Today, 12 October, is the 100-year anniversary of the 1918 eruption of Katla. The volcano is considered one of the most hazardous of Iceland's 32 active volcanic systems. During the last 1100 years, Katla has erupted at least 21 times, with an average repose interval of around 50 years. The current one-hundred-year repose marks the longest period since a Katla eruption. The Katla volcanic system is located in the eastern volcanic zone. It is characterized by an 80-km-long fissure swarm and an ice-clad central volcano. The central volcano is covered by the Mýrdalsjökull ice-cap and it includes a 9 by 14 km caldera, with ice-thickness up to 700 m.
Historical eruptions of Katla are predominantly explosive, generating ash-rich plumes and glacial outburst floods (jökulhlaups). In historical times, jökulhlaups have inundated Mýrdalssandur, to the east. Prehistoric jökulhlaups are also known to have drained to the west and north-west of the volcano, affecting Markarfljót.
Lava-forming eruptions can also occur on the volcano's fissure swarm, the most recent of which was the Eldgjá eruption around 939 CE that produced ~20 km3 of lava and tephra. In comparison, the Holuhraun eruption (2014-2015) produced about 1,5 km3 of lava.
Photo: Austmannsbunga is a nunatak in the northeast of the Katla caldera, surrounded by glacial ice. It is one of the few outcrops of bedrock on Mýrdalsjökull. A seismic and GPS station are located on Austmannsbunga. (Photo: Oddur Sigurðsson.)
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