Within 100 years of Iceland’s settlement by Vikings and Celts in the late 9th century, a devastating volcanic event wreaked havoc on the island. In a rare type of eruption known as a lava flood, Iceland’s Eldgjá volcano belched up 7.7 square miles of lava and spewed out thick clouds of sulfuric gases. The effects of the eruption—a persistent haze, droughts, harsh winters—were felt from northern Europe all the way to northern China.
Experts have long been unsure precisely when this catastrophic event occurred, but as Chase Purdy reports for Quartz, a new study has pinpointed a date for the Eldgjá. The research, led by a team from the University of Cambridge and published in the journal Climactic Change, also explores how the eruption may have led to a dramatic shift in Iceland’s religious culture, driving the island from paganism to Christianity.
To date the volcanic event, researchers analyzed ice core records from Greenland. As Sarah Laskow of Atlas Obscura explains, the ice cores showed clear evidence of both Eldgjá and the eruption of the Changbaishan volcano (also known as Mount Paektu and Tianchi volcano) in Asia, which is known to have occurred around 946 A.D. The team also looked at tree ring data from across the Northern Hemisphere, which showed that one of the coolest summers of the past 1500 years occurred in 940 A.D.—possibly because large quantities of sulfur were choking the atmosphere.
Based on this data, the researchers concluded that Eldgjá began in the spring of 939 and continued at least through the summer of 940, according to a University of Cambridge press release.
The team then consulted medieval texts from 939 and 940 that appear to chronicle the effects of the volcanic eruption. Accounts written in Ireland, Germany, Italy, China and Egypt describe bizarre and devastating atmospheric phenomena: a blood-red and weakened Sun, exceptionally harsh winters, severe droughts in the spring and summer, a suppression of the Nile’s flow. Climactic anomalies brought locust infestations, livestock deaths, dire subsistence crises, and vast human mortality.
“It was a massive eruption, but we were still amazed just how abundant the historical evidence is for the eruption's consequences,” Tim Newfield, study co-author and environmental historian at Georgetown University, said in the statement. “Human suffering in the wake of Eldgjá was widespread.”
No firsthand accounts from Iceland, the country most affected by Eldgjá, survive to the present day. But the study authors believe that a medieval poem written some 20 years after the eruption references Eldgjá’s devastation and attests to its profound effect on Icelandic society.
The Voluspá, a poem composed in approximately 961 A.D., tells of Iceland’s rejection of pagan deities and adoption of a single, Christian god. “The poem describes how the revered pagan god Odin raises a prophetess from the dead,” the researchers write in the study. “She foretells the end of the pagan pantheon and the coming of a new (and singular) god in a series of portents, one being the rearing of a monstrous wolf that will swallow the Sun.”
“[The wolf] is filled with the life-blood of doomed men, reddens the powers’ dwellings with ruddy gore,” a translation of the poem reads. “[T]he sun-beams turn black the following summers, weather all woeful: do you know yet, or what? 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 description of strange atmospheric phenomena—a darkened sky, strange weather, surges of steam—“suggest volcanic manifestations,” the authors of the study write. The Voluspá may include other impressions of Eldgjá’s fallout. One passage, for instance, describes “venom drops” flowing through roofs, which may be a reference to acid rain associated with volcanic plumes.
As the study notes, the widespread adoption of Christianity in Iceland was a gradual process that took place throughout the latter half of the 10th century. But based on the Voluspá’s account of a volcano-like event that brought paganism to its knees, the researchers posit that the terrifying Eldgjá eruption may have pushed Iceland’s population toward a new, monotheistic religion.