Washington (AFP)
The assassination of Julius Caesar, in 44 BCE, triggered a power struggle of almost two decades marking the beginning of the transition between the Roman Republic and the Roman Empire. According to historians, this period was marked by strange observations in the sky, a particularly cold climate and great famines. According to a new study, an eruption in Alaska could be the cause.
Analysis of volcanic ash (tephra) trapped in ice cores collected in the Arctic has enabled a team of international scientists to link the extreme weather then observed in the Mediterranean with the eruption of the Okmok volcano in Alaska. , in 43 BCE.
Their study was published in the journal PNAS (Proceedings of the National Academy of Sciences).
"Finding evidence that a volcano on the other side of the world erupted and actually contributed to (...) the rise of the Roman Empire is fascinating," said lead author Joe McConnell. , from the Desert Research Institute (DRI) of Reno, Nevada.
"It shows how interconnected the world was, even 2,000 years ago," he added.
He and Swiss scientist Michael Sigl began their research after the discovery last year of a particularly well-preserved layer of ash in an ice core.
New analyzes of other samples were then made in Greenland and Russia, some of which had been carried out in the 1990s and preserved in archives until today.
They were then able to identify two distinct eruptions: one powerful but brief in 45 BC, and the other much longer and extended, in 43 BC, with fallout lasting more than two years.
- Reduced harvests -
A geochemical analysis was then carried out on ice samples dating from the second eruption, and was found to correspond perfectly with that of the Okmok volcano - one of the largest eruptions in 2,500 years.
"The correspondence (between samples) could not be better," said volcanologist Gill Plunkett of Queen's University Belfast.
The team has also gathered other evidence from around the world, ranging from weather records based on the analysis of tree circles in Scandinavia, to the formation of caves in northern China.
These data were used to fuel a climatic model, according to which the two years following the eruption have been among the coldest in the northern hemisphere in the last 2,500 years.
According to this model, average temperatures were about 7 degrees below normal during the summer and fall following the eruption, and precipitation almost 400% higher than normal in southern Europe. during the fall.
"In the Mediterranean region, these humid and extremely cold conditions during spring and autumn, very important seasons for agriculture, probably reduced the yield of the crops and created supply problems, at the time of the political upheavals of this period, "detailed archaeologist Andrew Wilson of the University of Oxford.
These events also coincided with the inability of the Nile to cover the plains that year, which resulted in illnesses and famines, added Yale University historian Joe Manning.
The eruption could also explain the strange atmospheric phenomena observed then, such as solar halos, a darkened sun, or an optical phenomenon showing the image of three suns in the sky.
But the authors point out that many of these observations were made before the eruption in Alaska, and could be linked to a smaller eruption of Etna in 44 BC
According to Joe McConnell, if many factors contributed to the fall of the Roman Republic, as well as the Ptolemaic kingdom in Egypt - also precipitated by the advent of the Roman Empire -, the eruption in question played a role great role, and contributes to fill a lack of knowledge which left historians perplexed until now.
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