I think something that many conservative interpretations of the Flood will miss out on is that to the ANE writers and readers Earth was all they had. To put it pithily, they didn't have "Earth first - we'll stripmine the other planets later" bumper stickers. The global vs. local flood debate is often framed (unconsciously) by the Copernican worldview that the Earth is just one small tiny dot lost in a wash of stars and empty space, and that the important issue at hand is whether that tiny dot was all pale blue or only half so.
To the ANE though, the destruction written of in Genesis 6-8 was not just global, it was universal, cosmic even. Every locale in nature plays its part: the firmament gushes forth, the floodgates of the deep open, and the earth in the middle becomes thoroughly deluged. The creations of day 2, when the firmament was appointed to hold up waters above the sky, and day 3, when the sea (and by implication the deep) was constrained from flooding the land, have been undone. No human flood we see today poses such an affront to us because, even were we to see a global flood, we would think of it as just one watery planet among many. To the ANE however the flood was nothing less than God, angry at sin, threatening to "destroy the universe". (Finally that stock phrase has a use worthy of its magnitude!)
Was struck by these thoughts after having read T.F. Torrance's Divine Order and Contingence (a fantastic book, if a little dense). He says that the creation depends contingently (a sort of "independent dependence") on God. Namely, that creation has no "right" per se to exist, that it is held up completely and totally at all times and places by God's affirming decree, and that were God to rescind this favor at any time creation would simply collapse in back on itself into nothingness. Thus it depends on God. However, the very nature of God's affirming decree is that God has made the universe such that it possesses a rationality and reality all its own. It is really something existing separate from God with rules and reasons that it plays out with its own integrity. Thus it is independent from God - although that very independence is really part of God's creative decree on which its very existence is dependent in the first place. Thus contingence (or in everyday parlance, the fact that science can determine and predict the limiting workings of the universe without directly postulating the hand of God) has both a direction oriented towards God and a direction oriented away from God.
Sin, to Torrance, unhinges the direction of contingence that points away from God. It encourages us to see the universe purely as something that has its own rationality and its own existence, not as something dependent on God. And the Flood is a direct and fitting punishment for such designs. The processes operating in the Flood are natural, though exaggerated. Of course they are decreed by God (all things in creation are, both "natural" and not), but within the limits of God's decree it is seen that the Flood is just rain writ large, just the sea a few miles higher. When man overturns God's moral decrees, God allows His own physical decrees to be overturned for a while. When man tries to morally live without God, God gives creation a test to see if it can even physically exist without His creative, separative decrees of order.
Clearly it cannot, as creation threatens to collapse right back into the deep nothingness it was in Genesis 1:2. Natural forces gone wild punish and destroy humanity gone wild. And when God reinstates order and sets His rainbow in the sky, it isn't just a promise about ocean height. It is a promise to keep the very fabric of reality intact, even though humanity is hell-bent on turning the independence of contingency against God. It is a promise to keep the stars in their tracks as much as to keep the Earth dry; it is a promise not just for terrestrial beings but for all creation.
