Jökull - 01.12.1965, Page 26

Fig. 4. Cross section
through the highest parts
of the glacial spillways
and the ridges between
them.
support of this suggestion is the existence of a
smalf channef across the top of Kroppsmúli,
further to the North. Most of the water, how-
ever, would flow round the ends of the ridges,
either under the ice, or between ice and rock.
Since the mountain Hestfjall, at the end of the
Skorradalsháls ridge, projects further into the
lowland than the other ridges to the North, it
would have a large amount of water pondecl
behind it, with a hydrostatic pressure, added
to that of water running down Lunderreykja-
dalur itself, to lift the water over the Hestháls
ridge.
Fig. 5. Hestfjall from the Northwest, showing
the northern end of the Kvígsstaðasneið spill-
way (centre) opening on to the coastal fowland.
132 JÖKULL
The question arises as to how these channels
were derived frorn the pre-existing landscape.
It will be clear that the lowest channels coin-
cide with the area of weakest rocks, but the
higher channels also may have been determined
by pre-existing features. A view eastwards to
the highest channels (Figure 6) suggests that
these have been cut on a series of rock plat-
forms, and some of the channels are, in many
places, simply platforms with the back slightly
lowered (photograph). Others, which have the
steep-sided, flat-floored profile of classic chan-
nels (Figure 7), could have been formed by
the lowering of such platforms. The existence
of platforms is known from the fronts of several
of the nearby ridges, of which Kroppsmúli and
Síðumúli are two examples. I have described
some of the platforms founcl in Flókadalur else-
where (Ashwell, 1966).
IV
A series of deposits was found on both sides
of a well-developed channel, the floor of which
here lay at 193 m above sea level. The deposits
were exposed from 207—197 m in the wall of
the channel, ancl the arrangement is shown in
Table 1.
A layered silty material similar to 1 and 3
was found at 209 m above sea level on the
West side of the channel.