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Nature. 2015 Jan 8;517(7533):191-5. doi: 10.1038/nature14111. Epub 2014 Dec 15.

Segmented lateral dyke growth in a rifting event at Bárðarbunga volcanic system, Iceland.

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Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IS-101 Reykjavík, Iceland.
Centre for the Observation and Modelling of Earthquakes and Tectonics (COMET), School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK.
GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand.
Icelandic Meteorological Office, IS-150 Reykjavík, Iceland.
1] Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IS-101 Reykjavík, Iceland [2] Icelandic Meteorological Office, IS-150 Reykjavík, Iceland.
Canada Centre for Mapping and Earth Observation, Natural Resources Canada, 560 Rochester Street, Ottawa, Ontario K1A 0E4, Canada.
Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK.
Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA.
Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Department of Earth Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden.
Seismology Laboratory, School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland.


Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens, or magma flowing vertically into dykes from an underlying source, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the Bárðarbunga 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 Bárðarbunga 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 Bárðarbunga 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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