Lava lamp earth

Earth's Magnetic Field - Flipping and Lava Lamps

In this article the author writes that flipping of the earth's magnetic field may be caused by recently discovered "large-low-velocity-provinces" or "blobs" at the junction of the earth's core and mantle. These have been discovered by study of seismic oscillations caused by major earthquakes. 

As she writes :-

These regions might be less dense simply because they are hotter. But an exciting alternative possibility is that the chemical composition of these parts of the mantle cause them to behave like the blobs in a lava lamp. This would mean they heat up and periodically rise towards the surface, before cooling and splashing back down on the core.

Such behaviour would change the way in which heat is extracted from the core’s surface over millions of years. And this could explain why the Earth’s magnetic field sometimes reverses. The fact that the field has changed so many times in the Earth’s history suggests that the internal structure we know today may also have changed.

We know the core is covered with a landscape of mountains and valleys like the Earth’s surface. By using more data from Earth oscillations to study this topography, we will be able to produce more detailed maps of the core that will give us a much better understanding of what is going on deep below our feet.

I knew staring at these wasn't just a waste of time!