| 1. |
- 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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| 2. |
- 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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| 3. |
- Sigmundsson, F., et al.
(författare)
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Intrusion triggering of the 2010 Eyjafjallajökull explosive eruption
- 2010
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Ingår i: Nature. ; 468:7322, s. 426-430
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Tidskriftsartikel (refereegranskat)abstract
- Gradual inflation of magma chambers often precedes eruptions at highly active volcanoes. During such eruptions, rapid deflation occurs as magma flows out and pressure is reduced1–3. Less is known about the deformation style at moderately active volcanoes, such as Eyjafjallajo¨kull, Iceland, where an explosive summit eruption of trachyandesite beginning on 14 April 2010 caused exceptional disruption to air traffic, closing airspace over much of Europe for days. This eruption was preceded by an effusive flank eruption of basalt from 20 March to 12 April 2010. The 2010 eruptions are the culmination of 18 years of intermittent volcanic unrest4–9. Here we show that deformation associated with the eruptions was unusual because it did not relate to pressure changes within a single magma chamber. Deformation was rapid before the first eruption (.5mm per day after 4 March), but negligible during it. Lack of distinct co-eruptive deflation indicates that the net volume of magma drained from shallow depth during this eruption was small; rather, magma flowed from considerable depth. Before the eruption, a 0.05km3 magmatic intrusion grew over a period of three months, in a temporally and spatially complex manner, as revealed by GPS (Global Positioning System) geodetic measurements and interferometric analysis of satellite radar images. The second eruption occurred within the ice-capped caldera of the volcano, with explosivity amplified by magma–ice interaction. Gradual contraction of a source, distinct from the pre-eruptive inflation sources, is evident from geodetic data. Eyjafjallajo¨kull’s behaviour can be attributed to its off-rift setting with a ‘cold’ subsurface structure and limited magma at shallow depth, as may be typical for moderately active volcanoes. Clear signs of volcanic unrest signals over years to weeks may indicate reawakening of such volcanoes, whereas immediate short-term eruption precursors may be subtle and difficult to detect.
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| 4. |
- Arnadottir, Solveig A, 1968-, et al.
(författare)
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Application of rasch analysis to examine psychometric aspects of the activities-specific balance confidence scale when used in a new cultural context
- 2010
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Ingår i: Archives of Physical Medicine and Rehabilitation. - : Elsevier BV. - 0003-9993 .- 1532-821X. ; 91:1, s. 156-163
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Tidskriftsartikel (refereegranskat)abstract
- Arnadottir SA, Lundin-Olsson L, Gunnarsdottir ED, Fisher AG. Application of Rasch analysis to examine psychometric aspects of the Activities-Specific Balance Confidence Scale when used in a new cultural context. OBJECTIVE: To investigate by using Rasch analysis the psychometric properties of the Activities-Specific Balance Confidence (ABC) Scale when applied in a new Icelandic context. DESIGN: Cross-sectional, population-based, random selection from the Icelandic National Registry. SETTING: Community-based. PARTICIPANTS: Icelanders (N=183), 65 to 88 years old, and 48% women. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURE: ABC, an instrument used to evaluate how confident older people are in maintaining balance and remaining steady when moving through the environment. An Icelandic translation of the ABC (ABC-ICE) scale was evaluated by implementing Rasch rating scale analysis to transform ordinal ABC-ICE scores into interval measures and evaluating aspects of validity and reliability of the scale. RESULTS: Participants were not able to differentiate reliably between the 11 rating scale categories of the ABC-ICE. Additionally, 3 items failed to show acceptable goodness of fit to the ABC-ICE rating scale model. By collapsing categories and creating a new 5-category scale, only 1 item misfit. Removing that item resulted in a modified version of ABC-ICE with 5 categories and 15 items. Both item goodness-of-fit statistics and principal components analysis supported unidimensionality of the modified ABC-ICE. The ABC-ICE measures reliably separated the sample into at least 4 statistically distinct strata of balance confidence. Finally, the hierarchical order of item difficulties was consistent with theoretic expectations, and the items were reasonably well targeted to the balance confidence of the persons tested. CONCLUSIONS: Rasch analysis indicated a need to modify the ABC-ICE to improve its psychometric properties. Further studies are needed to determine if similar analyses of other versions of the ABC, including the original one, will yield similar results.
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| 5. |
- Arnadottir, Solveig A, et al.
(författare)
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Determinants of self-rated health in old age : a population-based, cross-sectional study using the international classification of functioning
- 2011
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Ingår i: BMC Public Health. - London : BioMed Central. - 1471-2458. ; 11, s. 670-
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Tidskriftsartikel (refereegranskat)abstract
- Background: Self-rated health (SRH) is a widely used indicator of general health and multiple studies have supported the predictive validity of SRH in older populations concerning future health, functional decline, disability, and mortality. The aim of this study was to use the theoretical framework of the International Classification of Functioning, Disability and Health (ICF) to create a better understanding of factors associated with SRH among community-dwelling older people in urban and rural areas.Methods: The study design was population-based and cross-sectional. Participants were 185 Icelanders, randomly selected from a national registry, community-dwelling, 65-88 years old, 63% urban residents, and 52% men. Participants were asked: "In general, would you say your health is excellent, very good, good, fair, or poor?" Associations with SRH were analyzed with ordinal logistic regression. Explanatory variables represented aspects of body functions, activities, participation, environmental factors and personal factors components of the ICF.Results: Univariate analysis revealed that SRH was significantly associated with all analyzed ICF components through 16 out of 18 explanatory variables. Multivariate analysis, however, demonstrated that SRH had an independent association with five variables representing ICF body functions, activities, and personal factors components: The likelihood of a better SRH increased with advanced lower extremity capacity (adjusted odds ratio [adjOR] = 1.05, p < 0.001), upper extremity capacity (adjOR = 1.13, p = 0.040), household physical activity (adjOR = 1.01, p = 0.016), and older age (adjOR = 1.09, p = 0.006); but decreased with more depressive symptoms (adjOR = 0.79, p < 0.001).Conclusions: The results highlight a collection of ICF body functions, activities and personal factors associated with higher SRH among community-dwelling older people. Some of these, such as physical capacity, depressive symptoms, and habitual physical activity are of particular interest due to their potential for change through public health interventions. The use of ICF conceptual framework and widely accepted standardized assessments should make these results comparable and relevant in an international context.
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| 6. |
- Arnadottir, Solveig A, 1968-, et al.
(författare)
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Participation frequency and perceived participation restrictions at older age : applying the International Classification of Functioning, Disability and Health (ICF) framework
- 2011
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Ingår i: Disability and Rehabilitation. - : Informa Healthcare. - 0963-8288 .- 1464-5165. ; 33:23-24, s. 2208-2216
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To identify variables from different components of International Classification of Functioning, Disability and Health (ICF) associated with older people's participation frequency and perceived participation restrictions. Method: Participants (N = 186) were community-living, 65-88 years old and 52% men. The dependent variables, participation frequency (linear regression) and perceived participation restrictions (logistic regression), were measured using The Late-Life Function and Disability Instrument. Independent variables were selected from various ICF components. Results: Higher participation frequency was associated with living in urban rather than rural community (beta = 2.8, p < 0.001), physically active lifestyle (beta = 4.6, p < 0.001) and higher cognitive function (beta = 0.3, p = 0.009). Lower participation frequency was associated with being older (beta = -0.2, p = 0.002) and depressive symptoms (beta = -0.2, p = 0.029). Older adults living in urban areas, having more advanced lower extremities capacity, or that were employed had higher odds of less perceived participation restrictions (adjusted odds ratio [OR] = 5.5, p = 0.001; OR = 1.09, p < 0.001; OR = 3.7, p = 0.011; respectively). In contrast, the odds of less perceived participation restriction decreased as depressive symptoms increased (OR = 0.8, p = 0.011). Conclusions: Our results highlight the importance of capturing and understanding both frequency and restriction aspects of older persons' participation. ICF may be a helpful reference to map factors associated with participation and to study further potentially modifiable influencing factors such as depressive symptoms and advanced lower extremity capacity.
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