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An international team of researchers led by the University of Geneva (UNIGE) has succeeded in dating the largest volcanic eruptions in history by studying medieval texts and other data sources. Their study, published in the Proceedings of the National Academy of Sciences, sheds new light on one of the most volcanically active periods in Earth’s history and provides valuable information for understanding the long-range societal effects of eruption-forced climatic shifts and the onset of the Little Ice Age.

Medieval monks inadvertently documented significant volcanic eruptions by observing the night sky, providing an unexpected source of information for modern-day researchers. By studying lunar eclipses, which were obscured by volcanic dust in the stratosphere, monks unintentionally recorded history’s largest volcanic eruptions. These eclipses were a useful tool for tracking volcanic activity and for understanding the impacts of eruption-forced climatic changes.

The researchers analyzed readings from 12th and 13th-century European and Middle Eastern chronicles, as well as ice core and tree ring data, to precisely date some of the world’s largest volcanic eruptions. By combining these sources of information, the team was able to establish a comprehensive chronology of volcanic eruptions throughout this period of history.

One of the key findings of the study was that many of the largest volcanic eruptions occurred during the Little Ice Age, a lengthy cooling era that saw European glaciers develop. This suggests a link between volcanic activity and long-term climatic changes, providing important insights into the complex interplay between volcanic eruptions and climate.

Accurately understanding the impacts of eruption-forced climatic changes requires knowledge of event chronologies and reliable estimates of both burden and altitude of volcanic sulfate aerosol. The research team’s findings underscore the need for further investigation into the climate response to volcanic eruptions on decadal to centennial timescales.

Overall, the use of medieval texts and other data sources has provided a new understanding of one of the most volcanically active periods in Earth’s history. The researchers’ findings have implications for our understanding of the complex interplay between volcanic activity and climate, and may contribute to efforts to mitigate the impacts of future volcanic eruptions.