Jökull - 01.12.1999, Page 70

central and northern part. It is thus probable that the
core of these forms was created by older end moraines
from the outer moraine range (the so-called “main
moraines”). The two ranges indicate that certain sec-
tions of the glacier snout oscillated at the turn of this
century.
Still younger end moraines, mapped earlier by
Kriiger and Humlum (1981) and Kriiger (1994) are
mainly found in the northern part of the forefield. Ac-
cording to above mentioned authors, these moraines
were formed after the “ Little Ice Age ” and probably
before 1945.
The youngest zone of end moraines is in close
proximity to the glacier snout. It is composed of 1-
4 moraine ranges, which are most clear in its cen-
tral and northern parts (Figures 4, 5, and 6). In the
southern part of the glacier snout, on both sides of the
Moldheiði rock massif, only one end moraine range
is present, formed during the advance of the glacier
since 1992 and most likely covering the 1960-1980
end moraines (Heim, 1983). Such partial advances
show that individual sections of the glacier snout are
controlled by different dynamics at different times.
The oldest outwash plain, occurring in the area
surrounding the Hafursey massif, considered to be
a pre-jökulhlaup 1918 level (Heim, 1983; Maizels,
1992), was most likely formed by meltwaters at the
end of the “ Little Ice Age ”, and is possibly connected
with the 1890-1900's end moraine range. Small frag-
ments of an outwash plain from this period have also
been preserved on the distal side of the moraines, in
the central part of the marginal zone. Fragments of the
outwash plain generated during the catastrophic 1918
jökulhlaup have been preserved in the southemmost
part of the study area.
Examining the meltwater role in the formation of
the Höfðabrekkujökullforefield, it is also necessary to
draw attention to their present-day activity, which is
manifested, for example, in the creation of numerous,
short proluvial sand and gravel cones at the glacier
snout, which encroach on to older outwash plains and
preserved ground moraine sheets, sometimes already
covered with moss.
Several genetic types can be distinguished among
the outwash plains. Maizels (1992) identified three
types of sandar on the forefields of some Icelandic
glaciers, based on hydrological and lithofacies criter-
ia, two of which she links with the sudden outflow
of meltwaters from the glaciers, i.e. at the time of a
jökulhlaup or during a sudden draining of dammed
or subglacial lakes. The third type of sandur is cur-
rently being formed by the normal activity of melt-
waters (termed active sandur by Maizels, 1992). We
basically agree with this classification but are inclined
to supplement it by subdividing the active sandur into
five morphogenetic sub-types (A-E) based on posi-
tion, method of formation, flowwaters, and also the
degree of transformation of their fluvioglacial relief.
A: Older outwash plains which formed during a halt
of the glacier at the end of the “ Little Ice Age ”. These
plains are losing their original fluvioglacial relief by
eolian processes.
B: wide water channels with several terraces, most of-
ten linked with the main outflows of the glacier rivers.
C: marginal depressions, parallel to the glacier snout,
connected to the course of the younger generation of
end moraines;
D: contemporary systems of proglacial cone forma-
tion;
E: a group of deeply cut melt water valleys of varying
width, cut into outcrops of the lava substratum.
CONCLUSIONS
Geomorphological mapping of the Höfðabrekkujök-
ull forefield using aerial photographs enabled four
generations of moraines to be distinguished, marking
the longer, successive halts by the glacier during the
Búði stage (i.e. in the Younger Dryas or Preboreal pe-
riod), during the “Little Ice Age”, prior to 1945, and
more recently (in 1992).
The end moraine series have been badly dam-
aged by meltwater activity, creating accumulative out-
wash plains which cover most of the forefield. The
oldest fragments of the outwash plains, preserved in
the southern part of the mapped area, formed before
and during the 1918 jökulhlaup. Taking into consid-
eration the distribution of the outwash plains, their
method of formation as well as the degree of trans-
68 JÖKULL, No. 47