Jökull - 01.12.1985, Blaðsíða 39

Fig. 6. Particle size distributions for selected sediments.
79/1, sand in middle part of esker in Eyvindará valley,
80/1, sand and rolled gravel, lower
Melar section,
80/2, Unsorted upper layer,
80/3, Skriðuklaustur material near
Bessastaðaá,
80/4, layered sand and gravel, esker on
Fljótsdalsheiði,
80/6, Fine layered material, lower part
of deposit, Ytri-Viðivellir,
80/8, Unweathered layered material,
mouth of Norðurdalur,
80/9, Contorted sands and gravel, low-
er part of Nordurdalur section,
80/10, Unsorted material covering 80/9.
6. mynd. Kornastœrðardreifing í set-
lögum.
son et al. 1981) and associated with the maximum dip of
the Lagarfljót flexure, (Fig. 2). The arrangement of the
debris, however, mainly in hillocks of apparently fine
material, at some distance from the cliff foot, suggests
that the fall could have been the result also of undercutt-
ing by ice or water and removal of debris on or in a
glacier.
As the valley opens out northwards, so closed chann-
els occur more frequently. These features, similar to
those described in W Iceland, (Ashwell 1975), are com-
paratively rare on the E side of the lake, being found
there mainly near Freyshólar, N of Hallormsstaðir and
in the Sjónarásar, S of Egilsstaðir.
The W side of the lake, however, is seamed with
these features, (Figs. 2 and 4), some even appearing
above Sandvatn stóra on the top of the Fljótsdalsheiði
plateau. Although the channels are usually associated
with depositional features, it seems logical first to
describe the channels, then the deposits and their con-
nections. The channels were best located first on the
good available air photographs, especially in the north-
ern part of the area, because they tend to occur on and
over spurs of the plateau which are not easily visible
from the lakeside road. In cross-section the channels are
steep-sided and comparatively flat-floored, often more
than 10 m deep, and in long profile they are hump-
backed, passing up and down over the spurs and the
valley-side.
The most southerly closed channels become apparent
in the narrow lowland between the plateau edge and the
farms of Droplaugarstaðir and Hrafnsgerði, which have
houses and cultivated ground perched on rock platforms
above the lake at 70 m and about 50 m altitude. The
main channel passes behind the cliffed hill Hrafngerð-
isbjarg, behind the farms, but the steep cliffs backing on
the farmland may also be marginal features connected
with the channel. As the edge of the heath plateau
trends away from the lake shore, so the gap is filled with
wider channel systems. Next to the N are the three
channels cutting through the Hnaus spur above the
Skeggjastaðir farms and debouching into the next
embayment near the farm Hof, where they are joined
by a further channel running from the lake-shore at that
farm.
This channel rises to the top of the Ásklif feature at
about 110 m, forming a depression to the W of the
summit in which the road runs for some distance, then
falls towards Ormarsstaðaá. The E facing cliff of Ásklif
is cut by several smail channels connected to the main
one above, and since its face has quite a smooth, almost
catenary profile, it appears to be a marginal feature of
some description.
Northwards again from here the width of the whole
channel system increases. On the W margin a shelf
follows the strike of the basalts along the line of the
Lagarfljót flexure right up to the edge of the plateau at
about 400 m. The whole of the Ormarsstaðir and
Refsmýri farms is a system of approximately parallel
closed channels, (Fig. 2), two of which are occupied by
narrow lakes, and associated high level shelves. All of
these trend to the NE to pass through the next spur at
Grasaklif. It is possible to trace 6 parallel features here.
The Ormarsstaðaá stream flows here through a deep
cleft and fall over the Sigurðargerðisbjarg cliff, forming
the plateau edge, and then cuts deeply into the floors of
two of the larger channels below which run along the
base of the cliff and probably created it. These channels
are up to 20 m deep and have similar width, with
JÖKULL 35. ÁR 37