Medieval monks made unexpected contribution to study of volcanos

(CN) — Bubonic plague. Famine. Civil and political unrest. Faithfully documented lunar eclipses between 1100 and 1300 A.D. Besides obvious medieval timelines, all share ties to something seemingly unrelated: volcanic eruptions.

A study published in the journal Nature on Wednesday from a team of international researchers led by the University of Geneva details the five years they spent pouring over European and Middle Eastern texts from the 12th and 13th centuries to identify some of the most prolific volcanic eruptions known to date — eruptions that occurred between 1100 and 1300 or the “High Medieval Period.”

The collective effect of volcanic eruptions during the High Medieval Period is thought to have led to the “Little Ice Age,” a climate interval between the early 14th and mid-19th centuries where mountain glaciers expanded in several locations and temperatures dropped, particularly in the Northern Hemisphere.

To find what they were looking for, researchers had to dig through hundreds of annals and chronicles in search of references to a total lunar eclipse and descriptions of coloration, which left clues as to whether a volcanic eruption occurred at the time.

“I was listening to Pink Floyd’s 'Dark Side of the Moon' album when I realized that the darkest lunar eclipses all occurred within a year or so of major volcanic eruptions,” said lead author Sébastien Guillet in a statement. “Since we know the exact days of the eclipses, it opened the possibility of using the sightings to narrow down when the eruptions must have happened.”

Researchers found that between 1100 and 1300 A.D., European chroniclers documented 51 out of 64 total lunar eclipses. In five cases, the chroniclers reported the moon was exceptionally dark, indicating a recent volcanic eruption. Additionally, the team found that observations of dark eclipses followed substantial eruptions during the High Medieval Period, where Western and Eastern Christian sources provided information on the color and brightness of the moon for 36 eclipses.

According to the study authors, references to a ‘blood-red moon’ in Western and Eastern Christian sources were likely informed by texts such as the Book of Revelation of John, where the blood moon — along with earthquakes and solar eclipses — foretell the end of times.

“Lunar eclipse coloration was imbued with particular significance for Christian observers and often regarded as an ill omen, presaging disasters emphasizing the influence of the Bible on the perception of natural phenomena during the Middle Ages,” the study authors wrote.

However, they said this does not mean that the physical causes of lunar eclipses were lost to all medieval chroniclers. They note ancient Babylonian, Greek and later Muslim astronomers understood eclipse mechanisms and even predicted lunar occultations, and this knowledge was subsequently transmitted to medieval Europe.

“Both natural and supernatural interpretations of lunar eclipses coexisted in the Middle Ages, underpinning the recovery of a near-complete series of lunar eclipse coloration spanning two centuries,” the researchers wrote in the study.

One of the most outstanding accounts came from Japan regarding a total lunar eclipse that occurred on Dec. 2, 1229, from the Meigetsuki written by Fujiwara no Teika: “… the old folk had never seen it like this time, with the location of the disk of the moon not visible, just as if it had disappeared during the eclipse… It was truly something to fear.”

Researchers believe all of the dark lunar eclipses they found on record correlate to five of the seven largest High Medieval Period volcanic sulfate signals recorded in polar ice cores, suggesting that the darkening of the eclipsed moon was related to the presence of volcanic aerosols in the stratosphere. This finding mirrors previous work that found that all previous dark total lunar eclipses since 1600 A.D. followed substantial volcanic eruptions.

The stratospheric dust following these catastrophic eruptions would not just filter the moon, however. They would also limit the sunlight in the sky, cooling summer temperatures and ravaging crops.

“We know from previous work that strong tropical eruptions can induce global cooling on the order of roughly 1° Celsius (1.8° Fahrenheit) over a few years,” said Markus Stoffel, co-author and professor at the Institute for Environmental Sciences at the University of Geneva, in a statement. “They can also lead to rainfall anomalies with droughts in one place and floods in another.”

Still, people at the time couldn’t have imagined their crop misfortune was due to volcanic activity in far-flung parts of the world they didn't even know existed. In fact, today's researchers wouldn’t know about the volcanic activity at all if the volcanic activity hadn’t documented itself.

“We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland,” said co-author Clive Oppenheimer, professor at the Department of Geography at the University of Cambridge, in a statement. “By putting together the information from ice cores and the descriptions from medieval texts we can now make better estimates of when and where some of the biggest eruptions of this period occurred.”

Using both data sources, the scientists then worked with climate modelers to compute the most likely timing of eruptions.

“Knowing the season when the volcanoes erupted is essential, as it influences the spread of the volcanic dust and the cooling and other climate anomalies associated with these eruptions,” Guillet said.

But as if the team’s literary endeavors are not admirable in their own right, their findings are scientifically significant for another reason. Besides narrowing down the timing and intensity of these volcanic events, the timeline between 1100 and 1300 is also known from ice core data to be one of the most volcanically active periods in history.

“Improving our knowledge of these otherwise mysterious eruptions, is crucial to understanding whether and how past volcanism affected not only climate but also society during the Middle Ages,” Guillet said.

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