Scientists have already mentioned that Surtsey and Geldingadalir eruptions have something in common. Both have the characteristics of effusive eruptions (shield volcanoes), and the flow rate of basaltic lava is similar. Looking at the convection rolls model, the two locations of ascending magma are exactly parallel to each other. Comparing the framework of the two polygons of Reykjanes and Westman Islands, they are alomost copy-paste of each other. In turn, Surtsey has the same location within Westman Islands Polygon as has the ascending magma where it flows into the dike of Geldingadalir eruption, close to Keilir Volcano.
The narrow, black line, parallel to the NW-SE trending convection rolls division line (blue), does cross the ascending spots of magma for Geldingadalir and Surtsey. The Geldingadalir eruption is fed by a dike, but the flow into the dike is not directly below the eruption site, but closer to Keilir Volcano, farther NE. Considering that the lower inflow of magma was more or less directly below Surtsey, the spots are identical for the polygon of Reykjanes and polygon of Westman Islands.
Scientists have reasoned that Surtsey eruption and Heimaey eruption in 1973 were actually connected events, meaning that magma from Surtsey was connected with Heimaey. Therefore we can draw a line in between Surtsey and Heimaey. That line is parallel to the dike formed at the Geldingadalir eruption site. It is tempting to consider that the dike did also extend to the SW from Surtsey, towards the downwelling division line (blue color).
Both eruptions have the same distance from the theoretical upwelling division line between convection rolls, which should be the original feeders of magma for those eruptions. The process is complicated, because the hot magma from underneath does melt material within the crust, which then erupts and forms lava on the surface. Some mixing takes place, as described in this article about the three magmatic components in the 1973 eruption of Eldfell volcano, Iceland: https://www.researchgate.net/publication/232395907_Three_magmatic_components_in_the_1973_eruption_of_Eldfell_volcano_Iceland_Evidence_from_plagioclase_crystal_size_distribution_CSD_and_geochemistry