Jökull - 01.12.1999, Page 63

branches of the gentle protuberance Goðalandsjökull,
which lies to the west of the Goðabunga dome, c) the
inter-dome col depression with a length of 5 km and
a width of 1.5 km (about 1350 m a.s.l.), and d) gentle
ice slopes under the domes.
B. A vast cone shaped icemass with a similar sur-
face area as the glaciomorphological centre, repre-
senting the northern radial sector of the run-off of the
icemass which flows out from the north-eastern part
of the ice cap centre. This icemass is bordered to
the north by the marginal rim of the Sléttjökull out-
let glacier and in a morphostructural sense, represents
a transitional zone between the glaciomorphological
centre and the primary, peripheral slope of the ice cap.
C. The peripheral part surrounding the glacio-
morphological centre which is composed of the fol-
lowing: a) the primary slopes of the glacier sur-
face, i.e. with greatest inclinations, encompassing the
greater part of the ice cap centre, particularly on the
western, southern, and central-eastern sides; b) outlet
glaciers from the rim of the ice cap centre which inter-
sect the peripheral zone. These include among others,
Entujökull to the west, Sólheimajökull to the south-
west, as well as Öldufellsjökull and Höfðabrekkujök-
ull to the east.
Taking into account its morphometric and mor-
phographical features, it is possible to distinguish four
sections within Höfðabrekkujökull. The source sec-
tion (1), situated within the zone of active ice balance,
is relatively narrow, with a width of 2-4 km and an in-
clination between 15 and 30 degrees. The upper part
of the glacier (2), which has a length of 5.5 km and
distinctly smaller inclination, is limited by two rocky
ridges, 3.5 km apart. The glacier width varies down-
wards from 4.2 km to 2.8 km. The bedrock shape
of this section of the glacier and its rocky upper edge
cause the difference in surface morphology, expressed
by the presence of distinct ice streams. The mid-
dle section of the glacier (3) has a steeper inclination
than the previous section and is delimited by ordinates
from about 700 m a.s.l. down to 430-500 m a.s.l. The
greater steepness of this section caused by a distinct
threshold in its bedrock. The lower section (4), whose
length varies from 2.4 km to 4.5 km, has the features
of a piedmont glacier, this being attested by the 12.6
km width of its snout. The altitude of the snout varies
from about 310 m a.s.l. in its northern part, to about
198 m a.s.l. in its southern part, at the outflow port of
the glacier river, Sandvatn.
SURFACE STRUCTURES OF THE
HÖFÐAB REKKUJÖKULL FOREFIELD
The relief of the Höfðabrekkujökull forefield has
mainly been formed by accumulative and erosive ac-
tivity of the glacier and its meltwaters. The largest
expanses are taken up by areas of glaciofluvial ac-
cumulation, i.e. sandar, and secondly by accumula-
tion forms rnade by the glacier, i.e. marginal or end
moraines and ground moraines (Kriiger, 1988). It
should be emphasized that within the study area there
is basically a lack of surface forms which testify to
its areal deglaciation. Instead, forms which document
the frontal variations of the glacier snout are predomi-
nant. These forms include end moraines and outwash
planes.
The characterization of selected genetic categories
of forms which predominate the relief of the Höfða-
brekkujökull forefield are explained below.
Forms linked with glacier accumulation
This genetic category of forms includes end moraines,
ground moraines, fluted ground moraines and erratic
boulders, and volcanic periglacial highland plateaus
with local cover of glaciogenic deposits. Surface
forms on the glacier include supraglacial ridges, cov-
ers of ablation moraines, and also on its snout, ice-
cored moraines.
End moraines
The end moraines furthest from the glacier snout are
found near Selfjall and Rjúpnafell (Figure 1, moraines
I on map). These moraines are relatively low, with
a maximum height of 3 m and sometimes form two
or three ranges within the hummocky zone. Chaotic
concentrations of boulders characterize their surfaces.
Taking into account the relatively large distance of
these moraines from the present glacier snout as well
as their state of preservation under periglacial con-
ditions, they probably formed at the end of the last
glacial (Younger Dryas) or the beginning of Holocene.
JÖKULL, No. 47 61