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Medieval monks’ moon journals aid modern volcano studies

Medieval monks’ moon journals aid modern volcano studies

Medieval monks observations: Reddish moon and stars above erupting volcano.
View at EarthSky Community Photos. | David Rojas captured the image from Pacaya volcano in San Vicente Pacaya, Guatemala, during the total lunar eclipse on November 8, 2022. This is a cropped view. You can view the full size image here. Thank you, David! Medieval monks wrote detailed journals of their moon-gazing, including strangely dark lunar eclipses, which helps researchers today pinpoint dates of erupting volcanoes.

Medieval monks made moon journals

Medieval monks took meticulous records of the world around them, including their view of total lunar eclipses. And – as sometimes happens around the time of major volcanic eruptions – some of those medieval eclipses were unusually dark. The darkness on the face of the moon comes from excess particles blasted to Earth’s atmosphere by active volcanoes. And check this out. Scientists are now using these journals to pin down dates of previously unrecorded volcanic eruptions. On February 5, 2023, a team, led by Sébastien Guillet of the University of Geneva, announced that the medieval texts of monks have allowed them to precisely date some of the largest eruptions in history.

Guillet explained what gave him the idea to look for evidence of volcanoes in monks’ descriptions of lunar eclipses:

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.

The scientists published their peer-reviewed findings in the journal Nature on April 5, 2023.

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Journals, ice cores and tree rings

Medieval monks took diligent note of their world, from war to the activities of kings and popes to cats visiting their garden. These notes include descriptions of lunar eclipses, including those that were darker than normal. Because the heavens move like clockwork, scientists can precisely date the times of past eclipses. That helps researchers narrow down the dates for volcanic eruptions that darkened some of the lunar eclipses on record.

It took the researchers nearly five years to pore over the monks’ writings from Europe and the Middle East. Besides these journals from the 12th and 13th centuries, they also analyzed ice core and tree ring data. This time period is notable as one of the most volcanically active periods in Earth’s history. In fact, scientists believe that the ash particles injected into Earth’s atmosphere from these eruptions led to the Little Ice Age.

Drawing of a ball and cone with animal heads and ancient writing.
Thirteenth-century depiction of a lunar eclipse by Johannes de Sacrobosco. Image via Nature/ The New York Public Library (De Sphaera, MssCol 2557, f112v).

The color of the moon

The focus of the medieval monks’ world was on prayer and scripture. In the bible’s book of Revelations, where it describes the end of times, it says:

… the full moon became like blood …

Therefore, the monks paid particular attention to the color of the moon. In the time period between 1100 and 1300 CE, Europe would have been able to see 64 total lunar eclipses. The researchers found monastic journals documenting 51 of those lunar eclipses. And, for five of those events, the monks noted the moon was exceptionally dark.

The dark total lunar eclipses occurred in the years 1110, 1172, 1229, 1258 and 1276 CE. This matched signs of volcanoes from ice cores in Greenland. The texts provided new evidence that these five eruptions were not the result of small, local eruptions near Greenland but instead were large enough to create vast stratospheric aerosol clouds.

Confirmation from Japanese texts

The researchers also found descriptions of dark lunar eclipses in old Japanese writings. Fujiwara no Teika, a Japanese poet from 1162-1241, observed the lunar eclipse of December 2, 1229. He wrote:

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.

Besides being an eerie sight, the volcanic dust in the atmosphere was fearful because it meant cooler temperatures and the possibility of ruined crops. Markus Stoffel of the University of Geneva talks about the link between volcanic eruptions and climate:

We know from previous work that strong tropical eruptions can induce global cooling on the order of roughly 1° C over a few years. They can also lead to rainfall anomalies with droughts in one place and floods in another.

Eruptions invisible to medieval monks

The medieval journalists didn’t record the volcanic eruptions themselves because the eruptions occurred in different parts of the world. The scribes lived at northerly latitudes, while the volcanoes would have erupted in the tropics.

Clive Oppenheimer of the University of Cambridge said:

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.

Dating volcanic eruptions

The researchers used climate modeling to come up with the most likely dates for the eruptions. Guillet said:

Knowing the season when the volcanoes erupted is essential, as it influences the spread of the volcanic dust and the cooling and other climate anomalies associated with these eruptions.

The researchers looked closely at 15 eruptions. One of them, which occurred in the mid-13th century, was likely about as strong as the 1815 eruption of Tambora, which produced the Year Without a Summer in 1816. Guillet said:

Improving our knowledge of these otherwise mysterious eruptions is crucial to understand whether and how past volcanism affected not only climate but also society during the Middle Ages.

An insight to future climate?

Matthew Toohey of the University of Saskatchewan helped translate the eclipse records into date estimates for the volcanic eruptions. His work involved using modern observations from satellites and computer models to simulate the spread of volcanic ash in our atmosphere. Toohey said:

This work is a really novel example of interdisciplinary research, bringing together threads of evidence from medieval history, paleoclimatology and atmospheric physics. Volcanic eruptions are really important for understanding past climate variability. And eclipse observations can be used to help determine the timing of past eruptions, many of which are otherwise only known of because of the chemical markers in polar ice cores.

The more accurately we can estimate the magnitude and timing of past eruptions, the better we can understand past climate variations and use that to test climate models that are used to predict future climate.

Bottom line: Medieval monks kept detailed nature journals, which included stories of strangely dark lunar eclipses. Today, those old journals are helping researchers pinpoint dates of past volcanic eruptions.

Source: Lunar eclipses illuminate timing and climate impact of medieval volcanism

Via University of Geneva

Via University of Saskatchewan


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