Jökull - 01.12.1980, Page 48

Fig. 4a,b. Profiles over the Vogar fissure swarm. The profiles are numbered 1 — 11 from
the west to the east. The height is given in meters above sea level, and the scale is the same
on all the profiles. — Mynd 4a,b. Sniðyfir sprunguþyrpinguna við Voga. Sniðin eru númeruð 1—11
frá vestn til austurs. Hæðin er gefin í metrum yfir sjávarmáli, og mælikvarðinn er sá sami á öllum
teikningunum.
completely within the same lava: this lava is
10000 years old (Jónsson 1978), and is probably
one of the oldést Postglacial lavas on the
Reykjanes Peninsula. Secondly, it is the bigg-
est fissure swarm not obscured by younger
lavas. Thirdly, detailed precision leveling
measurements have been carried out in this
area over many years. These make comparison
of horizontal and vertical movement possible.
Fourthly, because of the age of the lava, and
the size of the area covered by it, the total
dilation measured in this swarm is considered
to be a good estimate of the total dilation on
the peninsula as a whole, during the
Holocene.
Fig. 2 is a detailed map of the Vogar fissure
swarm. On this map, each perpendicular line
to a fracture is a point where significant throw
has been measured. Fig. 3 shows the location
of the profiles in Fig. 4a,b. All the profiles are
approximately perpendicular to the mean
orientation of the fissure swarm. Fig. 4a,b
shows how the form and structure of the fiss-
ure swarm changes from east to west.
The fractures are of two types: extension
fractures and faults. About 75% of the frac-
tures are classified as extension fractures,
although in some a few centimeters movement
along the fracture plane is evident. Most of the
faults are normal faults, but usually the walls
are vertical — as far down as can be seen. The
main results of the measurements are sum-
46 JÖKULL 30. ÁR