Well we can assume Old Hyrule was once a mountain realm due to the world being flooded thanks to Ganondork. So i'd say New Hyrule would be a relatively fresh land not to old obviously. THe fact remains though was it once a massive mountain or a conglomeration of them?
From what we've seen in the geography of OOT - TP the land seems to move in a more Northerly direction, judging on where the master sword ends up and the temple of time. I'd say eventually climate change and forest growth would have forced this but i can't really confirm it. I'd imagine the Lake...