Case in point: Flood legends I think that was due to humans handing down stories of land flooding that happened in the Northern Hemisphere as the glaciers melted from the last major Ice Age. It's likely that during the last Ice Age there were a good number of lakes formed by glacier-related ice dams, and when those dams broke the result was land flooding on a massive scale.
The best story is that is a remembered relic of the Black Sea flood. At one time there was no opening in the Bosporus connecting the Black Sea to the Mediterranean Sea. The Black Sea was a small inland lake like the Caspian Sea and at a far lower level. But as the Mediterranean Sea rose from glacial melting eventually it broke through the land barrier and started a MASSIVE flood that caused the Black Sea to rise enormously. It was highly settled around its shores so this would have caused a large migration of people as the settlements around the shores flooded.
http://www.nationalgeographic.com/blacksea/ax/frame.html
And if you want to go even father back, the Mediterranean Sea was blocked off from the Atlantic Ocean at one time and it too flooded.