The large convection rolls, spanning 30° from east to west, rule the main trend of tectonic drift. But the smaller rolls above, spanning 1.5° from east to west, make it more complicated. The Great Rift Valley of Africa is located above a main division line of up-welling within the lower mantle. At equator, the difference between convergent and divergent small scale rolls can be examined.
The red lines show the different points, one local diverging point, one large scale diverging point which is at the same time a local converging point. This seems controversial, but is an inherent factor of the convection rolls system.
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