Geodynamics of Iceland and the signatures of plate spreading

Abstract Iceland, rising to more than 2 km above sea level, originates from the interaction of a mid-oceanic ridge and excessive mantle upwelling. The plate boundary between the North American and Eurasian plates traverses Iceland as a series of seismic and volcanic rift zones. The building blocks of the volcanic zones are about 32 volcanic systems, typically consisting of a central volcano often with a caldera and an associated fissure swarm (one or more). Recent revision of geometry and nature of the volcanic systems include new constraints on the fissure swarms of Western Volcanic Zone, and the one active in 2014–2015 associated to the Barðarbunga central volcano. Countrywide seismic network, and historical earthquake activity, shows that seismicity is most pronounced in transform zones in south and north Iceland, and at central volcanoes undergoing volcanic unrest. In a two year period 2015–2016, the most seismically active volcanoes were Katla and Barðarbunga. Measurements of ground deformation, using both GPS geodesy and interferometric analysis of synthetic aperture radar images acquired by satellites (InSAR) reveal well the present day plate spreading process in Iceland. Geodetically measured spreading rate across Iceland is consistent with global plate motion models (MORVEL2010: 18–19 mm/yr in direction N(100–105)°E), accommodated by a single rift zone in north Iceland, overlapping rifts in south Iceland, and a highly oblique rift on the Reykjanes Peninsula. Glacial isostatic adjustment (GIA) in response to ice retreat since 1890 is an additional important processes on a regional scale in Iceland, responsible for rise of central part of Iceland of >30 mm/year.