Eyjafjallajökull consists of a volcano completely covered by an ice cap. The ice cap covers an area of about , feeding many outlet glaciers. The main outlet glaciers are to the north: Gígjökull, flowing into Lónið, and Steinholtsjökull, flowing into Steinholtslón. In 1967, there was a massive landslide on the Steinholtsjökull glacial tongue. On 16 January 1967 at 13:47:55 there was an explosion on the glacier. It can be timed because the seismometers at Kirkjubæjarklaustur monitored the movement. When about of material hit the glacier a massive amount of air, ice, and water began to move out from under the glacier into the lagoon at the foot of the glacier.