By Jean-Marie Prival, doctor in volcanology and founder of kīpuka magazine
Like other natural disasters, volcanic eruptions can have an impact on civilizations. Of course they can annihilate them, but they can also contribute to their economic development by providing a valuable resource (obsidian, for example). Finally, they can influence their culture, giving rise to myths. In the case of Iceland, two eruptions may have played a role in the Christianization of the island!
Let’s first set the scene before diving into Nordic sagas. When the Vikings settled in Iceland in the years 870, most of them were pagans: they worshiped the gods of the Norse mythology. A century later, around 980, Christian missionaries began to preach on the island, but with little success at first. Things changed in 998, when the Norwegian king Olaf Tryggvason converted to Christianity and pressured Icelanders to do the same. The monotheistic religion gained supporters, but the followers of the old faith remained numerous… By the end of the 10th century, Iceland was on the brink of civil war. And perhaps it was the fury of the island’s volcanoes that finally calmed the fury of mankind! Two eruptions, linked to two founding texts of the Viking history, are linked to the Christianization of Iceland.
Eldgjá and Völuspá
Eldgjá, which can be translated as “fire canyon”, is a vast system of eruptive fissures, about 75 km long, stretching between the Mýrdalsjökull and Vatnajökull glaciers. This system is geologically linked to the Katla volcano, located below the ice of Mýrdalsjökull, which is one of Iceland’s most active volcano with 22 eruptions recorded since the 10th century. The eruption of Eldgjá was previously mentioned as having taken place in 934, but a study of Greenland ice cores now estimates that it began during the spring of 939 and continued episodically at least until the autumn of 940. During this event, no less than 18.6 km3 of lava were emitted, 1 km3 of tephra, and 200 Mt of sulfur dioxide. By comparison, the nearby Laki fissure, famous for its eruption in 1783–1784, emitted “only” 14.7 km3 of lava, 0.4 km3 of tephra, and 122 Mt of sulfur dioxide. And as in the case of Laki, Eldgjá’s eruption had a severe impact on the climate, caused by the massive amount of sulphur aerosols absorbing solar radiation. In a reconstruction of Northern Hemisphere temperatures based on tree rings, 940 was the tenth coldest year in the last 1,500 years, with −1.38°C compared to the average (in the same study, the Laki eruption ranked 14th with −1.27°C). This cooling is also shown by various historical chronicles mentioning the particularly harsh winters of 939–940 and 940–941, famines, and livestock mortality.
Völuspá, or “Prophecy of the seeress”, is the best-known work in the Poetic Edda, a collection of anonymous poems in Old Norse that forms the base material of Norse mythology. In this poem, a soothsayer tells Odin the story of the creation of the world, then its apocalyptic destiny: Ragnarök. There have been numerous translations of the text over time, sometimes with significant variations between versions—underlining the difficulty of translating poetry, especially when the original language has been dead for several centuries. Nevertheless, the general layout remains the same. Völuspá consists of 66 stanzas of eight verses each. The one of particular interest is stanza 57, which takes place just after Thor, having defeated the snake, walked nine steps before succumbing in his turn. Here is a translation of this stanza by Henry Adams Bellows:
The sun turns black,
Earth sinks in the sea,
The hot stars down
From heaven are whirled;
Fierce grows the steam
And the life-feeding flame,
Till fire leaps high
About heaven itself.
The darkening sky, the steam, the flames… All this strongly suggests a volcanic eruption. The Völuspá is not precisely dated, but scholars agree that it was written around the year 1000. An international team, led by volcanologist Clive Oppenheimer, thinks that the events related in the poem were in part inspired by the Eldgjá eruption. After these apocalyptic descriptions, the world is reborn, and the “faithful […] for eternity will enjoy happiness”. Then follows this stanza, the penultimate:
There comes on high
All power to hold,
A mighty lord,
All lands he rules.
Some see this description as a representation of Christ. Völuspá would then be a prophecy of the replacement of paganism by Christianity. This stanza is the subject of much debate. It could be a late addition, subsequent to the original poem. In any case, some researchers propose that the eruption of Eldgjá served as material for the composition of Völuspá, and that this, in turn, would have served as a breeding ground for the Christian proselytizing that was happening in 10th century Iceland. In this hypothesis, the link between volcanism and conversion is admittedly tenuous, but it does exist.
Brennisteinsfjöll and Kristni saga
But another eruption and another text forges a link between the two events. Kristni saga tells the story of the Christianization of Iceland. This text, probably written in the 13th century and preserved in a 14th century manuscript (Hauksbók), recounts the rising tensions between pagans and Christians at the end of the first millennium. The conversion led by missionaries on behalf of King Olaf came up against a party loyal to the old Nordic pantheon. Tensions between the two sides led the country to the brink of civil war, as shown by this discourse from Þorgeir Ljósvetningagoði Þorkelsson, the “lawspeaker” of the time, that is, the president of the Icelandic parliament (Althing):
“And it seems advisable to me not to let those who oppose each other here with most vehemence prevail, and let us arbitrate between them, so that each side has its own way in something, but we all have the same law and the same religion, because this will prove true: if we tear apart the law, then we tear apart the peace.”
It is rather ironic that this ideological tear was set against a geological tear: the Althing met in Þingvellir at the time, where Iceland is dramatically split between the North American and Eurasian plates. Anyway, both parties agreed on one thing: Þorgeir was right, one law, one religion, was needed for the good of the island. Kristni saga then tells this story: when Hjalti and Gizurr, the envoys of King Olaf, had just eloquently addressed the assembly, a man came running up and announced that an eruption had just occurred, engulfing the house of one of the leaders of the Christian party. The pagans saw this as a message in their favor: “It is no wonder that the gods are enraged by such talk.” To which the Christians replied: “What were the gods enraged by when the lava we are standing on here and now was burning?” (see footnote) Did the argument work? The fact remains that the lawspeaker Þorgeir, himself a pagan at the time, was asked to settle the debate, with both factions promising to abide by his his judgment. He isolated himself for a day and a night and, after reflection, proclaimed that all Icelanders should be baptized and believe in one God. Concessions were made to the pagans, who were allowed to retain certain traditions—eating horse flesh, for example—but these were abolished a few years later…
The cause of this eruption has since been identified as Brennisteinsfjöll, another fissure system in southeast Iceland, which last erupted in the 14th century. It’s flow is known by two different names: Kristnitökuhraun, “the lava of the taking of Christianity”, which seems logical; and Svinahraunsbruni, “the burning pig lava”, the meaning of which is lost to me… For readers with Icelandic friends, there’s undoubtedly another story to dig into!■
This article was originally published in kīpuka, a quarterly, popular science magazine about volcanoes (in French). https://www.kipuka.fr [kipuka.fr]
 Larsen G, 2010. Katla: Tephrochronology and Eruption History. In: Developments in Quaternary Sciences 13, Elsevier, doi:10.1016/S1571-0866(09)01303-7
 Oppenheimer C, Orchard A, Stoffel M, Newfield TP, Guillet S, Corona C, Sigl M, Di Cosmo N, Büntgen U, 2018. The Eldgjá eruption: timing, long-range impacts and influence on the Christianisation of Iceland. Climatic Change 147, doi:10.1007/s10584-018-2171-9
 Thordarson T, Miller DJ, Larsen G, Self S, Sigurdsson H, 2001. New estimates of sulfur degassing and atmospheric mass-loading by the 934 AD Eldgjá eruption, Iceland. JVGR 108, doi:10.1016/S0377-0273(00)00277-8
 Stoffel M, Khodri M, Corona C, Guillet S, Poulain V, Bekki S, Guiot J, Luckman BH, Oppenheimer C, Lebas N, Beniston M, Masson-Delmotte M, 2015. Estimates of volcanic-induced cooling in the Northern Hemisphere over the past 1,500 years. Nature Geoscience 8, doi:10.1038/ngeo2526
 Bellows HA, 1936. The Poetic Edda. Princeton University Press
 Grønlie S, 2006. Íslendingabók. Kristni saga. The book of the Icelanders, The story of the Conversion. London: Viking Society for Northern Research, ISBN 978-0-903521-71-0
 Gudmundsson A, 2017. The Glorious Geology of Iceland’s Golden Circle. Springer, ISBN 978-3-319-55152-4
Footnote: This passage has interesting implications for the geological knowledge of the 10th century Icelanders. In Europe, at the end of the 18th century, the debate raged between proponents of Neptunism, who considered basalt to be a sedimentary rock formed under water, and those of Plutonism, who saw it as the result of volcanic activity. Perhaps the Icelanders had already settled the dispute eight centuries earlier!