Knowing about the mantle currents makes it possible for us to explain tectonics and topography. An EW-axis is found along Eyjafjallajökull through Fimmvörðuháls and farther to the east over the caldera of Katla. This is how it looks:
Try to look at Eyjafjallajökull and Mýrdalsjökull on Google Map yourself, and trace the EW-axis. The reason can be understood by referring to the pattern of magma currents under the tectonic plates of the Earth.