Jökull - 01.12.1990, Page 37

eyjarskagi. Concurrently with the advance of the local
glaciers a glacier tongue from the Bárðardalur outlet
glacier terminated just west of Ljósavatn in the eastem
part of Ljósavatnsskarð. The position of a contempo-
rary glacier terminus in Eyjafjörður, Fnjóskadalur and
Bárðardalur is still unknown (Fig. 3).
Chronologically the Fnjóskadalur Sequence spans
the period between the maximum glacier extent at
about 18,000 and the concluding phase of deglacia-
tion including the final departure of glaciers from the
North Icelandic lowlands (Norðdahl, 1990; 1991).
According to 14C dated limnic sediments in Flat-
eyjardalur (Fig. 3), this withdrawal did not occur
any later than 9,650 ± 120 B.P. (Lu-1433) (Norð-
dahl, 1979; 1991). Recently, the Fomhólar read-
vance and, thus, the Austari-Krókar ice-dammed lake
have been indirectly dated by the Skógar Tephra to
10,600 B.P. (Norðdahl and Hafliðason, 1990). Fur-
thermore, the 14C dated sample from Flateyjardalur
(9.650) probably postdates a Preboreal readvance of
local valley and cirque glaciers in the Flateyjardalur
nrea, and the water outflow from the youngest ice-
dammed lake along Flateyjardalur (Fig. 3) in North
Iceland (Norðdahl, 1979; 1991). Thismeans, thatthe
Fornhólar, Belgsá, and Ljósavatn/Langhóll advances,
and the formation of the Austari-Krókar and Fnjóska-
dalur ice-dammed lakes all occurred later than 10,600
B-P. but before the beginning of limnic sedimentation
in Flateyjardalur, 9,650 B.P. (Norðdahl, 1990).
Among many important results that have emerged
from the above cited studies of the sediments in
Fnjóskadalur, is the initiation of a complex multi ad-
vance deglaciation (MAD) model for North Iceland
(Norðdahl 1979,1983). Another major conclusion is,
that the glaciers in North Iceland were more extensive
'n Younger Dryas time than the foregoing DAD-model
suggested (Norðdahl and Hafliðason 1990, Norðdahl
1990). Numerous marginal deltas and raised marine
lerraces found at 20-25 m a.s.l. between Hörgá and
Akureyri in Eyjafjörður (Fig. 3) are heterochronous
features formed along with southward retreat of the
°utlet glacier in Eyjafjörður. Consequently, the ma-
nne limit in Eyjafjörður is younger than the Belgsá
readvance (Younger Dryas) and it probably reached its
ntost elevated position in the southem parts of Eyja-
Figure 4. Late Weichselian and early Holocene
end-moraines and marine-limit features in North-
west Iceland. Legend: 1) Occurrence of tephra
layers. 2) Raised beaches. 3) End-moraines. 4)
Terminal zones. —Jökulgarðar og sjávarborðsmenj-
arfrá síðjökultíma og upphafi nútíma á Norðvestur-
landi. Tákn: 1) Fundarstaður gjóskulaga. 2) Forn
fjörumörk. 3) Jökulgarðar. 4) Oviss lega jökuljaðars.
fjörður in Preboreal time (Norðdahl, 1991).
The four ice-dammed lake strandlines in Fnjóska-
dalur have distinct positive gradients of 2.22; 2.00;
2.65 and 1.59 m/km towards the south (Norðdahl,
1983). The different gradients indicate variable de-
pression of the land, due to glacier overburden load.
They are also diagnostic of different uplift durations
and clearly indicate that the four strandlines were
formed by four successive ice-dammed lakes; the Ytri-
Hóll, Grímsgerði, Austari-Krókar and Fnjóskadalur
ice-dammed lakes (Norðdahl 1981,1983).
NORTHWEST ICELAND
During the Weichselian maximum glaciation the
Vestfirðir peninsula was most likely covered by an ice
cap, that was dynamically independent of the main
inland ice sheet. The peripheral plateaux in Horn-
strandir (Fig. 4) — at about 400 m a.s.l. — were not
covered by active glaciers as no signs of glacial ero-
sion or depositionhave been found there (Hjort et al.,
1985). Earlier a similar conclusion, concerning the
JÖKULL,No. 40, 1990 35