Ice core records from the Arctic show that Alaska’s Okmok Volcano had a massive eruption in 43 BCE. Following the eruption, there was an abrupt cooling globally, which led to crop failures, famine, disease, and eventually, social unrest. The Mediterranean region was no exception to this.
Such a shift in climate, coming a year after the assassination of Caesar, would have put great pressure on local powers. Strain was also felt in Egypt.
Okmok has a very active history. At one time, it had a 150 meter deep lake in its crater. A notch in the rim eventually drained the lake, although some small remnant lakes remain near cones B & D.
The eruptions of Okmok 8300 and 2050 years ago earn a Volcanic Explosivity Index rating of 6, which puts it on par with Novarupta and Krakatoa.
On 12 July 2008, Okmok erupted without warning, sending ash 50,000 feet into the air. It erupted continuously for almost six full days, causing transportation problems in the air and on the water for the region. That eruption was ranked a 4 VEI, which is considered “cataclysmic”.
Back to 43 BCE. The decade following the eruption was one of the coldest in a millennia, with 43 and 42 BCE being some of the coldest years. It is believed that a temperature drop of 7C from normal was a result of the volcanic eruption on the other side of the globe.
The full, scientific report can be found here: