Convection within the mantle is the driving force of volcanic eruptions, earthquakes and geothermal activity. Therefore, we should look at the function of convection. When molten material is heated, it expands at the heat source and rises up. This happens within the Earth, and luckily we can find out where the main ascending locations of magma are found. We just have to compare Earth’s layers with physics, and there we have it, as shown here:
The convection rolls extend from equator to 67.3°N and S. A polar system is found separately, but it has the same physical properties as the equatorial system. Understanding this is the prerequisite for analyzing Earth’s main geological processes.