Another example of how the topography follows the division lines of convection rolls along equator is Indonesia. It spans 30° from east to west, just like South America. Also, the two points of east and west have exactly the correct position as compared to S-America. We find steps of 30° around the world!
So this pattern is obvious. The up-welling line is found at the western point of the 30° string, extending farther to the south where you find Krakatoa, one of the most famous volcanoes in the world. Therefore, behind the trench and relevant geology, there are geophysical preconditions we should look into.