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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, s. 191-U158
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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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| 2. |
- Magnusson, E., et al.
(författare)
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Development of a subglacial lake monitored with radio-echo sounding: case study from the eastern Skafta cauldron in the Vatnajokull ice cap, Iceland
- 2021
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 15:8, s. 3731-3749
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Tidskriftsartikel (refereegranskat)abstract
- We present repeated radio-echo sounding (RES, 5 MHz) on a profile grid over the eastern Skafta cauldron (ESC) in Vatnajokull ice cap, Iceland. The ESC is a similar to 3 km wide and 50-150 m deep ice cauldron created and maintained by subglacial geothermal activity of similar to 1GW. Beneath the cauldron and 200-400 m thick ice, water accumulates in a subglacial lake and is released semi-regularly in jokulhlaups. The RES record consists of annual surveys conducted at the beginning of every summer during the period 2014-2020. Comparison of the RES surveys reveals variable lake area (0.5-4.1 km(2)) and enables traced reflections from the lake roof to be distinguished from bedrock reflections. This allows construction of a digital elevation model (DEM) of the bedrock in the area, further constrained by two borehole measurements at the cauldron centre. It also allows creation of lake thickness maps and an estimate of lake volume at the time of each survey, which we compare with lowering patterns and released water volumes obtained from pre- and post-jokulhlaup surface DEMs. The estimated lake volume was 250 GL (gigalitres = 10(6) m(3)) in June 2015, but 320 +/- 20 GL drained from the ESC in October 2015. In June 2018, RES profiles revealed a lake volume of 185 GL, while 220 +/- 30 GL were released in a jokulhlaup in August 2018. Considering the water accumulation over the periods between RES surveys and jokulhlaups, this indicates 10 %-20% uncertainty in the RES-derived volumes at times when significant jokulhlaups may be expected.
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