What do medieval monks and volcanic eruptions have in common? According to a team of researchers led by the University of Geneva, quite a bit because chronicles from the 12th and 13th century are helping volcanologists to precisely date ancient eruptions based on descriptions of lunar eclipses.
Stemming from the idea that what happens on Earth is reflected in the heavens, medieval monks had a very keen interest in celestial phenomena like comets, meteors, and eclipses. Normally, the sky is completely predictable as the Sun, Moon, planets, and stars turn and follow their regular courses, but eclipses disrupt this tidiness, leading ancient societies to believe that something terrible is about to happen, like the death of a king, a plague, or a famine.
It's a small wonder then that when the monks wrote the annals and chronicles of the age they made sure to record such events. This is more than a matter of historical interest. It has also proven to be a powerful tool for scientists. For example, we know the exact day that the supernova that created the Crab Nebula detonated because Chinese astronomers recorded the sudden appearance of a "guest star" on July 4, 1054.
The Geneva team led by Sébastien Guillet looked at chronicles across Europe, the Middle East, and Japan in search of references to lunar total eclipses between the years 1100 and 1300. In particular they looked for descriptions of their coloring.
A total lunar eclipse occurs when the Earth passes between the Sun and the Moon, casting a shadow that is bathed in dark red light as the sunlight is bent through the Earth's atmosphere. This blood-red spectacle was more than a little unnerving, so the monks had an incentive to record what it looked like and this is of great value to modern volcanologists.
The color of a lunar eclipse is very sensitive to dust in the atmosphere. It can alter the hue and even cause the Moon to become invisible if it's thick enough. Of the 51 lunar total eclipses recorded for the 200-year period, five were unusually dark due to large amounts of volcanic dust being blown into the upper air during a major eruption.
Because the dates of the eclipses are precisely known, it was possible to use these events to date the eruptions with great accuracy. This not only allowed the team to pin down eruptions, it also helped in understanding climactic events caused by the dust reducing global temperature by about a degree Celsius (1.8 °F). Combined with increased darkness and disrupted rainfalls, these conditions could result in poor harvests and outbreaks of diseases.
"We only knew about these eruptions because they left traces in the ice of Antarctica and Greenland," said Clive Oppenheimer, professor in the Department of Geography at the University of Cambridge and co-author of the study. "By bringing together information from ice cores and descriptions from medieval texts, we can now better estimate when and where some of the largest eruptions of this period occurred."
The research was published in Nature.
Source: University of Geneva
