Kaymo the novelist replies to the previous post...

Most likely it just an "excursion"-- a massive tongue of superheated core material, heavy with iron, that's working up into the Mantle. But, it could be the beginning of a reversal. In which case compasses aren't gonna work very well for a few thousand years. We'll have lots of "little poles" and they'll migrate around etc. If that had happened during the 16th century etc. I think we might all still be in Europe, and the Injuns would have been left alone to get on with it.