Heidarspordar

The Heiðarsporðar volcanic system in the Northern Volcanic Zone is about 22 km long, consisting of a fissure swarm and a central volcano. It is embryonic, starting to develop in the marginal area of two adjacent fissure areas, Krafla and Fremrinámar, producing large-volume eruptions. No geothermal activity is present. Magma composition ranges from olivine-tholeiite through tholeiitic basalt and basaltic andesite to dacite. Characteristic activity consists of effusive basaltic eruptions and small predominantly effusive silicic eruptions. It has shown rather low activity in the Holocene but has produced substantial basaltic lava flows. Two eruptive periods have occurred in Holocene time separated by over 8,000 years. The last eruption took place about 2,200 years ago, producing a lava flow covering about 220 km2 and extending 60 km from source.