Big convection rolls obviously shape the Atlantic Ocean from underneath. Smaller convection rolls are responsible for marking the details of volcanic zones in Iceland. The upper most convection rolls are found side by side as this drawing shows:
The resemblance to this map is quite obvious, as the darkened areas show volcanic zones. The volcanic zones abbrevieated as WVZ and EVZ fit perfectly, along with CVZ and by referring to other convection layers the NVZ and SVZ along with ÖVZ can be explained. Each convection roll spans 1.5° from east to west, swaying according to calculation under the country. The rolls can not be straight, due to the rotation of the Earth and the fact that the mantle is flowing. This layer in particular has a horizontal flow component to the south, swaying slightly to the right as all moving particles have to do on or inside the rotating Earth.