The island was called Calliste, then Thera, now Santorini. The only big eruption in human times was about 199 BC. The caldera that is now the bay formed in an eruption at least 10s of 1000s of years ago. Nothing whatever to do with Atlantis, or with the end of the Palace-building period of the Minoan civilization.
https://freerepublic.com/focus/chat/4294521/posts?page=22#22
https://freerepublic.com/focus/chat/4294521/posts?page=17#17