Volcanic eruptions halfway around the world may have contributed to revolt in ancient Egypt

Atmospheric changes suppressing the Nile’s summer flooding likely contributed to societal revolt.

In a new study, researchers show a connection between volcanic eruptions and Nile flood suppression, which may have contributed to the demise of Ptolemaic Egypt (305–30 BCE). Ptolemaic Egypt relied heavily on the Nile’s annual summer flooding for its agriculture, so any disruptions could have contributed to societal unrest. We spoke with two of the study’s authors Francis Ludlow and Joseph Manning about the work.

ResearchGate: What originally motivated this study?

Francis Ludlow: I’m a climate historian, and I concentrate on how we can extract information on past climate conditions from both natural archives like tree-rings or ice-cores, as well as written records and archaeological evidence. As part of this, I am always trying to act as a bridge between natural scientists and historians.

I had moved to Yale in 2014 to pursue this type of work and met Joe Manning, an international expert on Ancient Egypt. Joe was speaking about the dates of major events in Ptolemaic Egypt, particularly the dates of major revolts against the Ptolemaic kings of Egypt, and how the motivations behind these are not very well understood. I realized that many of them were also the dates of major volcanic eruptions based upon work I’d done with Michael Sigl creating a record of volcanism from polar ice cores. So Michael and I started collaborating with Joe, and more and more of the dates he independently provided us for big historical and social events in Egypt seemed to line up with the dates of volcanic eruptions.

We already knew that Egyptian agriculture was almost wholly dependent on the summer flood of the Nile. So it seems logical to hypothesize that very poor flooding of the Nile driven by volcanism could lead to poor harvests and increased social tension in Egypt. When other social and economic conditions were right, including high levels of taxation and other pressures, this could be enough to trigger a revolt.


“I realized that many of them were also the dates of major volcanic eruptions.”


RG: Can you briefly explain the importance of the Nile’s annual flooding to the Ptolemaic dynasty.

Ludlow: The Nile was absolutely critical for Egyptian agriculture. Once you go inland from the Mediterranean, the average precipitation levels fall to effectively zero, so all water comes from the Nile. And in years in which the summer floodwaters did not overflow the Nile's banks, the soil would stay dry and the crops would most likely fail.

Manning: The Ptolemies were established in Egypt after Alexander the Great’s conquest. The dynasty established a new political regime and new economic institutions like coinage and banking. Another major change for them was their apparent shift to greater free-threshing wheat production. This was the preferred grain for bread among Greeks. But it may have been a bad idea in the light of frequent Nile flood failures, since it is less resilient in drought conditions.

RG: Where did the eruptions occur, and how did they affect the Nile?

Manning: The eruptions could have occurred anywhere globally, but it appears that high latitude northern eruptions—volcanoes in Iceland and Alaska for example—had stronger impacts on the African monsoon, which was the driver of the annual flood of the Nile.

Ludlow: One reason for reduced precipitation from a volcanic eruption is the surface cooling that occurs when large quantities of sulfurous gases are injected into the stratosphere. The gasses oxidize and form tiny particles, or sulfate aerosols. These aerosols reflect incoming sunlight back to space, meaning less energy reaches the earth's surface. So we have cooling, and where we have cooling, we also have less evaporation and less potential for rainfall.


“The twentieth and twenty first centuries have been relatively quiet in terms of major explosive eruptions. But that could change at any time.”


RG: How did these disruptions to the Nile affect the Ptolemaic dynasty?

Manning: Over time, the eruptions may have played a role in weakening the political system. We don't always know if Nile flood failures led to food crises. In many cases though, a Nile failure may have caused widespread panic.

Ludlow: The empire ended in 30 BCE, with the death of Cleopatra, the last Pharaoh and Ptolemaic king, through her suicide shortly after losing to the Romans led by Octavian at the naval battle of Actium in 31 BCE. It seems conspicuous, however, that the third largest eruption of the past 2,500 years occurred in the preceding decade, in 44 BCE, compounding the impact of an earlier event in 46 BCE. We also know of many troubles experienced by Egyptian society in the 40s BCE, including famine, disease, and land abandonment. Cleopatra did take, it seems, effective relief efforts with the opening of royal granaries and other measures, and unlike many of her predecessors did not experience revolt against her rule at this time. But it is hard to avoid the conclusion that the impacts of the 40s BCE did not weaken her position against Rome.

We are not claiming that the volcanic impacts on the Nile simply caused revolts. Environmental pressures don't act in a vacuum. Instead, what is likely to have happened is that the pressures from poor flooding coalesced at certain points of time with political and economic factors that included ethnic tensions and high levels of taxation levied by the state to trigger revolt. And in fact, you could see Ptolemaic Egypt as a success story. Certainly, they were hit by these eruptions, and political instability did follow. But they also managed to survive many big eruptions for a long period of time.

RG: Is there anything today’s governments can learn from the fate of Ptolemaic dynasty?

Ludlow: It's worth noting that the twentieth and twenty first centuries have been relatively quiet in terms of major explosive eruptions on the scale experienced in past ages. But that could change at any time, not only with another big eruption, but with closely recurring sequences of big eruptions. With around 70 percent of global population now in monsoon or monsoon-dependent agricultural regions, it's likely that eruptions will cause agricultural strain. For the Nile in particular, with tensions already high regarding the sharing of water from the Blue Nile between Ethiopia, Sudan and Egypt, the possibility of diminished supplies following the next big eruption needs to be included in any water sharing agreements.

Featured image: "The Battle of Actium, 2 September 31 BC" by Lorenzo A. Castro.