Jökull - 01.12.1983, Page 93

down the slopes, before they joined the main valley
glacier. On this basis I have therefore estimated the
mean thickness of the main valley glaciers, which
have formed the fjords and the valleys inland of
them, as well as showing their main direction of
flow. It should be pointed out that by the estimated
mean thickness I do not refer to any particular time,
but rather the mean thickness of glaciers respons-
ible for erosional forms. It is estimated by many
factors, such as the erosional forms of the main
fjords and valleys glacial cols the height of hanging
valley and corries and the spurs between them.
VVith the formation of the fjords the mean thick-
ness of the glaciers was 100 m above present sea
level at their mouth and increased slightly inland up
to 500-600 m a. s. 1. farthest up the valleys. Observ-
ations on the level of corries farthest out on the
fjords and promontories suggest that the glaciation
limit has been 350-450 m a. s. 1. facing the sun on the
northern side of the fjords, but about 100 m lower in
the shaded southern side of the Ijords. The glacia-
tion limit and therefore the corries level has then
usually increased gradually inland, but here it is
more diíficult to estimate because of the added fact-
or of the increasing thickness of the main valley
glacier.
Piedmont glaciers have spread out considerably
from the fjord mouths as the arrows in Fig. 4 show.
It is difficult to estimate their size. The accuracy of
marine charts is not sufficient to enable the deter-
mination of smaller landforms on the seafloor. The
ablation zone of the glaciers extended fairly far up
the fjords, and that makes it possible to conclude
that piedmont glaciers have never extended more
than a short distance outwards on the continental
shelf (5-10 km). This all suggests that there have
always been some ice free areas on the spurs and
farther out on the fjord slopes, as well as nuntaks on
steep slopes, serrated edges and homs above the firn
limit. On Fig. 4 those areas are marked where it is
very probable that there were always some ice free
areas.
In comparison with the alpine landscape of the
eastern fjords (Fig. 4), Fig. 5 shows the geomorpho-
Fig. 5. Glacial geomorphology in Mid-Hérad and Jökuldalur. Arrows show the main direction of flow of
glaciers which produced the landforms. Fellaheidi has probably been a glacier accumulation area.
Mynd 5. Jöklalandmótun á Mið-He'raði og Jökuldal. Örvarnar sýna megin skriðstefnu þeirra jökla er mótuðu
jöklalandformin. Fellaheiðin hefur líklega verið jökulsafnsvteði.
JÖKULL 33. ÁR 91