Deucalion starts out like most of the flood myths, with humanity doing something bad. Wicked, uncivilized behavior is the norm, and so Zeus needs to eliminate them. But while the Incan and Biblical stories show the ones responsible for the flood (the Incan gods and God, respectively) giving warning of the impending flood, that is not the case, here. Prometheus, instead, warns his son Deucalion, directing him to build a chest in which to safeguard himself and his wife Pyrrha from Zeus’s flood.
For nine days they are in the water in this chest, until they land on a mountain. Some believe it to be Etna, others Parnassus, but the result is largely the same, a sacred mountain to the culture.
The story takes a weird twist, now, as the means of repopulating the earth is not what would be expected given the Greek creation story. Instead of repopulating the old-fashioned way, as would be expected, Deucalion and Pyrrha—at the advice of an oracle—throw “the bones of the Earth” over their shoulders. The stones thrown by Deucalion become men, whereas the ones thrown by Pyrrha become women. Now, the why of this is left unsaid, but there are some interesting guesses that can be made. First is that Prometheus first made man from clay, so to go back to the bones of the earth is to make man from the original material again. This myth takes place well after the myth of fire and Pandora, since she was the first woman ever. And from this we know that Prometheus has either been released from his torment or he is able to speak great warnings. Given that Hercules is supposed to release Prometheus, and that the flood takes place well before Hercules, it is likely that Prometheus can make himself heard to people from his place of punishment.
Now, the chest is an interesting idea. It’s not a ship or a raft, but a chest, something for protecting precious items. Granted, it is a chest large enough for two people to survive for nine days, but it is still a chest. It would be tempting to draw more parallels to the myth of Pandora, but we know that her vessel was a jar and not a box as it is usually described. The chest, most likely made of wood, would be ideal for floating in the sea, but a clay jar would not hold up. It’s too fragile and heavy, especially with the weight of two people in it.
Now, like the myth of fire and Pandora, we have Zeus stepping into the role of the bad guy. He brings the flood, and stands as someone largely uninvolved, but there are two very important ideas that point to Zeus having an involvement. First, since he sent the floods, and has a birds-eye view of Earth, he would be in a position to see Deucalion’s survival. Now, it is possible that Zeus had no direct knowledge of their survival, since he is not omniscient.
However, after Deucalion and Pyrrha leave the chest, they give thanks to Zeus and consult an oracle of Themis. Themis is a consort of Zeus. Not only that, Zeus shares in the gift of prophecy, and so would not be in the dark about this event. Once again, Zeus gives a tacit approval of the situation. To avoid the perception of weakness, he can’t be seen to be invested in humanity’s continuance, but he can allow them to survive so long as his own hand is not seen overtly. This would explain how Prometheus is allowed to warn Deucalion, too, since he is Zeus’s . . . guest while chained to a rock.
And like with all flood myths, there is the establishment of a moral code. Zeus, by allowing Deucalion to live while destroying others, establishes what the correct behavior for humanity is. This is particularly important given the knowledge myth, where it’s established that, despite the idea of fate, humanity must still make choices regarding their lives, and are held to a standard in which they must use the divine gift of fire in the right way. Thus far, they have not.