A physical pole reversal (as opposed to magnetic pole reversals that DO happen) would require the earth to start spinning in the opposite direction, clockwise as seen from the north pole. The earth is massive, and spins a thousand miles an hour at the equator. It has a tremendous amount of rotational inertia. If this happened, the motion of every molecule on earth would have to stop. Where would all that one-half emm-vee squared kinetic energy go? It would have to be transformed into heat by friction.

I haven't bothered to figure it out, but I'd bet the whole crust would become molten well down into the mantle. Not only is it not likely to happen, it probably has never happened before, not since the moon was formed, anyway. If there was any life on earth when an event like that happened, not only would it be sterilized, but even all fossil evidence of it would be vaporized.

As for the magnetic/volcanic link, I don't know the answer to that. The two may have nothing to do with one another, for all I know. I've always understood the magnetic field was generated deep within the mantle, or even in the core, way below the level of volcanic activity, but that sounds like a Podrock problem to me..

I also suspect magnetic pole flips are rather gradual events, they may take decades, or even centuries. Their biggest physical consequences may be disruption of the magnetosphere, which might make us vulnerable to solar and cosmic radiation. Another possible extinction mechanism?