The Roman Republic Was Teetering. Then a Volcano Erupted 6,000 Miles Away. - The New Yo... - 0 views
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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.
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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.
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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.
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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,
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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.
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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.”
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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.
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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,”
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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.”
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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.
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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.
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“It’s an incredible coincidence that it happened exactly in the waning years of the Roman Republic when things were falling apart,”
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That climate shock came at precisely the wrong time, Dr. Clark said. “This was a period of Mediterranean-wide political, social and economic upheaval.”
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Historical records compiled by Roman writers and philosophers note food shortages and famines. In 43 B.C., Mark Antony, the Roman military leader, and his army had to subsist on wild fruit, roots, bark and “animals never tasted before,” the philosopher Plutarch wrote.
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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.
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Rain patterns changed as well — some regions would have been drenched by 400 percent more precipitation than normal, the modeling revealed.
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The links in the study are probable, but not definite. “They’re not being heavy handed and saying this is absolutely it,” Dr. Holmberg said.
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Egyptian society, before the installation of the Aswan Low Dam in the early 20th century, was anchored by the annual summer flooding of the Nile River. These summer floods, sustained by monsoon rains in the highlands of Ethiopia, delivered irrigation and silt, both critical to Egypt’s agrarian society. “The whole rhythm of the year was built around responding to the flood,” Dr. Manning of Yale said.
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But volcanic eruptions, even those on the other side of the world, could have disrupted that flooding, Dr. Manning and his colleagues recently showed. Using records from Cairo’s Nilometer — an octagonal marble column that was used for recording Nile flood height from 622 to 1902 A.D., the team found that flooding tended to be weaker, or entirely absent, during years when there was a large volcanic eruption somewhere in the world.
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he culprit, the team reasoned in a paper published a few years ago, was cooling caused by sulfate aerosols. When Earth cools after a large eruption, its atmospheric circulation patterns change. That can shift the invisible meeting point of Northern and Southern Hemisphere trade winds — the Intertropical Convergence Zone — that affects where monsoon rains tend to fall. When less precipitation falls over Ethiopia, home to a major tributary of the Nile, there’s less water available for flooding that year.
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Ptolemaic-era records revealed that this reduced flooding had socioeconomic and political consequences. Revolts increased in the years following “Nile failure,” Dr. Manning and his colleagues found. Priestly decrees — intended to establish the political legitimacy of Greek rulers — also became more commonplace.
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Right now, roughly a dozen volcanoes are erupting. In all likelihood, they’re nothing to worry about — it’s doubtful you’ve even heard of them. But every once in a while, there’s bound to be a really big eruption. How its effects ripple around the world awaits to be seen.