Náttúrufræðingurinn - 1960, Blaðsíða 60

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NÁTTÚRUFRÆÐINGURINN
interruption and bend to East where they form the soutli edge of the Sídufjöll
mountains. 3) It is not easy to point out the place of origin of a glacier which
could dam such a large lake in Skaftártunga. The only possibility left is there-
fore that the sea itself has made the cliffs.
On the west side of Snæbýlisheidi the author lias found two shore lines and
tlieir height corresponds with the uppermost end of two canyons that cut
across the heath. The author maintains that glaciers from the Mýrdals-
jökull ice cap have dammed up a lake west of Snæbýlisheidi. He also states
that the higher coastline is older, as the flow of the older lake has had an
erosion base of about 200 m above sea level. This lake was formed simul-
taneously with the first melting of the glacier in the district. The outlet of
the later lake has liad an erosion base of 140—160 m in most, but could easily
have been at the highest distinct terrace in 120 m height. In the author’s
opinion that lake was formed by a later glacier advance. He considers it
simultaneous to an advance which G. Kjartansson has proved to have taken
place in Hreppar. When this happened the shore seams to have been com-
paratively constant in Hreppar at about 100 m above sea level and this cor-
responds to the 120 m terrace in Skaftártunga. The author tries to explain
the height difference between the highest sea level in Hreppar and Skaftár-
tunga: 125 m resp. 265 m. He thinks it possible that the highest shore line in
Hreppar is not found or that it is younger there than in Skaftártunga and
that the landrise in the meantime counts for most of this height difference.
Finally, the author discusses whether it is possible that the land has been
pressed down by the glacier load to such an extent as to explain the shore
lines. In this connection the author drew a schematic isopachyte map of the
ice thicness at the culmination of the last Glacial in Icelancl (fig. 8). He then
uses the model to calculate the land depression by a method introduced by
Einarsson in “Jökull”.
By this the author gets rather a low value but due to weakness in the crust
of the earth not far from this district he considers the formula to be valid only
with modifications and that these modifications would show a greater land
sinking near the zone of weakness and consequently he claims that the glacial
load would suffice to explain the highest sea levcl in Skaftártunga.
Fig. 9 shows the author’s idea of how a few shore line movement diagrams
could be connected together. The lower step seems now to be from the Alleröd
time. The upper step must be older and has been considered to be 12.000 to
14.000 years old. It should be mentioned that according to Kjartansson the last
considerable advance of the Ice-Age glacier has happened at this upper step.
It then seems that the end of the Ice Age in Iceland was already in Alleröd
time and that never afterwards a continous ice cap has formed to cover the
high platcu of Iceland.