Jökull - 01.12.1985, Blaðsíða 14

Fig. 3. Block-field on the high plateau 5 km
northeast of Látrar in Adalvík. The altitude is
about 500 m and the plateau lacks any sign of
active glacial erosion or deposition. A small
perennial snowfield can be seen in the back-
ground. 3. mynd. Stórgrýtisdreif í um 500 m
yfir sjó, um 5 km norðaustan við Látra í
Aðalvík. A hásléttunni eru engin ummerki eftir
virka jökla.
unglaciated enclaves or plant refugia during the
Weichselian, anywhere in lceland. Contrary to this,
Sigbjarnarson (1983) emphasized the importance of
alpine-type glacial erosion on Vestfirdir and stated that
ice-free areas probably existed there throughout the
Pleistocene.
Only limited work has been done on the deglaciation
of the northern parts of Vestfirdir. Thoroddsen (1892a)
suggested two major stages in the deglaciation. During
an earlier phase the glaciers had retreated and the sea
transgressed to 60—70 m above present sea level, with
shorelines and terraces at those altitudes forming in the
outermost coastal areas while the glaciers still remained
in the valleys and fjords. During a later phase, when the
glaciers retreated from the lowlands, shorelines and
terraces were formed at 16—30 m above present sea
level. Thoroddsen (1892a) reported features indicating
ancient sea levels at 63 m above the present one in
Rekavík, at 30 m at Látrar in Adalvík and at 16 m in
Hornvík.
Kjartansson (1969) observed raised beaches in Horn-
vík and on the eastern flank of Kögur. He mapped
outcrops of till in Haelavík and Hlöduvík, and alluvial
and eolian deposits on most of the Hornstrandir low-
lands. He also observed glacial striae around Hornvík,
showing downvalley movements of the glaciers.
John (1974) stated that the highest marine terraces in
the area north and west of Jökulfirdir reached only 10 m
above present sea level, but Símonarson (1979), who
reviewed the geology of Hornstrandir, reported a
marine terrace at 16-20 m above the present sea level
in Hornvík, and suggested a similar elevation for a
marine terrace in Adalvík.
The present study
The maximum glaciation
As mentioned above, the morphology of Hornstrand-
ir is characterized by unconnected short U-shaped vall-
eys, with cirques in their sides and at their heads. The
morphology indicates that cirque glaciers coalesced to
form outlet glaciers which reached beyond the present
coastline. But the high plateaux show no sign of having
been inundated by active glaciers and are usually cover-
ed by mature block fields consisting of local bedrock
(Fig. 3). The very flat surfaces of these plateaux cont-
rast sharply with extensive lower areas which have been
intensely eroded by glaciers (Fig. 4), and with cirques
and different nivation features below the plateau edges
(Figs. 4 and 7).
Today most of the shelf around Hornstrandir is
shallower than 100 m. Thus it may have been dry, or at
least under very shallow water, during the Weichselian
maximum glaciation — provided that this coincided with
the maximum glaciation elsewhere around the North
Atlantic and with the contemporaneous global sea level
low.
An empirically derived absolute upper limit of
actively eroding ice at sites near the present coast,
defined as plateau surfaces without signs of glacial
erosion, plus the assumption that the ice was grounded,
allows us to approximate the outer edge of the glaciated
area at the maximum situation. Giving the large outlet
glacier from the Vestfirdir ice cap, which must have
existed in ísafjardardjúp, an Antarctic type B overall
gradient and a surface profile of a 60—100 km long
Greenland outlet glacier (Buckley 1969; as used for
central North Iceland by Norddahl 1983), it can be
12 JÖKULL 35. ÁR