Bulletin of Volcanology

, Volume 68, Issue 5, pp 420–431 | Cite as

Integration of micro-gravity and geodetic data to constrain shallow system mass changes at Krafla Volcano, N Iceland

  • Elske de Zeeuw-van Dalfsen
  • Hazel Rymer
  • Glyn Williams-Jones
  • Erik Sturkell
  • Freysteinn Sigmundsson
Research Article


New and previously published micro-gravity data are combined with InSAR data, precise levelling and GPS measurements to produce a model for the processes operating at Krafla volcano, 20 years after its most recent eruption. The data have been divided into two periods: from 1990 to 1995 and from 1996 to 2003 and show that the rate of deflation at Krafla is decaying exponentially. The net micro-gravity change at the centre of the caldera is shown, using the measured free air gradient, to be −85 μGal for the first and −100 μGal for the second period. After consideration of the effects of water extraction by the geothermal power station within the caldera, the net gravity decreases are −73±17 μGal for the first and −65±17 μGal for the second period. These decreases are interpreted in terms of magma drainage. Following a Mogi point source model, we calculate the mass decrease to be ∼2×1010 kg/year reflecting a drainage rate of ∼0.23 m3/s, similar to the ∼0.13 m3/s drainage rate previously found at Askja volcano, N. Iceland. Based on the evidence for deeper magma reservoirs and the similarity between the two volcanic systems, we suggest a pressure-link between Askja and Krafla at deeper levels (at the lower crust or the crust-mantle boundary). After the Krafla fires, co-rifting pressure decrease of a deep source at Krafla stimulated the subsequent inflow of magma, eventually affecting conditions along the plate boundary in N. Iceland, as far away as Askja. We anticipate that the pressure of the deeper reservoir at Krafla will reach a critical value and eventually magma will rise from there to the shallow magma chamber, possibly initiating a new rifting episode. We have demonstrated that by examining micro-gravity and geodetic data, our knowledge of active volcanic systems can be significantly improved.


Micro-gravity Deformation Krafla Askja Magma drainage InSAR Reservoir 



This work was supported by The Geological Society, London and an Open University studentship. H.R.'s work on this project (1990–2003) was supported by the Royal Society. We would like to thank all the people that have participated in collection of the data at Krafla, especially Ton de Zeeuw, Andrew J. Ball and Halldór Ólafsson who helped during the most recent surveys. The geodetic work on this project was supported by a grant from the Icelandic Research Council RANNĺS and F.S.'s work on this project has been supported by the Retina project (EVG1-CT-00046). An earlier version of the manuscript was greatly improved by discussion with Dave Rothery and reviews by J.T. Freymueller and an anonymous reviewer.


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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Elske de Zeeuw-van Dalfsen
    • 1
  • Hazel Rymer
    • 1
  • Glyn Williams-Jones
    • 2
  • Erik Sturkell
    • 3
  • Freysteinn Sigmundsson
    • 4
  1. 1.Volcano Dynamics Group, Department of Earth SciencesThe Open UniversityMilton KeynesUK
  2. 2.Department of Earth SciencesSimon Fraser UniversityBurnabyCanada
  3. 3.The Icelandic Meteorological OfficeReykjavikIceland
  4. 4.Nordic Volcanological Centre, Institute of Earth SciencesUniversity of IcelandReykjavikIceland

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