A simple 3D model can be made to understand better the arrangement of mantle currents under Iceland. It has three 2D components, surface, E-W vertical section along 64°N and N-S vertical section along 21°10’W. It looks like this:
The easy part to understand is the E-W arrangement, as the convection rolls of asthenosphere are always 1.5° wide along each latitude. The latitude chosen here is 64°N, so when you follow it you will always meet with intersection between rolls at the interval corresponding to 1.5° of longitude. This can be comprehended rater easily, and it is clearly drawn above.
A more difficult part is the N-S section, showing the sides of the convection rolls. There are two rolls found in between 120 and 410 km, usually, but here two systems intersect each other, so the rolls become 4! our mind is not trained for this, so we become tired when confronted with this puzzle. Still, this is very simple compared with the most complex things most of us need to learn one day or another.
The surface part might be most difficult, because the different lines separating the individual pairs of convection rolls are drawn there, showing a pattern of all four layers. It is very easy to imagine a line between two convection rolls, but many convection rolls side by side are more difficult, and four different layers add considerably to the complexity.
Therefore, this simple model, based on the fact that hot material rises up, flowing to the sides while cooling, then sinking and being heated again, becomes too complicated for us to understand without a considerable effort of study.
You can make this model by printing the picture, then cutting out the three parts separately and combine the dotted lines of the vertical parts, gluing with surface at the crossings of 64°N and 21°10’W.
You see why 64°N is chosen as E-W section. It is the only latitude where all the upper rolls have the same dimension and are regularly arranged. If you understand the model, you might be able to make similar sections at other latitudes.