A week of spectacular lava sprays on Sicily’s snow-capped Mount Etna, one of the world’s most active volcanos, has drawn thousands of people wanting to see the eruption.

Deep-seated mantle structures known as LLSVPs have been found to be over a billion years old, affecting tectonic activity.

Santorini, a volcanic island in the Aegean Sea, has been shaken by tens of thousands of mild quakes since late January, ...