Rit (Vísindafélag Íslendinga) - 01.06.1971, Side 124

124
GUÐMUNDUR PÁLMASON
Fig. 46. Central volcanoes in lceland (from Sigurdsson, 1967).
depth to layer 3 (cf. Fig. 37). He found a major Tertiary intrusive
centre, with a cone-sheet ring of 11 km diameter, centered about the
northem tip of the mountain Vididalsfjall. A similar relationship is
thus indicated here hetween a major Tertiary volcanic centre and
shallow depth to layer 3, as in eastem Iceland.
The question immediately arises whether a similar coincidence
of major volcanic centres with shallow depths to layer 3 is found in
other parts of Iceland. Sigurdsson (1967) has published a map of
central volcanoes in Iceland (Fig. 46). Some of them, e.g. Setberg
(Se), Vídidalsfjall (V), Húsafell (Hú), Hafnarfjall (H), Esja (E)
and Hengill (He) appear to be associated with shallow depth to layer
3. For others no such correlation is indicated, but this may at least
partly be due to lack of seismic data in the area of the central vol-
canoes. It should also be kept in mind that some of the Tertiary vol-
canic centres in westem and northem Iceland are less thoroughly
studied than those in eastem Iceland referred to above. Perhaps the
map of the depth contours of layer 3 may indicate promising areas
to look for such old volcanic centres.
The combined seismic and subsurface temperature data are con-
sistent with the hypothesis that in southem and westem Iceland the
cmst is in an active state, in the sense that the present temperature