An ice cap is a mass of glacial ice that covers less than 50,000 km² of land area covering a highland area and they feed outlet glaciers. Many Icelandic ice caps and glaciers lie above volcanoes, such as Grímsvötn and Bárðarbunga, which lie under the largest ice cap, Vatnajökull. The caldera of Grímsvötn is 100 km² in area, and Bárðarbunga is 60 km².