Volcano geodesy and magma dynamics in Iceland - Acri-ST

16E. Sturkell et al. / Journal of Volcanology and Geothermal Research 150 (2006) 14–3424ºW 22ºW 20ºW 18ºW16ºW 14ºW66ºNKrafla65ºN9.7 mm/yrAskjaNorth AmericanPlate64ºN100 kmHHeklaTEGjálpKatlaBGVatnajökullBEGHT9.7 mm/yrEurasian PlateBár arbungaEyjafjallajökullGrímsvötnHengill/HrómundartindurTorfajökullFig. 2. The different volcanoes in Iceland addressed in the text are shown and all of the active volcanic system are outlined in black.jökull, Katla and Hrómundartindur have shown measurabledeformation interpreted as the result of magmamovements at depth. Eysteinn Tryggvason initiatedseveral important time series in the mid-late sixtiesthat are still continued today. The aim of this paper isto provide a summary of recent deformation result.We will address the volcanic systems and eruptionsthat are currently studied by geodetic measurementsof crustal deformation, i.e., Hengill/ Hrómundartindur,Hekla, Eyjafjallajökull, Katla, Torfajökull, Grímsvötn,Askja, Krafla, and Gjálp.2. Geodetic techniques2.1. Early techniquesThe first geodetic project specifically aimed at monitoringof a volcano in Iceland was the establishment ofa leveling line at Askja in 1966 (Tryggvason, 1989).This technique was subsequently applied to severalvolcanoes, including Surtsey, Hekla, Katla, Hengill,and Krafla. A related technique, optical tilt measurements(or bdry tiltQ), has also been widely applied atsome of these volcanoes. Eysteinn Tryggvasoninstalled benchmarks around several lakes in Icelandand utilized lake surfaces as tiltmeters (Tryggvason,1987). By the time of the Hekla 1970 and 1980–81eruptions, electronic distance measuring (EDM) instrumentswere available (e.g., Decker et al., 1971;Kjartansson and Grönvold, 1983). EDM was alsoused extensively during the volcano–tectonic eventsat Krafla in 1975–1984. Electronic tiltmeters weredesigned and applied for continuous monitoring oftilt changes (e.g., Tryggvason, 1986). Extensometerswere installed across fractures to monitor changes intheir width (Hauksson, 1983). Additionally, gravitymeasurements were applied to monitor the extensivevertical movements at Krafla (Johnsen et al., 1980).A network of volumetric strainmeters (Sacks et al.,1971) was installed in the South Iceland SeismicZone in the late seventies for continuous monitoringof strain loading of the seismic zone. These instrumentshave shown strain changes associated with therecent Hekla eruptions and have proven to be veryimportant in the monitoring of Hekla (e.g., Linde etal., 1993).Advances in geodetic methods in the last decadehave brought new techniques that turn out to be veryvaluable in volcano monitoring in Iceland. Theseinclude GPS-geodesy (both campaign and continuousGPS), InSAR, and micro-gravity measurements.Older techniques, such as optical tilt and leveling,are also still widely applied.