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 before the present era ( BP ) . The subsequent Skaros caldera was created about 70,000 years BP , and the Cape Riva caldera about 21,000 years BP . The current caldera was formed about 3600 years BP during the Minoan eruption
Minoan eruption
Minoan eruption
Santorini caldera