Records from monks about lunar eclipses provide information about unusually violent volcanic eruptions in the Middle Ages. From hundreds of texts from Europe and Asia, an international research team concludes that five eruptions in the 12th and 13th centuries ejected enormous amounts of particles into the stratosphere. These eruptions could possibly have contributed to the beginning of the Little Ice Age, writes the group around Sébastien Guillet from the University of Geneva in the specialist magazine Nature.
Volcanism can eject gigantic amounts of gases into the atmosphere, cooling the climate for years. Evidence of such eruptions during the Middle Ages can be found in ice cores from the Arctic and Antarctic. However, their investigation does not allow any reliable conclusions to be drawn about the exact time and severity of an eruption, because the global distribution of the particles depends heavily on the season, on the prevailing air currents and also on the height of the ash clouds emitted.
The period from around 1100 to 1300 is considered to be a phase of strong volcanic activity – and this in turn as a possible contributory cause of the Little Ice Age, a cool climatic phase from around 1300 to 1800. In order to identify and date volcanic eruptions in the High Middle Ages, the research team has now developed a new one Source: Notes of contemporary chroniclers from Europe, East Asia and the Middle East on total lunar eclipses.
In Christian writings, a lunar eclipse was often seen as a dark omen
Because these celestial phenomena, in which the shadow of the earth covers the moon and bathes it in a reddish light, can be clearly dated astronomically. On the other hand, the visibility of the Earth’s satellite depends heavily on whether a layer of particles circulating in the atmosphere impairs the view or even completely obscures it. Christian sources in particular attached importance to such events as omens – even if the physical connection was known. For example, in the Revelation of the Evangelist John, a darkening of the moon is considered an indication of the imminent apocalypse.
Of the 64 total lunar eclipses that were basically observable in Europe from 1100 to 1300, 51 were documented. In five lunar eclipses worldwide, the moon has been described as particularly dark. The team believes all of these bursts ejected more than 10 teragrams (more than 10 million tons) of sulfur particles into the stratosphere — that part of the atmosphere beginning at roughly 15 kilometers.
“Each of these eruptions ranks among the top 16 such events over the past 2,500 years,” the group notes. After comparing drill core analyzes and data from tree rings, she determined not only the year for the five violent eruptions, but also the season in some cases. By far the strongest was the eruption of the Samalas volcano on the island of Lombok, now part of Indonesia, which the study dates to spring or summer 1257.
The other four eruptions – in which the volcanoes have not yet been identified – are therefore attributable to the periods between November 1108 and February 1109, May and August 1171, May and August 1129 and September 1275 and July 1276. The time window in which the ejected particles eclipsed the moon ranged from 3 to 20 months.
The study confirms that the High Middle Ages was a period of exceptionally violent volcanism. The eruptions not only darkened the firmament, but also cooled the climate significantly. They were therefore an important reason for the end of the medieval climate anomaly – a warm period spanning several centuries – and for the transition to the Little Ice Age, write Andrea Seim from the University of Freiburg and Eduardo Zorita from the Helmholtz Center Hereon in Geesthacht Nature-Comment.
“Guillet and colleagues’ results improve our understanding of how volcanic eruptions contributed to the onset of the Little Ice Age in relation to other factors, including a period of low solar activity between 1280 and 1340.” The volcanic cooling could have changed the climate system at that time.
In a second comment, the historian Anne Lawrence-Mathers from the University of Reading in England points to the inconsistencies between different sources regarding the lunar eclipses. These could come from weather-related factors, from the observability of the lunar eclipses in different regions of the earth and last but not least from calendrical differences. Having these discrepancies resolved makes the team’s performance all the more impressive.