The Fagradalsfjall–Geldingadalir eruption of 2021, and other Icelandic volcanoes

Huge changes to landforms in short periods of time

by Andrew Sibley

Volcanic eruptions in Iceland through recorded history have shown how landforms can change dramatically over a matter of several months or a few years. It is estimated that since AD 1500 a third of global lava has been released in Iceland.¹

The most notable recent eruption in Iceland was a volcanic fissure that began erupting in March 2021 in the Krýsuvík-Trölladyngja volcanic system, located in southwest Iceland. The eruption was centred around the Fagradalsfjall [‘fa gra tals fy atl] mountain and Geldingadalir [‘gel ding a ‘da ler] valley to the south. This area includes historic eruptive fissures, volcanic cones, and lava fields, and is located on the Reykjanes Peninsula in southwest Iceland.

Being near the main centre of population in Iceland it was relatively easy to access, and as a result well photographed by many people in the age of iPhones and camera drones. However, in the scale of Icelandic volcanoes, it was not especially large, with eruptions in recorded history being some 100 times larger.

The island of Iceland sits on the Mid-Atlantic Ridge, which is where the Eurasian and North American plates are moving apart along a divergent plate boundary. One explanation is that Iceland sits above a geological hot spot. This is co-located along the Greenland-Scotland Transverse Ridge, although not all scientists believe such a hot spot exists.^2,3 In Iceland, the mid-Atlantic ridge lies above sea level, and is identifiable by rift valleys in places.² The island largely consists of igneous flood basalt rock, which implies that enormous volumes of lava were released rapidly, on land and under water. Secular geologists have assigned Iceland a relatively young ‘age’ at 16–18 Ma. But from the perspective of Flood geology and biblical history (see the geology transformation tool) Iceland began to form during the tail end of the Noahic Flood, and continued to grow in the post-Flood Ice Age, followed by a subsequent gradual decrease in volcanic and tectonic activity.

The Reykjanes [‘ray ken ‘ess] Peninsula lies to the north of another significant volcano of the twentieth century—Surtsey. The eruption of Surtsey in the 1960s began 130 metres below sea level, producing a new island that has been the subject of much research and interest.^4,5,6

The Fagradalsfjall mountain itself is a flat-topped, steep-sided volcano, described as a tuya volcano that formed under an ice sheet. Based on long-age dating assumptions that was some 6,000 years ago, but from a biblical perspective, this would have been during the post-Flood Ice Age some 4,000 years ago. The previous major eruption in the Krýsuvík volcanic system occurred in the 12^th century, some 800 years ago. The most recent eruption in 2021 was a shield eruption, characterised by a low profile, resembling a warrior’s shield lying on the ground. It is formed by the eruption of highly fluid lava. Unlike many other Icelandic volcanoes that are fed by magma chambers, it is considered that this eruption is connected to magma at a depth of over 17 km. Such eruptions may last for several years, and overall, there are fears it may be evidence of an increase in volcanic activity in this area lasting decades.⁷

Earthquakes and eruptions

Following a series of earthquake swarms, involving tens of thousands of mainly small individual earthquakes from 2019 to 2021 (the largest earthquake was 5.7), the lava eventually reached the surface on the 19 March 2021 as an effusive eruption along a fissure (figure 1). Unlike explosive eruptions, that may occur under ice or under the sea, an effusive eruption releases magma at the surface—and lots of gasses, such as sulphur dioxide, some of which are harmful. The eruption was only about 20 km from the capital city, Reykjavik. It lasted 183 days, visibly ending on 18 September with no fresh lava reaching the surface, although volcanic gases were being released for weeks afterwards. It was the fourth longest eruption on Iceland over the past 120 years, according to geologist Sigurður Steinþórsson.⁸ The three eruptions of the twentieth century that were longer were: the Hekla eruption (1947 and 1948—390 days), the Surtsey eruption (1963 and 1967—1290 days), and the Krafla eruption (1975 and 1984—3180 days). However, the Hekla and Krafla eruptions were subject to lengthy periods of inactivity.

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During the 2021 eruption, rates of lava flow were estimated to be between 6 and 12 m³s^-1, sometimes along several fissures that opened up. The total volume of lava released has been estimated at 151 million m³ (0.151 km³), covering an area of 4.8 km². The lava filled several valleys to a depth of over 100 m, with the rim of the new mountain volcano reported at 334 m above mean sea level.⁹ Although dramatic because of its easy access and photogenic appeal, in terms of Icelandic volcanoes the scale of the eruption was relatively small.

Holuhraun

The effusive eruption of Holuhraun in 2014/15 was around 10 times larger, releasing an estimated 1.6 km³ of lava,¹⁰ but it was in a more remote location, which prevented easy access for photography (figure 2). The fissure is part of the Bárðarbunga system. The increase in earthquake activity, as molten magma made its way to the surface, initially occurred beneath the sub-glacial volcano with evidence of caldera collapse. This led to fears of an explosive eruption. The eruption eventually occurred away from the massive Vatnajökull ice cap, and lasted from 29 August 2014 to 27 January 2015. It was the largest release of lava in terms of volume since the Laki events of 1783/84.

Eldgjá and Laki

One of the largest eruptions in recorded history was that of the Eldgjá, which is connected to the Katla system. It erupted along a 75 km fissure and released some 20 km³ of lava. The formed canyon valley is also believed to be the largest of its type in the world, some 40 km in length, 270 m deep, and 600 m at its widest. This event is approximately dated to between the years AD 933 and 941, more tentatively to AD 939. This is from both written records (Iceland was permanently settled around AD 874), and scientific measurements: including sulfur dioxide in ice cores, and dendrochronology. Europe experienced cooler summers, estimated as a 2°C reduction in temperature, with poor harvests, together with reports of a dimmed sun in the following couple of years.^11,12

Another significant eruption was that of Laki, which is connected to the Grímsvötn system, and lies to the east of Eldgjá. The eruption lasted for eight-months between June 1783 and February 1784.¹³ The fissure is estimated to have released some 14 km³ of basalt lava, together with poisonous gases of hydrofluoric acid and sulfur dioxide. Many people died in Iceland from crop failures and poisonous gases, together with reduced global temperatures and further food shortages in parts of Europe.

Explosive eruptions and Jökulhlaups

While Geldingadalir was an effusive eruption, many of Iceland’s volcanoes lie under glaciers, and the resultant eruptions tend to be explosive. This is due to the action of the lava in melting the ice. As lava periodically rises to the surface it first melts the ice, forming sub-glacial lakes and superheated water and steam. If the pressure build-up is released then it can send a plume of ash and steam, and other gases, as high as the stratosphere. This occurred with the Eyjafjallajökull eruption in April 2010 with plume heights reaching around 9 km.

Volcanic eruptions under glacial ice like this can lead to a catastrophic flood, called a jökulhlaup. This is a glacial outburst flood, which occurs in association with volcanic activity. The melted sub-glacial water may escape into the surrounding area with tremendous rates of flow. With the Eyjafjallajökull eruption flow rates reached 3,000 m³/s. The Katla eruption of 1755, which lies under Mýrdalsjökull, experienced estimated discharge rates of 200,000 to 400,000 m³/s. They can be hugely destructive, eroding the ground, washing away roads and bridges, and reworking valley sediment. The flow picks up material as it runs down the valley, with 50%–80% ratio of water to solid matter, thus developing the characteristics of a lahar flood. A more recent jökulhlaup in 1918, with estimated maximum flow rates of 300,000 m³/s, deposited 2 km³ of sediment in the lower Mýrdalssandur valley and extended the coastline seaward by 3.6 km. This has largely eroded to the present day, but over the past 1000 years the coastline has seen a net growth.^14,15,16

Summary

Eruptions over recorded history show that the landform can change dramatically in a short period of time through volcanic activity and the release of massive amounts of lava. The recent Fagradalsfjall–Geldingadalir volcano was relatively small compared with other volcanoes over recorded history. The post-Flood era has seen volcanoes that were up to 100 times larger. Powerful jökulhlaups, often caused by volcanic activity, can also reshape the landscape in a matter of days. This level of activity highlights processes that have shaped the earth from the time of the biblical Flood. Many other Icelandic volcanoes have erupted after the Flood, but before the availability of human records. Thus, the dating of these becomes more tentative the further back in time we go. These huge eruptions illustrate how large geological changes can occur rapidly and provide an insight into the geological events during Noah’s Flood, which were many thousands of times greater in magnitude than what have occurred post-Flood.

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