Jökull - 01.12.1999, Blaðsíða 75

Figure 1B. A geomorphological sketch of the near
foreheld of Höfðabrekkujökull. 1) end moraine
ranges, 2) drumlinized ground moraine, 3) ground
moraine (flat, undulated and hummocky), 4) pitted
sandur, 5) the oldest sandur, 6) older sandur with
ringed kettles from the 1918 jökulhlaup, 7) young
sandur and erosional meltwater plains, 8) present-day
sandur, 9) marginal alluvial fans, 10) glacier surface
with fissures and a present-day ice-moraine ridge, 11)
rocky massifs, 12) the area encompassed in Figure 2.
— Kort af jarðmyndunum við Höfðabrekkujökul. Jök-
ulgarðar (1), drymilurð (botnurð með ávölum hœðar-
hryggjum) (2), bylgjótt botnurð (3), holóttur sandur
(4), elsti hluti sandsins (5), sandur með jökulkerjum
(6), yngri hluti sandsins með árfarvegum (7), nýleg-
ir árfarvegir (8), aurkeilur við jökuljaðar (9), jökul-
sporður (10), berggrunnur (11).
in moraine deposits, as ice-core moraine, are com-
monly known (Zubakov, 1951; Flint, 1957; Jewtu-
chowicz, 1970, 1973; Karczewski, 1982; Kozarski,
1982; Kozarski and Szupryczynski, 1973; Szponar,
1975; Lawson, 1979; Sugden and John, 1979; Paul,
1983; Krtiger, 1994). When melted they form hum-
mocky moraines with kettles. Boulton and Eyles
(1979) describe the formation of a large concentra-
tion of kettles due to subsurface ablation of in situ
glacier ice, aligned in accordance with the direction
of the glacier’s movement. Such concentration of ket-
tles can also emerge along the row of degraded middle
moraine within the so-called intramarginal zone (Ger-
man et al., 1979). Woldstedt (1954) underlined the
peculiarity of the genesis and evolution of kettles con-
nected with ground moraine till deposits in outwash
sediments, for example on Skeiðarársandur, Iceland.
Remains of glacier ice (ice-core moraine) was not
ascertained in the end moraines adjacent to the ket-
tle field or in several other moraines situated nearer
the glacier. At present, passive glacier ice has only
been located in moraines at the present glacier snout.
Nowhere outside the kettle field were similar forms
observed. Moreover, the lack of subglacial till facies,
i.e. from the glacier’s basal transport, beneath kettle
16 suggests that no stationary relict ice from the basal
zone of the glacier was deposited beneath the sedi-
ments filling up the kettle.
The immediate vicinity of the kettle field and the
tracks of the 1918 and 1955 jökulhlaups (Björnsson,
1976; Rist, 1967) indicates that the formation and de-
velopment of the kettle field is more complex than
of those formed by degradation of ice preserved in
situ (Jónsson, 1982; Maizels, 1991; 1992; Larsen
and Ásbjörnsson, 1995; Molewski, 1996). During
jökulhlaups, ice blocks tear away from the glacier
edge. The flood may also wash away ice blocks from
marginal ice-moraines. Following the flood, the ice-
bergs left on the sandur plain can thus be of different
origin. They can lie in situ as so-called autochtonic
ice or be transported as ice drift during the jökulhlaup,
i.e. of the allochtonic ice (Olszewski and Weckwerth,
1998a).
The aim of this study was to search for geomor-
phological and geological criteria determining the ori-
JÖKULL, No. 47 73