The caldera is composed of overlapping shield volcanoes, cut by at least four partially overlapping calderas, of which the oldest southern caldera was formed about 180,000 years ago. The subsequent Skaros caldera was created about 70,000 years ago, and the Cape Riva caldera about 21,000 years ago. The current caldera was formed about 3600 years ago during the Minoan eruption.