Convection of the mantle is too simple to discuss. Heat from the core is carried upwards with magma flow. And it must circulate, up and down.
But the 3D model is harder to explain. The effect of rotation forces the convection to adhere to the plane of rotation. A fraction vector of the flow is also horizontal. Here on the drawing the path of the division line between the upwelling convection cells of lower mantle, and the relevant backflow are shown. It is of course also circulating around the globe.
Looking at this map, you can see how Hawaii, Iceland, Indonesia, Japan and New Zealand are all a part of this main belt of magma flow. I include the estuaries two main rivers, Amazon and Nile. Take a look at equator, as land mass and ocean always seem to be divided where the magma division lines cross equator. And all the main ocean ridges are also found where the magma division lines cross equator. What else do we need to find? Well, remember that this bending line is calculated. It adheres to the Coriolis force always swaying in the same way mathematically for each latitude, with slow flow subject to no oscillation, with the same diameter as the radius of Earth as the basic length scale found along 32nd parallel where the flow is directly north-south.
Can you trace something more? I would like to see that, because I am interested in this 🙂
Magic Magma 