Iceland experiences frequent volcanic activity, due to its location both on the Mid-Atlantic Ridge, a divergent tectonic plate boundary, and being over a hotspot. Nearly thirty volcanoes are known to have erupted in the Holocene epoch; these include Eldgjá, source of the largest lava eruption in human history. Some of the various eruptions of lava, gas and ash have been both destructive of property and deadly to life over the years, as well as disruptive to local and European air travel.
Eyjafjallajökull, sometimes referred to by the numeronym E15, is one of the smaller ice caps of Iceland, north of Skógar and west of Mýrdalsjökull. The ice cap covers the caldera of a volcano with a summit elevation of 1,651 metres (5,417 ft). The volcano has erupted relatively frequently since the Last Glacial Period, most recently in 2010, when, although relatively small for a volcanic eruption, it caused enormous disruption to air travel across northern and western Europe for a week.
Katla is an active subglacial volcano in southern Iceland. This volcano has been very active historically with at least twenty documented major eruptions since 2920 BC. In its recent history though, Katla has been less active as the last major eruption occurred in 1918. These eruptions have had a Volcanic Explosivity Index (VEI) of between 4 and 5 on a scale of 0 to 8. In comparison, the Eyjafjallajökull 2010 eruption had a VEI of 4. Larger VEI-5 eruptions are comparable to Mount St. Helens 1980 eruption. These eruptions have produced very large glacial outburst floods. Several smaller (minor) events measuring VEI-1 and below have occurred since.
Kverkfjöll is a potentially active central volcano, fissure swarm, and associated mountain range situated on the northern border of the glacier Vatnajökull in Iceland.
Öræfajökull is an ice-covered volcano in south-east Iceland. The largest active volcano and the highest peak in Iceland at 2,110 metres (6,920 ft), it lies within the Vatnajökull National Park and is covered by part of the glacier.
Snæfellsjökull is a 700,000-year-old glacier-capped stratovolcano in western Iceland. It is situated on the westernmost part of the Snæfellsnes peninsula. Sometimes it may be seen from the city of Reykjavík over Faxa Bay, at a distance of 120 km (75 mi).
Laki or Lakagígar is a volcanic fissure in the western part of Vatnajökull National Park, Iceland, not far from the volcanic fissure of Eldgjá and the small village of Kirkjubæjarklaustur. The fissure is properly referred to as Lakagígar, while Laki is a mountain that the fissure bisects. Lakagígar is part of a volcanic system centered on the volcano Grímsvötn and including the volcano Þórðarhyrna. It lies between the glaciers of Mýrdalsjökull and Vatnajökull, in an area of fissures that run in a southwest to northeast direction.
Eldgjá is a volcano and a canyon in Iceland. Eldgjá is part of the Katla volcano; it is a segment of a 40 kilometres (25 mi) long chain of volcanic craters and fissure vents that extends northeast away from Katla volcano almost to the Vatnajökull ice cap. This fissure experienced a major eruption around 939 CE, which was the largest effusive eruption in recent history. It covered about 780 square kilometres (300 sq mi) of land with 18.6 cubic kilometres (4.5 cu mi) of lava from two major lava flows.
Grímsvötn is an active volcano with a fissure system located in Vatnajökull National Park, Iceland. The central volcano is completely subglacial and located under the northwestern side of the Vatnajökull ice cap. The subglacial caldera is at 64°25′N17°20′W, at an elevation of 1,725 m (5,659 ft). Beneath the caldera is the magma chamber of the Grímsvötn volcano.
The geology of Iceland is unique and of particular interest to geologists. Iceland lies on the divergent boundary between the Eurasian plate and the North American plate. It also lies above a hotspot, the Iceland plume. The plume is believed to have caused the formation of Iceland itself, the island first appearing over the ocean surface about 16 to 18 million years ago. The result is an island characterized by repeated volcanism and geothermal phenomena such as geysers.
Subglacial eruptions, those of ice-covered volcanoes, result in the interaction of magma with ice and snow, leading to meltwater formation, jökulhlaups, and lahars. Flooding associated with meltwater is a significant hazard in some volcanic areas, including Iceland, Alaska, and parts of the Andes. Jökulhlaups have been identified as the most frequently occurring volcanic hazard in Iceland, with major events where peak discharges of meltwater can reach 10,000 – 100,000 m3/s occurring when there are large eruptions beneath glaciers. It is important to explore volcano-ice interactions to improve the effectiveness of monitoring these events and to undertake hazard assessments. This is particularly relevant given that subglacial eruptions have demonstrated their ability to cause widespread impact, with the ash cloud associated with Iceland's Eyjafjallajökull eruption in 2010 resulting in significant impacts to aviation across Europe.
Torfajökull is a rhyolitic stratovolcano, with a large caldera capped by a glacier of the same name and associated with a complex of subglacial volcanoes. Torfajökull last erupted in 1477 and consists of the largest area of silicic extrusive rocks in Iceland. This is now known to be due to a VEI 5 eruption 55,000 years ago.
Bárðarbunga, is an active and productive stratovolcano located under Vatnajökull in Vatnajökull National Park which is Iceland's most extensive glacier. The second highest mountain in Iceland, 2,000 metres (6,600 ft) above sea level, Bárðarbunga is also part of the Bárðarbunga-Veiðivötn volcanic system that is approximately 190 kilometres (120 mi) long and 25 kilometres (16 mi) wide.
The Loki-Fögrufjöll is a subglacial volcano under the Vatnajökull glacier.
Gjálp is a hyaloclastite ridge (tindar) in Iceland under the Vatnajökull glacier shield. Its present form resulted from an eruption series in 1996 and it is probably part of the Grímsvötn volcanic system. However, not all the scientists were of this opinion, as seismic studies are consistent with a 10 km (6.2 mi) lateral dike intrusion at about 5 km (3.1 mi) depth from Bárðarbunga being the trigger event. This does not exclude a shallower secondary intrusion from Grímsvötn being important in the subaerial eruption itself.
Snæfell at 1,833 m (6,014 ft) high, is an ice-capped stratovolcano located in the north-east part of Vatnajökull National Park, Iceland. While it has been dormant in the Holocene, it is now known to have had repose times of over 100,000 years between eruptions, so it cannot be assumed to be extinct.
The Oddnýjarhnjúkur-Langjökull (Langjökull) volcanic system of Iceland last erupted about 3600 years ago and is associated with current geothermal activity. The area of its central volcano is at present under the second largest ice cap in Iceland.
