Jökull - 01.12.1978, Side 62

(see BLAD 62 Eyjafjördur). No glacier is
marked on the 1:100 000 map but the glacier
is a very prominent valley head feature, ex-
tending for about 1.6 kilometres, and 0.5
kilometres wide. The glacier appears to be
wasting and stagnant, with virtually no cre-
vassing present and a fairly gentle snout. In
cross profile the glacier is lowest in the centre
rather than towards the sides.
The glacier head occupies a col which on its
southern side hangs above a corrie basin at
the head of Thverárdalur. This valley head
appears empty of ice now but would appear to
have been a major supplier of ice for Hálsjök-
ull at some time.
Hálsjökull also has a small tributary glacier,,
which occupies a classic corrie basin directly
beneath Rimar and which appears to hang
above the main glacier basin. The early cre-
vasses on this stagnant glacier appear on this
steep hanging slope but even these are only
small cracks.
The valley trough, called Hálsdalur,
occupies a very deep trench cut transversely
across the dip of the basalt rock strata which
would appear to dip from west to east. Con-
sequently the very steep east sides of the valley
are rougher and craggier than the equally
steep west side. However lateral moraine in
the west side up to a height of approximately
900 meters covers and obscures much solid
rock on that side.
Survey of the glacier
A plane table survey was carried out at a
scale of 1:5000 with a contour interval of 10
meters. The intention had been to survey only
the snout, and control stations were set up for
this. Extension subsequently took place to the
upper glacier reaches mainly by intersection
and the accuracy no doubt lessens around the
upper glacier margins, but no checks were
made in the upper area. Heights were sur-
veyed from the Jöklamerki which represented
one end of the base-line and the height was
estimated from the Geodetic Institut map as
760 metres. Subsequently it was found that
the estimated height of the Jöklamerki by
Helgi Hallgrimsson was given as 900 m, so it
would seem to be important for a further ex-
pedition to establish a proper datum height. It
is possible that our estimated height is a little
low, but the height of 900 m seems very high.
Heights were made by level to some of the
major control points, but mainly by Indian
Clinometer, and closed satisfactorily. Paced
traverses were made along various controlled
lines up the glacier in order, by intersection, to
give a good height control from which to draw
up the contour pattern. The glacier snout was
fixed by resection at frequent intervals but
there was difficulty in establishing the exact
edge of the snout. There had been consider-
able snow cover and this had not all melted so
that the margins, particularly on the lower
glacier sides, may be rather higher than they
should be.
R. J. Metcalfe,
The High School of Glasgow.
60 JÖKULL 28. ÁR