Although dormant, Santorini is an active volcano. Numerous minor and medium-sized, mainly effusive, eruptions have built the dark-colored lava shields of Nea and Palea Kameni inside the caldera.

The caldera of Santorini lies in the center of the Christiana-Santorini-Kolumbo volcanic field, which comprises the extinct Christiana Volcano, the Santorini Caldera, the polygenetic submarine Kolumbo Volcano, as well as the Kolumbo Volcanic Chain. This volcanic lineament evolved during four main phases of volcanic activity, which initiated in the Pliocene from several local centers that only recently matured to form the vast Santorini edifice. The present-day 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.

Palea Kameni and Nea Kameni were formed as a result of multiple, initially submarine, smaller eruptions at the center of the caldera.