The Prestahnúkur volcanic system has been moderately active with six eruptions in Holocene time. The last eruption took place around 900. The volcanic system is located on the west margin of the Western Volcanic Zone. It is about 90 km long and 15 km wide, consisting of a central volcano marked by rhyolite and geothermal activity and a fissure swarm defined by prominent faults. The system is partly covered by up to 300 m thick ice.