Jökull - 01.12.1982, Síða 7

Fig. 3. Bedrock outcrop of Grímsey vvith two sets of
glacial striae. Older movement demonstrated by
the pencil.
Mynd 3. J'ökulsorfin kl'ópp í Grímsey. Jökulrákir syna að
jökull hefur skriðið yfir hana í tvœr mismunandi áttir.
Penninn sýnir skriðstefnu þess jökuls sem fyrr var á
ferðinni.
two sets of striae occur: one set shows the main flow
direction as coming from the south and another,
younger set, indicates ice movement from N 60° to
65°W (Fig. 3). Thefollowingexplanation wasgiven.
During an early stage of deglaciation the ice edge
lay far to the north ofGrímsey. At that time ice flow
everywhere over Grímsey was directed moreor less
toward the north. At a later stage ice retreat was
accelerated over the adjacent Skjálfandadjúp by
iceberg calving, causing the development ofa large
calving bay there; an ice cliff east of Grímsey was
oriented approximately north-south, parallel to the
depth contours. The ice movement over southem-
most Grímsey then changed to a direcdon perpen-
dicular to this north-south ice cliff.
The valley system of southern Grímsey with its
surprising slope to the south is an excellent and well
preserved example of a series of glacial drainage
channels. This interpretation is in full accord with
the ice retreat as demonstrated from the south head-
land locality and with the local topography. When
the north-south ice margin passed southern Gríms-
ey the meltwater streams were controlled by the
orientation of the margin and the topographical
situation to the south.
The observations quoted above provides convin-
cing evidence that Grímsey must have been totally
overridden by an ice sheet; i.e., the ice border then
stood several tens of kilometres north of Grímsey.
With Grímsey covered by ice from the southerly
mainland the area around Eyjafjördur and Skjálf-
andi must have been heavily glaciated; nunatak
areas, however, cannot be excluded. The well pre-
served meltwater channels and apparent absenceof
either solifluction cover or ofoldersoilsover the thin
deposits suggest a Weichsel age.
In a paper which appeared at the same time as
the present author’s, Einarsson arrived at the same
conclusion about the ice sheet over Grímsey; his
study also utilized striae observations (Th. Einarsson
1967). In a recent paper Norddahl (1981), on the
basis of his studies of the ice-dammed lakes in
Fnjóskadalur tentatively proposed that the oldest
lake existed 20,700 years BP. This means that „the
maximum extent of the Weichselian glaciation
possibly occurred before 18,000 BP“, earlier believ-
ed to be the time of the maximum. Further investi-
gations based on age determinations are highly
desirable.
SOUTHWESTERN ICELAND (Fig. 4)
For a long time comprehensive documentation of
a total ice cover of southwestern Iceland, at least of
syntbols: observations by G.H.; when thin they
show older flow directions. Short symbols: striae
mainly from the geological maps oflceland.
Mynd 4. Jökulrákir á suðvestanverðu íslandi.
JÖKULL 32. ÁR 5