Reykjanes Peninsula is closely related to the Reykjanes Ridge, that in turn can be looked at as a huge elongated volcano. https://en.wikipedia.org/wiki/Mid-Atlantic_Ridge
Keeping this in mind, the volcanic eruption at Geldingadalir is a small event in the large context of the Reykjanes Ridge. It has been found that this time the magma is very primitive, close to what is found on Mid-Ocean Ridges. https://grapevine.is/news/2021/03/23/lava-from-geldingadalur-is-the-most-primitive-iceland-has-seen-in-7000-years/
The ridge is about 900 km long and takes over a large part of the ocean floor. It is then subducted by the Icelandic Plateau, but the division line found on the top of the Reykjanes Ridge can be traced through Iceland. The red square is therefore both affected by the special conditions found in Iceland and the Reykjanes Ridge. This time, the magma must be originated relatively directly from the division of the Reykjanes Ridge, close to the so called MORB type of basalt. https://en.wikipedia.org/wiki/Basalt
