How a Japanese volcano ruined an Irish summer
Irish History

How a Japanese volcano ruined an Irish summer

IRISH SUMMERS have a certain reputation, so a manuscript telling of “heavy rain and bad weather in the summer and autumn” of 1109 might not seem remarkable – except for the fact that the likely culprit was an eruption thousands of miles away in Japan.

Medieval records reveal that bad weather brought famine and hardship to Europe between the years 1109 and 1111. French monks described how continuous and excessive rainfall during the summer and autumn of 1109 "drowned the crops, the barrenness of the earth cried aloud, and the grape harvest was an almost total failure".

While the French were mourning the loss of a season’s wine, in Ireland “fastings and abstinence were observed and alms given to God” so the “heavy rain and bad weather in the summer and autumn might be dispelled”. That’s according to the Annals of Inishfallen. Poor conditions were also recorded in Germany, Belgium, Northern Spain and Britain.

And apart from the constant rain, it was also much cooler than usual. Scientists have figured out that the summer of 1109 was one of the coolest in the past 1500 years. The likely cause was a dust veil hanging over Europe, formed by volcanic particles thrown high up into the stratosphere.

Poor weather conditions caused crop shortages and rising food prices, according to sources written at the time. In France, for example, wheat prices doubled between the autumn of 1108 and the summer of 1109. According to one source, “terrible famine decimated human beings everywhere”. Similar conditions were felt throughout Europe, including Ireland.

Piecing the Story Together

Scientists combined information from medieval manuscripts with records from tree-rings and ice cores to paint a picture of massive volcanic activity during these years. It’s known that Mount Asama in Japan erupted in the autumn of 1108 because a Japanese courtier called Fujiwara no Munetada recorded it in his diary. He wrote:

“On August 29, there was a fire at the top of the volcano, a thick layer of ash in the governor’s garden, everywhere the fields and the rice fields are rendered unfit for cultivation. We never saw that in the country. It is a very strange and rare thing.”

But scientists believe Mount Asama alone wasn’t responsible for the impact on Europe. They think several large eruptions occurred within a short space of time. At least one was in the Northern hemisphere, with another in the Southern hemisphere or near the equator.

Another vital piece of evidence helped scientists to piece the story together. It was an eyewitness account of an exceptionally dark lunar eclipse in May 1110.  The darkest total lunar eclipses of the last 400 years have all been linked to volcanic activity. This is because volcanic dust affects the brightness of the eclipsed moon.

According to the Anglo-Saxon Peterborough Chronicle, “On the fifth night in the month of May appeared the moon shining bright in the evening, and afterwards by little and little its light diminished, so that, as soon as night came, it was so completely extinguished withal, that neither light, nor orb, nor anything at all of it was seen.”

So, if you’re tempted to complain about the Irish summer, look on the bright side. At least we don’t have to contend with a volcanic dust cloud making it worse. Fingers crossed the weather gods smile kindly on us in 2020.


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