It is fascinating that the main division points of equator are directly above the division points between convection rolls of lower mantle, which are 30° apart! But details also tell a story. Let us look at the subduction points, exactly 180° apart on equator. This can be easily checked on a Google map:
The subduction zones have the same deviation from north on equator. This alignment of the red marks, exactly on equator, is the first derivation of convection cell alignment along with north-south pressure axis.
For S-America the point above large convection cells is within the trench. The relevant lines are down-welling at the point. At Indonesia the point is 1.5° east of the trench opening.
Just to explain the relevant conditions, The sites are here marked on the convection cell model:
All this is easily understood, once you have seen the basic pattern of convection rolls within the Eart’s mantle.
Magic Magma 