How was Atlantis actually destroyed?
By means of the giant cataclysm we call the Flood. The views on the Flood — and indeed on global cataclysms in general — has been grossly misstated by geologists ever since the times of Darwin and Lyell. Cataclysms of huge proportion range up to the Big Bang, and are a central feature of Evolution itself. They have occurred by the thousands on earth in the past, and are amply attested in the geological records, along with the extinctions of Life that they caused along time. Quite often they are caused by meteoritic/planetary impacts of extra-terrestrial origin. Far more often, they are caused by the cataclysmic endings of the Ice Age Episodes which have occurred fairly regularly at intervals of 30,000 years or so. The Flood was indeed caused by one such, and is just the last of a long series of similar cataclysms of global proportions. As many myths describe it, the Flood was caused by a giant submarine volcanic explosion that stirred up the seas, sending them over the continents. So,
