The interval between volcanic zones in Iceland is regular, as shown here:
As the arrows show, the NE-SW alignment is achieved along the same pattern, namely that of the Reykjanes Ridge. The red lines marking up-welling of convection rolls, fit for all four sets of volcanic zones.
The sequance can be made more clear, by widening the division lines between the upper most convection rolls, found at 120 km depth.
It should also be mentioned, that Öræfajökull is on the fourth line, in accordance with the interval between the up-welling NE-SE aligned division lines between convection rolls.
The so-called ‘jumps’ therefore always occur regularly in the SW of Iceland where the axis is aligned NE-SW. One jump occurs over exactly 3° from east to west along the relevant latitude. The distance between the North Volcanic Zone, and the recently extinct Skagafjörður Volcanic Zone is also 3° at the latitudes of the Tjörnes Fracture Zone. The reason is that each convection roll spans 1.5° from east to west, and a pair of convection rolls, representing one unit in the convection rolls system, spans 3° from east to west.
This can be compared with the results of ISNET measurements by the National Land Survey https://www.lmi.is/
The northern component of tectonic drift, in addition to the easterly and westerly components of the vectors is a rather new finding, after GPS was used to measure tectonic drift on global scale. The east and west components had been measured previously. Describing tectonic drift of Iceland, one should say that the western half drifts about 2.5 centimeters a year to the NW, and the eastern half drifts about 2 cm a year to the NE. As a consequence, the country widens up from the middle rift areas by about 2 cm a year, 1 cm to the east and 1 cm to the west.