Jökull - 01.12.1978, Síða 22

part, where intensive wind abrasion is going
on. Striae are scarce on hyaloclastites because
of its weak resistance to weathering. Some
areas, such as to the northeast of Miklafell and
south of Laugafellshnjúkur, are covered with
thick fluted lodgement till, leaving few
bedrock exposures. Fluted surfaces represent
the last movement of the ice, and are in fact a
better indicator of the direction of movement
than the striations, because the former are less
influenced by the local topography.
The directional elements and the end
moraines show that the retreat of the main ice
sheet has been towards southeast. This is in a
good agreement with the supposed Lateglacial
ice divide on a southwest-northeast lying
line from Mýrdalsjökull to Vatnajökull, to
the south of the present main watershed
(Kjartansson 1955). In the western part of the
study area directions from N50°V to N25°V
occur. In this area the variation in the direc-
tions is small. On the other hand the disper-
sion is greater in the eastern part of the area,
where directions between N62°V and N4°E
occur. This suggests that the ice retreated fas-
ter and more continuously in the western part,
which first was deglaciated. On the other
hand, several readvances with dispersion of
the ice flow near the front occurred in the
castern part.
Directions of flutes to the east of Miklafell
indicate an ice lobe between the Hofsjökull
mountain massif and the Tungnafellsjökull
area. The ice lobe has been directed by these
two mountain groups towards north and
northeast. Farther to the south, the ice move-
ment was not influenced by the above men-
tioned mountain massifs, and directions of the
striations are towards north and northwest
(.Kjartansson 1955, 1965).
ICE TERMINAL DEPOSITS
The ice recession in the study area was in-
terrupted by glacial stillstands and readvan-
ces. They are marked by terminal moraine
ridges, sandur deposits or kame terraces. Eight
end moraines which have been found in the
area are described below. They are listed in
the order of age from north to south: The
Raudhólar moraine, the Vesturbugur
moraine, the Strangilækur moraine I, the
Strangilækur moraine II, the Miklafell
moraine, the Fjórdungsalda moraine I, the
Fjórdungsalda moraine II and the Fjórdungs-
alda moraine III.
All the end moraines are supra-aquatic. The
Raudhólar moraine is a typical stillstand-
moraine formed when the glacier was
stationary for some time. The moraine ridge is
100—200 m broad, 20—30 m high and often
manifold. The material in the Raudhólar
moraine is almost unsorted till. The moraine is
fairly broad and often indistinct in the field.
Most of the other end moraines are push
moraines formed when the glacier margin ad-
vanced. The push moraines are narrow and
steep, and usually not more than 10 m high.
They consist mostly of coarse till, almost
without finer particles. In some places all the
fine material has been washed or blown away
so the ridges consist almost completely of
stones and boulders. Some of the push morai-
nes may represent surge moraines, in which
case the advances were not of climatic origin.
When the main ice sheet had retreated from
the narrow Skagafjördur valleys up to the
mountain plateau, the ice had become flat—
shaped and the topographical conditions seem
to have been similar to those which Thorarins-
son (1964) described for the surging Vatna-
jökull outlet glaciers in the years 1930—1964.
Raudhólasandur and the
Raudhólar moraine
Huge fluvioglacial deposits lie to the east of
Raudhólar, which is a north-south oriented
hyaloclastite ridge (Fig. 2). The southern and
eastern margin of this formation are terraced.
The terrace is highest at the southeastern
corner, where it reaches 18 m. From the
appearance the southern terrace could be
supposed to be erosional, formed by down-
cutting of the river Bleikálukvísl, as is the case
for the eastern terrace. However, closer inves-
tigations showed that it is a true ice-contact
20 JÖKULL 28. ÁR