Chaos and conflict roiled the Mediterranean in the first century B.C. 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 on Monday 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.”
Roughly 1,500 volcanoes are potentially active right now, meaning that they’ve erupted at some point in the last 10,000 years. While scientists today have sophisticated tools to monitor volcanoes, the vast majority of historical eruptions have gone unrecorded, at least by modern scientific instruments. Sussing out those eruptions requires patience and ingenuity, and a willingness to manage a lot of ice.
At the Desert Research Institute in Reno, Nev., it’s not unusual to find researchers in puffy parkas and wool hats handling chunks of ice in a minus 4 Fahrenheit “cold room.” Ice cores, typically drilled vertically from glaciers, hide bits of volcanic material that rained down from long-ago eruptions within their layers.
Joseph McConnell, a climate scientist at the institute, and his collaborators are in the business of looking for that debris. Using an instrument they designed and built, they melt the ice and pipe the water into an array of sensors. With hundreds of feet of tubing, the setup looks downright chaotic, but it’s exquisitely sensitive. The sensors pinpoint many substances, including about 30 different elements, and they do so by catching just tiny whiffs.
“They have sensitivities of parts per quadrillion,” Dr. McConnell said.
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 tephra comes from the magma itself,” said Michael Sigl, a chemist at the University of Bern in Switzerland who collaborates with Dr. McConnell. “It carries the composition of the rocks.”
Sulfur is also indicative of a past eruption. Sulfur dioxide, a gas commonly belched by erupting volcanoes, reacts with water in the atmosphere to create sulfate aerosols. These tiny particles can linger in the stratosphere for years, riding wind currents, but they, like tephra, eventually fall back to Earth.
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. But until now, “There hasn’t been the kind of data that these scholars brought forth to really get those theories into the mainstream,” said Jessica Clark, a historian of the Roman Republic at Florida State University who was not involved in the research.
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. “There are some events that are tricky. With Okmok, there’s nothing else that looks like it.”