Hengill

Geography & Climate

Hengill is located in Iceland, within the Iceland Neovolcanic Rift Volcanic Province of the broader Atlantic Ocean Volcanic Regions. Situated at 64.08° N, 21.42° W in the Northern Hemisphere, the volcano lies within a subarctic climate zone. With a summit elevation of 803 meters above sea level, Hengill is a moderately sized peak that remains accessible to hikers and researchers for much of the year. The volcanic landform is characterized as a cluster, which describes the physical shape and structure of the volcanic edifice as observed from the surface.

Geological Context

Hengill 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 Hengill 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. The dominant rock type is basalt / picro-basalt, a dark, fine-grained volcanic rock that forms from rapidly cooling, low-viscosity lava. Basaltic eruptions tend to be less explosive and produce fluid lava flows that can travel long distances. While less immediately dangerous than explosive eruptions, basaltic lava flows can destroy structures and infrastructure in their path, and volcanic gases released during these eruptions can affect air quality over a wide area.

Eruption History Summary

Hengill has 13 recorded eruptions in the geological database, spanning from 8350 BCE to 150 CE. The most powerful recorded event was an explosive event producing ash plumes up to several kilometers in 150 CE, reaching VEI 2 on the Volcanic Explosivity Index. This level of eruptive frequency indicates a persistently active volcanic system that warrants ongoing monitoring.

Significance

With 13 recorded eruptions, Hengill has a substantial eruptive history that provides valuable data for understanding volcanic behavior and assessing future hazards in the Atlantic Ocean Volcanic Regions region.

GVP Reference Summary

The Hengill volcanic system, cutting through Thingvallavatn lake, consists of a series of NE-SW-trending fissure vents, crater rows, and small shield volcanoes occupying a strongly faulted graben. Hengill is the easternmost of a series of four closely spaced basaltic fissure systems that cut diagonally across the Reykjanes Peninsula and lies at the triple junction of the Reykjanes Peninsula volcanic zone, the Western volcanic zone, and the South Iceland seismic zone. Postglacial lava flows surface much of the volcanic system. The latest eruption was radiocarbon dated about 1,900 years before present. An eruption in the Hellisheidi area once thought to have occurred around 1000 CE at the time of a meeting of the Icelandic parliament at Thingvellir is now known to have occurred at a vent about 5 km away in the Brennisteinsfjöll volcanic system. The high-temperature Nesjavellir geothermal area NE of the uplifted hyaloclastite ridge forming the Hengill central volcano and the Helllisheidi geothermal field SW of Hengill are major producers of geothermal energy for Reykjavik.

— Smithsonian Institution, Global Volcanism Program