The stratovolcano, whose vents follow an east–west trend, is composed of basalt to andesite lavas.
Most of its historical eruptions have been explosive.
However, fissure vents occur on both (mainly the west) sides of the volcano.

The volcano is fed by a magma chamber under the mountain, which in turn derives from the tectonic divergence of the Mid-Atlantic Ridge.
It is part of a chain of volcanoes stretching across Iceland.
Its nearest active neighbours are Katla, to the northeast, and Eldfell, on Heimaey, to the southwest.

The volcano is thought to be related to Katla geologically, in that eruptions of Eyjafjallajökull have generally been followed by eruptions of Katla.

Eyjafjallajökull erupted in the years 920, 1612 and 2010.
The stratovolcano, whose vents follow an east–west trend, is composed of basalt to andesite lavas. Most of its historical eruptions have been explosive. However, fissure vents occur on both (mainly the west) sides of the volcano.
The volcano is fed by a magma chamber under the mountain, which in turn derives from the tectonic divergence of the Mid-Atlantic Ridge. It is part of a chain of volcanoes stretching across Iceland. Its nearest active neighbours are Katla, to the northeast, and Eldfell, on Heimaey, to the southwest.
The volcano is thought to be related to Katla geologically, in that eruptions of Eyjafjallajökull have generally been followed by eruptions of Katla.
Eyjafjallajökull erupted in the years 920, 1612 and 2010.
Eyjafjallajökull