Well, based on some things the sand people were going on about, humans were very busy fucking and making more of themselves, in part to mine that rock and...serve (?) were making way to much noise and making the "gods" nervous. Probably thought there would be another revolt. Anyhow, they decided to flood the planet. Where the amount of water for this came from is debatable, but basically, they figured their chimeras could not swim. However, one "god" did not want the project to go to waste, and convinced Noah, Atrahasis, Deucalion, etc. to build a craft that could ride the storm out. What really happened? Probably Younger Dryas impact near Canada did fuck all to the ice and parts may have struck nearby.