Katla, Mýrdalsjökull, Mýrdalssandur
Katla volcano is one of the most active volcanoes in Iceland and is underneath Mýrdalsjökull glacier. The caldera of Katla is about 100 km2 but the volcanic system of Katla is much larger, or about 110 km long and 30 km in width, extending to the north-east in the direction of Vatnajökull glacier. Katla has erupted at least 20 times since settlement (874 A.D.) and many of them have caused large glacial outburst floods, with a discharge of up to 100.000-300.000 m3/s, and heavy ash fall. The last confirmed eruption in Katla was in 1918, but there might have been three small eruptions since then in 1955, 1999 and 2011. Eruptions in Katla melts about 5-10% of Mýrdalsjökull glacier and it takes the glacier a few decades to recover after each eruption.
Mýrdalsjökull glacier is the fourth largest glacier in Iceland, covering an area of 535 km2 and is 140 km3. The highest points are Hábunga (1497 m), Goðabunga (1510 m), Austmannsbunga (1377) and Kötlukollar (1320 m), which form the outer line of the caldera of Katla volcano. Many cauldrons, up to 50 m deep and a few hundred meters in diameter, are in the glacier that are formed due to geothermal areas underneath the glacier. The thickness of the glacier varies greatly between areas, with the average thickness being 230 m and the thickest part about 740 m in the northern part of the caldera of Katla. Many outlets glaciers flow from Mýrdalsjökull glacier and the most well-known are Sólheimajökull, Entujökull and Kötlujökull.
Mýrdalssandur, the vast desert east of Mýrdalsjökull glacier, is a outwash plain where glacial outburst flooding has continued to pummel the landscape. It is believed to have once been a fertile farming community that was entirely destroyed by repeated glacial flooding through the centuries. In each glacial outburst, more and more sediment gathers in the area. Given the eruption average of around 50-60 years, the sand has ample oppurtunity to grow. Many are of the oppinion that Katla is long overdue to erupt, giving the Mýrdalssandur plain a (possible) chance to grow even further in the near future.