Jökull - 01.12.1967, Blaðsíða 55

Fig. 5. A view towards
east across lake Langi-
sjór. In the eastern side
the two shorelines can
be seen. The foreground
shows the pumice into
which the shorelines are
cut. Indistinct lower shore-
lines are also distinguish-
able there.
Mynd 5. Séð til austurs
yfir Langasjó. A austur-
ströndinni sjdst strandlín-
urnar tvœr. I forgrunni
sést vikurinn, sem strandlínurnar eru myndaðar i. Einnig sjcist ógreinilegar lœgri strandlinur.
1938. The area was again photographed and
mapped in 1946, this time by the U.S. Army
Map Service. Geologic investigations at Langi-
sjór did not begin until in the year 1956. To
begin with they were carried out by G. Kjartans-
son, geologist (Kjartansson 1957).
The maps on Fig. 7 show the major morpho-
logical changes, that have taken place at the
north-eastern end of Langisjór from the year
1889, when Thoroddsen described the condi-
tions there, up to the year 1966. At present an
outwash plain lies between the lake and the
glacier. On this outwash plain are found re-
mains of three terminal moraines lying at dif-
ferent distances from the lake shore. Of the
outermost one, lying closest to the lake and
being the oldest, only small remnants are still
to be seen at the bast of Fögrufjöll. The next
terminal moraine, the one in the middle, is
situated on the middle of an alluvial cone
built by the southern glacier river. The micldle
moraine is about 200 m farther away from the
lake shore than the outermost one. The third
ancl uppermost moraine is by far the greatest
with some of its parts reaching up to 30 m in
height. It lies about 300 m farther from the
Jake than the middle one. This terminal mo-
raine marks the position ol' the glacier margin
in 1946, cf. Figs. 6A ancl 7C. About 300—400 m
inside the uppermost moraine the glacier ice
is now visible, but all the space between it
and the uppermost terminal moraine is sand-
coverecl stagnant ice. The glacier margin is flat
and its limits with the stagnant ice are in-
distinct.
For a greater part of the time two glacier
rivers seem to liave issued from the glacier,
one of which formed the alluvial cone on the
southern part of the cutwash plain. For distinc-
tion we have termed it the southern glacier
river. The other glacier river has come from
a nook at the Tungnaárfjöll mountains and
drained alongside them into the lake. This
river lias as a rule liad greater discharge tlian
the other. We have namecl it the northern
glacier river.
At Langisjór two distinct shorelines are
found, which can be traced easily around the
lake. The elevation of the higher one, when
measured by the SEA Hyclrological Survey in
August 1959, proved to be 668.9 m above sea-
level. By then the water level of Langisjór was
in 662.7 m elevation, i.e. 6.2 m lower than the
shoreline. The lower shoreline was not measur-
ed, but it is about 2 m lower than the upper
one. Besides these two shorelines there is a
series of other indistinct shorelines between the
lower one and the present lake level. All shore-
lines encountered bv the authors are cut into
loose and often very ashy layers. At the south-
ern end of the lake the shorelines are cut into
pumice from the Laki eruption of 1783, but
the eruption fissure lies at only 12 km distance
south ancl south-east of Langisjór, cf. Fig. 1.
At the north-eastern end of Langisjór the
glacier extended into the lake in 1889, but
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