Katla, Mýrdalsjökull, Mýrdalssandur
Katla is one of the largest central volcanoes in Iceland and is covered by the Mýrdalsjökull ice cap. The volcanic system, including Mýrdalsjökull area and the fissure swarm Eldgjá northeast of it, is about 30 km wide in its south-western part, narrowing gradually to the northeast and reaches a length of 78 km. The caldera sits under the ice cap and is about 100 km2 and covered by ice up to 700 m.
The Katla volcanic system is famous for numerous subglacial eruptions where 21 eruptions are known in historical time. The total amount of tephra produced has been estimated to have been around 0.7 cubic kilometres and the glacial outburst flood (jökulhlaup) about 8 cubic kilometres
Katla is considered by many to be one of the greatest threats known to man due to its potential for devastation. Hidden deep below the Mydalsjökull ice cap, Katla´s crater is about 30 km in diameter and its peak reaches over 1400 m above sea level. Within the crater lies a 400-700 m thick layer of ice. As stated above, Katla is thought to have erupted at least 20 times in recorded history, or every 54 years on average, last erupting in 1918 but did not cause any serious damage.The flood discharge at the peak of the eruption in 1755 has been estimated at 200,000–400,000 cubic-meter per second (7.1-14.1 million cubic-feet per second), comparable to the combined average discharge of the Amazon Missisippi, Nile and Yangtze rivers (about 266,000 m3/s (9.4 million cu ft/sec.)
Mýrdalssandur, the vast desert east of the glacier, is the 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.