Jökull - 01.12.1990, Blaðsíða 62

South Iceland that Kjartansson (1943) considered to be
synchronous and named the Búði moraine, are formed
in front of two ice lobes, in the river basins of Hvítá and
Þjórsá respectively (Fig. 10 A). Sigbjamarson (1967)
pointed out that the correlation is far from certain. At
this moment we assume that these moraines are similar
in age.
The age relationship between these two lobes and
the lobe in the Blanda valley is not known, but re-
garding the distance from the ice divide, the Blanda
moraines are probably younger than the Búði moraines
(Fig. 10 B).
Next in age are the end moraines in the Haukadals-
heiði area, which are of similar age as the moraines
to the east of Hvítárvatn (Fig. 10 C) and possibly the
moraines to the west of Blágnípa too. The correlation
between the areas to the SW and NE of Hofsjökull is
difficult because of the present ice cap and because
some important areas have not been mapped yet. In
view of the topography beneath Hofsjökull (Bjöms-
son, 1988) it seems reasonable to imagine the Blágnípa
moraines to be of similar age as some of the moraines
to the NE of Hofsjökull.
The end moraine pattem shows that the recession
has been much more rapid in the Hvítá area than in
the Þjórsá area and during the formation of the Fitja-
skógar end moraines there seems to be only one broad
ice lobe (Fig. 10 D). These moraines seem to be of
similar age as the southemmost moraines to the east
of Hofsjökull, but one can not assert anything about it
until the area at the southern margin of Hofsjökull has
been mapped. Fluted moraine in front of Þjórsárjökull
(outside the 1890 moraines which mark the largest ex-
tent in Postglacial time) indicate some ice flow from
the Hofsjökull area at this stage.
From the Fitjaskógar moraines the glacier retreated
inland and the ice movement direction shifted gradu-
ally to the NW and finally towards the north. The
youngest end moraine is the one on the Búðarháls
ridge(Fig. 10 E).
It is evident from the data presented here, that the
direction of the ice movement in the southem high-
lands gradually was tumed more and more towards
west and then towards NW as the glacier retreated
from the Búði end moraine to the Tungnaáröræfi. This
indicates that the culmination area of the inland ice was
gradually moved towards south.
COMPARISON TO PREVIOUS WORK
The data presented here is in good agreement with
the data used as a basis of older deglaciation syntheses
but due to more extensive data the interpretation is
different.
Already in 1900 Pjeturss found striae of more than
one direction in South Iceland and concluded that the
southwards movement was older than the westward
one. He observed less deflection and greater degree
of erosion accompanying the older than the younger
one and concluded that the ”southward moving ice-
sheet was more important or thicker than the other“.
Kjartansson (1940) concluded that, due to the in-
significant erosion, the last ice movement direction
had lasted only for a short while. He also disproved
Knebel’s (1905) theory, maintaining that the different
ice movement directions were due to different glacia-
tions, but suggested that the two systems were due
to
1. shift in ice centre from the central highlands to
the mountain area in South Iceland and
2. changes in flow near the ice terminus as the low-
land was transgressed and a bay was formed on
the southem lowland.
He stressed that further data was needed before defi-
nite conclusions could be drawn.
Our conclusions is in good agreement with this
early opinion of Kjartansson (1940), but later he grad-
ually became convinced that the age relationship of the
striae systems was indicating that the ”glacier from
east“ (Tungnaáröræfi) was thicker than the "glacier
from north“ (central highlands) throughout the We-
ichselian, and that at the time of the Búði readvance,
practically all ice had melted away except remnants
of the thickest part (Kjartansson, 1955; 1957; 1964a).
The main argument for this conclusion was the lack
of table mountains in the Tungnaá region, an area of
active volcanism during the last glaciation.
Kjartansson assumed the proglacial lake in the
Kjölur area to be synchronous with the Búði end
moraine and he postulated an ice margin that extended
60 JÖKULL, No. 40, 1990