What purposes does the flood myth serve the ancient Greeks?

Answer 1

The same purpose it serves in any religious or mythological text; it provides a means to explain natural features, a thinning of population and a "clean slate" from which to establish the current relationship with the deity of choice.

The Greek Flood marks the end of the Bronze Age, the third of the five ages of Ancient Greek, according to myth. According to myth, Zeus made men from Ash Trees during this age, making them hard and firm. As a result, they were warlike and wicked, and in the end, Zeus destroyed them because they refused to acknowledge his greatness over theirs. The only survivors were Deucalion, son of Prometheus, and his wife, Pyrrha. They repopulated the Earth by tossing stones (the bones of their mother) over their shoulders; those he threw became men, and those she threw became women. And from them man learned to fear and revere the gods of Olympus. Thus began the Heroic Age.