Jökull


Jökull - 01.01.2015, Side 30

Jökull - 01.01.2015, Side 30
Þorsteinsdóttir et al. GEOLOGICAL SETTING OF THE KATLA AND HEKLA VOLCANIC SYSTEMS: A SHORT OVERVIEW The Katla Volcanic System Substantial parts of the volcanic zones in Iceland are covered with ice. Eruptions that begin below glaciers are therefore nowhere more common than here in Ice- land (e.g. Thordarson and Larsen, 2007). One of those partly ice-covered volcanic systems is the Katla vol- canic system which is situated in the southern part of the Eastern Volcanic Zone, and has been one of the most active ones during the Holocene (Larsen, 2000, 2010; Björnsson et al., 2000; Óladóttir et al., 2005, 2008; Thordarson and Höskuldsson, 2008). Katla volcanic system is about 80 km long and with an southwest-northeast direction. It consists of a central volcano situated in the southern part of the system, under the 600 km2 Mýrdalsjökull ice cap, and a fis- sure swarm located mostly outside the glacier (Figure 1) (Jakobsson, 1979; Larsen, 2000, 2010; Óladóttir et al., 2005, 2008). The Katla volcanic system has most likely been active for several hundred thousand years (Björnsson et al., 2000; Óladóttir et al., 2007, 2008). Holocene volcanic activity within Katla volcanic system has been divided into three categories (Larsen, 2000, 2010): 1. Explosive hydromagmatic/phreatomagmatic basal- tic eruptions on short volcanic fissures below the Mýr- dalsjökull ice cap are the most frequent type of Katla eruptions. They commonly take place within the Mýr- dalsjökull caldera. 2. Explosive silicic eruptions are believed to be the second most common type of Katla eruptions during the Holocene. They originate on vents beneath the ice cap, either inside the caldera or on the caldera frac- ture, and these eruptions are generally less volumi- nous than the basaltic eruptions. Figure 1. Katla volcanic system (Larsen, 2000) and Hekla Volcanic System (Larsen et al., 2013; Jóhannesson and Sæmundsson, 1998). – Eldstöðvakerfi Kötlu (Larsen, 2000) og Heklu (Larsen og fl., 2013; Jóhannesson og Sæmundsson, 1998). 30 JÖKULL No. 65, 2015
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