Illustration of a medieval monastery.
An international team of researchers, led by the University of Geneva (UNIGE), drew on readings of 12th and 13th century chronicles, along with ice core and tree ring data, to accurately date some of the biggest volcanic eruptions the world has ever seen.
Their study uncovers new information about one of the most volcanically active periods in Earth’s history, which some think helped to trigger the Little Ice Age.
It took the researchers almost five years to examine hundreds of annals and chronicles from across Europe and the Middle East, in search of references to total lunar eclipses and their coloration.
Medieval monks and scholars recorded lunar eclipses as they believed that such celestial phenomena might foretell calamities on Earth like earthquakes. Mindful of the Book of Revelation, a vision of the end times that speaks of a blood-red Moon, the monks were especially careful to take note of the Moon’s coloration.
Of the 64 total lunar eclipses that occurred in Europe between 1100 and 1300, the chroniclers had faithfully documented 51. In five of these cases, they also reported that the Moon was exceptionally dark.
Total lunar eclipses occur when the Moon passes into the Earth’s shadow. Typically, the Moon remains visible as a reddish orb because it is still bathed in sunlight bent round the Earth by its atmosphere. But after a very large volcanic eruption, there can be so much volcanic dust in the stratosphere – the middle part of the atmosphere – absorbing this residual light that the eclipsed Moon almost disappears.
“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. 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,” explains Sébastien Guillet, senior research associate at the Institute for environmental sciences at the UNIGE and lead author of the study.
The researchers found that scribes in Japan took equal note of lunar eclipses. One of the best known, Fujiwara no Teika, wrote of an unprecedented dark eclipse observed in December 1229.
“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.”
The stratospheric dust from large volcanic eruptions was not only responsible for the vanishing Moon. It also cooled summer temperatures by limiting the sunlight reaching the Earth’s surface. This in turn could bring ruin to agricultural crops.
“We know from previous work that strong tropical eruptions can induce global cooling on the order of roughly one degree over a few years. They can also lead to rainfall anomalies with droughts in one place and floods in another,” explains Markus Stoffel, a specialist in converting measurements of tree rings into climate data at the UNIGE and coauthor of the study.
Despite these effects, people at the time could not have imagined that the poor harvests or the unusual lunar eclipses had anything to do with volcanoes, as most volcanic eruptions happened in remote areas or were not recorded in written documents.
“We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland,” explains coauthor Clive Oppenheimer, volcanologist and professor at the Department of Geography at the University of Cambridge. “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.”
As well as helping to narrow down the timing and intensity of these events, what makes the findings significant is that the interval from 1100 to 1300 is known from ice-core evidence to be one of the most volcanically active periods in history.
Of the fifteen eruptions considered in the new study, one in the mid-13th century rivals the famous 1815 eruption of Tambora that brought on “the year without a summer” of 1816.
The effect of the medieval eruptions on Earth’s climate may have led to the Little Ice Age, a 500-year-long interval of cooling with severe winter weather, poor harvests and advancing glaciers in medieval Europe.
“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,” so the conclusion of the researchers.
The study “Lunar eclipses illuminate timing and climate impact of medieval volcanism” was published in the journal Nature. Material provided by the University of Geneva.
