How Medieval Monks Are Increasing Our Understanding of Volcanic Activity

Five years of research delving through the manuscripts recorded by monks in Medieval times is shedding more light on the effect of the volcanic eruptions which took place at that time.

lava flowing
Photo by Brent Keane on

An international team of researchers, led by the University of Geneva (UNIGE), drew on readings of 12th and 13th century European and Middle Eastern chronicles, along with ice core and tree ring data, to accurately date some of the biggest volcanic eruptions the world has ever seen. 

The eruptions had a devastating effect on the world’s climate and the failure of harvests.

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.

Making these connections between what was documented at the time and using the scientific research methods we have today has increased out understanding of these events.

 Sébastien Guillet, senior research associate at the Institute for environmental sciences at the UNIGE,  explained how it came about. He said:

“I was listening to Pink Floyd’s Dark Side of the Moon album when I realised 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.”

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 on 2 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.

 Clive Oppenheimer, professor at the Department of Geography at the University of Cambridge commented:

 “We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland. 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.”

 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 15 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 collective effect of the medieval eruptions on Earth’s climate may have led to the Little Ice Age, when winter ice fairs were held on the frozen rivers of Europe. 

Click on this link to access the article, Lunar eclipses illuminate timing and climate impact of medieval volcanism, published in Nature.

Men observing the stars, from Bartholomaeus Anglicus' De Proprietatibus rerum, Italy (Mantua), c. 1300-1310, Add MS 8785, f. 108v
Men observing the stars, from Bartholomaeus Anglicus’ De Proprietatibus rerum, Italy (Mantua), c. 1300-1310, Add MS 8785, f. 108v Stars in Their Eyes: Art and Medieval Astronomy

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