Our eruption history guide covers what happened and when. This page is the plain-language version of what that eruption actually left behind — the specific things you'll notice looking at the cliffs, beaches and rock as you get around the island.
Why the caldera cliffs look striped
The layered, almost stacked-pancake look of the cliffs below Fira and Oia is a direct record of past eruptions — each distinct band is a separate layer of ash, pumice or lava from a different volcanic event, stacked over hundreds of thousands of years. The thick, pale band visible for much of the caldera's height is ash from the massive Bronze-Age eruption itself.
Why the beaches are three different colours
Beach colour comes directly from the rock nearest each beach: black sand (Kamari, Perissa) comes from basaltic lava; red sand and cliffs (Red Beach) come from oxidised, iron-rich volcanic rock — essentially rusted; and the pale cliffs at White Beach and Vlychada are eroded volcanic ash and pumice, naturally light in colour. See our beaches guide for where to find each.
What pumice actually is
The light, porous, almost floating rock you'll see scattered around parts of the island (and sometimes sold as souvenir chunks) is pumice — volcanic rock that cooled so quickly, with gas still escaping, that it froze full of tiny air pockets. It's the same material, at a finer grade, that makes up much of the island's pale volcanic soil.
The caldera itself
"Caldera" specifically refers to the large, roughly circular depression left when a volcano's chamber empties in a major eruption and the ground above it collapses — as opposed to a crater, which is a smaller feature formed by a single explosive vent. Santorini's caldera, now flooded by the sea, is one of the largest and most dramatic examples in the world.
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