Jökull - 01.12.1965, Page 25

Fig. 2. Tlie steeply inclined encl of two of the
channels in Lundarreykjadalur, from the Hest-
háls road.
ridges. In the present case we can eliminate pro-
glacial lakes as a cause of the channels, since,
with such a lake in Lundarreykjadalur, we
would expect the channel heights to fall re-
gularly in one direction so that drainage
through them could take place as they were un-
covered by successive retreat of ice. We woulcl
also expect, if a lake were present, that the
mouth of the valley was blocked by thick low-
lancl ice, and the valley filled with a thinner
tongue of ice, which was retreating, which hard-
ly seems likely.
A more likely hypothesis is that both low-
land and the ridges and valleys between were
covered by a thick ice cover. The sub-glacial
drainage of Lundarreykjadalur would tend to
flow down the present valley, but would be
held up both by the presence of ice in the
lowland and the mass of Hestfjall, which partly
closes off Lunclarreykjadalur from the lowland.
The existence of ice in the lowland is indica-
ted by the fact that the most westerly of the
drainage channels, the Kvígsstaðasneið, actually
begins in the lowland rather than in I.undar-
reykjadalur. (Figure 5.) The direction of flow
of the lowland ice was probably from the ENE,
since large ice scratches on rock exposures at
the mouth of I.undarreykjadalur, the Stekkj-
arás, point directly from this direction, in
which lies tlie volcanic shield of Ok. It seems
probable that this ice lay closely against the
fronts of the ridges, and that the steep fronts
of these ridges, running approximately along
the line of strike of the country basalts, may
be due to either ice erosion, or to water chan-
neled between the ice and the ridges, or both.
If the whole ice-mass, both in highland and
lowland, was moving from the NE, as other
indications show (Kjartansson, 1955), then eacli
ridge of the Borgarfjarðardalir would act as a
barrier to sub-glacial drainage. The water would
tend to flow over the ridge if possible, and in
Fig. 3. Tlie Hestháls
glacial spillways from the
Skorradalur. Hestfjall lies
to the left, at the end of
the ridge, and the large
channel below it is Kvígs-
staðasneið. The channels
slope gently into Skorra-
dalur.
JÖKULL 131