Jökull - 01.12.1990, Blaðsíða 60

Figure 8: Glacial directional features in the
Fljótsdalsheiði area. For legend, see Fig. 2. — Skrið-
stefna jökuls og jaðarmyndanir á Fljótsdalsheiði. Sjá
skýringar á mynd2.
the behavior of the present Brúarjökull.
Farther east, on Fljótsdalsheiði, Múli and Hraun,
striae of more than one direction are commonly found
on the same bedrock exposure (Víkingsson, 1982;
Víkingsson and Guðjónsson, 1985). The older di-
rection is towards NE on Fljótsdalsheiði but towards
east on Hraun (Fig. 8), i.e. towards the present water-
shed. The younger direction is away from that same
watershed towards the valleys of Fljótsdalshérað.
From this change in ice flow direction the follow-
ing can be concluded: At first (possibly at the We-
ichselian maximum) glacier flow was dominated by
an ice dome situated somewhere to the west of Snæ-
fell, but later glacier flow from the present watershed
becomes dominant in the Hraun and Múli areas.
This change seems to be in harmony with glacial
features known elsewhere in East Iceland (Hjartarson
et al., 1981; Sigurðsson and Guðjónsson, 1983), where
glaciation on the coastal mountains seems to intensify
compared to the interior during the deglaciation pe-
riod.
DISCUSSION
AGE
There are very few absolute datings to rely on in
an attempt to ascertain the age of the events discussed
in this paper, but the relative age is comparatively well
established.
Ahsolute age — The Búði end moraine has re-
cently been dated as being 9750-9600 B. P. (Hjartar-
son and Ingólfsson, 1988). Hitherto it has been re-
garded of YoungerDryas age (Einarsson, 1964; 1968;
Einarsson and Albertsson, 1988). 14C datings of plant
remains in lacustrine sediments in the area to the
NW of Mýrdalsjökull, indicate an open lake about
9400-8700 B. P. (preliminary results from: Institute
of Physics at the University of Aarhus, Science Insti-
tute in Reykjavík and Kaldal and Vilmundardóttir, Na-
tional Energy Authority, Reykjavík). The vast Þjórsá
lava, which was erupted somewhere to the SE of Þóris-
vatn (Vilmundardóttir 1977) and flowed all the way to
the sea at the south coast, has been dated to 8000-7800
B. P. (Kjartansson, 1964b, 1966; Hjartarson, 1988). At
this time the central highlands were mostly ice free.
All the end moraines in the southern highlands are def-
initely younger than the Búði moraine and we assume
the same also applies to the end moraines to the north
of the present watershed. It is therefore reasonable to
believe that the recession took place in Preboreal time.
Relative age — Fig. 9 shows all the end moraines
in the westem part of the central highlands. The his-
tory of the recession of the Weichselian ice sheet may
have been as follows: The end moraines in Central
58 JÖKULL, No. 40, 1990