Crust at many divergent plate boundaries forms primarily by the injection of vertical sheet-like dykes, some tens of kilometres long1. Previous models of rifting events indicate either lateral dyke growth away from a feeding source, with propagation rates decreasing as the dyke lengthens2,3,4, or magma flowing vertically into dykes from an underlying source5,6, with the role of topography on the evolution of lateral dykes not clear. Here we show how a recent segmented dyke intrusion in the 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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Support for this work was received from the European Community’s Seventh Framework Programme Grant No. 308377 (Project FUTUREVOLC), the Icelandic Research Fund (Project Volcano Anatomy), the Research Fund at the University of Iceland, NERC, the Geological Survey of Ireland and the US National Science Foundation (NSF). COSMO-SkyMed data were provided by the Italian Space Agency (ASI) and TerraSAR-X data by the German Space Agency (DLR) through the Icelandic Volcanoes Supersite project supported by the Committee on Earth Observing Satellites (CEOS). RADARSAT-2 data were provided by the Canadian Space Agency and MDA Corporation. Natural Resources Canada Earth Sciences Sector contribution number 20140314. An intermediate TanDEM-X digital elevation model was provided by DLR under project IDEM_GEOL0123. We thank the following key persons for help with instrumentation and data: B. H. Bergsson, Þ. Jónsson, V. H. Kjartansson, S. Steinþórsson, P. Erlendsson, H. Ólafsson, J. Söring and D. Craig. We also acknowledge the many others who have contributed to GPS, seismic and other field work in the study area. For GPS equipment and support, we acknowledge services provided by the UNAVCO Facility with support from the US NSF and National Aeronautics and Space Administration (NASA) under NSF Cooperative Agreements Nos EAR-0735156 and EAR-0711446. S. Jónsson (KAUST, Saudi Arabia) and T. Villemin (EDYTEM, Université de Savoie, France) also provided support to GPS. Seismic equipment: The British Geological Survey donated several of the broadband seismic sensors around Vatnajökull. We thank the SEISUK facility for loans to R.S.W. of seismometers under loan 980. Landsvirkjun contributed GPS instruments and seismic sensors north of Vatnajökull. The surveying aeroplane of Isavia (Icelandic Aviation Operation Services) mapped the subsidence of Bárðarbunga. The Icelandic Coast Guard provided aeroplane and helicopter support for field studies.

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  1. Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, IS-101 Reykjavík, Iceland

    • Freysteinn Sigmundsson
    • , Elías Rafn Heimisson
    • , Stéphanie Dumont
    • , Michelle Parks
    • , Vincent Drouin
    • , Thóra Árnadóttir
    • , Magnús T. Gudmundsson
    • , Thórdís Högnadóttir
    • , Hildur María Fridriksdóttir
    • , Páll Einarsson
    • , Eyjólfur Magnússon
    • , Bryndís Brandsdóttir
    • , Ásta Rut Hjartardóttir
    • , Rikke Pedersen
    • , Helgi Björnsson
    •  & Finnur Pálsson
  2. Centre for the Observation and Modelling of Earthquakes and Tectonics (COMET), School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK

    • Andrew Hooper
    •  & Karsten Spaans
  3. GNS Science, PO Box 30368, Lower Hutt 5040, New Zealand

    • Sigrún Hreinsdóttir
  4. Icelandic Meteorological Office, IS-150 Reykjavík, Iceland

    • Kristín S. Vogfjörd
    • , Benedikt G. Ófeigsson
    • , Gunnar B. Gudmundsson
    • , Kristín Jónsdóttir
    • , Hildur María Fridriksdóttir
    •  & Martin Hensch
  5. Canada Centre for Mapping and Earth Observation, Natural Resources Canada, 560 Rochester Street, Ottawa, Ontario K1A 0E4, Canada

    • Sergey Samsonov
  6. Department of Earth Sciences, University of Cambridge, Madingley Road, Cambridge CB3 0EZ, UK

    • Robert S. White
    • , Thorbjörg Ágústsdóttir
    • , Tim Greenfield
    •  & Robert G. Green
  7. Department of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

    • Richard A. Bennett
  8. Department of Geosciences, The Pennsylvania State University, University Park, Pennsylvania 16802, USA

    • Halldór Geirsson
    •  & Peter C. La Femina
  9. Department of Earth Sciences, University of Gothenburg, SE-405 30 Gothenburg, Sweden

    • Erik Sturkell
  10. Seismology Laboratory, School of Geological Sciences, University College Dublin, Belfield, Dublin 4, Ireland

    • Christopher J. Bean
    • , Martin Möllhoff
    • , Aoife K. Braiden
    •  & Eva P. S. Eibl


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The writing of the paper, and the research it is based on, was coordinated by F.S., A.H., S.H., K.S.V., B.G.Ó. and other members of Icelandic Meteorological Office (IMO) seismic monitoring team. All authors contributed ideas and input to the research and writing of the paper. Modelling of geodetic data was done by A.H., E.R.H. and Th.A. Analysis and operation of continuous GPS sites were carried out by S.H., B.G.Ó., H.M.F, R.A.B., V.D., H.G. and P.C.L. Relative earthquake locations were calculated by K.S.V., seismic data presentation and relative locations were by G.B.G., focal mechanisms were determined by M.H. and single earthquake location determination was led by K.J. and SIL seismic monitoring group. Interferometric analysis was carried out by S.D., K.S., M.P., V.D. and S.S., with a composite digital elevation model prepared by E.M. The combined strain and gravity potential in relation to the dyke propagation was modelled by E.R.H. in consultation with A.H. and F.S. Campaign GPS measurements were carried out by S.D., V. D., M.P., Á.R.H., E.S., F.S. and others. M.T.G. and Th.H. mapped the collapse of the Bárðarbunga caldera and the formation of ice cauldrons over the path of the dyke with aircraft radar profiling. Á.R.H., E.M. and P.E. led mapping of graben formed and of the eruptive fissure as shown here. P.E., B.B. and R.P. contributed to the interpretation of events, and H.B. and F.P. provided bedrock topography and ice thickness for Vatnajökull ice cap. R.S.W., Th.Á., T.G., R.G.G., C.J.B., M.M., A.K.B. and E.P.S.E. contributed and analysed seismic data.

Competing interests

The authors declare no competing financial interests.

Corresponding author

Correspondence to Freysteinn Sigmundsson.

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