Scandinavia is marked by one convection roll of lower mantle. The coast of Norway is the down-welling side, and the up-welling is found east of the White Sea and Finland.
As Iceland is one of the Scandinavian countries, the system of a pair of rolls, with down-welling in the middle, more and less marks the area.
For those really interested, the middle of the Scandinavian Peninsula, and all Iceland, are found within an intersection zone of two different convection rolls, although closely related to each other. The rolls reaching from equator meet the rolls extending to the North Pole.
But for the sake of simplicity, this is the picture we should comprehend at first. Also, please note that this is found within a 3D globe, but this is an over-simplified 2D drawing 🙂