Volcano geodesy and magma dynamics in Iceland - Acri-ST

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E. Sturkell et al. / Journal of Volcanology and Geothermal Research 150 (2006) 14–34 31sional tectonic forces generate a pressure drop in thelower and ductile part of the crust to accommodateongoing magma drainage from the shallow magmachamber.A combination of different monitoring methods isessential to obtain the best possible information onmagma sources and movements within volcanoes.Today, the real-time network in Iceland consists of40 seismic stations, 17 permanent GPS stations andsix volumetric strainmeters. Five analogue seismicstations maintained by the Science Institute at theUniversity of Iceland complement these networks.Both networks play an important role in eruptionprediction. Data from volumetric strain meters haveenabled detection and monitoring of dyke propagationpreceding eruptions of Hekla. The initial sign of aforthcoming eruption of Hekla in 2000 was the onsetof small earthquakes, known from previous eruptionto be associated with opening of a dike under thevolcano. The BUR strain station then recorded contraction(Figs. 1 and 10) beginning 30 min before theeruption, and was at that time recognized as resultingfrom a dike propagating to the surface (Agustsson etal., 2000). It was used along with the seismic data in asuccessful prediction of the eruption that was issued tothe civil defense authorities and broadcast as well tothe public.5. ConclusionsCrustal deformation measurements in Iceland havesignificantly advanced our understanding of volcanicprocesses, with new geodetic techniques allowingincreasingly detailed views of magma dynamics. Seismicmethods complemented with various geodeticmethods, including leveling, GPS, volumetric strainand InSAR, have provided the most important data.The longest time series extend from the mid-sixties tothe present time. Forecasting volcanic activity is challenging,but geodetic measurements are providinguseful constraints (location, amount and timing ofmagma movements), which can be interpreted alongwith other data. The most successful monitoring programsare based on a combination of seismic anddeformation methods, as the recent eruptions inGrímsvötn demonstrated. In recent years Katla andGrímsvötn have shown the highest inflation rates withca. 3 cm/a. and tilt data from Hekla suggest thatmagma accumulation is taking place. At Katla, continueduplift coincides with elevated seismicity. Ifuplift and internal pressure build-up continues atthese volcanoes, eruptive activity is a likely consequencewithin several years.AcknowledgmentsThe paper is dedicated to Eysteinn Tryggvason, thepioneer of deformation studies at Icelandic volcanoes,who turned 80 on July 19, 2004. We like to thank allthe people who participated in collection of geodeticdata. Guðmundur Gudfinnsson commented on earlierversions of this paper. The colleagues at the IcelandicMeteorological Office are thanked for their help, especiallyMatthew J. Roberts. Comments from the twoanonymous reviewers helped us to significantlyimprove the paper. Also the suggestions of the guesteditor Mike Poland have been most helpful. Thefigures were prepared with the public domain GMTsoftware. This work was supported by a grant fromthe Icelandic Research Council RANNÍS, and by theRetina project (EVG1-CT-00046).ReferencesAgustsson, K., Stefansson, R., Linde, A.T., Einarsson, P., Sacks,I.S., 2000. Successful prediction and warning of the 2000 eruptionof Hekla based on seismicity and strain changes. Eos Trans.AGU, Fall Meet Suppl., Abstr., V11B-30.Árnadóttir, Th., Sigmundsson, F., Delaney, P.T., 1998. Sources ofcrustal deformation associated with the Krafla, Iceland, eruptionof September 1984. Geophys. Res. Lett. 25, 1043–1046.Árnadóttir, Th., Rögnvaldsson, S., Ágústsson, K., Stefánsson, R.,Hreinsdóttir, S., Vogfjörð, K., Thorbergsson, G., 1999. Seismicswarms and surface deformation in the Hengill area, SW Iceland.Seismol. Res. Lett. 70, 269.Björnsson, H., 2002. Subglacial lakes and jökulhlaups in Iceland.Glob. Planet. Change 35, 255–271.Björnsson, A., Sæmundsson, K., Einarsson, P., Tryggvason, E.,Grönvold, K., 1977. Current rifting episode in north Iceland.Nature 266, 318–323.Björnsson, A., Johnsen, G., Sigurðsson, S., Thorbergsson, G.,Tryggvason, E., 1979. Rifting of the plate boundary in northIceland 1975–1978. J. Geophys. Res. 84, 3029–3038.Björnsson, H., Pálsson, F., Guðmundsson, M.T., 2000. Surface andbedrock topography of the Mýrdalsjökull ice cap. Jökull 49,29–46.
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