IAVCEI 2013 Scientific Assembly - July 20 - 24, Kagoshima, Japan
Forecasting Volcanic Activity - Reading and translating the messages of nature for society

4A1_2C-O4

Room A2

Date/Time: July 24 9:30-9:45

Deformation sources at a divergent plate boundary: interplay between volcano
deformation, geothermal processes, and plate spreading in the Northern Volcanic Zone,Iceland.
Vincent Drouin1 , Karsten Spaans2 , Sigrun Hreinsdottir1 , Benedikt Ofeigsson3 , Freysteinn
Sigmundsson1 , Erik Sturkell4 , Rikke Pedersen1 , Amandine Auriac1 , Andy Hooper2 , Pall Einarsson1 ,Theodor Theodorsson51

Nordic Volcanological Center, Institute of Earth Sciences, University of Iceland, Iceland, 2 University ofLeeds, United Kingdom, 3 Icelandic Meteorological Office, Iceland, 4 University of Gothenburg,
Department of Earth Sciences, Sweden, 5 Landsvirkjun, IcelandE-mail: vjp1@hi.isIceland is a subearial part of the Mid-Atlantic Ridge, where the divergent plate boundary between theNorth-American and Eurasian Plates can be studied. The Northern Volcanic Zone (NVZ) of Iceland, divided into
volcanic systems, is particularly well suited to study interplay between volcanoes, geothermal areas, and plate
spreading as the zone is relatively simple and accommodates the full spreading of the plates (18.6 mm/yr in a
direction of 105 degrees according to NUVEL-1A predictions). The most recent volcanic activity in the area was
the Krafla rifting episode 1975-1984. Extensive crustal deformation studies have been carried out in the NVZ;
we report the results of recent GPS and Interferometric Synthetic Aperture Radar (InSAR) studies focusing on
Krafla and Theistareykir volcanic systems at the northern part of the NVZ. A GPS survey in 2012, more extensive
than previous measurements, with over 121 stations measured was evaluated together with data from 2010 and2011 to generate a velocity field for 2010-2012. Three continuous GPS stations have been installed in the area
2011-2012, complementing one previous station. The 2010-2012 GPS velocities can be compared to earlier GPSresults, and complementary analysis of InSAR images. The plate spreading is the most significant signal visible
with an E-W velocity of about 12 mm/yr over a 30 km wide area. Earlier studies have shown that the Krafla caldera
uplifted during 1984-1989 under the influence of a shallow magma chamber in its center and then subsided. Since
1995, the maximum subsidence in Krafla has shifted from directly above the shallow magma chamber towards anarray of boreholes (geothermal exploitation) in Leirbotnar. Similar subsidence has been observed around anotherarray of boreholes in Bjarnaflag, 7 km further south. In the 1990s, an uplift was detected at edge of the geodetic
network in Krafla. Recent InSAR studies have shown that this deformation took place over a very large area eastof Theistareykir with both E-W horizontal as well as vertical displacements. Velocities calculated from the 2010,2011 and 2012 GPS campaign results show an ongoing pressure decrease in Krafla caldera. The subsidence inLeirbotnar and Bjarnaflag caused by geothermal exploitation is still continuing. However, the broad deformation
area east of Theistareykir seems to have changed in shape, with an uplift concentrated on a smaller area situatedon the plate boundary. ERS, Envisat, and TerraSAR-X images have been acquired over the NVZ areas of interest forInSAR studies. By combining InSAR and GPS data, an enhanced spatial and temporal resolution of the deformation
history within the area is achieved. The planned expansion of geothermal utilization and new power plants in thearea may produce additional deformation signals. Continuous monitoring for the upcoming years may deliver
information on further magmatic activity as well as the effects of geothermal exploitation on the volcanic systems.

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