Volcanoes Have Shaped Human History Since the Beginning

It's difficult to imagine that a volcano erupting clouds of rock and ash into the skies above Alaska's Aleutian Islands could influence goings on in ancient Rome.

But that's exactly what a team of scientists say happened. A new paper published June 22 in the Proceedings of the National Academy of Sciences claims that the 43 B.C. eruption of Okmok volcano spurred climatic changes that led to the fall of the Roman republic and, subsequently, the rise of the Roman empire.

During an eruption, a volcano can belch out millions of tons of ash and sulfate aerosols into the atmosphere. They can blot out the sun and, in the short term, dramatically cool down the global climate, often leading to devastating crop losses, famine, and disease. These aerosols also become trapped in ice, providing scientists with a critical window into the world's climate history.

Researchers probed ice cores and found samples of volcanic ash and sulfur. They tried to match these samples with rocks from Russia's Shiveluch volcano, Italy's Mount Etna, and Apoyeque in Nicaragua. Okmok volcano's eruption in Alaska, however, matched perfectly. “It’s an incredible coincidence that it happened exactly in the waning years of the Roman Republic when things were falling apart,” climate scientist and study co-author Jospeh McConnell of the Desert Research Institute in Reno, Nevada, told the New York Times.

Over 1,500 volcanoes around the world have been active in the past 10,000 years. Okmok isn't the only volcanic eruption to have played a central role on the world's stage. Here are seven other volcanic eruptions that changed the course of history.