Jökull - 01.12.1986, Page 18

Fig. 6. The volcanic strips. The vol-
canic systems are composed of vol-
canic strips and lava shields (Sigurðs-
son 1985, based on Jónsson 1978).
Mynd 6. Gosreinar. Dyngjur og gos-
reinar mynda gosfylki (eldstöðva-
kerfi) (Freysteinn Sigurðsson 1985,
byggt á Jóni Jónssyni 1978).
Explanations/Skýringar: 5. Lava shields / Dyngjur.
1. Volcanic strip / gosrein. 6. Locations of olivine-tholeiitic crater / Lítil ólívin-
2. Uncertain location / Óviss lega. þóleiít gosstöð.
3. Boundaries of hyaloclastite zone / Jaðar móbergs- 7. Locations of picrite lava shields/Pikrít-gosstöð.
fjalllendis.
4. Central belt of the volcanic zone / miðrœma gos-
beltis.
year (Klein et al. 1973, 1978; Einarsson & Björnsson
1980).
In the Reykjanes Volcanic Zone more than 160
postglacial eruptive fissures or crater rows and up to
30 lava shields have been identified (Jónsson 1978),
although some of them also belong to the Western
Volcanic Zone. These volcanoes are not evenly distri-
buted over the area. The eruptive fissures appear in
groups, forming narrow bands or volcanic strips (fig.
6).
The volcanic strips are most distinctive in the east
but become more diffuse to the west. There are dif-
ferences in petrology between the lavas of adjoining
strips (based on Jónsson 1978), which strengthens the
impression that the volcanic strips represent some
kind of real volcanic units. The volcanic strips also
appear to be grouped together in distinct bands across
the volcanic zone. Every group seems to be connected
with a lava shield and the smaller olivine tholeiite
volcanoes associated with them. The groups corre-
spond to the volcanic systems, that have been classi-
field on the Reykjanes peninsula (Jakobsson et al
1978; Sœmundsson 1980). As elements of the vol-
cano-tectonic structure of the peninsula they seem to
be the major volcanic divisions of the volcanic zone,
with the volcanic strips inclusive the olivine-tholeiitic
groups as the next subdivisions.
If the distribution of recent lava shields and olivine-
tholeiite volcanoes is analyzed together with the dis-
tribution of older rocks of the same type (tablemoun-
tains and isolated hyaloclastite hills, classified chiefly
according to Jónsson 1978), they also appear on dis-
tinct strips, orientated 30—40° E (fig. 7).
The intervals between the lava shields/tablemoun-
tain strips are close to 15 km, but with some devi-
ations. Lava shields or tablemountains can also be
found at similar intervals far out on the Reykjanes
Ridge (Jakobsson 1974) and eastwards across the
southern lowlands (Sigurðsson 1985).
The hyaloclastite mountains appear to be arranged
in the same way as the postglacial volcanoes (fig. 3).
They even correspond to them in site, extension and
volume of extruded lava. Just as the volcanic strips
are composed of closely sited eruptive fissures, so are
the larger hyaloclastite ridges composed of a number
of distinct volcanic ridges, e.g. Vesturháls and Sveiflu-
háls. They are certainly the product of numerous
eruptions. It is therefore very probable that the vol-
canological pattern has not changed notably for a long
time. It should therefore be possible with a notable
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