Jökull - 01.12.1980, Page 45

The Vogar Fissure Swarm, Reykjanes Peninsula,
SW-Iceland
ÁGÚST GUÐMUNDSSON
Menntaskólinn vid Sund, Reykjavík, Iceland
ABSTRACT
The paþer descnbes the Vogar fissure swarm, and
discusses the origin of the fractures. The swarm lies
almost completely within the same 10000 years old
lava. Detailed measurements were carried out on the
swarm, and the main results are as follows: About
25% of the fractures are faults; the others are
extension fractures. The mean orientation of all the
fractures is 54°, and the distribution follows the
normal curve. There is no significant change in the
orientation of the fractures along the fissure swarm.
The average length of the fractures is 611 m, and the
mean width is 0.6 m. The maximum width and throw
on a single fracture are 7.5 m and 20 m respectwely.
Most of the faults are vertical, but some are steeply
reversely inclined; the majority are closed. The linear
correlation coefficient for the various parameters is
generally small; the highest value is 0.65 for length
and maximum width. Maximum dilation across the
fissure swarm is 15 m.
Various hypotheses have been proposed to explain
the fissure swarms on the Reykjanes Peninsula. They
are all found to be inadequate, and a new solution is
suggesled: an intrusion. Two models are discussed in
detail: a vertical dyke or dykes, and a horizontal sill or
sills. These are tested by data from the Vogar fissure
swarm. It is concluded that many intrusions, sills in
particular, could explain the Vogar fissure swarm.
HOLOCENELAVAS
PLEISTOCENE ROCKS
FAULTS AND FISSURES
VOLCANIC FISSURES
Nútíma hraun
Jarðmyndanir eldri en nútími
Gjár og misgengi
Reykjavik
Fig. 1. Location of the research area, and an outline of the geology of the Reykjanes
Peninsula. — Mynd 1. Staðsetning rannsóknarsvœðisins og helstu drœttu í jarðfræði Reykjanesskag-
JÖKULL 30. ÁR 43