Jökull - 01.12.1999, Page 67

Figure 7. Altimetric profile across the outwash plains west of Hafursey (see map). — Þversnið yfirfarveg
Sandvatns, frá Hafursey vestur í Vatnsrásarhöfuð.
also Olszewski and Weckwerth, this issue) are an ad-
ditional proof of the link between this level and the
last phase of a jökulhlaup. We are of the opinion that
this level formed during the last phase of the large
1918 jökulhlaup rather than during the small jökul-
hlaup from Katla in 1955. However, the three lowest
levels (VIII-X) within the Sandvatn basin have formed
without any major jökulhlaups.
In the central part of the Höfðabrekkujökull fore-
field, fragments of the oldest outwash plains are
found on the distal side of the 1890-1900's moraines,
whereas the youngest outwash plains occupy wide ex-
panses in the central part of the forefield (Figures 8
and 9) and are linked with end moraine ranges closest
to the glacier. However, the meltwaters which formed
these levels have completely erased the moraines in
many places.
Alluvialfans
Alluvial fans are small fan-shaped surfaces generated
by accumulative activity of proglacial short but dis-
tributive stream systems. They are made up of mul-
tifractional dark-coloured, horizontally bedded sands.
The cones mainly develop on contact with a relatively
stable position of the glacier snout.
Two generations of alluvial fans were distin-
guished within the marginal zone of the glacier. The
older fans are located where the glacier snout inter-
sects older moraine ranges whereas fans appearing at
the glacier margin are mainly situated in the south-
Figure 8. A large, active outwash plain with traces of
meltwater channels in the central part of the Höfða-
brekkujökull forefield. The pre-1918 plain is located
at the base of the Hafursey massif. — Horft í átt
að Hafursey yfir grófan, rásaðan árbotn við miðbik
Höfðabrekkujökuls.
ern part of the marginal zone. The largest group of
young alluvial fans is found immediately north of the
Moldheiði hill where they form a 2 km long and 200-
750 m wide zone. In many places, they overlap older,
stony or moss-covered outwash plains and moraine
surfaces (Figure 10). The thickness of the character-
istic, vari-grained black tephra of which the fans are
made reaches about 2 m at their base. Heim (1983)
classified this zone of fans as “ the high sandar”.
JÖKULL, No. 47 65