Fagradalsfjall and Surtsey are tuyas, and the eruptions and magma composition are different from all other eruptions which have occurred in Iceland recently. This time it could be studied thoroughly at Fagradalsfjall, how relatively primitive magma rose from mantle to surface. But for me it was intriguing that the two spots, where magma rose up from down below to form a dyke feeding the volcanic sites, are at exactly parallel locations according to the convection rolls model. The two red spots roughly indicate the two locations:
The dykes formed are heavier than the surrounding rock, and therefore each eruption adds to the average specific weight of rock within a given area. The eruptions took place in line with the V-shaped ridges, which are gravity anomalies, aligned askew compared with the tectonic drift creating magnetic anomalies rather uniformly at each side of the Reykjanes Ridge. The formation of V-shaped ridges, not found in conformity with tectonic drift, is poorly understood. But they can be explained referring to these two eruptions. On the Reykjanes Peninsula, earthquake faults are found in a swayed pattern approaching the Reykjanes Ridge in the same way as the V-shaped ridges. These earthquake faults also create the final weakness the magma makes use of to make it up through the crust. As the dykes add to specific gravity, and the V-shaped ridges are gravity anomalies, and the formation of the faults coincides with the V-shaped ridges, I really would like to suggest that V-shaped ridges are actually a manifestation of a row of magma filled faults. It is really a temptation here to add quod erat demonstrandum. The dykes are also stronger than the surroundings, and should add to the local height of the sea bottom, withstanding erosion better than ordinary lava.
The symmetry of Iceland compared to the Reykjanes Ridge, V-shaped ridges is culminated by the elliptical plateau on which the country is located. The theoretical continuation of the Reykjanes ridge does cross the exact central point of the elliptical plateau, as it can be traced mathematically. Therefore, a similar mechanism at both sides of the Reykjanes Ridge can be expected, leading to parallel formations at both sides of it.
Talking about symmetry, it is facinating how those two eruptions occur geologically almost simultaneously, resembling each other so closely. The polygon of the Vestmanna Islands and Reykjanes Peninsula must have an identical pattern of earthquake faults. This should be detectable, and is therefore a theory that can be tested.
The idea that V-shaped ridges are correlated with volcanic zones is not new, though, as described in this paper: https://www.researchgate.net/publication/228737092_Propagating_rift_model_for_the_V-shaped_ridges_south_of_Iceland