Jökull - 01.12.1990, Page 45

probably reflect regional climatological changes in the
North Atlantic region and an altered mass-balance of
the inland ice sheet. Although an Older Dryas advance
has not yet been positively recognized and dated out-
side West Iceland (Fig. 10), comparison with Scan-
dinavia (Berglund, 1979; Mangerud, 1980; Berglund
and Mömer, 1984) lends support to an idea that a
glacial event equivalent to the Older Dryas Skipanes
event in West Iceland may also have occurred in other
parts of the country. An apparent Bolling glacier ad-
vance (Fig. 10) is as yet only found on Melrakkaslétta
inNortheast Iceland (Pétursson, 1986; 1991).
The increased research efforts in deglaciation stud-
ies in Iceland have not only led to a revision of the num-
ber of glacier readvances and their chronological po-
sition, but have also radically changed the concept of
areal extent of the Icelandic inland ice sheet during the
mdividual Late Weichselian readvance episodes. The
concept of the D AD-model of Late Weichselian glacier
extent in West Iceland was questioned by Ingólfsson
(1985, 1988) when he pleaded for a heavier Older
and Younger Dryas glaciation of the area by demon-
strating that the major outlet glaciers in Borgarfjörður
and Hvalfjörður terminated on two separate occasions
(about 11,800 and 10,600 B.P.) in the vicinity of Akra-
fjall in the outer parts of the West Icelandic lowlands
(Figs. 5 and 11).
The DAD-model’s concept of glacier extent was
also disputed in Northeast Iceland, when Pétursson
(1986; 1991) presented a Younger Dryas glacier ad-
vance that reached at least as far north as the Röndin
sediments at Kópasker on westem Melrakkaslétta
(Pigs. 6 and 11), about 75 km north of the previously
defined Younger Dryas glacier margin. A compara-
ble conclusion was reached when Norðdahl and Hjort
(1987) described a probable Preboreal glacier advance
>n the inner parts of Hofsárdalur and Vesturárdalur in
^opnafjörður in Northeast Iceland (Figs. 6 and 11).
New stratigraphical and chronological evidence
Places the Búði moraine in South Iceland within the
Preboreal Chronozone (Figs. 8 and 11). Furthermore,
a lack of sediments of Allerpd age in the area beyond
Ihe Búði moraine (Fig. 10) is believed to indicate
that the South Icelandic lowlands were ice-covered
during the Younger Dryas glaciation (Hjartarson and
Ingólfsson, 1988). AccordingtoHjartarson(1989)the
Reykjavík area in Southwest Iceland was at least once
overridden by glaciers in the period between 9,815 and
11,000 B.P., i.e. during the Younger Dryas Chrono-
zone. Furthermore, a termination of a glacier advance
in the area northeast of Reykjavík around 9,815 B.P. in-
dicates that the glaciers may possibly have been more
extensive in early Preboreal time, than was previously
indicated by the DAD- model (Figs. 9 and 11).
New results from investigations in the Fnjóska-
dalur area in North Iceland also render support to a
modification of the DAD-model’s concept of glacier
extent (Norðdahl, 1990; 1991 Norðdahl and Hafliða-
son, 1990). The existence of the Austari-Krókar ice-
dammed lake in Fnjóskadalur at about 10,600 B.P.,
shows that during the Younger Dryas Chronozone
the outlet glaciers in Eyjafjörður and Bárðardalur ex-
tended at least north beyond Dalsmynni and Ljósa-
vatnsskarð, respectively (Figs. 3 and 11). This great
extent of glaciers in Younger Dryas time is further-
more supported by the great southward gradient (2.65
m/km) of the corresponding strandline of the Austari-
Krókar ice-dammed lake, a gradient that definitely
reflects an increased glacier load on the crust in the i
Fnjóskadalur area (Norðdahl, 1983).
This review of the Late Weichselian deglaciation
history of Iceland, leads to the conclusion that the
above outlined MAD-model now contains four plau-
sible glacier readvances in the period between 12,655
and 9,650 B.P. Two of these advances, the early Pre-
boreal and Younger Dryas advances, which have been
14C dated in a few localities in Iceland, probably oc-
curred simultaneously throughout the country. On
the other hand, the Older Dryas advance has as yet
only been securely dated in West Iceland, and the
presumed Bolling readvance has only been dated in
Northeast Iceland. The previous DAD-model con-
tained two widespread glacier readvances, while the
present MAD-model additionally includes two locally
identified readvances. In early Preboreal time consid-
erable portion of present day land area, although at that
time submerged in the sea, may have protruded beyond
the margin of the inland ice sheet in South, Northeast,
North and West Iceland. In Younger Dryas time a
continuous inland ice sheet probably reached beyond
JÖKULL,No. 40, 1990 43