Looking at the foundations of Iceland at 64°N shows how the geology along the latitude is divided into distinct ‘chapters’.
The convection roll shown farthest to the left is at the main division line over the large convection cells of lower mantle. It is marked with bold black line over the country from SW to NE. With 3D models like this one it becomes possible to understand the pattern of convection rolls under the tectonic plates all over the world.
Of course, this can still not be understood by looking at this model. The picture is published here just to show that the model has been derived, and everyone interested in the subject can learn about it. This has hitherto been a huge gap in the knowledge spectrum of geoscience.