Jökull


Jökull - 01.12.1987, Page 55

Jökull - 01.12.1987, Page 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
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