Jökull - 01.12.1978, Page 15

Fig. 13. Ice wedge casts at Vatnsá assumed to be of Younger Dryas age. The section shows
a sediment filled Kettle. Key: 1. Fluvioglacial, stony gravel, 2. Lacustrine silty sand, 3.
Fluvial sand and gravel, 4. Ice wedge casts, 5. Eolian soil.
Mynd 13. Fornir ísfleygar viö Vatnsá, sem taldir eru vera frá yngra holtasóleyjarskeiði. Sniðið synir
setfyllt jökulker. Skýringar: 1. grófl jökulárset, 2. vatnaset (sandur og méla), 3. ármöl og sandur, 4.
ísfleygafyllingar, 5. fokjarðvegur.
of polygons on patterned ground. Remnants
of a homogenous stony gravel layer are located
aside of the top of some of the narrowest
wedges. This is thought to be the last active
layer before the melting of the wedges. This
is seen at the left side of the wedge on Fig.
15. At the top of the broader wedges this
material is absent, and there are low
depressions on the surface of the deposit. This
indicates that the active layer fell as a whole
into the broadest wedges when the ice melted,
but some of it was left at the top of the nar-
rower ones.
The ice wedges are considered to have
developed under plurannual permafrost con-
ditions. Ice wedges which form during one
winter and are subject to melting in the next
summer will never reach more than a few mm
width. Such wedges will be filled by sand, and
even if they develop year by year, each year no
greater grains than sand are able to penetrate
down the narrow openings (Washburn 1973).
In the ice wedge casts described above stones
up to 20 cm in diameter are observed.
On top of the fluvial material there is an up
to 1 m thick layer of silty sandy eolian soil. It is
rather homogenous, but near the bottom of it
a 2 cm thick light coloured (acid) fine sandy
tephra layer was found. It is very distorted but
nevertheless it can easily be followed across
Fig. 14. Ice wedge casts at
Vatnsá. Note the bending down
of layers at the cast margins and
the coarse material in the casts.
Cf. Fig. 13.
Mynd 14. Fornir ísfleygar við
Vatnsá. Lögin milli fleyganna hogna
niður hjá þeim. Hið grófa efni í
fleygunum sést vel á myndinni.
JÖKULL 28. ÁR 13