Along the 64th parallel over the Southen Lowlands area the fracture zone occationally causing large earthquakes is found. An older version is found in the Borgarfjörður area. An EW-axis is also found along Eyjafjallajökull and through the Katla caldera.
As the lines represent divisions between convection rolls, the coherence between these EW-axis and the convection rolls is amazing. Remember that Hekla and Hallarmúli are found at the eastern end points of the relevant axis. The large flows caused by Katla euruptions are originated from an opening on the east end, through which Kötlujökull slides out from the caldera.
So should we explain this, or can anyone realize why this is so? The polygons are subject to pressure and tension from nearby polygons and the mantle flow below. As they are mainly made of ductile material, they break in the middle from one corner to the other. It is pure physics.