Jökull - 01.12.1989, Page 30

Fig. 5. The Álftanes peninsula and the Álftanes
end-moraine formed by a short glacial advance dur-
ing Younger Dryas or Preboreal times. Photo B.
Aðalsteinsson.
Mynd5. Álftanes og Álftanesgarðurinn. Jökulgarður
frá stuttu framskriði Suðvesturlandsjökulsins í eða
skömmu eftir ísaldarlok. Ljósm. B. Aðalsteinsson.
marine sediments by the erosion of the glacier that
deposited the upper till. The outermost end-
moraines from the Younger Dryas glacier are still
unknown, but most likely they lie on the floor of the
Faxaflói bay a bit further out.
The Weichselian glaciation ended 10,000 years
BP, and the Holocene began. It is not known when
the glaciers of the Younger Dryas retreated from
their outermost position. Their retreat seems to have
been rapid, although not continuous. It slowed down
from time to time, and stopped at times, and the gla-
ciers even advanced again for a while. The Álftanes
end-moraine, and the group of moraines by Kópa-
vogur are examples of such advances during late
Younger Dryas or early-Preboreal.
SEA LEVEL CHANGES
The sea followed the retreating glaciers behind
the present coast line. Sediments were deposited on
top of the ground moraine on the sea floor and sea
shells occupied the area. The age determinations
from Austurströnd at Seltjarnarnes, and Hótel Loft-
Fig. 6. Raised beach of early Preboreal age 43 m
a.s.l. at the Öskjuhlíð hill in Reykjavík. Photo Á.Hj.
Mynd 6. Strandlína frá upphafi nútíma í Oskjuhlíð í
43my.s. Ljósm. A.Hj.
leiðir, indicate that the glacier had left the area
9800-9900 BP.
Preboreal coast lines are 43 m above sea level on
Öskjuhlíð (Fig. 6), just over 40 m at Nónhæð south
of Kópavogur, and 32 m at Hvaleyrarholt. There are,
however, no indications regarding the sea level dur-
ing Alleröd. According to Ingólfsson (1987a,b) the
sea level on the outer part of Borgarfjörður was
about 60 m above present sea level during late
Younger Dryas, and at 80-90 m during late Older
Dryas. In Reykjavík, it is therefore likely, that the
sea rose higher during Alleröd than it did later,
perhaps up to about 50-100 m above sea level.
SUMMARY
The Fossvogur layers at Nauthólsvík and Skerja-
fjörður are a well preserved geological formation of
late Weichselian and Holocene sediments. The sedi-
ments and the age determinations presented here
reflect the following geological development:
28 JÖKULL, No. 39, 1989