Jökull - 01.12.1965, Page 27

Fig. 6. View across Hest-
háls towards Skorradals-
háls showing the hori-
zontal nature o£ the
ridges and some o£ the
spillway channels.
TABLE 1.
Deposits found in the E side of spillivay No. 2.
Thick-
ness No.
5 m 1
7 m 2
3 m 3
Nature o£ material
Top of Exposure.
Beclded silty material with a i'ew
small rouncled stones. Bedding
is unconformable with surround-
ing basalts. Material cracked and
cracks filled with white hard de-
posit.
Silty conglomerate, with stones
varying in size from 4 cm to 4
mm in diameter. No sign of re-
gular arrangement.
Layered silt without any stones.
(Base o£ exposure.)
When tested by sieving and plotting on a
log-probability grapli (Fig. 9) all three layers
show an approximately parallel arrangement,
especially in the smaller grain sizes, the lower
silt being best sorted. The steepness of the
plots, and the marked discontinuities indicate
that there is little degree of sorting, and that
the deposits have probably been deposited as
a result of a turbidity flow of some description,
a glacial melt-water stream being the most like-
ly agency. The fact tliat this deposit has been
cleanly cut through by the present spillway
suggests that the old spillway cut in basalt was
filled in by the deposits of the first melt-water
activity, perhaps at time of higher base-level,
and re-cut by a second period of melting, with
lower base-level, perhaps when the older de-
posits were somewhat hardened by age.
V
Although the cutting of these channels seems
to liave occurred mainly at a time of heavy
glacial cover, it seems possible that they were
finally used when a large part of the glacial
Fig. 7. A shallow channel on the higher part
of the Hestháls system, possibly cut on a pre-
existing platform.
JÖKULL 133