The dynamic geology of Iceland Ólafur Ingólfsson 1 , Olgeir Sigmarsson 1,2 , Freysteinn Sigmundsson 3 and Leifur A. Símonarson 1 1 Institute of Earth Sciences, University of Iceland, Sturlugata 7, IS-101 Reykjavík, Iceland 2 Laboratoire Magmas et Volcans, Centre National de la Recherche Scientique et Université Blaise Pascal, 63038 Clermont-Ferrand, France 3 Nordic Volcanological Center, Institute of Earth Sciences, Sturlugata 7, IS-101 Reykjavík, Iceland oi@hi.is, olgeir@raunvis.hi.is, fs@hi.is, leifuras@raunvis.hi.is The geology of Iceland is widely recognized in the international geological community in terms of plate tectonics, with Iceland being the product of excessive volcanism caused by mid-ocean rifting plate bound- aries above a mantle plume/hotspot. Iceland has since the 1960’s been a natural laboratory where many questions regarding processes operating in connection with diverging plates and mantle plume have been put to the test. Increased understanding of the tectonic structure of Iceland has contributed to better appre- hension of how mid-ocean ridges develop, with paleo- magnetic surveys and mapping of magnetic anomalies in and around Iceland playing a major role for the un- derstanding sea oor spreading. Studies of Icelandic geology have also led to better understanding of silicic magma formation and rate of magma generation, new ideas on protocontinental crustal formation as well as geodynamic and geothermal processes and prod- ucts. Being the largest subaerial part of the mid-ocean rift system, Iceland provides a unique setting for re- search in volcanology. Volcanic eruptions in Iceland occur under diverse environmental conditions, being subaerial, subaqueous and subglacial. Studying these has greatly advanced our understanding of how volca- noes work and how to prepare for future hazards, such as lava ows, lahars, jökulhlaups and airborne vol- canic gases. Tephrochronological studies in Iceland have laid foundations for regional North Atlantic cor- relations and highlighted the dynamic histories of the different volcanic systems in Iceland. The geological history of Iceland reects environmental development in the North Atlantic region since Miocene times, and its stratigraphic record holds evidence of >20 ma- jor glaciations for the past 2.5 million years. A key site in Northern Iceland, Tjörnes, spans the Pliocene- Pleistocene transition and records the shift from Ter- tiary greenhouse conditions to the frigid icehouse con- ditions of the Quaternary period. The unique glacial record in Iceland is due to interglacial lavas cap- ping and preserving glacial sediments from preced- ing glaciations. Complex glacier-volcanic interac- tions are reected in the Palagonite Formation of Ice- land, where subglacial volcanism during glacials pro- duced systems of hyaloclastite ridges and table moun- tains. Rapid isostatic crustal movements in connec- tion with deglacial events have resulted in excessive volcanism producing huge shield volcanoes as well as major ood basalts, highlighting interactive connec- tions between glacial load and volcanism. The Late Quaternary glacial- and climatic record shows great sensitivity to North Atlantic climatic and oceanic os- cillations. Iceland is situated at the boundary of air and water masses of tropical and Arctic origin and the Icelandic glaciers respond dynamically to climatic uctuations. Iceland is an important laboratory for understanding atmospheric and oceanographic pro- cesses and for identifying past climate variability. JÖKULL No. 58, 2008 1