Iceland experiences frequentvolcanic activity, due to its location both on theMid-Atlantic Ridge, a divergenttectonic plate boundary, and being over ahotspot. Nearly thirty volcanoes are known to have erupted in theHolocene epoch; these includeEldgjá, 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.
Holocene volcanism in Iceland is mostly to be found in theNeovolcanic Zone, comprising theReykjanes volcanic belt (RVB), theWest volcanic zone (WVZ), theMid-Iceland belt (MIB), theEast volcanic zone (EVZ) and theNorth volcanic zone (NVZ). Two lateral volcanic zones play a minor role:Öræfi volcanic belt (ÖVB also known as Öræfajökull volcanic system) andSnæfellsnes volcanic belt (SVB).[1] Outside of the main island are theReykjanes Ridge (RR), as part of theMid-Atlantic Ridge to the south-west and theKolbeinsey Ridge (KR) to the north. Two transform zones are connecting these volcano-tectonic zones: theSouth Iceland seismic zone (SISZ) in the south of Iceland and theTjörnes transform zone (TFZ) in the north.
The island has around 30active volcanic systems. Within each are volcano-tectonic fissure systems and many, but not all of them, also have at least onecentral volcano (mostly in the form of astratovolcano, sometimes of ashield volcano with amagma chamber underneath). Several classifications of the systems exist, for example there is one of 30 systems,[2]: 10 and one of 34 systems, with the later currently being used in Iceland itself.[3] There are 23 central volcanoes using the definition that they: erupt frequently; extrude eitherbasaltic, intermediate orfelsic lavas; have an associated shallow crustal magma chamber, and are often associated with collapse caldera or fissure systems.[2]: 11 Shield volcanoes, as the term is used in the Iceland context, tend to erupt only once, so havemonogenetic characteristics. However many shield volcanoes outside Iceland are associated with oceanic island volcanism such as inHawaii where they have been built up over many eruptions.[2]: 11–12 Fissure vents in Iceland tend to produce calmer effusive eruptions, but can be associated with large volumes of lava (flood basalt events) and some have had prolonged eruptions with numerous eruptive episodes, lasting for years.[2]: 12–13
Up to 2008, thirteen of the volcanic systems had hosted eruptions since thesettlement of Iceland in AD 874.[4] Nearly thirty volcanoes are known to have erupted in theHolocene epoch and so are active.[5]
Of these active volcanic systems, the most active isGrímsvötn.[6] Over the past 500 years, Iceland's volcanoes have produced a third of the total globallava output.[7] Current productivity, which is known to be cyclical, has been estimated to be between 0.05–0.08 km3 (0.012–0.019 cu mi) per year which is higher than the output rate of the Hawaiian volcanoes, and would be double or even triple this figure if intrusive volumes are included.[4]: 205
The types of eruptions most likely in a particular Icelandic volcanic system or zone are now understood. Earthquakes and volcanism have patterns in time and place that can be combined into a consistent tectonic process that is explained by thegeological deformation of Iceland. In summary in Iceland there are four main types of tectonic zones:[8]
These tectonic zones result from the interaction of combination of the spreading activity of the Mid-Atlantic Ridge which is spreading in a general east and west direction while themantle plume activity that results in the hotspot, has been migrating over at least the last 25 million years in a west to slightly south-east direction.[2]: 4–6
Fissure vents are found predominantly in what are termed fissure swarms (a combination of tectonic related fissures and faults) that are also associated with crater rows and smallercinder orspatter cones.[9] Where such eruptions interact with water the eruptions become more explosive and thesephreatomagmatic eruptions produce tephra and possiblymaars andtuff rings or cones.[8][9]
The composition of the lava reflects the tectonic factors above and are consistent with the influence of the hotspot so the trend is forocean island basalts (OIB) type to predominate overmid ocean ridge basalts (MORB) which are only found in the north of the NVZ.[10]: 133–4 The compositional series are thustholeiitic basalt, transitional alkalic basalts and alkalic (felsic).[10]: 134
Large extrusive, predominantlytholeiitic basaltic lava fields and shields with theoleiitic lava are the predominant material erupted and are found in the RVB, WVZ, MIB, EVZ and NVZ.[3] They are associated with divergence tectonics of the ridge plate boundaries.[8]: 40 Central volcanoes, with associated fissure swarms are typical, except in the RVB.Hengill is the only active central volcano in the far east of the RVB, and this is likely to be because here atriple junction exists, resulting in a volcano with somerhyolytic anddacite components due to the complexity of its rift propagation formation.[11][12]: 1128 The island ofEldey off the south-west of the RVB has similar geological formations to the RVB but has a basalt composition with tholeiites andpicrites.[13]Hofsjökull, a large volcano with a caldera and rhyolite lavas in the MIB has explosive eruption potential but has not erupted underneath its ice cover for several thousand years and its companion Kerlingarfjöll for even longer.[14]
Arc volcanism has been thought to be occurring in the Snæfellsnes volcanic belt withalkaline magma series volcanism in the stratovolcanoes such asSnæfellsjökull which usually erupt effusive basaltic lava but can have infrequent explosive silicic eruptions followed by extrusion of intermediate composition lava.[15] However the modelling of the processes involved is incomplete and almost certainly involves primarily fractional crystallization of primary basaltic magma with limited input from pre-existing crustal material as is the case in arc volcanism.[16] The ÖVB is represented by theÖræfajökull (Hnappafellsjökull) stratovolcano which has a history of violent rhyolite to alkali basalt eruptions with tephra volumes up to 10 km3 (2.4 cu mi) and accompanyingjökulhlaup.[17]
The islandVestmannaeyjar volcano to the south east of Iceland has in its recent activity formed the island ofSurtsey and cones such asEldfell onHeimaey. It is the southern tip of the EVZ propagating rift in what is an off rift region called the South Iceland Volcanic Zone (SIVZ),[18] and the older alkaline basalts were alkaliolivine and more recentmugearite in composition.[19] The basalts of the southern EVZ on land are rarely silicic but the volcanoes can have explosive phreatomagmatic eruptions.[20]
Overall the surface area of post glacial erupted rocks of Iceland is 92% basalt, 4%basaltic andesites, 1%andesites, and 3% dacite-rhyolites.[21]
See also :List of volcanic eruptions in Iceland
Due to incomplete surveys, which also need to be confined tosubaerial eruptions and not includeigneous intrusions, the accumulative amounts ofdense-rock equivalent erupted in Iceland will be underestimated.[4] The amounts known are some of the most significant contributions to recent eruptive volumes on Earth.[4] Since the last ice age 91% of the magma erupted in Iceland has beenmafic, 6% intermediate in composition and 3%silicic.[4]: 203 The number of eruptions estimated in this 11,700 odd year period can only be an approxiamate figure,[a] but about three to four explosive ones occur for every purely effusive one.[4]: 203
| Volcanic Zone or Belt | LavaDRE[b] | Tephra DRE[c] | Total DRE[b][c] | Number eruptions[a] | Comment |
|---|---|---|---|---|---|
| Eastern volcanic zone | 175.2 km3 (42.0 cu mi) | 164.3 km3 (39.4 cu mi) | 339.4 km3 (81.4 cu mi) | 2026 | [23][24][25] Includes individual eruptions fromLaki 15.1 km3 (3.6 cu mi),Eldgjá 19.6 km3 (4.7 cu mi) andÞjórsá Lava 25.0 km3 (6.0 cu mi).[4] |
| Western volcanic zone | 94.0 km3 (22.6 cu mi) | 0.0 km3 (0.0 cu mi) | 94.0 km3 (22.6 cu mi) | 47 | |
| Northern volcanic zone | 90.7 km3 (21.8 cu mi) | 3.3 km3 (0.8 cu mi) | 94.0 km3 (22.6 cu mi) | 146 | |
| Reykjanes volcanic belt | 22.3 km3 (5.3 cu mi) | 22.0 km3 (5.3 cu mi) | 29.2 km3 (7.0 cu mi) | 151 | [26] Ongoing as of 2024 |
| Snæfellsnes volcanic belt | 7.7 km3 (1.8 cu mi) | 1.3 km3 (0.3 cu mi) | 9.0 km3 (2.2 cu mi) | 57 | |
| Öræfajökull volcanic belt | 0.6 km3 (0.1 cu mi) | 2.4 km3 (0.6 cu mi) | 3.0 km3 (0.7 cu mi) | 8 | |
| Mid-Iceland belt | 1.0 km3 (0.2 cu mi) | 0.0 km3 (0.0 cu mi) | 1.0 km3 (0.2 cu mi) | 9 |
Hekla has erupted more than 20 times in recorded history. It was known to medieval Europeans as the Gate of Hell; that reputation persisted into the 19th century.[27]
The most deadly volcanic eruption of Iceland's history was the so-calledSkaftáreldar (fires ofSkaftá) in 1783–1784.[28] The eruption was in thecrater rowLakagígar (craters of Laki) southwest ofVatnajökull glacier. The craters are a part of a larger volcanic system with the subglacialGrímsvötn as a central volcano. Roughly a fifth of the Icelandic population died because of the eruption.[28] Most died not because of the lava flow or other direct effects of the eruption but from indirect effects, including changes in climate and illnesses in livestock in the following years caused by the ash and poisonous gases from the eruption.[28] The eruption resulted in the second largest basaltic lava flow from a single eruption inhistoric times.[29]
Eldfell is a volcanic cone on the east side of the island ofHeimaey which formed during an eruption in January 1973.[30] The eruption happened without warning, causing the island's population of about 5,300 people to evacuate on fishing boats within a few hours. Importantly, the progress of lava into the harbour was slowed by manual spraying of seawater. One person died, and the eruption resulted in the destruction of homes and property on the island.[31]: 11
The eruption underEyjafjallajökull in April 2010 caused extreme disruption to air travel across western and northern Europe over a period of six days in April 2010. About 20 countries closed their airspace to commercial jet traffic and it affected approximately 10 million travellers.[32]
The eruption had aVEI of 4, the largest known from Eyjafjallajökull.[33] Several previous eruptions of Eyjafjallajökull have been followed soon afterwards by eruptions of the larger volcanoKatla, but after the 2010 eruption, no activity occurred at Katla.[34]
The eruption in May 2011 atGrímsvötn under theVatnajökull glacier sent thousands of tonnes of ash into the sky in a few days, raising concerns of the potential for travel chaos across northern Europe although only about 900 flights were initially disrupted.[35]
Bárðarbunga is astratovolcano and is roughly 2,000 metres (6,600 ft) above sea level in central Iceland, i.e. in the northern edge of Vatnajökull.[36] This makes it the second highest mountain in Iceland.
Holuhraun is an older lavafield situated 50 km (31 mi) north-east of Bárðarbunga, 20 km (12 mi) south ofAskja (last eruption 1961), at an altitude of about 700 m (2,300 ft). Here the eruption started on August 17, 2014, and lasted for 180 days.[37] The 2014–2015 eruption was Iceland's largest in 230 years.[38] Following a major earthquake swarm, multiple lava fountain eruptions began inHoluhraun.[39] The lava flow rate was between 250 and 350 m3/s (8,800 and 12,400 cu ft/s) and came from adyke over 40 km (25 mi) long.[40][41] An ice-filledsubsidence bowl over 100 km2 (39 sq mi) in area and up to 65 m (213 ft) deep formed as well.[37] There was very limited ash output from this eruption. The primary concern with this eruption was the large plumes ofsulphur dioxide (SO2) in the atmosphere which adversely affected breathing conditions across Iceland, depending on wind direction. The volcanic cloud was also transported toward Western Europe in September 2014.[42]
Following a three-week period of increased seismic activity, an eruption fissure developed nearFagradalsfjall,[43] a mountain on theReykjanes Peninsula. Lava flow from a 200-meter fissure was first discovered by anIcelandic Coast Guard helicopter on March 19, 2021, in theGeldingadalur area nearGrindavík, and within hours the fissure had grown to 500 m (1,600 ft) in length.[44]
Another eruption, very similar to the 2021 eruption, began on 3 August 2022,[45] and ceased on 21 August 2022.
.jpg)
On 10 July 2023 at 16:40 UTC, a fissure eruption began adjacent to the summit ofLitli-Hrútur.[46]
On December 18, 2023, at 22:17 near Hagafell, the volcano began a fissure eruption.[47] In January, 2024 lava from this eruption destroyed 3 houses in the nearby town ofGrindavík.[48]
The smooth flowing basaltic lavapāhoehoe is known in Icelandic ashelluhraun[ˈhɛtlʏˌr̥œyːn].[Islandsbok 1] It forms smooth surfaces that are quite easy to cross. More viscous lava formsʻaʻā flows, known in Icelandic asapalhraun[ˈaːpalˌr̥œyːn].[Islandsbok 1] The loose, broken, sharp, spiny surface of an ʻaʻā flow makeshiking across it difficult, slow and dangerous, it is easy to stick a foot into a hole and break a leg.
