An unusually powerful volcanic eruption in 43 BCE has been linked to political upheaval on the other side of the globe, including the fall of the Roman Republic and the Ptolemaic Kingdom.
Julius Caesar was assassinated by a group of rebellious senators in 44 BCE, triggering a chain of events that led to the demise of the Roman Republic and the Ptolemaic Kingdom (a long standing Egyptian dynasty) and the rise of the Roman Empire. These historic political events were set against a backdrop of environmental and social instability, including unusually cold and wet weather, crop failures, famine, and disease.
New research published this week in Proceedings of the National Academy of Sciences has identified a potential catalyst for these events: the eruption of Okmok volcano in Alaska’s Aleutian Islands. Historians had previously suspected a volcano, but the new research finally identifies the offending culprit, which erupted 2,063 years ago. The evidence points to a particularly powerful eruption, which had a dramatic effect on the Mediterranean climate and quite possibly its political climate as well.
The new research, led by Joe McConnell from the Desert Research Institute in Reno, Nevada, was a collaborative effort involving both paleoclimatologists and classic historians.
“To find evidence that a volcano on the other side of the earth erupted and effectively contributed to the demise of the Romans and the Egyptians and the rise of the Roman Empire is fascinating,” said McConnell in a press release. “It certainly shows how interconnected the world was even 2,000 years ago.”
By gathering and dating volcanic fallout, known as tephra, from six Arctic ice cores, the researchers showed that Okmok erupted not once but twice, within the span of two years. Five ice cores analysed in the study came from northern Greenland and one from Russia.
The first eruption, Okmok I, happened in early 45 BCE and was powerful and short. The second, Okmok II, happened two years later in early 43 BCE, but it was far more powerful, producing fallout that lasted for over two years. In fact, it now appears that Okmok II is one of the most powerful volcanic eruptions in the past 2,500 years, according to the new research.
A geochemical analysis of the ice cores matched the tephra to the same time period.
“The tephra match doesn’t get any better,” explained Gill Plunkett, a scientist from Queen’s University Belfast and a co-author of the new paper, in the press release. “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.”
Climate records as chronicled in tree rings and other natural sources indicates that the years 43 and 42 BCE were “among the coldest years of recent millennia in the Northern Hemisphere at the start of one of the coldest decades,” as the authors wrote in the paper. An Earth-modelling system suggested this eruption altered water cycles and season temperatures in the Mediterranean. Temperatures were as much as 13 degrees Fahrenheit (7 degrees Celsius) below average during the two years after the eruption. This period was also very wet, with summer precipitation 50% to 120% above normal in southern Europe and autumn precipitation 400% above normal.
The new research lends “credibility to reports of cold, famine, food shortage and disease described by ancient sources,” said Andrew Wilson, a classical archaeologist from University of Oxford and a co-author of the study, in the press release. His co-author, historian Joseph Manning from Yale University, said the “climate effects were a severe shock to an already stressed society at a pivotal moment in history.”
Connecting social and political events to a volcanic eruption so far away isn’t easy, but as the authors note in their paper, such “shocks must be seen as having played a role in the historical developments for which the period is famed.” Indeed, the Okmok II eruption may not have been the immediate cause of these disruptions, but it certainly appears to have been a contributing factor.
Other past volcanic eruptions are thought to have had dramatic impacts far across the globe. The summer of 1816, for example, was famously no summer at all, with persistent darkness and frost leading to widespread crop failure and famine in North America and Europe. This “year without a summer” was likely caused by the eruption of Mount Tambora in Indonesia the year before, which sent particles into the atmosphere that blocked out sunlight.