In reply to GrahamD:
> Of course there must be a 500 tonne block to be shifted first
Quite possible that there'll be no trace of the fallen block at all - the sea's a powerfull thing.
I remember seeing Bishop's Rib at Chair Ladder after the significant block had come off the first pitch many years ago; thought there's a rock trench below which should have caught it, where's the fallen block - not a smidgen of a trace - totally just gone.