, we provide discrete element method modelling which shows that, following the pressurisation of a dyke, the damage within weak hydrothermally altered host-rock is greater and more widespread than for strong hydrothermally altered host-rock. Because the rocks in volcanic and geothermal settings are likely to be altered, our results suggest that future modelling should consider the tensile strength of hydrothermally altered volcanic rocks.
26.	Heap, Michael J., et al. (författare) The tensile strength of volcanic rocks : Experiments and models 2021 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 418 Tidskriftsartikel (refereegranskat)abstract The tensile strength of volcanic rock exerts control over several key volcanic processes, including fragmentation and magma chamber rupture. Despite its importance, there is a paucity of laboratory data for the tensile strength of volcanic rocks, leading to an incomplete understanding of the influence of microstructural parameters, such as pore size and shape (factors that vary widely for volcanic rocks), on their tensile strength. To circumvent problems associated with the variability of natural samples, we provide here a systematic study in which we use elastic damage mechanics code "Rock Failure Process Analysis" to perform numerical experiments to better understand the influence of porosity, pore diameter, pore aspect ratio, and pore orientation on the tensile strength of volcanic rocks. We find that porosity and pore diameter exert a first-order control on the tensile strength of volcanic rocks, and that pore aspect ratio and orientation also influence tensile strength. Tensile strength is reduced by up to a factor of two as porosity is increased from 0.05 to 0.35 or as pore diameter is increased from 1 to 2 mm. Small, but systematic, reductions in tensile strength are observed as the angle between the loading direction and the major axis of an elliptical pore is increased from 0 to 90 degrees. The influence of pore aspect ratio (the ratio of the minor to major axis of an ellipse) depends on the pore angle: when the pore angle is 0 degrees, a decrease in pore aspect ratio, from 1 (a circle) to 0.2, increases the tensile strength, whereas the same decrease in pore aspect ratio does not substantially change the tensile strength when the pore angle is 90 degrees. These latter numerical experiments show that the tensile strength of volcanic rocks can be anisotropic. Our numerical data are in broad agreement with new and compiled experimental data for the tensile strength of volcanic rocks. One of the goals of this contribution is to provide better constrained constitutive models for the tensile strength of volcanic rocks for use in volcano modelling. To this end, we present a series of theoretical and semi-empirical constitutive models that can be used to determine the tensile strength of volcanic rocks, and highlight how tensile strength estimations can influence predictions of magma overpressures and assessments of the volume and radius of a magma chamber. (c) 2021 Elsevier B.V. All rights reserved.
27.	Heap, Michael J., et al. (författare) The thermal properties of porous andesite 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : ELSEVIER. - 0377-0273 .- 1872-6097. ; 398 Tidskriftsartikel (refereegranskat)abstract The thermal properties of volcanic rocks are crucial to accurately model heat transfer in volcanoes and in geothermal systems located within volcanic deposits. Here we provide laboratory measurements of thermal conductivity and thermal diffusivity for variably porous andesites from Mt. Ruapehu (New Zealand) and variably altered basaltic-andesites from Merapi volcano (Indonesia) measured at ambient laboratory pressure and temperature using the transient hot-strip method. The specific heat capacity of each sample was then calculated using these measured values and the bulk sample density. Thermal conductivity and thermal diffusivity decrease as a function of increasing porosity, but specific heat capacity does not vary systematically with porosity. For a given porosity, saturation with water increases thermal conductivity and specific heat capacity, but decreases thermal diffusivity. Measurements on samples from Merapi volcano show that, compared to the unaltered samples from Mt. Ruapehu, hydrothermal alteration deceases thermal conductivity and thermal diffusivity, and increases specific heat capacity. We use an effective medium approach to parameterise these data, showing that when the porosity and pore-fluid properties are scaled for, the measured values agree well with theoretical predictions. We find that despite the microstructural complexity of the studied andesites, porosity is the principal parameter dictating their thermal properties. To understand whether the measured changes in thermal properties are sufficient to influence natural processes, we model heat transfer from magma to the surrounding host-rock by solving Fick's second law cast in 1D Cartesian (dyke geometry) and cylindrical (conduit geometry) coordinates. We provide models for different host-rock porosities (0-0.6), different initial magmatic temperatures (800-1200 degrees C), and different levels of host-rock alteration. Our modelling shows how the cooling of a dyke and conduit is slowed by a higher host-rock porosity and by increased hydrothermal alteration. The thermal properties provided herein can help improve modelling designed to inform on volcanic and geothermal processes. (C) 2020 Elsevier B.V. All rights reserved.
28.	Hidalgo, Silvana, et al. (författare) SO2 degassing at Tungurahua volcano (Ecuador) between 2007 and 2013: Transition from continuous to episodic activity 2015 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 298, s. 1-14 Tidskriftsartikel (refereegranskat)abstract We present continuous SO2 measurements performed at Tungurahua volcano with a permanent network of 4 scanning DOAS instruments between 2007 and 2013. The volcano has been erupting since September 1999, but on the contrary to the first years of eruption when the activity was quasi-continuous, the activity transitioned in late 2008 towards the occurrence of distinct eruptive phases separated by periods of quiescence. During our study period we distinguish 11 phases lasting from 17 to 527days separated by quiescence periods of 26 to 184days. We propose a new routine to quantify the SO2 emissions when data from a dense DOAS monitoring network are available. This routine consists in summing all the highest validated SO2 measurements among all stations during the 10h of daily working-time to obtain a daily observed SO2 mass. Since measurement time is constant at Tungurahua the "observed" amounts can be expressed in tons per 10h and can easily be converted to a daily average flux or mass per day. Our results provide time series having an improved correlation on a long time scale with the eruptive phases and with quiescence periods. A total of 1.25Mt (1.25×109kg) of SO2 has been released by Tungurahua during the study period, with 95% of these emissions occurring during phases of activity and only 5% during quiescence. This shows a contrast with previous volcanic behaviour when passive degassing dominated the total SO2 emissions. SO2 average daily mass emission rates are of 73±56t/d during quiescent periods, 735±969t/d during long-lasting phases and 1424±1224t/d during short-lasting phases. Degassing during the different eruptive phases displays variable patterns. However, two contrasting behaviours can be distinguished for the onset of eruptive phases with both sudden and progressive onsets being observed. The first is characterised by violent opening of the conduit by high energy Vulcanian explosions; and the second by a progressive, in crescendo, development of the activity. The first case is becoming more frequent at Tungurahua making the volcano more dangerous and less predictable.
29.	Jaxybulatov, Kairly, et al. (författare) Evidence for high fluid/melt content beneath Krakatau volcano (Indonesia) from local earthquake tomography 2011 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 206:3-4, s. 96-105 Tidskriftsartikel (refereegranskat)abstract Within the KRAKMON project for multiparameter monitoring of Anak Krakatau volcano (Indonesia), a network of temporary stations was installed on the islands of the Krakatau complex as well as in the surrounding areas of the Sunda Strait, Sumatra and Java. The network was operated from June 2005 until January 2006. More than 700 local events were recorded during this experiment, and travel times from these events were used to perform a tomographic inversion for P and S velocities and for the Vp/Vs ratio. In this study, special attention was paid to the validation of the computed model based on different tests, such as inversion of independent data subsets and synthetic modeling. Although the network configuration and the distribution of the events are not favorable for high-quality tomographic imaging, we have obtained some important and robust features which give information about sources of volcanic activity in the Krakatau complex. The most interesting feature of this study is a zone of high Vp/Vs ratio beneath the Krakatau complex. At depths down to 4 km depth we observe anticorrelation of higher P- and lower S-velocities that leads to Vp/Vs ratio higher than 2. This is a probable indicator of the presence of partially molten and/or with high fluid content material with a composition corresponding to deeper layers. It is important that the anomaly of high Vp/Vs ratio beneath the Krakatau complex appears to be separated in two parts at a depth of 5-6 km. This fits to results of geobarometric analysis that presume the existence of several levels of magma chambers beneath Anak Krakatau.
30.	Jeddi, Zeinab, et al. (författare) Ambient-noise tomography of Katla volcano, south Iceland 2017 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 347, s. 264-277 Tidskriftsartikel (refereegranskat)abstract A shear-wave velocity model of subglacial Katla volcano, southern Iceland, has been developed using ambient seismic noise tomography based on data from a temporary network operating between May 2011 and August 2013 and permanent stations around the volcano. Phase-velocity dispersion curves were obtained using cross correlations of vertical components of 136 station pairs and non-linearly inverted for phase-velocity maps between 1.7 and 7.5 s. Local dispersion curves were inverted for shear-velocity variation with depth using a grid search imposing a fixed ice layer at the top. The resulting one-dimensional (1-D) velocity models were combined to obtain a pseudo three-dimensional (3-D) model with estimated lateral resolution of 8 km and depth resolution varying from close to 1 km near the surface to about 8 km at 10 km depth. Shear wave velocities are generally higher within the Katla central volcano than in its surroundings. The most striking feature of the model is a high-velocity anomaly beneath the caldera at >6 km depth interpreted to be due to cumulates resulting from differentiation of shallower magma intrusions and remelting of subsiding upper crust. No shallow low-velocity anomaly is resolved beneath the central caldera, but a low-velocity region is found at 2-4 km depth beneath the western half of the caldera. V-p/V-s ratios, estimated from average velocity-depth profiles from surface-wave data and higher frequency P-wave data, are anomalously high (>1.9) compared to average Icelandic crust, particularly in the top 2-3 km. This is argued not to be an artifact due to lateral refraction or topography. Instead, this anomaly could be explained as an artifact caused by velocity dispersion due to attenuation and a difference in frequency content, and possibly to a degree by the compositional difference between the transalkalic Fe-Ti basalts of Katla and average tholeiitic Icelandic crust.
31.	Juncu, Daniel, et al. (författare) Injection-induced surface deformation and seismicity at the Hellisheidi geothermal field, Iceland 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 391 Tidskriftsartikel (refereegranskat)abstract Induced seismicity is often associated with fluid injection but only rarely linked to surface deformation. At the Hellisheidi geothermal power plant in south-west Iceland we observe up to 2 cm of surface displacements during 2011–2012, indicating expansion of the crust. The displacements occurred at the same time as a strong increase in seismicity was detected and coincide with the initial phase of geothermal wastewater reinjection at Hellisheidi. Reinjection started on September 1, 2011 with a flow rate of around 500 kg/s. Micro-seismicity increased immediately in the area north of the injection sites, with the largest seismic events in the sequence being two M4 earthquakes on October 15, 2011. Semi-continuous GPS sites installed on October 15 and 17, and on November 2, 2011 reveal a transient signal which indicates that most of the deformation occurred in the first months after the start of the injection. The surface deformation is evident in ascending TerraSAR-X data covering June 2011 to May 2012 as well. We use an inverse modeling approach and simulate both the InSAR and GPS data to find the most plausible cause of the deformation signal, investigating how surface deformation, seismicity and fluid injection may be connected to each other. We argue that fluid injection caused an increase in pore pressure which resulted in increased seismicity and fault slip. Both pore pressure increase and fault slip contribute to the surface deformation.
32.	Jägerup, S. B., et al. (författare) Silicic frothy xenoliths (xeno-pumice) in recent volcanics from Gran Canaria, Canary Islands 2023 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 440 Tidskriftsartikel (refereegranskat)abstract The Quaternary small-volume alkaline magmatic episode on Gran Canaria erupted dominantly basanite and nephelinite lavas and scoria deposits that contain a range of mantle and crustal xenoliths. These xenoliths comprise peridotite nodules, partially melted plutonic and volcanic rock fragments, and a group of light colored, felsic, and commonly frothy quartz-bearing rock fragments (xeno-pumice) that show evidence for intense interaction with their host magmas. Here we study a selection of these felsic and, in part, glassy and vesicular xenoliths from North and North-East Gran Canaria, with the aim to unravel their ultimate origin and learn more about magma storage and ascent within and below the island. Inspection of textures, mineral assemblages and glass compositions reveal one group of felsic xenoliths with fresh to partly altered igneous phenocryst assemblages and relict magmatic textures in addition to 818O values of 3.6 to 6.6%o. This group is interpreted to be of igneous origin. A second group of frothy felsic xenoliths displays mineralogy and textural characteristics more similar to sedimentary rocks with frequent occurrence of quartz, a mineral usually not present as phenocrysts in magmatic rocks from the Canary Islands. This second group displays relatively high 818O values (8.1 to 16.8%o), more typical for sedimentary lithologies, and is thus interpreted to represent material derived from the extensive pre-island sedimentary part of the ocean crust. The investigated xenoliths from North Gran Canaria thus provide a snapshot of pre-island sedimentary geology as well as the island's "magmatic" interior. These new data help constrain the available subsurface compositional variations within and below the Canary Islands and will hence be useful in interpreting magma evolution trends and magma storage levels.
33.	Kalscheuer, Thomas, et al. (författare) Electromagnetic evidence for an ancient avalanche caldera rim on the south flank of Mount Merapi, Indonesia 2007 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 162:1-2, s. 81-97 Tidskriftsartikel (refereegranskat)abstract Long-Offset Transient Electromagnetic (LOTEM) data and VIBROTEM data from the south flank of Mount Merapi on Java island, Indonesia, are interpreted with one-dimensional (1D) inversions as well as two-dimensional (2D) forward modelling. One-dimensional joint inversions of several components of the electromagnetic field with Occam's method reduce the number of equivalent models, which were derived from inversions of single components and fit the data to a similar misfit. The 1D results, together with results from other geophysical measurements, serve as the basic model for further 2D forward modelling. The final model depicts a layering that follows the topography of the strato-volcano. In the depth range of 500 m to 1000 m, the resistivity of the layers decreases rapidly downwards into a good conductor with resistivities below 10 Ohmm. The deepest layer has a resistivity of 0.4 Ohmm which is quantitatively explained with a combination of saline fluids and hydrothermally altered minerals. Furthermore, the final model supports a hypothesis from the interpretation of central-loop TEM (Transient Electromagnetic) data that there is a fault structure below the southern flank, approximately 7.3 km south of the summit. To the north of the fault, the top of the good conductor is lowered from a depth of 500 m to 1000 m. We propose that the fault structure coincides with an ancient avalanche caldera rim.
34.	Kim, Doyeon, et al. (författare) Magma "bright spots" mapped beneath Krafla, Iceland, using RVSP imaging of reflected waves from microearthquakes 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : ELSEVIER. - 0377-0273 .- 1872-6097. ; 391 Tidskriftsartikel (refereegranskat)abstract The geometry and distribution of magma in the crust remain controversial topics with recent studies questioning the role of large magma chambers. In this investigation, high-resolution 3D reflection images of crustal discontinuities beneath the Krafla geothermal field in northern Iceland were generated by applying Vertical Seismic Profiling (VSP) techniques adapted from reflection seismology to microearthquake data. Exceptionally large amplitude reflections (bright spots) at a depth of 2.1 km correlate with rhyolitic magma encountered in the IDDP-1 borehole. Although similarly bright reflectors at about 4 km correspond in depth to the top of an inferred magma chamber from previous seismic studies, the scattered reflectivity that persists beneath this deeper reflector argues for a distributed magma system rather than a large feeder chamber.
35.	Li, Ka Lok, et al. (författare) Seismicity of the Hengill area, SW Iceland : Details revealed by catalog relocation and collapsing 2019 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 376, s. 15-26 Tidskriftsartikel (refereegranskat)abstract The spatial distribution of seismicity in the Hengill region, SW Iceland, is analyzed by relocation and collapsing. The Hengill region is a diffuse triple junction with volcano-tectonic activity associated with rifting, tectonic activity on a transecting transform and induced seismicity due to drilling and injection of fluid into geothermal fields. The Icelandic Meteorological Office has compiled 114,000 events over a 20-year period within an area of approximately 600 km2. The events in their catalog are relocated by application of empirical travel-time tables using a non-linear location strategy. The relocations are then redone applying a Bayesian inversion using the catalog event density as a prior. Finally, they are collapsed using the same catalog density as an attractor. We show that this catalog processing reproduces details of the spatial pattern of seismicity that independently emerges from relative relocations of a small subset of the catalog events (swarm activity). In particular, the predominant faulting orientations are reproduced in different parts of the region and the depth distribution of events resembles that obtained by dense deployments in the area. Its depth extent varies between 5 and 7 km in the northern part of the region, where volcanic processes dominate, and between 7 and 8 km in the southern part, where tectonic deformation is predominant. Induced seismicity is shallower than adjacent natural seismicity. An intriguing lineation emerges in the lateral distribution of inferred depth to the brittle-ductile transition in the northern volcanic part of the region, which is parallel to the strike of the fissure swarms in the area. Associating this transition with an isotherm (650 °C), the Hengill volcanic system and its fissure swarm appear to be considerably cooler than the Hrómundartindur system. This may relate to a recent intrusion into the latter or more efficient cooling in the Hengill fissure swarm due to deeper penetrating permeability. In both cases this has potential consequences for geothermal exploitation in the area.
36.	Lopez, T., et al. (författare) Geochemical constraints on volatile sources and subsurface conditions at Mount Martin, Mount Mageik, and Trident Volcanoes, Katmai Volcanic Cluster, Alaska 2017 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 347, s. 64-81 Tidskriftsartikel (refereegranskat)abstract We use the chemical and isotopic composition of volcanic gases and steam condensate, in situ measurements of plume composition and remote measurements of SO2 flux to constrain volatile sources and characterize subvolcanic conditions at three persistently degassing and seismically active volcanoes within the Katmai Volcanic Cluster (KVC), Alaska: Mount Martin, Mount Mageik and Trident. In situ plume measurements of gas composition were collected at all three volcanoes using MultiGAS instruments to calculate gas ratios (e.g. CO2/H2S, SO2/H2S and H2O/H2S), and remote measurements of SO2 column density were collected from Mount Martin and Mount Mageik by ultraviolet spectrometer systems to calculate SO2 fluxes. Fumaroles were directly sampled for chemical and isotopic composition from Mount Mageik and Trident. Mid Ocean Ridge Basalt (MORB)-like 3He/4He ratios (~ 7.2–7.6 Rc/RA) within Mount Mageik and Trident's fumarole emissions and a moderate SO2 flux (~ 75 t/d) from Mount Martin, combined with gas compositions dominated by H2O, CO2 and H2S from all three volcanoes, indicate magma degassing and active hydrothermal systems in the subsurface of these volcanoes. Mount Martin's gas emissions have the lowest CO2/H2S ratio (~ 2–4) and highest SO2 flux compared to the other KVC volcanoes, indicative of shallow magma degassing. Geothermometry techniques applied to Mount Mageik and Trident's fumarolic gas compositions suggest that their hydrothermal reservoirs are located at depths of ~ 0.2 and 4 km below the surface, respectively. Observations of an unusually reducing gas composition at Trident and organic material in the near-surface soils suggest that thermal decomposition of sediments may be influencing gas composition. When the measured gas compositions from Mount Mageik and Trident are compared with previous samples collected in the late 1990's, relatively stable magmatic-hydrothermal conditions are inferred for Mount Mageik, while gradual degassing of residual magma and contamination by shallow crustal fluids is inferred for Trident. The isotopic composition of volcanic gases emitted from Mount Mageik and Trident reflect mixing of subducted slab, mantle and crustal volatile sources, with organic sediment and carbonate being the predominant sources. Considering the close proximity of the target volcanoes in comparison with the depth to the subducted slab we speculate that Aleutian Arc volatiles are fed by a relatively homogeneous subducted fluid and that much of the apparent variability in volatile provenance can be explained by shallow crustal volatile sources and/or processes.
37.	Mancini, Andrea, et al. (författare) Origin of the compositional diversity in the basalt-to-dacite series erupted along the Heidarspordur ridge, NE Iceland 2015 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 301, s. 116-127 Tidskriftsartikel (refereegranskat)abstract The Heidarspordur ridge, located in the Northern Volcanic Zone of Iceland, was formed approximately 9000 years ago by a volcanic episode known as Ludent Fires. The episode produced a broad spectrum of different magma types, forming approximately 50 small scoria cones and two larger craters (Ludent and Hraunbunga). The bulk compositions cluster in five distinct groups: (1) olivine basalts, (2) Fe-Ti basalts, (3) basaltic icelandites, (4) icelandites, and (5) dacites. Major and trace element trends, together with mineral chemistry and isotopic ratios, suggest that the dominant process involved in generating the evolved magmas was crystal fractionation occurring at variable depth. An origin by polybaric differentiation is confirmed by MELTS modeling. Magma mixing played a dominant role in the formation of the basaltic icelandites. Additionally, the Fe-Ti basalts, which erupted shortly after the dacites and used approximately the same vent area, display unusually high concentrations of Fe, Ti, P, and Sr. Their composition is best explained by some pyroxene-dominated fractionation (prior to Fe-Ti oxide stability), and by entrainment of some crystal cumulate material at shallow depth, mostly left over from the silicic differentiation stage. Textural and chemical features of the minerals (e.g., presence of glomerocrysts, two populations of plagioclase in these basalts) support this interpretation of evolved cumulate remobilization. Fe-Ti basalts with the same field, compositional and textural characteristics have also been erupted in the nearby but magmatically independent Krafla Volcanic System, suggesting that a similar differentiation trend occurs also in this larger central volcano. (C) 2015 Elsevier B.V. All rights reserved.
38.	Mattsson, Hannes B., et al. (författare) Contemporaneous phreatomagmatic and effusive activity along the Hverfjall eruptive fissure, north Iceland : Eruption chronology and resulting deposits 2011 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 201:1-4, SI, s. 241-252 Tidskriftsartikel (refereegranskat)abstract The 2500 BP Hverfjall eruption in northern Iceland produced pyroclastic and effusive deposits of widely different characteristics along the length of the eruptive fissure. The southern half of the fissure was located in a shallow lake, whereas the northern part of the fissure extended onto dry land. This specific setting, with overlapping periods of activity at the different vents, resulted in various mingling features between fine-grained phreatomagmatic deposits and lava flows. Here we reconstruct the course of events during this eruption based on field observations and granulometric analyses of the resulting deposits. The eruption can be divided into three main phases depending on the main depositional characteristics and vent locations. The initial phase is dominated by phreatomagmatic fall deposits which are attributed to an overall high eruption rate in a shallow lacustrine setting. The second phases involved opening of two new vents on dry ground, and deposition of scoria and lava flows. The third and final phase of the eruption is associated with a lowering of the eruption rate in the southernmost vent, with a shift in the activity from continuous uprush and fall deposits to discrete explosions and emplacement of base surges. These surges display features consistent with drying up with increasing distance from the vent, suggesting that their dynamics changed during emplacement. Most wet surges were channelized within a preexisting graben structure close to the vent, but some more dilute (i.e., dry) surges were able to flow over this obstacle and continued to flow for more than 5 km away from the vent and 100 m uphill before stopping. (C) 2010 Elsevier B.V. All rights reserved.
39.	Mattsson, H B, et al. (författare) Crustal xenoliths in the 6220 BP Saefell tuff-cone, south Iceland : Evidence for a deep, diatreme-fonning, Surtseyan eruption 2005 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 145:3-4, s. 234-248 Tidskriftsartikel (refereegranskat)abstract Three types of xenoliths were collected from a 80 in high vertical section of the Refell tuff-cone on Heimaey, Iceland. These types are: alkali basaltic (Type I), sedimentary (Type II) and cpx-bearing basalts (Type III). They are distinct in hand specimen, thin section and geochemistry. Near the base of the eruptive succession only juvenile material and Type I xenoliths are present. The middle section has Type II xenoliths in addition to Type I. Xenoliths of Type III first appear in the uppermost xenolith-rich horizons, where they are found together with all other types. Juvenile Swfell clasts are present in various amounts throughout the investigated section. A downward migration of explosion foci during the eruption is established based on the distribution of the different types of xenoliths in the tuff-cone (i.e. the appearance of Type I-Type II-Type III xenoliths with increasing stratigraphic height) in combination with the observed relations in basement stratigraphy beneath Heimaey. In the beginning of the eruption a combination of high eruption rate and abundant seawater resulted in shallow-seated explosions depositing only juvenile material and Type I xenoliths. The downward migration of explosion foci is suggested to be the result of lowered influx of seawater (due to the formation of a cone that reached 50-75 in a.s.l.) in combination with lowered eruption rate. As the basement stratigraphy beneath Heimaey is well documented by a 1565 in deep drill-hole, the depth of the explosions can be constrained to vary between less than 170 in in the beginning of the eruption and exceeding 820 in in the final phases. This is much deeper than previously reported for any Surtseyan tuff-cone forming eruption and consistent with the downward penetration of a diatreme. (c) 2005 Elsevier B.V. All rights reserved.
40.	Mattsson, Hannes B., et al. (författare) Depositional characteristics and volcanic landforms in the Lake Natron-Engaruka monogenetic field, northern Tanzania 2011 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 203:1-2, s. 23-34 Tidskriftsartikel (refereegranskat)abstract The Lake Natron-Engaruka monogenetic volcanic field (LNE-MVF) is situated in the East African Rift of northern Tanzania, where it comprises approximately 200 vents scattered over an area of 2500 km(2). Similar to most other monogenetic volcanic fields in the world, the landforms of the LNE-MVF are characterized by a wide array of morphologies, such as maar-diatreme volcanoes, tuff cones and tuff rings, scoria cones and spatter cones. However, in contrast to most other MVFs (which are basaltic in composition) the magmas erupted within the LNE-MVF are predominantly of olivine-melilititic to nephelinitic compositions. Here we show by field observations, granulometric analyses and morphological studies of particle shapes from a large selection of different landforms from the LNE-MVF that there are some crucial differences compared to the more common basaltic equivalents. These differences are reflected in both eruption dynamics and fragmentation mechanisms as well as the overall characteristics of the deposits. Landforms within the LNE-MVF that resemble those produced by phreatomagmatic eruptions in morphology, display strong evidence for dry fragmentation and also dry deposition. Therefore, to reconcile the observed depositional characteristics with eruptive processes within the LNE-MVF we propose a hypothetical eruption scenario. Partial melting of a carbonate-bearing mantle source produces small volume volatile-rich melilititic melts (rich in phlogopite and amphibole). These volatile-rich, and mantle xenolith-bearing, magmas ascend rapidly from the mantle to the surface without being subject to significant degassing. The volatile-rich nature of these melilitite magmas, in combination with a significant exsolution of CO2 during decompression (ascent) can explain the dry characteristics of these apparent “phreatomagmatic” landforms. (C) 2011 Elsevier B.V. All rights reserved.
41.	Mattsson, H B, et al. (författare) Eruption reconstruction, formation of flow-lobe tumuli and eruption duration in the 5900 BP Helgafell lava field (Heimaey), south Iceland 2005 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 147:1-2, s. 157-172 Tidskriftsartikel (refereegranskat)abstract The 5900 BP Helgafell eruption started with an intense fire-fountaining phase that deposited scoria and spatter near the vent. Spatter accumulated, agglutinated, and was subsequently emplaced. as clastogenic flows. The intense initial phase was followed by effusive emplacement of tube-fed pahoehoe. This type of lava emplacement makes up the bulk of the lava field, and contains abundant inflation features such as tumuli and pressure-ridges. We measured the depths of 358 inflation clefts in tumuli and the thicknesses of the upper-vesicular crust in flow-lobes from the Helgafell lava field. Measurements of altitude between a point-source of lava tubes and the depth of inflation clefts in tumuli suggest that the magmastatic pressure affects initial tumuli formation. The overall growth of tumuli is, however, more dependent on effusion rate and collapse/clogging of individual tubes than on the magmastatic head within tubes. Three areas with abundant tumuli are recognized in the Helgafell lava field, each of which was active for at least 47 days. The average time for tumuli formation is 32 days. Using the crustal measurements of inflation features we test the hypothesis that the total eruption duration can be estimated for a pre-historic volcanic eruption. We chose the Helgafell lava field to test this hypothesis because it has (1) abundant inflation features that are easily measured, and (2) the majority of lava flows emplaced during the eruption are well exposed. Our result shows that the duration of the Helgafell eruption can be estimated to 11-12 months, yielding an average volumetric effusion rate for the Helgafell eruption of 0.05-0.06 km(3)/month. This result is very similar to the effusion rates for two known eruptions in the same volcanic system (i.e. the 1963-1967 Surtsey and the 1973 Eldfell eruptions, with effusion rates of 0.02 and 0.04 km(3)/month, respectively). Given that all three eruptions occurred within the same volcanic system and that they have similar volumetric effusion rates, we suggest that our estimated eruption duration for Helgafell is reasonable. Our results, building on the suggestion by Hon et al. (1994) [Hon, K., Kauhikaua, J., Denlinger, R., MacKay, K., 1994. Emplacement and inflation of pahoehoe sheet flows: observations and measurements of active lava flows on Kilauea Volcano, Hawaii. Geol. Soc. Amer. Bull. 106, 351-370] that the duration of inflation can be estimated for individual flows by measuring inflation features, show that by combining abundant and measureable inflation features with a well-established stratigraphy the duration of an entire pre-historic eruption can be estimated. (c) 2005 Elsevier B.V. All rights reserved.
42.	Mattsson, H B, et al. (författare) Petrogenesis of alkaline basalts at the tip of a propagating rift: : Evidence from the Heimaey volcanic centre, south Iceland 2005 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier B.V.. - 0377-0273 .- 1872-6097. ; 147:3-4, s. 245-267 Tidskriftsartikel (refereegranskat)abstract Heimaey is the volcanic centre in the Vestmannaeyjar Volcanic System, situated at the tip of Iceland's propagating Eastern Volcanic Zone (EVZ). The Heimaey lavas are slightly alkaline, ne-normative, basalts with plagioclase, olivine and Ti-magnetite as phenocryst phases. Inversion modelling using REE suggests that a primary magma is generated by fractional melting over a depth interval of 100–65 km beneath Heimaey of a source similar to that of MORB. The primary magma fractionated 31% olivine and clinopyroxene en route to ponding at the base of the crust (30–35 km depth). Tectonic events as a result of the extensional stress exerted by the southwards propagating EVZ causes magmas to be emplaced into different levels of the crust where they evolve by fractional crystallization independently of each other (i.e. polybaric fractionation). During residence in a parental magma chamber at the mantle/crust boundary the fractionating assemblage is dominated by olivine and clinopyroxene, whereas olivine and plagioclase dominates the fractionating assemblage during residence in crustal magma chambers. The most evolved magma composition can be related to a parental Heimaey melt by 73% fractional crystallization of predominantly plagioclase, clinopyroxene and olivine. The residence times in crustal magma chambers are short as indicated by the absence of equilibrium phenocryst assemblages (e.g. lack of cpx-phenocrysts). Oxygen and radiogenic isotopes suggests that no crustal contamination occurred, and that the role of magma mixing is insignificant in the evolution of the Heimaey lavas. The polybaric evolution of the Heimaey lavas in small, isolated, magma chambers at different levels in the crust fits well with a southward propagation of the EVZ, with the rift-tip currently located beneath the Vestmannaeyjar Volcanic System.
43.	Mattsson, Hannes B. (författare) Rapid magma ascent and short eruption durations in the Lake Natron-Engaruka monogenetic volcanic field (Tanzania) : A case study of the olivine melilititic Pello Hill scoria cone 2012 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 247, s. 16-25 Tidskriftsartikel (refereegranskat)abstract The Pello Hill scoria cone displays widely different characteristics dependent on which side of the cone is studied. This follows as a direct result of a strong depositional asymmetry (i.e., the crater rim varies between 14 and 111 m in height), preferentially depositing material to the northwestern side of the construct. This is interpreted to reflect sedimentation from a sustained eruption plume (with prevailing winds at the time of the eruption coinciding with the direction of maximum deposition). The scoria deposits on this side of the cone form relatively fine-grained and well-sorted deposits which are laterally continuous over distances of 10’s of meters. To all other sides of the vent, deposits are characterized by coarse-grained lenticular deposits rich in mantle xenoliths, occasionally showing inverse grading (consistent with an origin as ballistic ejecta and slight reworking down-slope as grain-flows). The pyroclastic textures are dominated by a moderate vesicularity (similar to 40 vol. %) in combination with smooth, fluidal, outer surfaces. Two other features that stands out in comparison with “normal” scoria cones, these are defined by the absence of: (i) inward dipping layers into the crater area, and (ii) no agglutination/welding features can be found in any of the exposed outcrops. Calculated magma ascent rates yields values between 8.5 and 36.0 m s(-1), which is similar to that previously reported for kimberlitic magmas. Building on these ascent rates, and the volume of the pyroclastic construct (similar to 5 x 10(6) m(3) DRE), the eruption duration is estimated to less than 6 hours (for any vent area larger than 28 m(2)). Therefore, it may not have taken longer time than 9 hours from the time the magma started to ascend from upper-mantle depth (90 km) and the point at which the eruption halted. Overall, the olivine melilititic Pello Hill scoria cone displays many characteristics that can also be found in the vent-facies deposits of kimberlite eruptions. Therefore, further detailed studies of well-preserved, CO2-rich, olivine melilitite eruptions (such as the provided by the landforms within the LNE-MVF and Pello Hill) could provide a tool to understand the emplacement dynamics of the vent-facies of kimberlitic eruptions. (C) 2012 Elsevier B.V. All rights reserved.
44.	Mattsson, Hannes B. (författare) Textural variation in juvenile pyroclasts from an emergent, Surtseyan-type, volcanic eruption : The Capelas tuff cone, Sao Miguel (Azores) 2010 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 189:1-2, s. 81-91 Tidskriftsartikel (refereegranskat)abstract Here I present textural data (i.e., vesicularity, vesicle size distributions (VSD), plagioclase crystallinity, crystal size distributions (CSD), combined with fractal analyses of particle outlines) from a natural succession of alternating fall and surge deposits in the emergent Capelas tuff cone (Azores). The textural variation in the Capelas succession is surprisingly small considering the wide variety of fragmentation processes, vent activity and emplacement mechanisms that are characteristic of emergent eruptions. The plagioclase crystal content varies between 24 and 33 vol.% CSD analyses of plagioclase show near-linear trends with a slight increase in time for the smallest crystal sizes (with surge deposits having more groundmass plagioclase when compared with fall deposits). This is consistent with crystallization induced by degassing and decompression at lower eruption rates. The vesicularities of the Capelas pyroclasts are more variable (18 to 59 vol.%), with VSDs displaying kinked trends characteristic of coalescence. This is especially evident in the fall deposits, and consistent with being formed in continuous uprush (jetting) with an overall shallow fragmentation level within the conduit. Bubble coalescence can also be identified in the surge deposits, although to a much lesser extent. The amount of bubble coalescence is negatively correlated with the amount of groundmass crystallization (i.e., plagioclase) in the Capelas deposits. A relatively broad range of fractal dimensions (with average D-box = 1.744 and sigma = 0.032) for the outlines of pyroclastic fragments emplaced by fall or as surges indicate that there is little difference in the fragmentation process itself at Capelas. In addition to this, the fact that the fractal dimensions for both the fall and surge end-members completely overlap suggests that shape modification due to abrasion and chipping of grain edges was minor during emplacement of base surges. These results are consistent with emergent eruptions, building tuff cones, to be a relatively low-energy phreatomagmatic landform (e.g., at least when compared with more energetic phreatomagmatic eruptions producing tuff rings and maar volcanoes). (C) 2009 Elsevier B.V. All rights reserved.
45.	Mattsson, Hannes, et al. (författare) Geology of the Heimaey volcanic centre, south Iceland: early evolution of a central volcano in a propagating rift? 2003 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 127:1-2, s. 55-71 Tidskriftsartikel (refereegranskat)
46.	Merle, Renaud E., 1976-, et al. (författare) Segregation vesicles, cylinders, and sheets in vapor-differentiated pillow lavas : examples from Tore-Madeira Rise and Chile Triple Junction 2005 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273 .- 1872-6097. ; 141:1, s. 109-122 Tidskriftsartikel (refereegranskat)abstract We conducted a detailed field and laboratory study of internal segregation structures of two hand-size pillow lavas samples. They were dredged, respectively, on the Josephine seamount, Tore-Madeira Rise (TMR), and on a small quaternary volcanic edifice located on the continental edge of the trench close to the Chile Triple Junction (CTJ). Both pillows display a combination of four types of segregation structures (spherical vesicles, pipe vesicles, vesicle cylinders, and vesicle sheets) observed so far only within subaerial basalt flows typically 2–10 m thick. In particular, the samples offer a remarkable exposure of the transition between pipe vesicles and cylinders. We show that the vesicle sheets are not generated by the same mechanism in both occurrences; they do not seem to be connected to cylinders in the CTJ pillow as they are in the TMR pillow. The two pillows are geochemically distinct, the TMR being alkaline and the CTJ calc–alkaline. Two types of internal differentiation are proposed. The first one implies the extraction of the residual liquid from the host lava and transport towards the segregation structures, whereas the other one results from in situ crystallization within one given structure. In the latter case, glass composition is highly dependant on the nature of the neighbouring crystallizing minerals. The degree of crystallization required to produce a crystal framework strong enough for generating the segregation structures seems to be lower in pillows (ca. 25% crystallization) than in vapor-differentiated basaltic lava flows (35% crystallization).
47.	Merle, Renaud E., et al. (författare) Segregation vesicles, cylinders, and sheets in vapor-differentiated pillow lavas: examples from Tore-Madeira Rise and Chile Triple Junction 2005 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. Tidskriftsartikel (refereegranskat)
48.	Mouyen, Maxime, 1982, et al. (författare) Gravity monitoring of Tatun Volcanic Group activities and inference for underground fluid circulations 2016 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273. ; 328, s. 45-58 Tidskriftsartikel (refereegranskat)
49.	Pfeffer, M. A., et al. (författare) SO 2 emission rates and incorporation into the air pollution dispersion forecast during the 2021 eruption of Fagradalsfjall, Iceland 2024 Ingår i: Journal of Volcanology and Geothermal Research. - 0377-0273. ; 449 Tidskriftsartikel (refereegranskat)abstract During the low-effusion rate Fagradalsfjall eruption (19 March – 18 September 2021), the emission of sulfur dioxide (SO2) was frequently measured using ground-based UV spectrometers. The total SO2 emitted during the entire eruption was 970 ± 540 kt, which is only about 6% of the SO2 emitted during the similar length Holuhraun eruption (2014–2015). The eruption was divided into five phases based on visual observations, including the number of active vents and the occurrence of lava fountaining. The SO2 emission rate ranged from 44 ± 19 kg/s in Phase 2 to 85 ± 29 kg/s in Phase 5, with an average of 64 ± 34 kg/s for the entire eruption. There was notable variability in SO2 on short timescales, with measurements on 11 August 2021 ranging from 17 to 78 kg/s. SO2 flux measurements were made using scanning DOAS instruments located at different distances from and orientations relative to the eruption site augmented by traverses. Four hundred and forty-four scan and traverse measurements met quality criteria and were used, along with plume height and meteorological data, to calculate SO2 fluxes while accounting for wind-related uncertainties. A tendency for stronger SO2 flux concurrent with higher amplitude seismic tremor and the occurrence of lava fountaining was observed during Phases 4 and 5 which were characterized by intermittent crater activity including observable effusion of lava and gas release interspersed with long repose times. This tendency was used to refine the calculation of the amount of SO2 emitted during variably vigorous activity. The continuous seismic tremor time series was used to quantify how long during these eruption phases strong/weak activity was exhibited to improve the calculated SO2 flux during these Phases. The total SO2 emissions derived from field measurements align closely with results obtained by combining melt inclusion and groundmass glass analyses with lava effusion rate measurements (910 ± 230 kt SO2). Specifically, utilizing the maximum S content found in evolved melt inclusions and the least remaining S content in accompanying quenched groundmasses provides an identical result between field measurements and the petrological calculations. This suggests that the maximum SO2 release calculated from petrological estimates should be preferentially used to initialize gas dispersion models for basaltic eruptions when other measurements are lacking. During the eruption, the CALPUFF dispersion model was used to forecast ground-level exposure to SO2. The SO2 emission rates measured by DOAS were used as input for the dispersion model, with updates made when a significant change was measured. A detailed analysis of one mid-distance station over the entire eruption shows that the model performed very well at predicting the presence of volcanic SO2 when it was measured. However, it frequently predicted the presence of SO2 that was not measured and the concentrations forecasted had no correlation with the concentrations measured. Various approaches to improve the model forecast were tested, including updating plume height and SO2 flux source terms based on measurements. These approaches did not unambiguously improve the model performance but suggest that improvements might be achieved in more-polluted conditions.
50.	Riley, Teal R., et al. (författare) Cretaceous arc volcanism of Palmer Land, Antarctic Peninsula : Zircon U-Pb geochronology, geochemistry, distribution and field relationships 2020 Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 401 Tidskriftsartikel (refereegranskat)abstract The Cretaceous marks an episode of enhanced magmatism, sedimentation and tectonic processes along the entire proto-Pacific convergent margin of West Gondwana. Cretaceous magmatism across the Antarctic Peninsula is dominated by the intrusive Lassiter Coast intrusive suite which developed as episodic ‘flare-up’ events during the mid-Cretaceous, at a time of increased convergence. Volcanic rocks of this age are poorly defined, as a consequence of limited field observations and an absence of accurate geochronology. Recent field mapping, combined with unpublished field observations has identified a region >10,000 km2 of dominantly subaerial rhyolitic pyroclastic and epiclastic successions from northern Palmer Land of the Antarctic Peninsula. Volcanic successions up to 1500 m in thickness consist of dominantly silicic ignimbrites, lavas, heterolithic breccias and lahar deposits, fed by caldera-forming eruptions. The volcanic rocks of this region were widely considered to be Early Cretaceous in age based on field relationships and early geochronology. New U-Pb zircon ages identify three distinct volcanic episodes during the Late Cretaceous/Early Cenozoic at ~108 Ma, ~93 Ma and ~64 Ma. Lu-Hf data indicate significant proportions of ancient crust in the petrogenesis of the volcanic rocks and the slightly negative εHf values are consistent with a mid-position (~120 km) within the magmatic arc, relative to more juvenile compositions close to the trench.

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