Jökull - 01.11.1998, Síða 27

glacier of a glaciogenic origin, described by Corte
(1987), based on its geomorphology (Figure 4) and
internal structure (Figure 5). This interpretation is
supported by comparing debris relocation from aerial
photographs taken at different times. Surface move-
ments of 2 m/a to 16 m/a, indicating active ice under
the debris cover, were measured from aerial pho-
tographs taken between 1979-1987. In this period, the
movement took place mostly within 700 m from the
interface zone, i.e. along the debris-ice boundary on
the surface (Figure 4). Therefore, either active or
stagnant ice exist within an area of ca. 700 m distance
north of the ice-debris contact on the surface of the
Klofajökull rock glacier (Figure 4).
At present the main debris source of the Klofa-
jökull rock glacier are avalanches onto the glacier sur-
face. The glacier then carries the material down to the
interface zone mainly along the margins of the glacier
(Figure 4). The mean surface velocity of the glacier
has been measured 27 m/a between 1979 and 1987
which means that if the present rate of debris accumu-
lation on the top of the glacier has been continuous
via the two lateral moraines, minimal 19-20.000 m3 of
- Breytingar í legu sporða fjögurra skriðjökla Eiríksjökuls
frá lokum litlu ísaldar til 1987.
ice-free debris is transported annually by the glacier
and deposited at the interface zone. The sub- and
englacial transport is unknown.
The Klofajökull rock glacier was probably formed
during repeated advances in the latter part of the
Holocene. According to detailed studies of the Holo-
cene glacier fluctuations in Iceland the onset of the
Neoglaciation occurred around 5000 BP (Guðmunds-
son, 1997). This could imply that the initial advance
that formed the Klofajökull rock glacier might be of a
similar age since it can be dated prior to the Norse Set-
tlement of Iceland at ca. 900 AD. During the maxi-
mum advance of the LIA in the late 19th century, the
glacier advanced probably to the outermost limit of the
formation. This can be depicted from lichenometric
evidence. This late 19th century advance might have
destroyed evidence indicating a pre-historical exten-
sion of other outlet glaciers of the Eiríksjökull ice cap.
This assumption would imply that these advances did
not exceed the LIA maximum extension.
The existence of pre-LIA advances is known in
Iceland and has been reported by Thórarinsson (1956,
1964), Dugmore (1989), Stötter (1991), Haberle
(1991) and Guðmundsson (1997). ELA estimations
indicate that a cooling of 1.5 °C had to take place to
form the outermost moraines on the Stallurinn plateau
(Figures 3 and 6). This cooling fits reasonably well
with other temperature estimations during the LIA pe-
riod in Iceland (cf. Bergthórsson, 1969) implying that
the outermost moraines on Stallurinn are from the late
19th century advance.
The different spatial and temporal pattern of
glacier fluctuations of the Eiríksjökull ice cap can be
explained with the aspect of different outlets. The
main precipitation source in Iceland is generally from
south east. This means that Langjökull ice cap forms a
precipitation shadow east and south of the Eiríks-
jökull ice cap. Therefore, the ice cap is dependent on
precipitation from north. The Ögmundarjökull outlet
is thus probably more or less starved of precipitation
and therefore depicting a different and rnore restricted
fluctuation pattem compared with other outlets facing
the main precipitation source. This can be further sub-
stantiated by looking at the Klofajökull glacier. This
outlet is facing the main precipitation source in north
JÖKULL, No. 46, 1998
25