The Eyjafjallajökull volcanic system, Iceland: Insights from electromagnetic measurements

Electromagnetic (EM) measurements were performed 1 yr after the most recent eruption of the Eyjafjallajökull volcano (2010 March-May), southern Iceland, to investigate the geometries of structures of the volcano system through imaging lateral and vertical electrical resistivity variations. High quality magnetotelluric (MT) and transient EM data were acquired at 26 sites around Eyjafjallajökull and the southern part of Mýrdalsjökull (the glacier covering the Katla volcano). For some locations the steep topography has influence on the MT responses, but this can be compensated by static shift correction using the transient EM data and/or including topography in the modelling mesh. As expected, qualitative indicators, such as phase tensor ellipses and induction arrows, infer a concentration of conductive material beneath Eyjafjallajökull. 2-D resistivity models are presented from data along three profiles: Along the river valley ofMarkarfljót in the north, along the coast to the south of Eyjafjallajökull and across the mountain ridge Fimmvörduháls between Eyjafjallajökull and Katla. In numerous previous studies elsewhere in Iceland a conductive layer at about 10-30 km depth was identified. From our data, such a conductor is also present in the northeastern part of the investigated area. Additionally, all profiles show a conductive, near-surface layer at about 1-2 km depth, as seen previously for example at the Hengill geothermal region. A connection between those two conductive layers is indicated by the resistivity models, and the dyke (flank eruption) and the conduit (summit eruption) appear as vertical conductive structures. It is uncertain if the vertical connection is permanent or a transient feature as consequence of the eruptive sequences. Subsequent measurements are required when the volcano system is quiescent.