Bulletin of Volcanology

, 68:689 | Cite as

Constraints on the dynamics of subglacial basalt eruptions from geological and geochemical observations at Kverkfjöll, NE-Iceland

  • Armann Höskuldsson
  • Robert S. J. Sparks
  • Michael R. Carroll
Research Article

Abstract

The Kverkfjöll area, NE Iceland is characterised by subglacial basalt pillow lavas erupted under thick ice during the last major glaciation in Iceland. The water contents of slightly vesiculated glassy rims of pillows in six localities range from 0.85±0.03 to 1.04±0.03 wt %. The water content measurements allow the ice thickness to be estimated at between 1.2 and 1.6 km, with the range reflecting the uncertainty in the CO2 and water contents of the melt. The upper estimates agree with other observations and models that the ice thickness in the centre of Iceland was 1.5–2.0 km at the time of the last glacial maximum. Many of the pillows in the Kverkfjöll area are characterised by vesiculated cores (40–60% vesicles) surrounded by a thick outer zone of moderately vesicular basalt (15–20% vesicles). The core contains ∼1 mm diameter spherical vesicles distributed uniformly. This observation suggests a sudden decompression and vesiculation of the still molten core followed by rapid cooling. The cores are attributed to a jökulhlaup in which melt water created by the eruption is suddenly released reducing the environmental pressure. Mass balance and solubility relationships for water allow a pressure decrease to be calculated from the observed change of vesicularity of between 4.4 and 4.7 MPa depressurization equivalent to a drop in the water level in the range 440–470 m. Consideration of the thickness of solid crust around the molten cores at the time of the jökulhlaup indicates an interval of 1–3 days between pillow emplacement and the jökulhlaup. Upper limits for ice melting rates of order 10−3 m/s are indicated. This interpretation suggests that jökulhlaups can reactivate eruptions.

Keywords

Pillow lavas Subglacial volcanism Iceland Ice thickness estimates Jökulhlaups 

Notes

Acknowledgements

This research project was supported by the Icelandic ministry of education and culture grant no. 83.232-13/25.111-6, the Icelandic council of science, and the Commission of the European Communities grant no. ERB4001GT922172. Partial support for the FTIR spectroscopic work was provided by a European Union Environment Program grant nr. EVSV-CT92-0178. Jackie Dixon is thanked for advice in relation to the role of CO2 on water solubility and for providing a spreadsheet for application of her model. Alex Nicholls is thanked for permission to reproduce analyses of the glassy margins of the Kverkfjöll pillows. Andy Sparks and Rob Wilcock are thanked for help in measurements of pillows. RSJS acknowledges a NERC Research Professorship and the Royal Society for the Wolfson merit Award. Finally we would like to thank Lionel Wilson and Jennifer Barclay for thorough and constructive review.

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Copyright information

© Springer-Verlag 2005

Authors and Affiliations

  • Armann Höskuldsson
    • 1
    • 2
  • Robert S. J. Sparks
    • 1
  • Michael R. Carroll
    • 3
  1. 1.Department of Earth SciencesUniversity of BristolBristolUK
  2. 2.Institute of Earth SciencesUniversity of IcelandReykjavikIceland
  3. 3.Dipt. di Scienze della Terra, Via Gentile III da VaranoUniversita’ di CamerinoCamerinoItaly

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