Earth Crust Shift

I read somewhere that the crust of the earth can shift all as a unit like the skin of an orange. It seems that when the ice builds up on the poles the weight causes the crust to break free of the core and slip around. They didn't say what caused the force, but it seems to me it has to be the turning of the earth. Just like a spinning top can do a lot of funny moves.

Now one thing has made me ponder for a number of years. On the sea bed there are cracks in the earth where liquid earth core comes up. From looking at this rock we can tell that the magnetic poles of the earth have reversed a number of times in the past.

Lets say that this process takes a few 100 years. That is, from the time the ice builds up enough for the poles to start going toward the equator, until the crust again stops moving.

Now my question to you is this. Where do the poles stop? Half way around the earth at the equator? Or just a little way from where they started? Or has the ice melted away by the time the poles got to the equator so that the crust again has the weight distribution it had before this whole process started, and thus continues right on past the equator to again be at the pole. Only this time it is the opposite pole.

I like this last one because it explains how the crust of the earth could show marks that the magnetic poles of the earth have reversed.