Jökull - 01.12.1987, Síða 55

and also shows displacements of boulders on the sur-
face as recorded between 1977 and 1985. The maxi-
mum movement was recorded near the snout and de-
creased with distance both laterally from the medial
furrow and from the snout. In these areas of little or
no movement no melt of the ice contained within the
rock glacier was evident. In general it may be said that
the main body of the rock glacier is virtually static.
It is evident from figures 2 and 3 that there is a dis-
tinct break between the talus which surrounds the
rock glacier sides and the limits of the feature itself. A
snow patch lying in the Iateral furrows marks the edge
of the rock glacier all year. The valley sides show fea-
tures of downslope movement of talus (such as stone
stripes and talus lobes) and rock falls can be heard
throughout the summer. However, there is no obvious
transfer of debris across the snow patches to the
lateral edges of the rock glacier. Therefore, it appears
unlikely that the rock debris involved in the rock gla-
cier originated directly as talus from the valley sides.
An alternative origin for the debris is that of
transfer from the glacier. The ice exposed in the rock
glacier is glacial in nature with a considerable amount
of debris contained within it. It has already been
shown that debris previously contained within the ice
of the corrie glacier, has accumulated on the ice sur-
face. It appears likely that the rock glacier surface
may be a direct result of debris release from glacial ice
as a result of increased ablation.
As already described in the preceding discussion of
the corrie glacier debris can also accumulate on the
glacier surface from rockfalls from the corrie back-
wall. Rockfalls occur during the summer months from
the corrie backwall and can be observed as debris fans
covering winter snow or as isolated boulders with skid
marks trailing behind them back up to the corrie
Figure 7: Nautadalur rock glacier —
snoutsurvey 1977—1985.
7. mynd: Sporður grjótjökuls í
Nautadal árin 1977 og 1985.
NAUTADALUR ROCK GLACIER:
SNOUT SURVEYS 1977 AND 1985
53