When the Athenian lawgiver Solon visited Egypt in the sixth century BC, scribes there told him of the disappearance of an ancient civilization thousands of years before. This civilization (as reported by Plato in his Critias) comprised two islands, one long and one round ("Strongyle" in Greek), united by a common culture and one rule. The ancient Minoan culture originated on the long island of Crete and had a strong presence on Santorini as well, centered around Akrotiri in the south of the island. This civilization thrived from about 3000BC until after 2000BC. They traded all around the Mediterranean and created technological advances not seen again until thousands of years later (hot and cold running water and flush toilets, for heaven's sake!). At the time of the Minoan culture, Santorini was round; its outline can still be seen today in the present islands of Santorini and Therasia.
The Egyptian scribes also told Solon of the lost land of Atlantis, made of red, white, and black volcanic rock (all found on Santorini). They said that the city of Atlantis vanished in a single day. Could this have been the Minoan center on Santorini?
Somewhere between 1650 and 1500BC, the volcano on Strongyle, the island that would become Santorini, erupted, blasting the entire center of the island away, and creating the caldera we now see. The town of Akrotira was buried under as much as eight meters (27 feet) of volcanic debris, which has preserved the town on a scale comparable to Pompeii, but much older. The eruption left a thick layer of volcanic ash on the seabed southeast of Santorini, covering an area of more than 900 by 300 kilometers. In Crete, only 110 kilometers away, volcanic tephra from three to twenty meters thick covers some Minoan sites.
But the volcanic tephra that fell on Crete was probably not enough to destroy the civilization there. More likely, it was the tidal wave that did it. To understand the size of this event, we can compare it to Krakatoa. The explosion of Krakatoa in 1883 was heard three thousand miles away in Australia. It created a caldera with an area of 8.3 square kilometers. The resulting tsunami tidal wave was over two hundred meters high, destroying everything in its path for over 150 kilometers. By comparison, the caldera created by the explosion at Santorini is 22 square kilometers--almost three times as big. The estimated DRE (Dense-rock equivalent) of the Minoan eruption is more than 60 cubic kilometers (14 cubic miles)--more than four times as much as that of Krakatoa. The tidal wave from the Santorini eruption is estimated, when it reached Crete, to still be between 35-150 meters (115-492 feet) high. Minoan civilization was utterly destroyed.
According to Wikipedia, the plume from the eruption added sufficient particulates to the atmosphere to reduce temperatures around the world. By affecting atmosphere and crops, it may have contributed to the fall of the Xia dynasty in China.