Jökull - 01.12.1973, Síða 17

Fig. 4. Geologic outline map of the area covered by the ERTS-1 image of Vatnajökull.
Mynd 4. Örnefni og helstu drœttir jarðfraði á því svœði, sem sést á ERTS-1 gervihnattarmynd-
inni.
of Tungnafellsjökull is an area of rhyolitic
volcanism with some mountains as high as
1200—1400 m. Some distance to the southwest
the rhyolite domes of Hágöngur, both nearly
1300 m in elevation, appear as part of tliis
large central volcano complex. High-tempera-
ture thermal activity is associated with the
rhyolitic volcanism in this area. NE—SW-trend-
mg fissure volcanism is very subordinate but
becomes conspicuous from Hágöngur south-
westward. The dividing line between tltese two
JÖKULL 23. ÁR 1 5
types of volcanism may, as has been previously
discussed, be an extension of the volcano-tec-
tonic line which strikes northwestward, north
of Grænafjall. The Tungnafellsjökull—Hágöng-
ur relationship is strikingly similar to the geo-
logic setting at Grímsvötn, where there is a
large volcano with a caldera, and an area of
rhyolitic volcanism trending southwest from it
south to Geirvörtur. Once the Bárdarbunga has
been recognized as a central volcano it seems
entirely possible that the relationship between