Jökull - 01.01.2015, Síða 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