Hengill
The Hengill volcanic system is around 60 km long and has been relatively active, having erupted 9 times in the Holocene. The Hengill system is located where the West Volcanic Zone and the South Iceland Seismic Zone meet. The area is characterized by faults formed during series of eruptions. Hengill is home to Iceland’s second-largest geothermal area.
Grímsnes
The Grímsnes volcanic system is located at the eastern edge of the West Volcanic Zone and has not been active for 7,000 years. It is 12 km in length and up to 5 km wide, making it one of the smallest and least active volcanic systems in Iceland. It contains 12 minor eruption sites which have produced a small amount of basaltic lava and tephra.
Langjökull – Prestahnúkur
The Prestahnúkur volcanic system has been relatively active and has erupted six times in the Holocene, most recently around the year 900. The system is located at the western edge of the West Volcanic Zone. It is around 90 km long and 15 km wide and contains a central volcano characterized by rhyolite. The area is geothermally active and has fissure swarms with conspicuous faults. The volcano is covered in parts by 300 metre thick ice.
Hekla
Hekla is one of the most active and famous volcanoes in the world. In the Middle Ages, it was rumoured to be the gateway to hell. The Hekla volcanic system has been highly active in the Holocene. It last erupted in 2000 and has erupted 23 times in the last 1,000 years, making it the third most active volcanic system in Iceland.
The length of the preceding period of dormancy determines the silica content of the first magma to reach the surface and the volume of the volcanic material, meaning that the shorter the period of dormancy, the smaller the eruption. Eruptions in Hekla can range from pure explosive eruptions to pure effusive eruptions.
The Hekla volcanic system is located in the East Volcanic Zone. The fissure swarm is approximately 60 km in length and the volcano reaches a height of 1490 m above sea level. Eruptions are most frequent in the central volcano and are generally a mix of tephra and lava eruptions. The initial phase of Hekla eruptions tends to be short, with an explosive eruption followed by lava flows.
Vestmannaeyjar
Activity in the Vestmannaeyjar has been limited in the Holocene. There was a series of eruptions from 1963 to 1973, first around Surtsey (1963-67) and then at Heimaey in 1973. The system is 30-35 km in length and 20-25 km wide and forms an archipelago 10-30 km off the south coast of Iceland, whose highest point is Heimaklettur at 283 m. The most recent eruption before the last series of eruptions was believed to have been at Helgafell, 5,900 years ago. The archipelago comprises 15 islands and 30 skerries which are the remains of craters and islands formed during the Holocene.
The Heimaey eruption
The Heimaey eruption was a fissure eruption that opened up at the edge of the town and then became concentrated in a single crater, Eldfell. Almost the entire population of the town, around 5,000 people, was evacuated to the mainland on the night the eruption began. Around 400 houses were buried under tephra and lava. The eruption lasted for almost five and half months. Only one person died in the eruption, a victim of poisonous gases in the basement of a house. There was some concern that the lava would close off the harbour, but in fact, it improved it, providing more shelter. Hot lava was used to heat houses in the town for around 15 years after the eruption ended, probably the only case of lava-heated homes in the world.
Eyjafjallajökull
The central volcano Eyjafjallajökull has been relatively active over the last 8,000 years. The last eruption occurred in 2010 when 0.27 km3 of tephra and 0.023 km3 of lava was ejected. Eyjafjallajökull is 1651 m high and is located in the East Volcanic Zone and the central volcano is considered to be an independent volcanic system. The summit contains a 2.5 km wide ice-filled caldera. The upper part of the volcano is largely covered by a glacier that is up to 200 metres thick.
The ash plume from the 2010 eruption consisted of such fine ash that it posed a major threat to jet engines. As a result flight routes and airports across much of Europe were closed for a week in mid-April. Routes from Keflavík to North America did remain open but they nevertheless represented the most wide-reaching restrictions on global flights since the Second World War.
Torfajökull
The Torfajökull area has been fairly active in the Holocene. The last eruption was in 1477 along a 40 km long volcanic fissure northeast of Landmannalaugar. This eruption created such well-known geographical features as Veiðivötn, Laugahraun, Námshraun, Norðurnámshraun, Ljótipollur and much of the pumice sand covering the northern part of the Fjallabak Nature Reserve. Torfajökull is in the East Volcanic Zone.
The area saw a high level of volcanic activity during the last glacial period, creating the tuff peaks Löðmundur and Mógilshöfðar, and the rhyolite mountains Bláhnúkur, Brennisteinsalda and Kirkjufell. Rhyolite from the last interglacial period can be found at Norður-Barmur and Brandsgil. The Fjallabak Nature Reserve is home to numerous well-known geothermal areas, such as Landmannalaugar, Hrafntinnusker, Kaldaklof, Jökultungur and Reykjadalir.
Katla
The Katla volcanic system, which is partly covered by Mýrdalsjökull, has been highly active in the Holocene and the past 11 centuries have seen at least 21 eruptions. The last eruption to break through the ice cap was in 1918 and it was considered a major eruption. People have been waiting for an eruption in Katla for some time; there have been some minor eruptions but they have not penetrated the ice.
Katla is a major central volcano, one of the largest and most active in the country. It is about 30 km in diameter and reaches a height of 1480 m. In the centre of the volcano is the Katla caldera which covers an area of 100 km2 and is up to 700 metres deep. The ice in the caldera is in many places 400-700 m thick. The caldera is divided into three drainage areas: Kötlujökull, Sólheimajökull and Entujökull.
Bárðarbunga
The Bárðarbunga system has been highly active in the Holocene and there have been at least 26 eruptions in the past 11 centuries. The most recent eruption was a large fissure eruption (volume of lava >1.5 km3) in the Holuhraun area north of Vatnajökull which lasted from August 2014 to February 2015. Several smaller eruptions beneath the ice may have occurred before the main eruption.
Grímsvötn
The Grímsvötn volcanic system has erupted more frequently than any other volcanic system in Iceland in the Holocene. The system comprises a central volcano and a fissure swarm which is around 100 km long and up to 20 km across. The highest point is Grímsfjall at 1722 m. The most recent eruption was in 2011 which produced approximately 0.8 km3 of tephra. The Grímsvötn system is part of the East Volcanic Zone and much of it lies beneath the thick ice of Vatnajökull. The Grímsvötn caldera is mostly covered by the glacier. Another central volcano in the Grímsvötn system is Þórðarhyrna to the south-west. This has seen little recent activity, erupting most recently in 1903.
Öræfajökull
Öræfajökull has been relatively active in the Holocene. The most recent eruption was a medium-sized explosive eruption in 1727. Öræfajökull is located outside the main volcanic zones and is one of the few volcanic systems which does not have a fissure swarm, only a central volcano. The central volcano is 20 km in diameter and reaches a peak of 2110 m at Hvannadalshnjúkur, which is also Iceland’s highest mountain. The volcano is covered with ice.
Hrómundartindur, Hofsjökull, Tindafjallajökull and Esjufjöll are volcanoes in Southern Iceland which have only seen limited eruptions in the Holocene.