Sir,
Allow me to make three points which I hope will clarify my position for Dr Andrews:
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1. As a matter of observation I have suggested that cold glaciers and temperate glaciers transport subglacially derived debris in rather different positions. In the former, it is disseminated through a relatively large thickness of basal ice (100–200 ft (30.5–61 m) on the Barnes Ice Cap), and in that ice has bulk concentrations which in most cases average about 5% by volume, although individual debris bands may contain much higher concentrations. In temperate glaciers, the debris tends to be restricted to a thin basal layer rarely more than 1 m thick. I have not attempted to contrast the debris discharge of these glaciers, but the position in which debris is carried. Dr Andrews’ calculation of a 0.01% debris content in the whole of the ice of the ablation area is interesting but not pertinent to my suggestion.
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2. If the above contrast exists, what is the reason for it? I have suggested that the difference in thermal regimes may be responsible, and have proposed mechanisms of inclusion beneath cold ice in Spitsbergen. Dr Andrews says that the debris in the Barnes Ice Cap is incorporated in the terminal zone. It would be very interesting to have details of the sections quoted by him and an opinion of whether they are compatible with Reference WeertmanWeertman’s (1961) hypothesis for Baffin Island glaciers of an origin by basal freezing.
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3. In answer to Dr Andrews’ query. It is true that many temperate glaciers have large terminal and lateral ice-cored moraines. I believe this stems from the fact that many such glaciers are valley glaciers in which englacial debris is introduced not from the bed but from valley sides, nunataks and cirque headwalls. Where these latter features do not occur, there is almost no englacial debris above the basal layer. Cold ice caps with no source of supraglacial material do, however, contain englacial debris and produce large terminal ice-cored moraines.
