After the end of the Ice Age, the mountain was temporarily an island, which is still recognisable, hence the name. However, in the case of an island of a special kind, the numerous jökulhlaups of the Katla repeatedly remade it and contributed to its erosion. Kötlujökull plays a leading role in this, because it has the largest amount of glacier ice and water, which can then be released with a volume of up to 100,000 or even 200,000 m2 / sec. running over the outwash plain.