One Day and One Night
Earthquakes and floods strike, and in a single day and night the island of Atlantis sinks into the sea.
Soon after the war, about 9600 BCE by Plato's count
What the text says
But afterwards there occurred violent earthquakes and floods; and in a single day and night of misfortune all your warlike men in a body sank into the earth, and the island of Atlantis in like manner disappeared in the depths of the sea.
Timaeus 25c-d
For which reason the sea in those parts is impassable and impenetrable, because there is a shoal of mud in the way; and this was caused by the subsidence of the island.
Timaeus 25d
when afterwards sunk by an earthquake, became an impassable barrier of mud to voyagers sailing from hence to any part of the ocean.
Critias 108e
The story
After the war comes the end. Violent earthquakes and floods strike. In one terrible day and night, the army of Athens sinks into the earth, and the whole island of Atlantis slides beneath the sea.
What is left is mud. The priest says the sea out there can no longer be crossed, because the sunken island left a shallow bank of mud in the way.
Plato does not say whether anyone escaped Atlantis, or what happened to its people. In the Critias, Plato adds that Athens too was changed by floods, and that its hills lost their soil until only 'the bones of the wasted body' were left.
Plate tectonics rules out a lost continent sinking in the Atlantic in the recent geological past; the sea floor there is young rock spreading out from the Mid-Atlantic Ridge. Real lands have drowned, though. Doggerland, between Britain and Europe, was slowly covered by rising seas between about 10,000 and 7,000 years ago, and a tsunami from the Storegga slide off Norway hit it about 8,200 years ago. Around 1600 BCE a huge eruption blew apart the island of Thera (Santorini) and buried the town of Akrotiri; the archaeologist Spyridon Marinatos, who later excavated Akrotiri, suggested the eruption may lie behind the Atlantis tale. These are theories about what might have inspired Plato, and none of them sank in a single day 9,000 years before Solon.