Did volcanic eruptions spark revolts in Ancient Egypt?

The Ptolemaic Kingdom was a prosperous time in Egypt’s ancient history, nearly three centuries from 305 BC to 30 BC that for all intent and purposes ended with the reign of Queen Cleopatra VII (69-30 BC). Yes, I know, her son Caesarion ruled Egypt for just two weeks after Cleopatra's death before he was murdered by the Romans.

[Yearly flooding of the Nile]

But during that Ptolemaic Kingdom there were several bloody Egyptian revolts against the ruling Greeks. A team of historians and climate scientists say that the unrest and uprisings may have been tied to volcanic eruptions that triggered climatic changes[1].

When large volcanoes erupt, they spew large quantities of ash and sulfur high into the stratosphere. There, the sulfur oxidizes into sulfate aerosols that reflect sunlight back to space, reducing evaporation on the planet’s surface. This in turn may suppress monsoons, diminishing the annual floods of the river Nile and leading to food shortages in Egypt.

[Variation in water levels of the Nile]

But to establish a connection between volcanoes and revolts in ancient Egypt, the team first had to determine the dates for when the volcanoes erupted.

They began by looking at ice core data from Greenland and Antarctica, which contain trapped sulfur from ancient volcanic eruptions. The scientists then turned to papyrus records to figure out when the Nile River failed to flood as usual. But these records from the Ptolemaic period were all qualitative, not quantitative. So, the team turned to the Nilometer record, which contains measurements taken by large instruments built during Egypt’s early Islamic period to monitor the Nile River’s annual flood level.

[Nilometer]

The Islamic Nilometer was constructed in 622 AD. In 1902 the Nilometer only became obsolete because of the completion of Aswan Low Dam. The scientists looking at ice core data identified 61 eruptions between those years. On average the Nile flood level was nearly 22 centimeters lower during eruption years, the team discovered.

After confirming a link between volcanic eruptions and poor Nile flooding, the team then matched the dates of Ptolemaic eruptions with papyrus records of well-known rebellions. They found that eight out of ten large uprisings happened within two years of a volcanic eruption.

[1] Manning et al: Volcanic suppression of Nile summer flooding triggers revolt and constrains interstate conflict in ancient Egypt in Nature Communications -2017