Fimbulwinter and the Climate Catastrophe of the Migration Period

Eruption on Iceland
Photo: Sigurður Jónsson

When the sun suddenly darkened over Europe in 536, the continent approached the end of an extremely violent and devastating epoch: the Migration Period. The seemingly never-ending migrations and wars of Germanic tribes had destroyed the Western Roman Empire and its culture and changed the map of Europe forever. The Visigoths, Suebians, and Franks had divided the western provinces of the Empire among themselves; the northern part, the provinces of Britain, had been annexed by North Sea Germanic groups led by the Angles and Saxons. The Ostrogoth Empire, established in Italy under Theoderic the Great, was in the middle of a war with the Eastern Roman Emperor Justinian I. Only two years earlier, Justinian and his commander Belisar had smashed the Vandal Kingdom in North Africa and now, due to the changed strategic situation, he was sure that he could also expel the Ostrogoths from Rome and Ravenna. In short: The peoples of Europe had already experienced an indescribable amount of disaster. But what was about to happen in the year 536 should literally put everything else in the shade.

Researchers have long been aware that something very serious must have happened. Already the historians of late antiquity reported of very low temperatures and snowfall in summer. According to them, the sun was only as weak as the moon all year round due to an ever-present fog, which is said to have led to many crop failures, famines and epidemics. The investigations of tree rings in the 1990s showed an unnaturally low growth for the year 536, and even in the following years the situation hardly seemed to have returned to normal again. In 2015, a research team led by Michael Sigl succeeded in synchronizing ice cores from Antarctica and Greenland with the tree ring chronology.1 Their study concluded that a massive volcanic eruption must have occurred in the winter of 535/536, presumably in the northern hemisphere. But the data showed even more: Only four years later another large eruption must have occurred, which plunged the slowly returning climate into a deep depression again. Further crop failures and famines are the result. The events even seem to have had an impact as far as China, where there are also reports of crop failures and snow in summer.


The time around 540 is considered today as the coldest period of the last 2300 years. And when no one in Europe could imagine that things could get any worse, the so-called Plague of Justinian broke out in 541. Within a few months it spread from Egypt to Constantinople and over the entire Mediterranean. Finally, with a short delay, the plague also reached the western and northern parts of Europe. How many millions of people died in the following years because of this plague alone cannot be said with certainty today due to the lack of historical sources. In the following two centuries, however, the plague will continue to reappear, claiming an estimated 50 million lives in total.2 Considering that the entire world population in those centuries comprised only about 200 million people, one immediately understands why the Justinian plague is considered one of the deadliest plagues of all time.

Iceland: the origin of disaster?

Now, a research team around the glaciologist Paul Mayewski  and the historian Michael McCormick may have achieved another breakthrough: An improved high-resolution analysis of an ice core from the Swiss Alps revealed volcanic glass particles chemically similar to those from Greenlandic ice cores and associated with the volcanic eruption of 536.3 At a small conference at Harvard University in November of this year,4 the team announced that the particles found had great similarities with volcanic rock samples from Iceland.5 According to the ice core analysis, a volcano somewhere on Iceland must have exploded in a massive eruption early in 536. This was followed by two further eruptions of comparable strength in the years 540 and 547, which would explain the long-lasting climate deterioration known from the data.

Eruptions on Iceland

Eruptions on Iceland during the 20th and 21st centuries (Graphics: Wissensplattform “Erde und Umwelt”)

A catastrophic concatenation of volcanic eruptions which, starting from Iceland, brought years without summer, failed harvests, famines and ultimately also epidemics across Europe in the late 530s and 540s?6 It would not be too much of a surprise. The list of volcanic eruptions on Iceland in recent centuries is long, very long. There is for example the Katla, one of the most active volcanoes of the island: From out of its extensive system of volcanic canyons, such as the Eldgjá (which means “fire canyon”), an eruption has occurred practically every century since humans inhabited the island. The last major eruption took place in 1918 and caused an 18 km (about 11 miles) high eruption column. Even more active is the Hekla, which in medieval times was seen as the gateway to hell. Virtually every inhabitant of Iceland in the last thousand years has probably witnessed one of its numerous eruptions. The so-called Hekla 3 eruption, which took place about 3000 years ago, was so massive that it probably eclipsed even the famous eruption of Mount Vesuvius near Pompeij in 79. Finally, the last eruption of Eyjafjallajökull in 2010 will be unforgettable for most Europeans. It caused major disruptions to air traffic on the continent, but was also responsible for some spectacular sunsets.

Europe sinks into darkness

Wherever the eruption took place, it is clear that the events heralded the final demise of the ancient world. The restoration of the Western Empire, driven forward by the Eastern Roman Emperor Justinian I, was finally abandoned along with his expansive policy. The emperor himself almost died of the plague bearing his name. He devoted the rest of his life to the internal and religious affairs of his empire. With the deaths of the last great historians of antiquity, Jordanes, Cassiodorus, Procopius and Gregory of Tours, a dark age for literature dawned in Europe. Finally, the Migration Period ended with the Lombard invasion of Northern Italy in 568 and the emergence of the Slavs on the Balkans and the territories previously inhabited by the East Germanic tribes. Both peoples probably benefited from the power vacuum created by the catastrophic events and from the large-scale depopulation of entire regions.

However, Central and Northern Europe were hit particularly hard. Computer simulations of the volcanic activities suggest that the negative climatic effects in this area must have been even greater and more dramatic than south of the Alps.7 Archaeology also provides clues to this. The Swedish archaeologist Bo Gräslund, for example, has linked the widespread decline of settlements throughout Scandinavia during the 6th century to this climate catastrophe and investigated the cultural influence these events might have had on the population. He referred to the similarities between the myth of the Fimbulwinter (from Old Norse fimbulvetr meaning ‘mighty winter’), which is handed down in Old Norse literature,8 and the events of the 530s and 540s.9 Snorri, for example, describes the Fimbulwinter as a cold period of three consecutive hard winters, which followed each other without summer. The decisive event that ultimately initiates Ragnarök. According to Gräslund, the myth could have been inspired or at least shaped by the real events of the 6th century. For Anders Andrén, the darkening of the sun and the resulting catastrophic consequences could even be the reason for the disappearance of the previously very dominant solar symbolism in Nordic art.10

Monumental volcanic eruptions on Iceland, which drive the whole of Europe into a dark decade of death and decay, leaving deep traces in the legends of the north; in those very legends which were later recorded on Iceland and thus saved from oblivion…? Should this theory be confirmed, it would once again underline the great influence this legendary island of the North has on the climate and culture of us all. Back then just as today.


1.   Sigl et al. 2015. (back)
3.   Loveluck et al. 2018. (back)
5.   Cf. Kurbatovs lecture: (back)
6.   Cf. Helama et al. 2018. (back)
7.   In addition: Toohey et al. 2016 and Widgren 2013. (back)
8.   Cf. Vafþrúðnismál 44 and Gylfaginning 50. (back)
9.   Gräslund 2008; Gräslund & Price 2012. (back)
10.  Andrén 2014, 183–186. (back)



Andrén 2014: Tracing Old Norse Cosmology. The world tree, middle earth, and the sun in archaeological perspectives. Vägar till Midgård 16 (Lund 2014).

Gräslund 2008: Fimbulvintern, Ragnarök och klimatkrisen år 536–537 e. Kr. Saga och Sed 2007, 93–123.

Gräslund & Price 2012: Twilight of the gods? The ‘dust veil event’ of AD 536 in critical perspective. Antiquity 86 (332), 2012, 428–443.

Helama et al. 2018: Volcanic dust veils from sixth century tree-ring isotopes linked to reduced irradiance, primary production and human health. Scientific Reports 8 (1339), 2018, 1–12.

Loveluck et al. 2018: Alpine ice-core evidence for the transformation of the European monetary system, AD 640–670. Antiquity 92 (366), 2018, 1–15.

Sigl et al. 2015: Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature 523, 2015, 543–549.

Toohey et al. 2016: Climatic and societal impacts of a volcanic double event at the dawn of the Middle Ages. Climatic Change 136, 2016, 401–412.

Widgren 2013: Climate and causation in the Swedish Iron Age: learning from the present to understand the past. Geografisk Tidsskrift 112, 2012, 126–134.

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