Sat. Oct 1st, 2022
The 10 km wide caldera on Alaska's Unmak Island was formed during the eruption of Okmok II in 43 BC.
enlarge The 10 km wide caldera on Alaska’s Unmak Island was formed during the eruption of Okmok II in 43 BC.

Kerry Key (Columbia University, New York, NY)

Roman writers described unusual weather and famines in the years following the assassination of Julius Caesar in 44 BCE, adding to the turbulence of the Civil War that marked the transition from Republic to Empire. A recent study has now identified the culprit: a volcano 9,000 km (6,000 miles) away in Alaska.

“Madness of wolves in winter”

“Wolf madness in winter; in summer no grain is harvested,” cried a voice from the Oracle of Apollo, at Delphi, in the months after the death of Julius Caesar. Ancient writers who survived the period describe cold weather, short growing seasons, and widespread famine around the Mediterranean, from Rome to Egypt. Throughout the empire, famine led to disease and fueled growing civil unrest in an already turbulent time.

For years, modern historians have speculated that a major volcanic eruption could be the culprit. An erupting volcano blasts sulfur dioxide high into the atmosphere. As the sulfur dioxide spreads into the stratosphere, chemical reactions turn it into other sulfur compounds that reflect solar radiation and block the sun’s light and heat. Huge areas of the planet are getting colder, often continents away from the eruption.

But no one is sure which volcano is to blame for Rome’s troubles. It could have been as far away as Shiveluch in Kamchatka or Apoyeque in Nicaragua. On the other hand, it could have been as close as Mount Etna, which famously exploded in 44 BCE—not long before Caesar’s death—probably causing some of the strange omens and omens described that year.

A recent study of ice cores in Greenland now suggests the culprit is Mount Okmok, in what is now Alaska, half a world away from Rome. Every year in the Arctic, new snow accumulates and is compressed into layers of ice, which keep a record of what has fallen with the snow. In north-central Greenland, environmental researcher Joe McConnell (of, ironically, the Desert Research Institute) and his colleagues found volcanic ash and sulfuric acid in ice sheets that had been deposited in the early winter of 43 BCE and persisted for the next two years.

blame okmok

“We found Okmok II’s sulfur loss in every Arctic ice core record we had access to, including five from all over Greenland and one from Akademii Nauk in Russia’s Arctic,” McConnell told Ars. “The layer of elevated sulfur concentration is about a foot to 50 cm thick, depending on the ice core, and we would expect the sulfur to be deposited throughout the Northern Hemisphere, but not uniformly.”

The geochemistry of that frozen ash matched layers of rock fragments called tephra associated with an ancient eruption of Mount Okmok. Known as Okmok II, this was one of the largest eruptions of the last few thousand years, comparable to Mount Pinatubo in 1991, Krakatoa in 1883, or Tambora in 1815. But volcanologists don’t know exactly when the eruption happened; radiocarbon dates on organic material buried under the tephra only narrowed it to a window between 190 BCE and 50 CE.

“For volcanic eruptions that have not been historically documented (and most are not), absolute data comes from ice core studies like this one,” McConnell explained in an email to Ars.

Arctic ice cores hold records of atmospheric events going back millennia.
enlarge Arctic ice cores hold records of atmospheric events going back millennia.

Joseph R. McConnell

And you, volcano?

McConnell and his colleagues used a computer simulation to model how the Okmok eruption would have affected the ancient world. The models predicted that summer temperatures in the years following the eruption would be 2⁰C to 3⁰C cooler than normal in most of the Northern Hemisphere. That’s consistent with what ancient writers described, and it’s supported by climatic cues such as growth rings.

“Geochemically fingerprinting the ash was key to identifying the volcanic source, and that knowledge underpinned the detailed climate modeling,” McConnell told Ars.

Okmok II’s eruption lasted from 43 BCE to 41 BCE, but the effects on the other side of the world lasted more than a decade. Spring came later, autumn came earlier, and the summer growing season fell short. It was also way too rainy for healthy crops. Ancient writers describe crop failures and famines in northern Italy and northern Greece from April 43 BCE to 36 BCE. With famine came disease and an increase in civil unrest.

With the Republic already shaken by infighting in the wake of Julius Caesar’s death, years of famine likely contributed to undermining what little stability remained. “It is historically known that natural disasters create a ‘state of exception’ where ‘business as usual’ becomes unfeasible and political and cultural norms are suspended, leaving room for rapid social and political change,” McConnell and his colleagues wrote.

Things like volcanic eruptions and pandemics don’t happen in a vacuum. They influence – and are influenced by – political and social events. For example, when Augustus Caesar’s political opponent, the military leader Sextus Pompeius (whose father, Pompey the Great, was a major opponent of Augustus’ adopted father, Julius Caesar), mounted a naval blockade of Italian ports, he exacerbated the food shortages in the heart. from Rome. But he may have gained a little extra influence from the fact that people in Italy were already faced a famine, so they were even more vulnerable to cutting off the outside supply.

denial river

While farmers along the Mediterranean coast faced too much rain, farmers along the Nile in Egypt faced the opposite problem. Egypt’s survival has always depended on the summer floods of the Nile, which bring water and fertile soil to the narrow strip of land along the river’s banks. But two years in a row, 43 and 42 BCE, the floods did not come. Documents from that period describe a terrible famine in those years.

McConnell and his colleagues’ climate models suggest that as Mount Okmok cooled the Northern Hemisphere, it also short-circuited the weather systems that cause the annual flooding of the Nile. “The differential cooling moves the equatorial rain belts north or south,” McConnell explains. “Eruptions in high northern latitudes like Okmok cause a failure of the East African summer monsoon, resulting in drought in the upper reaches of the Nile and thus a failure in the all-important summer flood.”

Meanwhile, Octavian (who would become Augustus Caesar, the first emperor of Rome) and his ally Mark Antony were still fighting Brutus (the one with the knife) and Cassius for supremacy, and neither side could get grain from Egypt to support their armies. to feed. Cassius reportedly asked Cleopatra for military help, and she turned it down because her country was already struggling with famine and disease.

But the volcanic eruption in Alaska may have ultimately contributed to Cleopatra becoming Egypt’s last Ptolemaic ruler. Military conflicts raged and almost every corner of the ancient Roman Republic was in desperate need of food, which probably made Egypt look very attractive as a potential “breadbasket.” At the same time, the failure of the Nile floods in 43 and 42 BCE likely made Cleopatra’s Egypt much more vulnerable to outside attack.

History on ice

Some of the political and economic consequences of the Okmok eruption in 43 BC. can be seen in the same ice cores that helped identify them. Lead pollution from mining, smelting and other industrial work across Europe also often ends up in Greenland ice, thanks to atmospheric circulation. In the years when old Europe had to deal with plague, war or famine – and therefore less silver was mined and melted – less lead from Europe came into the snow that fell over Greenland.

So the ice on another continent records the economic history of ancient Rome. That’s basically what McConnell and his colleagues were studying when they found the evidence of Okmok II. As McConnell told Ars, “We’ll extend these studies involving detailed ice core measurements to ancient history through the Bronze Age and even the Neolithic — should be fun!”

PNAS2020 DOI: 10.1073/pnas.2002722117 (About DOIs).

By akfire1

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