Links from 2017-11-12
Because the ancient Egyptians were a farming culture that lived and died by the harvest, the annual Nile flood was key to survival. Floods meant nutrient-rich waters fed the fields and everyone could eat. Nile levels were so important to the Egyptian economy that the government based tax amounts on readings from "Nilometers," stone wells fed by the river where they could measure its height in cubits. If the levels were trending too high (destructive flooding) or too low (drought), taxes were scaled back to account for people’s diminished fortunes.
Years with low rainfall inevitably meant people wanted for more and had less to lose. Gripes with the government became full-scale rebellions, like the 20-year "Theban revolt" that started in 207 BCE and the "Egyptian revolt" against Ptolemy III between 245-238 BCE. Both came after periods of increased volcanic activity. Though many other factors were in play, there is an undeniable correlation between eruptions and rebellion against the Ptolemaic regime.