Jökull - 01.12.1978, Page 16

Fig. 15. Ice wedge casts at
Vatnsá.
Mynd 15. Fornir ísfleygar við
Vatnsá.
the underlying ice wedge casts. The tephra
layer is of an unknown age and origin. The
eolian sediment displays more than average
consolidation, indicating a rather high age. A
high sedimentation rate is indicated by the
great thickness (1 m) of the ashfree eolian
deposit overlying the tephra layer. The oldest
light tephra layer commonly found in soil
profiles in the Skagafjördur valley is called H5,
and has been dated at 6600 C14 years BP
according to Thorarinsson (Kjartansson et al.
1964). Gudbergsson (1975) found a light
coloured tephra layer, which he called Ö, in 2
of 27 profiles in the Skagafjördur district. In
the 2 profiles the layer was interbedded in an
eolian sand deposit, commonly found under
loeásial soil. The tephra layer H5 was found in
the overlying loessial soil. The eolian sand was
probably deposited in the period after the
land became ice free and before the vegetation
cover prevented further deflation, i. e. in the
pre-Boreal period.
The cold climate suggested by the ice
wedges is likely to have caused a readvance of
the ice front. If the eolian deposit on top of the
casts is of Pre-Boreal age, as assumed above,
the minimum age of the readvance is Younger
Dryas. A higher age is rather unlikely. With
regard to the great extent of the ice in South-
west Iceland in Older Dryas time (Einarsson
1968), it is most likely that the Skagafjördur
valley was glaciated at that time.
TIME OF DEGLACIATION
No datings of late glacial sediments in the
area are available. In the Saudárkrókur ter-
race there are considerable layers of a fine
texture which might well conserve marine
shells, but none have been found. Other late-
glacial marine sediments are coarse grained
and shell findings are not expected. No dat-
ings are available from other places in Central
North Iceland either. Einarsson (1967) sug-
gested an Álftanes stage (Older Dryas) age of
an end moraine, which can be traced from
Hrútafjördur to Blönduós (both localities are
to the west of the Skagafjördur district) and
that the damming up of the Fnjóskadalur
valley by the Eyjafjördur valley glacier, sug-
gested by Áskelsson (1956), occurred at the
same time. If these suggestions are right, the
ice front must have reached far out into the
Skagafjördur inlet in Older Dryas time. On
the highland to the south of the Skagafjördur
district, Kaldal (1976, 1979) and Kaldal and
Víkingsson (1978) have found an end moraine
of probable Búdi stage (Younger Dryas) age:
These estimates are mainly based on the most
probable extent of the main ice to the north
with regard to the dated readvances in the
south and southwest of the country (Kjartans-
son et al. 1964, Kjartansson 1966, Ashwell 1967,
Einarsson 1973).
The ice wedge casts at Vatnsá show that
14 JÖKULL 28. ÁR