The symmetry around the coastal point of Iceland at 66°N, 30° to East and West, is coherent with the analytical result that the span of one convection roll of lower mantle is 30° along each latitude. Still, the West Fjords Peninsula is not located over the division line of large convection rolls of lower mantle, but the tectonic drift has resulted in this symmetry.
The coast of Norway is 6° farther to the East (the span of 2 upper mantle convection rolls), where the main division line between lower mantle convection rolls is found. These are down-welling lines closest to the tectonic plate at 120 km depth below Earth’s surface. It is therefore to be understood that at those three points, the down-welling division lines also mark the division lines between topographic and bathymetric features.