The rise of the Roman Empire may have been helped along by an unlikely factor – a colossal volcanic eruption that took place on the opposite side of the Earth. The eruption was the largest in the northern hemisphere for the last 2,500 years, and the fallout from it could have dramatically altered the ancient climate, triggering famine, disease and social unrest in the period following the death of Julius Caesar.
Scientists have long suspected that a period of extreme cold – referenced in historical reports and climate proxy records following the assassination of Julius Caesar in 44 BCE – may have been triggered by a powerful volcanic eruption. However, up until now, it was not known where or when this volcano erupted.
A newly published study may have finally discovered the answers to these questions, and also shed light on the effect that the fallout may have had during this tumultuous time of political upheaval. For the purpose of the study, the team undertook a fresh analysis of six ice cores harvested from the Arctic, as well as others taken from Greenland and Russia.
From material deposits preserved within the cores, the researchers were able to identify two distinct volcanic events. The first was a powerful but relatively short eruption that is estimated to have taken place in the January or February of 45 BCE. The second, much larger eruption took place early in the year 43 BCE.
Those ice core records show that the second eruption event was truly massive, and that the extreme effects of the volcanic fallout lasted for over two years.
The team then performed a chemical analysis of volcanic ash known as tephra located in the ice samples, and compared it to debris from the eruption of an Alaskan volcano called Omok II. This caldera-forming volcanic event is thought to be one of the largest eruptions to take place in the past 2,500 years.
"The tephra match doesn't get any better," said one of the study authors, Gill Plunkett, Ph.D 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."
With the location and date of the eruption now known, the team members gathered climate proxy data from around the world, partly in the form of tree-ring analysis and cave formation climate records. They then fed their data into a computer model of the Earth in order to determine the effect that the eruption may have had on the ancient climate.
The results indicated that the two years following the eruption would have been among the coldest that the Northern Hemisphere had experienced in the last 2,500 years. Furthermore, the 10 years that followed the event were the fourth coldest in that timeframe. The findings are backed up by the historical data that has survived to this time.
Average temperatures could have dropped by as much as a total of 7 °C (13 °F), and summer rainfall could have risen by 50 to 120 percent normal levels throughout Southern Europe. In the autumn that followed, there may have been 400 percent the usual amount of rain.
This extreme shift in climate and weather would have played havoc with ancient agriculture, leading to crop failures, famine and outbreaks of disease. According to the team, the shift in climate also greatly affected the seasonal flooding of the Nile River – an event that was vital to Egyptian farmers, and without which their crops would wither and die. Even prior to this calamity, food security in Egypt was a serious issue.
Relatively soon after the Omok II eruption, as the world struggled with the ensuing climate fallout, both the Roman Republic and and the Egyptian Ptolemaic Kingdom fell. In their place rose the largely autocratic Roman Empire.
"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," comments study author Joe McConnell, Ph.D of the Desert Research Institute in Reno. "It certainly shows how interconnected the world was even 2,000 years ago."
The team believe that the fallout from the Okmok II eruption played a significant role in the unraveling of these ancient empires, which, despite being extremely advanced for that period of Earth’s history, were unprepared to deal with the unexpected volcanic shock.
Volcanic events that directly proceeded the Okmok II eruption also help explain certain atmospheric and seemingly celestial phenomenon that were interpreted as omens in the time surrounding Julius Ceasar’s death. These include the darkening of the Sun in the sky, and the appearance of solar halos.
The study has been published in the journal Proceedings of the National Academy of Sciences.
Source: Desert Research Institute, Yale University