Jökull - 01.12.1970, Side 70

Section throuqh Ga/t afell
Fig. 4. Interglacial lava flows on the summit of Galtafell.
Mynd 4. Ungu hrajmin i Galtafelli. Langskurður af vesturhlið fjallsins og þversnið i gegnum
fjallið. Ungu hraunin fimm talsins eru sý?id með lóðréttri strikun (stuðlaberg) og rúðustrikun
(kubbaberg).
thickness of only 1 m was observed near Sumar-
lidabaer. Near Gíslholtsvötn the substratum was
only seen where rocks of the Hreppar Series
reach high up into the young lavas — again
only reaching a maximum thickness of 1 m.
The localities where the sedimentary sub-
stratum outcrops usually do not coincide with
the depressions of the old relief in which the
greatest thickness of sediments would be ex-
pected. The borehole at Arbaejarfoss in which
5 m sediments were found at 24 m above sea
level, may be located in a place where the
sediments attian a considerable thickness. At
Aegissídufoss at 14 m above sea level the base
of the young lavas is not seen, however, sedi-
mentary material squeezed into fissures from
below may indicate the presence of the sub-
stratum at shallow depth.
68 JÖKULL 20. ÁR
It is evident that the main features of the
present topography are older than the young
lava flows, because the lavas spread in part
over an erosional plain nearly similar to the
one presently existing. North of Thjórsá only
remnants of the lavas are left and variations
in their base altitude indicate valley topo-
graphy. The base of the young lavas to the
north of Thjórsá rises continuously towards the
north. In Hólahnúkur and Háholt the base
lies at 150—180 m altitude. Further north it
lies nowhere below 220 m. Just north of
Thjórsá the base lies somewhere near 100 m.
On the other hand the young lava flows im-
mediately to the south of Thjórsá have their
base below 60 m at least. From there the base
falls off gradually to the south (24 m at Árbaej-
arfoss, 30 m at Raudilaekur, 14 m at Aegisídu-