Catastrophe: Vesuvius and Thera/Santorini

The eruptions of Vesuvius and Thera are possibly the best known volcanic events from antiquity in Europe. Millions every year visit the sites at the Bay of Naples and on Santorini. But what was their wider effect of these eruptions, Thera is often credited with the fall of the Minoan civilization, while Vesuvius appears to have had little effect on the wider Roman empire.

Are these assessments actually true? What does modern research tell us about the effect of these eruptions?