Eyjafjallajökull is one of the smaller ice caps of Iceland, situated to the north of Skógar and to the west of Mýrdalsjökull. The ice cap covers the caldera of a volcano with a summit elevation of 1,651 metres (5,417 ft). The volcano has erupted relatively frequently since the last glacial period, most recently in 2010.
Eyjafjallajökull consists of a volcano completely covered by an ice cap. The ice cap covers an area of about 100 square kilometres (39 sq mi), feeding many outlet glaciers. The main outlet glaciers are to the north; Gígjökull, flowing into Lónið, and Steinholtsjökull, flowing into Steinholtslón. The glacier is the 4th largest in Iceland. In 1967 there was a massive landslide on the Steinholtsjökull glacial tongue. On January 16, 1967 at 13:47:55 (or 1:47:55 PM) there was an explosion on the glacier. It can be timed because the earthquake meters in Kirkjubæjarklaustur monitored the movement. When about 15,000,000 cubic metres (529,720,001 cubic feet) of material hit the glacier a massive amount of air, ice, and water began to move from under the glacier out into the lagoon at the foot of the glacier.
The mountain itself, a stratovolcano, stands 1,651 metres (5,417 ft) at its highest point, and has a crater 3–4 kilometres (1.9–2.5 mi) in diameter, open to the north. The crater rim has three main peaks, being (clockwise from the north-east) Guðnasteinn, 1,500 metres (4,900 ft) (approx), Hámundur, 1,651 metres (5,417 ft) and Goðasteinn, 1,497 metres (4,911 ft). The south face of the mountain was once part of Iceland's Atlantic coastline, from which, over thousands of years, the sea has retreated some 5 kilometres (3.1 mi). The former coastline now consists of sheer cliffs with many waterfalls, of which the best known is Skógafoss. In strong winds, the water of the smaller falls can even be blown up the mountain. The area between the mountain and the present coast is a relatively flat strand, 2 to 5 km (1 to 3 miles) wide, called Eyjafjöll.
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.