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by Spektrum der Wissenschaft
Volcanic eruptions paved the way for the plague
13.12.2025
Translation: machine translated
Millions of people died of the plague in the late Middle Ages. We know where the pathogen came from. However, it is unclear why it travelled from Central Asia to Europe. Now there is a plausible suspicion.
Volcanic eruptions could be the reason why the medieval plague reached Europe. They may have triggered a series of events that led to the outbreak of the Black Death in the middle of the 14th century. This is the conclusion drawn by Ulf Büntgen from the University of Cambridge and Martin Bauch from the Leibniz Institute for the History and Culture of Eastern Europe in Leipzig from the tree rings of medieval plants. The researchers also analysed historical documents and looked at climate data from ice cores, as they report in the «Nature» journal «Communications Earth & Environment».
Between around 1347 and 1353, the plague was rampant in Europe. In many regions of the continent, an estimated 60 per cent of the population died from the disease, which is caused by the plague bacterium Yersinia pestis. It is certain that the epidemic began in Central Asia and was introduced to Italian harbour cities, among other places, with grain shipments via the Black Sea region. But why, Büntgen and Bauch asked, did the regions come into contact with each other in the first place?
The researchers set out in search of clues and analysed tree ring data from the Pyrenees, the Alps, Corsica, Greece and Scandinavia. The sequence of tree rings for the years 1345 to 1347 revealed areas that indicate weather anomalies: Central and Western Europe may have become very dry during the warm months; Southern Europe, on the other hand, experienced heavy rainfall. The two scientists also found corresponding information in contemporary sources: Heavy rainfall and flooding are recorded from Italy in the autumn and spring of those years, as well as very cold and humid summers there and in France. According to the sources, famines also broke out in southern Europe and the eastern Mediterranean.
Dark skies, poor harvests and famines
The researchers discovered a possible cause in ice cores from Greenland and Antarctica: deposits point to one or more volcanic eruptions around 1345. It is not known which fire mountains spewed ash and gas at that time, but they were probably those in tropical zones.
The volcanic ejecta darkened the sky. As a result, less sunlight reached the earth and temperatures fell. This had serious consequences for agriculture and caused famines, according to historical sources.
To avert the emergency, cities such as Venice, Genoa and Pisa tried to import grain. They agreed a truce with the Mongols of the Golden Horde, who ruled the granary on the Black Sea at the time. Around 1347, ships set sail from there for Italy - and brought not only grain, but also fleas infected with Yersinia pestis to Europe.
As Büntgen and Bauch discovered, the first plague outbreaks in Europe occurred in those cities that imported grain from the East. Others were spared precisely for this reason: «We were also able to prove that many Italian cities, even large ones such as Milan and Rome, were most likely not affected by the plague, apparently because they no longer had to import grain after 1345», explains Bauch in a press release. Depending on their size, population density and agriculture in the surrounding area, the towns were able to meet their food requirements to varying degrees.
In 2022, experts identified the origin of the medieval plague in Kyrgyzstan. There, traces of the pathogen were found in human remains from 1338 and 1339. The tombstones of the dead also mentioned an unknown epidemic, which was probably the plague.
Spectrum of science
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Original article on Spektrum.de
Header image: Shutterstock / Wolh
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