Katla and Eyjafjallajökull are the southernmost volcanoes, except for the Westman Islands. The framework extending from Hekla to Katla, along with Eyjafallajökull and Torfajökull exhibit the main tectonic fault directions. Usually we emphasize on the alignment of the Eastern Volcanic Zone in general (to the NE), but a simplified drawing of the polygons formed by the convection rolls look like that:
What is specially pointed out here is the connection of Katla with Torfajökull. The light coloured area shows two different alignments, originated from the NS-axis of the polygon. The NW trending faults are mirrored against the NE faults, having the same deviation from North, in opposite directions. The Torfajökull area is in a way confined south of the EW central polygon axis.
This interplay of EW-NE-NS-ES factors and even combinations of these have to be screened to understand the tectonics and distribution of volcanic sites. As previously mentioned, Hekla itself is askew with the system, but it can also be easily calculated like the rest of the southern features.