Thordarhyrna

The Þórðarhyrna central volcano has been moderately active during the Holocene, with the last eruption occurring in 1903 CE. It is the second and less active central volcano of the Grímsvötn-Laki volcanic system, located about 20 km SW of the more active Grímsvötn central volcano and connected to it by a subglacial mountain ridge. The volcano has a diameter of 15 km, and is covered by ice 100-600 m thick within the Vatnajökull glacier. The last eruption occurred in 1903 CE. The recent activity has been explosive (phreatomagmatic) basaltic eruptions with tephra volumes ranging from 0.01-1 km3, but several rhyolitic nunataks characterize this volcano. Eruptions are accompanied by jökulhlaups. Being the only second central volcano on a volcanic system with considerable historical volcanic activity, Þórðarhyrna is treated as an independent volcano although the fissure swarm events are shared with the Grímsvötn system.