The central volcano Katla is hidden under the southeastern part of the ice cap Myrdalsjokull. It has usually erupted at intervals of 40 to 80 years and melted such volume of ice, that the flood waves have covered most of the Myrdalssandur outwash plain. The peak volume can be compared with River Amazon. Documented sources about earlier eruptions and floods seem to be relatively reliable from around 1179.

The eruptions in 1245 and 1262 are said to have created most of the outwash plain Solheimasandur and the 1311 eruption caused the so-called Sturla Flood, which devastated the farming area called Lageyjarhverfi on the outwash plain Myrdalssandur. The 1416 and 1490 eruptions caused the thickest ash layers in the Southwest, now the capital area. In 1755 (Oct. 17^th), the eastern part of the Myrdalssandur was once more flooded, when quite a few people were travelling across. All escaped, some narrowly though, but some sheep were lost. The ash layers were very thick and poisonous. This caused great losses of livestock and consequently human lives.

The 1860 eruption caused floods to the west of the freestanding mountain Hjorleifshofdi. The 1918 eruption lasted from October 12^th to November 4^th. The flood created a spit of land east of Hjorleifshofdi, which became the southernmost point of the country until it was gradually transported away by the ocean currents. Before the eruption, the depth of the sea, where it was created, was measured between 2000 and 3000 fathoms.