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Geodetic data shed light on ongoing caldera subsidence at Askja, Iceland

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Abstract

Subsidence within the main caldera of Askja volcano in the North of Iceland has been in progress since 1983. Here, we present new ground- and satellite-based deformation data, which we interpret together with new and existing micro-gravity data, to help understand which processes may be responsible for the unrest. From 2003 to 2007, we observe a net micro-gravity decrease combined with subsidence and from 2007 to 2009 we observe a net micro-gravity increase while the subsidence continues. We infer subsidence is caused by a combination of a cooling and contracting magma chamber at a divergent plate boundary. Mass movements at active volcanoes can be caused by several processes, including water table/lake level movements, hydrothermal activity and magma movements. We suggest that, here, magma movement and/or a steam cap in the geothermal system of Askja at depth are responsible for the observed micro-gravity variations. In this respect, we rule out the possibility of a shallow intrusion as an explanation for the observed micro-gravity increase but suggest magma may have flowed into the residing shallow magma chamber at Askja despite continued subsidence. In particular, variable compressibility of magma residing in the magma chamber as well as compressibility of the surrounding rock may be the reason why this additional magma did not create any detectable surface deformation.

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Acknowledgements

This project was financed by a Marie Curie intra-European fellowship (from EDZ). EDZ thanks Claude Jaupart, Eleonora Rivalta, Petar Marinkovic, Judicael Decriem, Florian Lhuillier, Rósa Ólafsdóttir and Thom Warmerdam for discussion, help with data processing, MATLAB programming, GMT plotting, DEM preparation and other computer issues. EDZ thanks Rósa Ólafsdóttir for preparation of Fig. 1c. The CSA provided RADARSAT images for this project as part of a DRU proposal. MDA assisted with the data selection and ordering procedures. Financial support to RP was received from Rannís. The DEM and xy data files were produced by the Icelandic Geodetic Survey. GMT public domain software was used to prepare Fig.1a and b. We thank Glyn Williams-Jones, Takao Ohminato and an anonymous reviewer for their constructive comments.

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  1. Elske de Zeeuw-van Dalfsen

    Present address: Department 2 - Physics of the Earth, GFZ German Research Centre for Geosciences, Potsdam, Germany

Authors and Affiliations

  1. Institut de Physique du Globe de Paris, Paris, France

    Elske de Zeeuw-van Dalfsen

  2. Faculty of Science, The Open University, Milton Keynes, UK

    Hazel Rymer

  3. Institute for Geosciences, Göteborg, Sweden

    Erik Sturkell

  4. Nordic Volcanological Centre, Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland

    Erik Sturkell, Rikke Pedersen, Freysteinn Sigmundsson & Benedikt Ófeigsson

  5. Delft University of Technology, Delft, the Netherlands

    Andy Hooper

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  1. Elske de Zeeuw-van Dalfsen
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Correspondence to Elske de Zeeuw-van Dalfsen.

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Editorial responsibility: T. Ohminato

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de Zeeuw-van Dalfsen, E., Rymer, H., Sturkell, E. et al. Geodetic data shed light on ongoing caldera subsidence at Askja, Iceland. Bull Volcanol 75, 709 (2013). https://doi.org/10.1007/s00445-013-0709-2

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