Vulcanologists have discovered that volcanic ash from the Wrangell Mountains in eastern Alaska found its way to medieval Europe in the 9th century, which may explain unusually harsh winters and celestial phenomenon recorded in Dark Age chronicles.
Intrepid drivers on the Klondike Highway in Alaska will notice a 2 feet band of whitish grit in exposed road cuts through the Yukon Territory. The grit is White River Ash, and its source is the volcanic Wrangell Mountain range in eastern Alaska. A massive series of eruptions occurred here about 1,150 years ago, dumping around 12 cubic miles of ash over 130,000 square miles of Alaska, the Yukon and Canada’s Northwest Territories.
The extensive ash deposits were first recognized in 1883, but it wasn’t until the 1960s that geologists traced their source back to the Wrangell Mountains. Only very recently have vulcanologists discovered, almost by chance, that the White River Ash also found its way to medieval Europe.
Britta Jensen, of the University of Alberta, studies volcanic ash layers in northwest Canada and Alaska. At the upper White River in the Yukon, she and her colleagues cored the trunks of dead spruce trees smothered by White River Ash and radiocarbon dated them to around 843 AD, plus or minus 20 years. Meanwhile, UK researchers independently dated a mysterious ash layer found in Irish peat bogs, but familiar throughout Europe, to an unknown eruption which happened sometime between 846 and 860 AD. When they published their findings, the date match caught Britta’s immediate attention. She said, “We saw this and thought it was too good to be true.” When Britta analysed the Irish ash, she found it had the same unique geochemical signature as the White River Ash. “Morphologically, it even looks like the same ash,” she said.
At the time of the 9th century eruptions, North America and Europe were vastly different places. Alaska and Canada were largely wilderness, occasionally roamed by nomadic Native American hunter gatherers. Medieval Europe, while comparatively civilised, was still in the post-Roman period of upheaval, war and plague known as the Dark Ages. Adding to their woes, two remarkably cold winters struck Europe over the period 855–60 AD, which climate scientists have previously linked to volcanic activity.
In the Annales de Saint-Bertin, Prudentius, bishop of Troyes, reports that the winter of 855–56 in France was “most harsh and dry” and accompanied by a plague which killed a large part of the population. The Annals of Ulster report that Ireland received so much snow and ice over the same period that “the principal lakes and rivers of Ireland could be crossed by people on foot and on horseback.”
The winter of 859–60 was reportedly much harsher, particularly in France, Germany, and northern Italy. Prudentius reports a strange celestial phenomenon that made parts of the night sky look as bright as day, with blood red columns extending out in different directions. This went on during August – October 859, and is consistent with the presence of volcanic aerosols in the atmosphere. The subsequent winter was unremittingly harsh from November 859 through to April 860. The Fulda Annals, which chronicled events in what is now Germany, reported that the weather had a devastating effect on crops and tree fruit, and that blood red snow fell in many places. Off the coast of Italy, the Adriatic Sea froze solid allowing merchants to transport their goods to Venice by horse and cart, rather than by boat. According to Andrew of Bergamo, snow persisted in the plains of Italy for a hundred days and wine froze in its containers.
Any similar experiences by Native American populations are not recorded, but it’s safe to assume that, completely unknown to each other, they were united with medieval Europeans in suffering the devastating effects of volcanic activity in Alaska.
Volcanoes and the Climate Forcing of Carolingian Europe, AD 750–950 – Michael McCormick, Paul Edward Dutton and Paul A. Mayewski