Jökull - 01.12.1976, Page 7

TABLE I
Mechanical characteristics of deposits
Standard
Reference No. Location Height range, m Description Mean size Phi units Deviation (sorting) Plii units Skewness Plii units
2 Egilsáfangi 418 Eroded till 2.2 1.97 -0.24
30n West of Lundur tún 78-81 Laminated glacial-marine drift 4.5 1.64 0.32
31n West of Lundur tún 44-47 Massive glacial marine drift 5.3 1.64 0.35
36n Above Lundur farm 88 Massive glacial marine drift 5.3 1.47 0.34
37n Above Lundur farm 144 Cobble drift 3.7 1.39 0.09
in a pocket below main subglacial flow over
Tungufellsflói, or, alternatively, it could be
the result of a later stage when, in response to
a lowered base-level downstream, the main flow
left the rock platform and flowed round its
rim, cutting the sharp edge and marginal shelf
at about 110 m, rising into the channel across
the point of Tungufell at 111 m.
Although Röthlisberger, (1972, p. 191), point-
ed out that theoretically there should be little
upward movement from the sub-glacial valley-
guided flow into the partly englacial ice-direct-
ed flow, in this case there does seem to be
evidence of connection between the two types
of flow, especially near the point of Tungufell.
If Jökulhlaups, sub-glacial eruptions on the
high central plateau, were responsible for the
water flow, however, the head of water might
be sufficient to account for differences from the
theoretical case and for considerable rise and
fall of water in the ice sheet.
FEATURES NEAR LUNDUR
In the high northern valley side to the east
of the Lundur church-farm lies the gap of
Lundarsneid, at the eastern end of which lie
the Hrafnatjarnir lakes (Fig. 1). This gap seems
to have been a channel for sub-glacial water
and the forms resulting are illustrated in Figs.
4 and 5.
Much of the upper hillside is covered in
rather rounded material similar in appearance
to the cobble drift found elsewliere in the
district (Ashwell, 1975). A thick deposit of this
material, sample 37n in Table I, lies over part
of an ill-defined spur running from the Lundar-
sneid gap down to the valley floor. In a ravine
on the east side the material appears to be
about 20 m thick, but this may well be an
effect of slumping or sliding of the material
over a hidden rock surface. On the west side of
the deposit, tillites are extensively exposed in
waterfalls in a small brook. It seems possible
that the spur is an early deposit from an ice
tongue moving into the valley from the Lundar-
sneid gap, but tliat the loose material lying on
it and on the upper valley side is a very late
glacial deposit.
Between the spur and the road on the north
side of the valley floor is a series of low hills.
There are no clear sections to show the struc-
ture but exposures of dark-coloured silty ma-
terial (deigulmór) occur on the slope (Figs. 4
and 5). This material, examples of which are
samples 30n, 31n and 36n in Table I, is iden-
tical to other glaciomarine drift found on the
coastal lowland and at the mouths of the val-
leys, and attributed to deposition in water from
JÖKULL 26. ÁR 5