Jökull - 01.12.1979, Page 31

3 Volcanic activity in historical time
SIGURDUR THORARINSSON
Science Institute, University of Iceland, Reykjavík
and
KRISTJÁN SAEMUNDSSON
National Energy Authority, Reykjavík
The volcanic activity in Iceland during its eleven
centuries of settlement is a direct continuation of
the prehistoric Postglacial activity and is confined ■
to almost the same areas (Fig. 1), within the
neovolcanic zones. The activity has been similar,
characterized by massproduction of predominantly
basaltic lava and a greater diversity of volcanic
phenomena than one might expect on an oceanic
island. Nearly every type of volcano found on the
face of our globe is represented in Iceland. From a
petrogenetic point of view two main types of vol-
canoes have been active: purely basaltic ones and
central volcanoes producing intermediate and acid
rocks besides basalt.
The basaltic volcanoes display a variety of forms,
depending on magma type and extrusion rate and
influenced also by extraneous factors such as water
mixing with the magma. The main types are listed
in Table 1. Lava rings and probably also lava
shields started to form on a short fissure, but as the
eruption proceeded the emission of lava concen-
trated at one point, developing a more or less cir-
cular vent. The only lava shield that has been
formed in Iceland’s historical time is the shield on
Fig. 1. Volcanic activity in Iceland in historical time.
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