Jökull - 01.12.1983, Page 94

logy of ice sheets from the central highlands, show-
ing Mid-Hérad, Fellaheidi, and themouth ofjökul-
dalur. The landscape forms are rather different
from those shown on Fig. 4. The arrows show the
main direction of flow of those glaciers responsible
for the formation of the landscape. From them it can
be seen that these glaciers have moved over an
undulating surface and eroded it according to their
direction of flow. On the other hand it can also be
seen that the main direction of flow has adapted
itself somewhat to the Iarger landforms such as
Fljótsdalshérad and Jökuldalur where glacial ero-
sion has been very active. Fellaheidi displays con-
siderably less of the characteristics ofglacial erosion
so that the glaciers there have been considerably
less active, and in all probability itwas an accumu-
lation zone, so that it was completely ice covered,
although it can be considered likely that Rangár-
hnjúkur and Sigurdargerdisbjarg where nunataks
for long periods of time (Fig. 5).
MARINE EROSION
As to be expected in an oceanic island the coast of
Iceland is much eroded by the sea i.e. wave-cut
clifFs, sea crags and íjord promontories. The more
outstanding examples ofsuch formations are shown
on the map of Iceland in Fig. 3. There it can be seen
that they surround the land almost completely ex-
cept in the geologically youngest parts and farthest
inland in the íjords and inlets. Their development is
at various stages, depending on situation and part
of the country. It is noteworthy that highly develop-
ed marine erosion is associated with the alpine geo-
morphology in all headlands and fjord promontor-
ies, where coastal clifís rising several hundred met-
ers directly out of the sea are widespread or have a
low coastal rim beneath them.
Relative to the present day strandline the strand-
flats appear to be higher in the south and westofthe
country than in the north. From Gerpir southwards
and westwards as far as Stálfjall and Látrabjarg
there are strandflats in front ofalmost all headlands,
but hardly at all underneath headlands in the west-
ern fjords, northern Iceland or the eastern fjords
north of Gerpir. I have not seen or found any satis-
factory explanation for this phenomenon, but the
strandflat is ofgreat importance to the road system.
Where the marine terrace is availabfe the mountain
roads are both few and Iow.
The Norwegian Reusch (1901) introduced the
term strandjlat in 1894, and he believed it to be the
result of marine erosion. Since then various theories
have been put forward as to its formation, for in-
stance Nansen (1922) and Holtedahl (1960), the form-
er rather favouring marine erosion with a mixture of
glacial erosion, and the latter favouring nearly en-
tirely glacial erosion. As regards strandflats in Ice-
land, I lean towards the opinion that marine erosion
in collaboration with piedmont glaciers and sea ice
are responsible for their formation. It is also advis-
able to keep in mind that when marine erosion at
the coastline of an ice covered land, in the Quat-
ernary Era, is compared to the coast of an ice free
land then relative strandline changes are very un-
like because of the interplay of land submergence
caused by ice pressure and a Fa.ll of sea level due to
glacier formation. Marine erosion could have been
more effective on a glacially eroded land, especially
since erosion by fjord glaciers helped to keep the
coast open for attack by the sea.
It is clear that most of the more important wave-
cut cliffs and promontories in the south and west of
the country have been eroded and have acquired
their present appearance at a higher strandline than
that of today. Widespread erosional forms suggest a
strandline 20-40 m higher and even higher, for in-
stance in the inner part of Faxaflói, where marine
erosional forms appear to extend upwards to over
100 m a.s.l. It is now known that the strandline in
Iceland reached from 40 m and up to as high as 100
m in different areas, at the close of the last glaci-
ation. On the other hand I consider it out of the
question to attribute to such a sea level rise ofshort
duration, the formation of wave-cut cliffs and pro-
montories such as Gvendarnes, Austurhom and
Vesturhorn, Lómagnúpur, Eyjafjöll, Esjuhlídar at
Kjalarnes, or Hafnarfjall, to name a few examples.
In fact nearly all the coasts of Iceland display evid-
ence of severe marine erosion in Quaternary time
(Fig. 3). In my opinion another explanation must
be sought for this, rather than the short-term, re-
lative rise in sea level, at the end ofeach glaciation.
Because of the storage of water in Pleistocene
glaciers the surface of the world‘s oceans fell about
100-125 m during the last glaciaúon and even as
much as 160 m when the ice age glaciers reached
their greatest extent in the Quatemary Era (Seibold
1974), but in addition Iceland was submerged to
some extent due to the weight of ice. Most authors
have however tended to the opinion that the strand-
line in Iceland has been somewhat lower than to-
day, even to the extent of several tens of meters. I
92 JÖKULL 33. ÁR