The layers between 120 and 410 km depth affect the tectonics of Iceland. Within the division lines between the rolls, Munroe effect sends magma up into the tectonic plate, marking polygons at the surface. The four sets of division lines of the four layers are drawn here, red for upwelling and blue for downwelling.
The situation in Iceland is exceptional, as south of 60.7°N there are only two layers within the range of 120-410 km.
These four layers have to be looked at in context with the large convection rolls of lower mantle. The tectonics of Iceland can then be studied in detail by referring to the convection rolls system.
By drawing all the lines on one map, the pattern ruling the formation of tectonics in iceland is shown.