Jökull - 01.12.1966, Page 6

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Fig. 3. Ancient shorelines and present uplift of Scandinavia. G = Gedynia (ice margin about
14000 B.P.), C = centre of uplift of Littorina level. 1. Yoldia sea, about 9500 B.P. l'. Same cor-
rected for stand of absolute sea-level. 2. Ancylus lake, about 8500 B.P. 3. Littorina sea, about
7000 B.P. 3'. Same corrected for stand of sea-level. 4. Velocity of present uplift in arbitrary units.
3. mynd. Gamlar strandlinur í Skandinaviu (1—3) og lyftingarhraði nú d tirnum (4).
below the present stage. On the other hand the
lake was probably 10—20 m above sea-level of
that time, but an accurate figure is not avail-
able; so we assume that the two corrections
compensate each other. For the Littorina level
we apply a correction of 10 m to get line 3'.
Comparing curves l', 2, 3' and 4, we must
conclude that after Yoldia time there was no
systematic movement of a hingeline or a „wave-
motion“ towards the centre of glaciation. All
the levels cut each other in very much the
same area, indicating synchronous movement
in the whole affected area. See also Flyyppá
(1963).
It seems at first strange that the levels meet
in a zone about 200—300 km inside the margin
of the glacier at its maximum stage, see Fig. 4.
This may be understood with reference to Fig.
5. Suppose a thick glacier reaching to the stage
1. It will create a bowl below itself and a
corresponding low rise outside. Suppose now
that the glacier extends with a thin marginal
sheet to stage 2, then the weight of this sheet
may have very little isostatic effect. It may
perhaps lower the rise somewhat, but there
need not be created a new and wider bowl.
Furthermore, just as it is questionable whether
a 100 m ocean layer has an isostatic effect,
the same applies to an ice-sheet of 110 m thick-
ness.
The hingeline of the movement, or axis of
rotation of the levels, then seems not to have
advanced gradually towards the centre, and
lines 3 and 4 in Fig. 3 demonstrate very clear-
ly that the present uplift is nearly identical
in character with the average picture during
the last 7000 years. Only in the first 1000 years
after the ice of the Yoldia time disappeared, it
seems (cf lines 1 and 2 in Fig. 3) that there was
a temporary rapid uplift of the newly deglaciat-
ed area.
For the earliest time the synchronous char-
acter of the uplift of the Scandinavian area
may in part be due to the fact that retreat
of the margin and thinning of the glacier were
synchronous but at any rate after about An-
cylus time this character is a purely hydrodyna-
mical feature on which studies of viscosity may
be based.
3. ICELAND.
Iceland is roughly of a slightly oval shape,
with an average diameter of about 450 km.
Raised beaches are found all around the coast
except at the mouth of Eyjafjörclur on the
middle northern coast, where the terraces along
the fjord come just down to sea-level (Einars-
son 1959). The age of the highest beaches is
about 11.000 years (see below) at which time
the sea was about 30 m below the present level.
160 JÖKULL