cut for spoilers
I just thought of something. Granted, I haven't been doing much message board surfing so maybe there's already a brilliant explanation for this. But really, in the flashsideways we saw that the island was sunk at the bottom of the ocean. Why?
The flashsideways was a sort of almost-afterlife/limbo created by the Losties so they can meet up with each other. I thought that maybe a sunken island a part of their fantasy world, a part of their desires or something that would help them get over their issues and give them closure. But then, isn't the flashsideways limbo in an of itself, and it's the CHURCH that was created by the Losties so they can all move on together? In that case, is this also the island's afterlife? If the island is a life force in and of itself, maybe the island goes through limbo like everyone else before 'moving on'. In which case its closure would be to be sunken at the bottom of the ocean because too many people use it for evil means etc. etc.
Okay that last one is pretty cracky.
But seriously, was it ever explained why the island is at the bottom of the ocean at all? What do you think is going on?