That's a timely posting for me personally as I was just looking into the prevalence of flood myths around the world. Apparently there are indeed hundreds of them. Given this, it only makes sense to at least entertain the idea that perhaps, just maybe, they're based on something that actually happened.

A friend of mine recently brought to my attention the underwater 'ruins' of Yonaguni, which lie just over 100KM east of Taiwan (see pic below). When I look at the images of these underwater structures, they do look absolutely man-made to me. Having said that, I'm not a diver so perhaps such formations are common. Still...

You can research Yonaguni easily enough. The one thing that bothers me about this particular case is that people seem to get emotional about it, taking sides, leading to a lot of very unscientific information. For example, some sites that post Yonaguni pictures and videos go on to speculate about aliens, while scientists who discount Yonaguni appear to be overly invested in a scientific model that, if they were to refute or question, would call into question everything they've been taught and taught for decades. But still, the structures are there.

Moving on, there has been an increasing body of evidence that the American continents have been populated by humans for much longer than I was taught, and that migration to what is now North and South American has been going on for at least tens of thousands of years by boat. We were always taught that a few strong souls followed deer over an ice bridge from Asia. Right. If we were deep sea fishing 50,000 years ago, we clearly knew how to sail. (See http://www.livescience.com/17186-oldest-fish-hooks-early-humans.html.) There has been a number of finds in the Americas of human activity reaching back over 30,000 years ago.

So, with regards to flood myths, it's becoming clear to me that during earlier ice ages, the ocean level would have been much lower, and the land masses greater. During one or more of these periods, people may have built huge structures, entire cities, entire civilizations even, on land that was flooded when the ice melt, and it may have melt relatively quickly. Volcanic activity, a meteor, or whatever could have started a chain reaction that melted an enormous amount of ice in a matter of years or even months, leading to floods across the globe.

So, this is an exciting area of inquiry, but scientist get extremely rooted in their models and they guard them jealously.

EDIT: The information I've seen on Yonaguni suggests that it may have been built after the last glacial period, not ice age. (See http://en.wikipedia.org/wiki/Last_glacial_period). The last glacial period ended about 18,000 years ago. Still, if people built the structures of Yonaguni, this would have been far, far before we thought people were capable of building anything. We were supposedly living in caves at the time.

A photo of Yonaguni structure. Not only is it hard to imagine this as being a natural formation (thought it's certainly possible), it's striking how man-made it looks.