Jökull - 01.12.1999, Blaðsíða 69

Figure 11. Geological structure of kame terraces near
the Sandvatn river basin. — Þversnið af malarhjalla
skammt vestan við farveg Sandvatns. Sniðið er um 10
m hátt og kornagerð þess sýnir að setið hefur sest til í
lygnu vatni.
Numerous steep, proluvial cones, 200-400 m in
length, have formed at the mouth of these niveofluvial
valleys and at the base of rocky massif slopes.
Denudational forms
Denudational forms labelled on the map include:
volcanic periglacial highland plateaus, a periglacial
plateau with a denudational cover, a denudational-
periglacial mountains outcrop bed, a denudational-
periglacial outcrop bed with glacigenic deposits, and
forms which are mainly developed within the high,
steep slopes of rocky massifs, i.e. corrasion troughs,
delles, and talus cones. Their genesis is linked with
the detachment of rock blocks which fall or are trans-
ported downslope and create deep, narrow corrasional
troughs. High-angled talus cones are created at their
mouth, near the base of the rocky massifs.
THE DEVELOPMENT OF THE
HÖFÐABREKKUJÖKULL FOREFIELD
A considerable wealth of landforms of complex and
variable genesis is present in the study area. The fun-
damental forms owe their creation to the accumulative
and erosive activity of the glacier and its meltwaters.
However, it should be particularly emphasized that the
accumulative meltwater plains (sandar) predominate
the landscape of the Höfðabrekkujökull forefield.
Within the mapped area, four generations of
moraines can be distinguished. A fragmented zone
of the oldest end moraines is located south of our map
at the confluence of the Sandvatn river, about 5 km
from the Höfðabrekkujökull snout. As these moraines
are situated north of the so-called “ outer moraines -
Y”, demarcated and dated by Jóhannesson (1985) to
have formed during the Older Dryas period or earlier,
we consider them to have formed during the “ Búði ”
stage, i.e. either during the Younger Dryas period or
Preboreal (Hjartarson and Ingólfsson, 1988; Kaldal
and Víkingsson, 1990; Norðdahl, 1990; Ingólfsson,
1991; Hjartarson, 1991). It should also be mentioned
that other views exist on glacier extent in Iceland at
the end of the Pleistocene and the beginning of the
Holocene periods, such as Geirsdóttir et al. ’s opinion
(1997), that the ice cap in southern Iceland calved into
the ocean at the location of the Búði moraine complex
at that time.
A younger generation of end moraines lies close
to the glacier snout, arranged in two distinct ranges,
recognized by Heim (1983) as the main moraines de-
marcating the glacier’s halts at the turn of this century,
i.e. at the decline of the “ Little Ice Age ” (Björnsson,
1979; Grove, 1988). A second range of end moraines,
about 200 m closer to the glacier, has been overrid-
den by the glacier in several places, especially in its
JÖKULL, No. 47 67