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Photo: Volcano Discovery

I love stories about volcanoes that change the flow of history. The really big ones, you know, darken the skies for months — even years — and disrupt the sea like a tsunami.

As Katherine Kornei reports at the New York Times, there are other effects that researchers are just beginning to discover.

“Chaos and conflict roiled the Mediterranean in the first century B.C.,” she reports. “Against a backdrop of famine, disease and the assassinations of Julius Caesar and other political leaders, the Roman Republic collapsed, and the Roman Empire rose in its place. Tumultuous social unrest no doubt contributed to that transition — politics can unhinge a society. But so can something arguably more powerful.

Scientists [in June] announced evidence that a volcanic eruption in the remote Aleutian Islands, 6,000 miles away from the Italian peninsula, contributed to the demise of the Roman Republic.

“That eruption — and others before it and since — played a role in changing the course of history.

“In recent years, geoscientists, historians and archaeologists have joined forces to investigate the societal impacts of large volcanic eruptions. They rely on an amalgam of records — including ice cores, historical chronicles and climate modeling — to pinpoint how volcanism affected civilizations ranging from the Roman Republic to Ptolemaic Egypt to pre-Columbian Mesoamerica.

“There’s nuance to this kind of work, said Joseph Manning, a historian at Yale University who has studied the falls of Egyptian dynasties. ‘It’s not “a volcano erupts and a society goes to hell.” ‘ But the challenge is worth it, he said. ‘We hope in the end that we get better history out of it, but also a better understanding of what’s happening to the Earth right now.’ …

“Joseph McConnell, a climate scientist at the [Desert Research Institute in Reno, Nev.], and his collaborators are in the business of looking for debris [from long ago eruptions]. …

“Volcanic ash, more generally known as tephra, sometimes hides in ice. It’s a special find because it can be geochemically tied to a specific volcano. … The ice also carries a time stamp. Dr. McConnell and his colleagues look for variations in elements like sodium, which is found in sea spray that’s seasonally blown inland. By simply counting annual variations in these elements, it’s possible to trace the passage of time, Dr. McConnell said. ‘It’s like a tree-ring record.’

“Dr. McConnell and his collaborators recently analyzed six ice cores drilled in the Arctic. In layers of ice corresponding to the early months of 43 B.C., they spotted large upticks in sulfur and, crucially, bits of material that were probably tephra. The timing caught the scientists’ attention. Researchers have previously hypothesized that an environmental trigger may have helped set in motion the crop failures, famines and social unrest that plagued the Mediterranean region at that time. …

“Gill Plunkett, a paleoecologist at Queen’s University Belfast, set out sleuthing. After extracting 35 pieces of tephra from the ice, she pored over the rock chemistry of likely volcanic suspects. Nicaragua’s Apoyeque. Italy’s Mount Etna. Russia’s Shiveluch.

“But it was Okmok, a volcano in Alaska’s Aleutian Islands, that turned out to be the best match, at least on paper. Sealing the deal would require testing two tephra samples — one from the ice and one from Okmok — on the same instrument.

“Dr. Plunkett arranged for a tephra handoff at a conference in Dublin. A colleague from the Alaska Volcano Observatory, Kristi Wallace, packed four bags of Okmok tephra in her carry-on luggage. The match was spot on, Dr. Plunkett said. …

“This eruption was one of the largest of the last few millenniums, Dr. McConnell and his collaborators concluded, and the sulfate aerosols it created remained in the stratosphere for several years. These tiny particles are particularly good at reflecting sunlight, which means they can temporarily alter Earth’s climate. …

“There’s good evidence that the Northern Hemisphere was colder than normal around 43 B.C. Trees across Europe grew more slowly that year, and a pine forest in North America experienced an unusually early autumn freeze. Using climate models to simulate the impact of an Okmok eruption, Dr. McConnell and his collaborators estimated that parts of the Mediterranean, roughly 6,000 miles away, would have cooled by as much as 13.3 degrees Fahrenheit. … Rain patterns changed as well — some regions would have been drenched by 400 percent more precipitation than normal, the modeling revealed.

“That climate shock came at precisely the wrong time, Dr. [Jessica Clark, a historian of the Roman Republic at Florida State University] said. ‘This was a period of Mediterranean-wide political, social and economic upheaval.’

“These cold, wet conditions would have almost certainly decimated crops, Dr. McConnell and his colleagues said. Historical records compiled by Roman writers and philosophers note food shortages and famines. … For a society already reeling from the assassination of Julius Caesar the year before, such trying conditions might have exacerbated social unrest, the researchers concluded. They might even have kick-started transfers of political power that led to the rise of the Roman Empire.

“ ‘It’s an incredible coincidence that it happened exactly in the waning years of the Roman Republic when things were falling apart,’ said Dr. McConnell, who published the team’s results in Proceedings of the National Academy of Sciences.”

This was a long, fascinating article. For additional details, including details about the effects of distant volcanic eruptions on the Nile River in Egypt, click here.

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