Infrared image of Mount Tambora, Sumbawa Island, Indonesia. Taken from the space shuttle Endeavour in 1992. The most striking geologic feature in this photograph is the large circular Tambora Volcano caldera, the diameter of which is slightly more than 3 miles (5 kilometers). Prior to the disastrous eruption of 1815 when the volcano blew away most of its top, Tambora’s summit was approximately 13 000 feet (4000 meters) above sea level. The present elevation of the caldera rim is more than 9000 feet (2700 meters) above sea level. Credit: Image Science and Analysis Laboratory, NASA Johnson Space Center
Key points:
- Ancient monks' details of lunar eclipses tie into some of the largest volcanic eruptions in history.
- Based on descriptions, researchers have narrowed down the timing of the eruptions.
- These mysterious eruptions are crucial to understanding how past volcanism affected not only climate but also society.
By observing the night sky—particularly lunar eclipses—medieval monks unwittingly recorded some of history’s largest volcanic eruptions. In a new study, an international team of researchers 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.
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.
The researchers found that scribes in Japan took equal note of lunar eclipses, including Fujiwara no Teika who wrote of an unprecedented dark eclipse observed on December 2,1229: ‘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.’
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 dust in the stratosphere that the eclipsed moon almost disappears.
“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 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.”
Sébastien Guillet, lead author of the study and senior research associate at the Institute for environmental sciences at the University of Geneva, worked with climate modelers to compute the most likely timing of these eruptions.
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 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.
“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,” said Guillet.