Náttúrufræðingurinn - 1960, Síða 59

NÁTTÚRUFRÆÐINGURINN
225
S U M M A R Y
Snæbýlisheiði
by Haukur S. Tómasson
The State Electricity Authority.
The district, subject to the author’s research, is situated in V. Skaítafells-
sýsla, S. Iceland, where the geomorphological agents have been extremcly
active in post-Glacial time and it is therefore quite difficult to find in the
lowlands soils and subsdils which were formed at the encl of the last Glacial.
Furthermore, this place has been left completely out of all geological studies
apart from those of recent volcanism.
In this district there is a large valley which has not been covered by lava
since the end of the last Glacial. It is this valley and the heath-ridge west of it,
Snæbýlisheidi, which the author has studied. Through the valley runs the river
Y ungufljót. Due to a rapid soil formation and consequently thick soil cover
it is only possible to work there with stratigraphy and large morpliological
[ormelements.
Snæbýlisheidi, a long ancl comparatively narrow lieath ridge which extends
to South-East from the high plateu of Iceland, is formed of palagonite-breccia,
a soft and easily worked rock type. The súrface is mainly moraine but to the
East in the lowlands it is a loessial soil 4—8 m in thickness, underneath is
respectively dark bedded clay, moraine and finally the bedrock itself. On the
hillsides facing East gravel is immediatefy beneath the soil. The explanation
oí these stratigraphies east of the heath is, that the district has once been
covered by sea. The gfacial rivers liave carried the clay to the sea where it has
settled down and the gravel on the liill sicles is formed by the shore of this sea.
Nevertheless, the author has not íound any definite shore line.
The clay reaches at least 180 m above the present sea level and tlie gravel
certainly something over 200 m. For a more exact determination morphological
studies are necessary. The author describes a few cliffs and caves on the east-
side of the Snæbýlisheidi. Fig. 3 is a schematic picture of the eastside of the
heath, showing cliffs and caves. The highest cave is 265 m above sea levef and
a few others in about 240 m height. The author therefore considers the
liighest sea level to have been in about 265 m height, ancl that this height
gradually decreased towards South. In the author’s opinion the land lias been
iri a fast upheaval after the ice of the last Glacial melted away from it and
the cliffs therefore been formed simultaneously to thc quick lowering of the
sea level but only where there existed a steep hill-side.
Tlie author also discusses the possibilities of a different explanation of this
shore line, i.e. that is has not been formed by the sea, but in an icc dammed
lake. But he discovers that it is impossible by 3 reasons: 1) The shore seems to
have moved down constantiy, but not up and down by turns as it should have
done in an ice dammed lake. 2) The limits of such a lake have not been cliscove-
red. On the other side of Skaftártunga are also some cliffs, wliich continue without