Jökull - 01.12.1978, Blaðsíða 29

ever, this cannot be decided without further
investigations.
When the glacier margin was at the Mikla-
fell end moraine the glacier did not overrun
the 1300 m high Miklafell (ca. 500 m above
the surroundings). This can be seen from the
ice-contact slope on the mountain side. In the
north it lies at about 800 m a.s.l. and rises
southwards to about 840 m. Further south all
evidence of the ice margin along Miklafell is
destroyed by glacial rivers, recent end morai-
nes and talus.
The Fjórdungsalda moraines I, II and III
Three end moraines were found on the
plains to the east of Miklafell. They trend in
an east-westerly direction perpendicular to
the present Hofsjökull margin. Since there are
only 1—2 km between them they will be dis-
cussed together. The northernmost one,
Fjórdungsalda I, can be traced over a distance
of about 14 km, from Kvíslarhæd to Fjórd-
ungsalda, from which it derives its name (Fig.
1). The ridge is 200—300 m broad, and not
more than a few meters high, so it is not very
prominent except on airphotos. To the west
the end moraine disappears beneath a wide
outwash plain from the Fjórdungsalda III
moraine and a recent glacial river from Hofs-
jökull. The material in the ridge is a rather
coarse grained till with a stony surface. The
two other ridges are not as broad as the first
one and cannot be traced as far.
Inside Fjórdungsalda II the fluted moraine
indicates an ice movement towards north-
northeast and even more easterly inside
Fjórdungsalda III.
FLUVIOGLACIAL DEPOSITS
The major part of the fluvioglacial deposits
in the present area are proglacial sandur-
plains, formed in front of the retreating glacier
at different stages. Such deposits are found in
front of the Raudhólar, Vesturbugur-, Mikla-
fell- and Fjórdungsalda III end moraines. The
material in most of these deposits is very
similar to the material in the Raudhólasandur
formation (Fig. 6) but for the boulder content.
Fig. 11 shows a reconstruction of the
position of the glacier margin at different
stages and the respective proglacial sandur-
plains. On Fig. 11 IV the present Hofsjökull is
shown. The dark colored sandur-plains on the
figure have been deposited by glacial rivers
from Hofsjökull. At present the glacial rivers
only deposit material near the glacier, but
farther downstream they cut channels into
older sandur-plains or other sediments. Fossá
in the west of the area and Austari-Jökulsá in
the east can be mentioned as examples. Most
of the fluvioglacial deposits in the area shown
on Fig. 11 originate from the retreating ice in
Lateglacial and Pre-Boreal time, and not from
the present Hofsjökull.
Hofsjökull reached its maximum extent in
Holocene time about the year 1890, but since
1920 it has been retreating from its outermost
moraines. Hence, the meltwater supply from
Hofsjökull can be assumed to have been
greater during this century than ever before
during the Holocene, and furthermore, most
of the fluvioglacial sandur-plains formed by
the rivers from Hofsjökull were deposited
during this century.
DISCUSSION
The position and direction of the Late-
glacial end moraines indicate that the Hofs-
jökull area was not an independent glaciation
centre as it is at the present time. Most likely
no glacier existed on the Hofsjökull mountain
area except on the highest peaks, when the
Miklafell moraine was formed. The explan-
ation for this was the almost complete rain
shadow to the north and northwest of the in-
land ice sheet. Today the prevailing rain car-
rying wind direction in Iceland blows from the
south and southeast. There is a great dif-
ference in the amount of precipitation south
and north of the large ice caps, because the
humid winds loose their precipitation on their
way over the mountains. To the south of
Vatnajökull the precipitation is 2000—4000
mm/year but only 400— 1200 mm /year to the
JÖKULL 28. ÁR 27