“THIS is what happens when an Old Norse specialist, medieval/environ­mental historians, tree-ring and ice-core experts, and a volcanologist team up,” Dr Clive Oppenheimer, Professor of Volcanology at Cambridge University, wrote on Twitter this week.

He was heralding a paper that suggests that memories of the largest lava flood in the history of Iceland, recorded in an apocalyptic medieval poem, were harnessed to drive the country’s conversion to Christianity.

In the paper, published in the scientific journal Climatic Change, the study’s authors represent five countries and cross the science/arts divide. A team of scientists and medieval historians used informa­tion contained within ice cores and tree rings to date the eruption of the Eldgjá from the spring of 939 to at least the autumn of 940.

They were then able to study the effects, as recorded in chronicles and in tree rings. “It was a massive eruption, but we were still amazed just how abundant the historical evidence is for the eruption’s consequences,” Dr Timothy Newfield, from Georgetown University’s Departments of History and Biology, said this week.

“Human suffering in the wake of Eldgjá was widespread. From northern Europe to northern China, people experienced long, hard winters and severe spring-summer drought. Locust infestations and livestock mortalities occurred. Famine did not set in everywhere, but, in the early 940s, we read of starvation and vast mortality in parts of Germany, Iraq, and China.”

Although there are no surviving texts from Iceland that provide direct accounts of Eldgjá, the country’s most celebrated medieval poem, Voluspá (“The prophecy of the seeress”), which can be dated as far back as 961, describes an eruption: “The sun starts to turn black, land sinks into sea; the bright stars scatter from the sky. Steam spurts up with what nourishes life, flame flies high against heaven itself.”

This imagery is used in passages that predict the end of Iceland’s pagan gods and the coming of a new, singular god. The country’s conversion to Christianity took place at about the turn of the 11th century, within two generations of the Eldgjá eruption.

“The poem’s interpretation as a prophecy of the end of the pagan gods, and their replacement by the one, singular god, suggests that memories of this terrible volcanic eruption were purposefully provoked to stimulate the Christianisation of Iceland,” Dr Oppenheimer says.