The two ridges soutn and north of Iceland are actually of the same origin. This can be shown by comparing their location with the convection rolls model. This map shows the alignment of Kolbeinsey Ridge:
Within the interval of close to 63°N to 67°N, the two ridges are separated within the intersection zone of convection rolls.
Njörður Caldera is found within the Reykjanes Ridge:
The Reykjanes Ridge resembles a volcanic zone, as we see in Iceland. The volcano is found at a special location, where the upper most polar convection rolls division line does approach the division line between the equatorial convection rolls, responsible for the southern half of the Reykjanes Ridge. The faults stretching northwards from the caldera enter a micropolygon, shaped by four convection rolls layers.
The Reykjanes Ridge Polar Upper Mantle Rolls Division Line is up-welling, and works agains the drift direction of the North American Tectonic Plate, resulting in similar rifting process as within the volcanic zones of Iceland.
The Large Scale Lower Mantle Rolls are found deeper below, that is at 410 km depth. The Polar Upper Mantle Rolls upper limit is at 120 km depth, where the tectonic plate (the ductile part of it) meets with the convecting mantle.
Tristan da Cunha is centrally located according to this video
South Hemispher Tectonic Drift: https://www.facebook.com/GeomorphologyRules/videos/1868246676644895/
This video shows how the Atlantic Ocean devlopes from the center. Tristan da Cunha is found close to the ridge itself.
Juan de Fuca follows a convection rolls division line.
This arrangement is comparable to the Reykjanes Ridge and the volcanic zones in Iceland.
The ridge does originally not follow the main division line, because it is down-welling and therefor convergent.
The position of the two ridges can be compared:
Note that the main ridges are mainly found 1.5° west of the division line between large convection rolls of lower mantle.
Same kind of shift from western side to eastern side, a jump of 3°, is found in both cases. From the Reykjanes Ridge, a jump occurs to the East Volcanic Zone of Iceland, but at Juan de Fuca, a jump of 3° is found for the Gorda Ridge.
The fact that Juan de Fuca and Reykjanes Ridge show two aspects of consistency, that is they both follow the same formula of alignment, and are found 1.5° west of main division lined of lower mantle, is an argument for siting that the model is in harmony with real circumstances within the Earth’s mantle.
For reference, look for instance at
https://americastectonics.weebly.com/juan-de-fuca-explorer-and-gorda-plates.html
The concection rolls system within the Earth is regularly shaped, carrying heat to the surface. Two layers within the depth of 120-410 km are responsible for many tectonic and topographic features. The volcanic zones of Iceland can be traced accordingly. The first step is to see how the upper most rolls shape two of the main volcanic zones in Iceland, the West Volcanic Zone and the East Volcanic Zone.
Here, the upper most rolls are drawn with thicker lines for clarity.
Blue lines show down-welling, and there the volcanic zones terminate sharply at the eastern side. The East Volcanic Zone is the best example, because the rifting takes place exactly within the area marked by up-welling and down-welling lines.
The Reykjanes Ridge itself also provides a very easily understood example of how this system works. Therefore, the two rolls are drawn there.
As this is nature, not man made system, it is represented in countless ways throughout the country. The earthquake epicenters also show some functional aspects of the grid of division lines of different layers.
It also has to be kept in mind that under Iceland between 120-410 km depth, there are actually four layers, due to the intersection between the two layers north of the country, and the other two layers south of it.
Magic Magma 