The fall of the Roman Republic may have been caused in part by a massive volcanic eruption across the globe in Alaska, new research suggests.
And we get that information courtesy of the Desert Research Institute in modern-day Nevada.
The DRI’s Joe McConnell led an international team of scientists and historians that reports finding evidence in Arctic ice cores connecting an eruption of the Okmok volcano with an unexplained period of extreme cold in the Mediterranean around 43 BCE.
Written sources describe subsequent crop failures, famine, disease and unrest in the region, which ultimately contributed, historians believe, to the downfall of both the Roman Republic and the Ptolemaic Kingdom of Egypt.
A volcano has long been suspected to be the cause of the cold, but it has not been clear where or when it occurred, or how severe it was. Now the study of tephra (volcanic ash) found in Arctic ice cores points the finger at the caldera-forming eruption of Okmok.
“People have been speculating about this for many years, so it’s exciting to be able to provide some answers,” says McConnell.
The investigation began in the lab at DRI when an unusually well-preserved layer of tephra was found in an ice core sample. New measurements of other cores archived in the US, Denmark and Germany helped reveal two distinct volcanic eruptions, with volcanic fallout from the second lasting more than two years.
“The tephra match doesn’t get any better,” says Gill Plunkett, from Queen’s University Belfast. “We compared the chemical fingerprint of the tephra found in the ice with tephra from volcanoes thought to have erupted about that time and it was very clear that the source of the 43 BCE fallout in the ice was the Okmok II eruption.”
A team from the US, the UK, Switzerland, Ireland, Germany and Denmark next gathered supporting evidence from around the globe, including tree-ring-based climate records from Scandinavia, Austria and California’s White Mountains, and cave formations in China.
As described in a paper in the journal Proceedings of the National Academy of Sciences, they then used Earth system modelling to develop a more complete understanding of the timing and magnitude of volcanism during this period and its effects on climate and history.
According to their findings, the two years following the Okmok II eruption were some of the coldest in the Northern Hemisphere in the past 2500 years, and the decade that followed was the fourth coldest.
“In the Mediterranean region, these wet and extremely cold conditions during the agriculturally important spring through autumn seasons probably reduced crop yields and compounded supply problems during the ongoing political upheavals of the period,” says classical archaeologist Andrew Wilson, from the University of Oxford.
“These findings lend credibility to reports of cold, famine, food shortage and disease described by ancient sources.”
The researchers say volcanic activity also helps explain unusual atmospheric phenomena described by ancient Mediterranean sources around the time of Caesar’s assassination and interpreted as signs or omens: things such as solar halos, the sun darkening in the sky, or three suns appearing in the sky.
However, many of these observations took place prior to the eruption of Okmok II and are likely related to a smaller eruption of Sicily’s Mt Etna in 44 BCE.
Nick Carne is editor of Cosmos digital and editorial manager for The Royal Institution of Australia.
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