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.
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.
Extended data figures
This file contains Supplementary Figures 1-8 and Supplementary Tables 1-3.