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- Hreinsdottir, S., et al.
(författare)
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Volcanic plume height correlated with magma-pressure change at Grimsvotn Volcano, Iceland
- 2014
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 7:3, s. 214-218
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Tidskriftsartikel (refereegranskat)abstract
- Magma flow during volcanic eruptions causes surface deformation that can be used to constrain the location, geometry and internal pressure evolution of the underlying magmatic source(1). The height of the volcanic plumes during explosive eruptions also varies with magma flow rate, in a nonlinear way(2,3). In May 2011, an explosive eruption at Grimsvotn Volcano, Iceland, erupted about 0.27 km(3) dense-rock equivalent of basaltic magma in an eruption plume that was about 20 km high. Here we use Global Positioning System (GPS) and tilt data, measured before and during the eruption at Grimsvotn Volcano, to show that the rate of pressure change in an underlying magma chamber correlates with the height of the volcanic plume over the course of the eruption. We interpret ground deformation of the volcano, measured by geodesy, to result from a pressure drop within a magma chamber at about 1.7 km depth. We estimate the rate of magma discharge and the associated evolution of the plume height by differentiating the co-eruptive pressure drop with time. The time from the initiation of the pressure drop to the onset of the eruption was about 60 min, with about 25% of the total pressure change preceding the eruption. Near-real-time geodetic observations can thus be useful for both timely eruption warnings and for constraining the evolution of volcanic plumes.
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- Ng, M Y M, et al.
(författare)
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Meta-analysis of 32 genome-wide linkage studies of schizophrenia
- 2009
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Ingår i: Molecular Psychiatry. - : Springer Science and Business Media LLC. - 1359-4184 .- 1476-5578. ; 14:8, s. 774-785
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Tidskriftsartikel (refereegranskat)abstract
- A genome scan meta-analysis (GSMA) was carried out on 32 independent genome-wide linkage scan analyses that included 3255 pedigrees with 7413 genotyped cases affected with schizophrenia (SCZ) or related disorders. The primary GSMA divided the autosomes into 120 bins, rank-ordered the bins within each study according to the most positive linkage result in each bin, summed these ranks (weighted for study size) for each bin across studies and determined the empirical probability of a given summed rank (P(SR)) by simulation. Suggestive evidence for linkage was observed in two single bins, on chromosomes 5q (142-168 Mb) and 2q (103-134 Mb). Genome-wide evidence for linkage was detected on chromosome 2q (119-152 Mb) when bin boundaries were shifted to the middle of the previous bins. The primary analysis met empirical criteria for 'aggregate' genome-wide significance, indicating that some or all of 10 bins are likely to contain loci linked to SCZ, including regions of chromosomes 1, 2q, 3q, 4q, 5q, 8p and 10q. In a secondary analysis of 22 studies of European-ancestry samples, suggestive evidence for linkage was observed on chromosome 8p (16-33 Mb). Although the newer genome-wide association methodology has greater power to detect weak associations to single common DNA sequence variants, linkage analysis can detect diverse genetic effects that segregate in families, including multiple rare variants within one locus or several weakly associated loci in the same region. Therefore, the regions supported by this meta-analysis deserve close attention in future studies.
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- Sigmundsson, F., et al.
(författare)
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Segmented lateral dyke growth in a rifting event at Bardarbunga volcanic system, Iceland
- 2015
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 517:7533
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Tidskriftsartikel (refereegranskat)abstract
- Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long(1). Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens(2-4), or magma flowing vertically into dykes from an underlying source(5,6), with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bardarbunga volcanic system grew laterally for more than 45 kilometres at a variable rate, with topography influencing the direction of propagation. Barriers at the ends of each segment were overcome by the build-up of pressure in the dyke end; then a new segment formed and dyke lengthening temporarily peaked. The dyke evolution, which occurred primarily over 14 days, was revealed by propagating seismicity, ground deformation mapped by Global Positioning System(GPS), interferometric analysis of satellite radar images (InSAR), and graben formation. The strike of the dyke segments varies from an initially radial direction away from the Bardarbunga caldera, towards alignment with that expected from regional stress at the distal end. A model minimizing the combined strain and gravitational potential energy explains the propagation path. Dyke opening and seismicity focused at the most distal segment at any given time, and were simultaneous with magma source deflation and slow collapse at the Bardarbunga caldera, accompanied by a series of magnitude M > 5 earthquakes. Dyke growth was slowed down by an effusive fissure eruption near the end of the dyke. Lateral dyke growth with segment barrier breaking by pressure build-up in the dyke distal end explains how focused upwelling of magma under central volcanoes is effectively redistributed over long distances to create new upper crust at divergent plate boundaries.
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| 14. |
- Geirsson, H., et al.
(författare)
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Overview of results from continuous GPS observations in Iceland from 1995 to 2010
- 2010
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Ingår i: Jökull. - 0449-0576. ; 60:1, s. 1-21
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Tidskriftsartikel (refereegranskat)abstract
- Iceland is a natural laboratory for a variety of processes associated with crustal deformation, such as earthquakes, magmatic events, tectonic plate motions, and glacial load changes. Continuous GPS (CGPS) measurements started in Iceland in 1995, and since then data from the network have helped to shed light on many different active deformation processes. The number of CGPS sites in Iceland tripled during 2006–2008, as a result of an international collaborative effort coordinated by Icelandic scientists. By early 2010 the number of CGPS stations in Iceland had reached 64, located primarily around and within the North- American–Eurasian plate boundary zone. Since its initiation, the CGPS network has played an important role in monitoring volcanoes and seismogenic areas, most notably during the 2009–2010 Eyjafjallajökull volcano unrest. Plate spreading of up to 2 cm per year usually dominates the horizontal motion observed at the CGPS sites, while uplift is observed at many of the stations due to recent retreat of the Icelandic ice caps. Co-seismic and post-seismic deformation of the largest earthquakes in 2000 and 2008 in the South Iceland Seismic Zone were captured by the network, and high-rate (1 Hz) CGPS observations helped to identify two magnitude 6 mainshocks in 2008 that were separated in time by only 2–3 seconds. The CGPS network has thus enabled us to monitor deformation occurring over days to months caused by migration of magma or fluids, post-seismic transients, rapid deformation caused by earthquakes and eruptions, as well as the long term plate spreading signal.
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| 15. |
- Lewis, Cathryn M, et al.
(författare)
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Genome scan meta-analysis of schizophrenia and bipolar disorder, part II : Schizophrenia
- 2003
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Ingår i: American Journal of Human Genetics. - 0002-9297 .- 1537-6605. ; 73:1, s. 34-48
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Tidskriftsartikel (refereegranskat)abstract
- Schizophrenia is a common disorder with high heritability and a 10-fold increase in risk to siblings of probands. Replication has been inconsistent for reports of significant genetic linkage. To assess evidence for linkage across studies, rank-based genome scan meta-analysis (GSMA) was applied to data from 20 schizophrenia genome scans. Each marker for each scan was assigned to 1 of 120 30-cM bins, with the bins ranked by linkage scores (1 = most significant) and the ranks averaged across studies (R(avg)) and then weighted for sample size (N(sqrt)[affected casess]). A permutation test was used to compute the probability of observing, by chance, each bin's average rank (P(AvgRnk)) or of observing it for a bin with the same place (first, second, etc.) in the order of average ranks in each permutation (P(ord)). The GSMA produced significant genomewide evidence for linkage on chromosome 2q (PAvgRnk<.000417). Two aggregate criteria for linkage were also met (clusters of nominally significant P values that did not occur in 1,000 replicates of the entire data set with no linkage present): 12 consecutive bins with both P(AvgRnk) and P(ord)<.05, including regions of chromosomes 5q, 3p, 11q, 6p, 1q, 22q, 8p, 20q, and 14p, and 19 consecutive bins with P(ord)<.05, additionally including regions of chromosomes 16q, 18q, 10p, 15q, 6q, and 17q. There is greater consistency of linkage results across studies than has been previously recognized. The results suggest that some or all of these regions contain loci that increase susceptibility to schizophrenia in diverse populations.
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| 16. |
- Pinel, Virginie, et al.
(författare)
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Consequences of local surface load variations for volcanoes monitoring: Application to Katla subglacial volcano, Iceland
- 2009
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Ingår i: The VOLUME Project. VOLcanoes: Understanding subsurface mass moveMEnt. Edited by C.J. Bean, A.K. Braiden, I. Lokmer, F. Martini, G.S. O´Brien. - Dublin, Ireland. - 9781905254392 ; , s. 25-39
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Surface load variations occur frequently in the vicinity of volcanoes inducing deformation and stress field perturbations that can be recorded by geophysical monitoring. It is thus necessary to discriminate these perturbations from those caused by shallow magma movement and to understand their potential influence on themagmatic plumbing system. Discrimination can be performed by modelling the deformation induced by surface load variations using integration of Green's function. This method was applied to the Katla volcano located beneath the Mýrdalsjökull ice cap, Iceland, where an annual cycle in ice load occurs as well as a gradual ice retreat. We also estimated pressure changes induced by the seasonal ice load variation within a magma reservoir, and calculated the deformation field and the Coulomb stress changes induced by the combined effect of the ice load variation and the magma pressure re-equilibration. Seismicity rate response to the seasonal perturbation strongly depends on the shape and state of the magma reservoir. Finally, introducing a rupture criterion, we conclude that, in the case of spherical or horizontally elongated reservoir and a slow magma inflow, eruptions at Katla volcano are more likely during the summer period, which is consistent with historical observations.
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