Thordarhyrna

Geography & Climate

Thordarhyrna is located in Iceland, within the Iceland Neovolcanic Rift Volcanic Province of the broader Atlantic Ocean Volcanic Regions. Situated at 64.27° N, 17.62° W in the Northern Hemisphere, the volcano lies within a subarctic climate zone. With a summit elevation of 1,650 meters above sea level, Thordarhyrna is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a composite, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Thordarhyrna is situated along a rift zone, where tectonic plates are pulling apart. As the crust thins and fractures, magma rises to fill the gap, creating volcanic activity. Rift volcanism typically produces more fluid lava flows rather than explosive blasts, which means communities near Thordarhyrna in Iceland generally face slower-moving hazards like lava flows and ground fissures rather than sudden pyroclastic events. However, rift volcanoes can still generate significant ash emissions and gas releases that affect local air quality.

Eruption History Summary

Thordarhyrna has 3 recorded eruptions in the geological database, spanning from 1823 CE to 1902 CE. The most powerful recorded event was a cataclysmic eruption with ash columns reaching the stratosphere in 1902 CE, reaching VEI 4 on the Volcanic Explosivity Index. These eruptions span roughly 79 years of volcanic history. The most recent eruption in 1902 CE places this volcano within the modern era of volcanological observation.

Significance

With a maximum recorded VEI of 4, Thordarhyrna has demonstrated the capacity for significant explosive eruptions that can impact regional aviation, agriculture, and communities tens of kilometers from the summit. VEI 4 eruptions produce ash columns reaching 15-25 kilometers into the atmosphere.

GVP Reference Summary

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.

— Smithsonian Institution, Global Volcanism Program