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Report on the Victoria University of Wellington Antarctic Expedition 1960-61: VUWAE 4

Glacier Thicknesses

Glacier Thicknesses

The route taken in this gravity traverse included the crossing of three glaciers. From the measurements of gravity on the glacier approximate estimates can be made of the thickness of ice under the gravity staton. The method has been fully described elsewhere (C. Bull and J. R. Hardy, “Gravity Measurements on a Glacier,” Journal of Glaciology, March 1957). Values of the Bouguer anomaly obtained on rock at the sides of the glacier are interpolated across rhe glacier, to determine the value of the Bouguer anomaly which would occur at the gravity stations on the glacier, if the ice of the glacier (density about 0.9 gm.cm−3) were replaced by “standard” rock of density 2.67 gm.cm−3. In fact the values of gravity on the glacier ore less than those required to give the values of Bouguer anomaly obtained by interpolation in this way; the deficit is attributed directly to the replacement of “standard” rock by the much less dense ice.

In the three glaciers measured by this method the Bouguer anomaly expected at the glacier stations (assuming that all of the glacier ice were replaced by rock) can be interpolated with some confidence to an accuracy of 2 milligals. The maximum gravity deficiencies on the three Glaciers are 25 mgals (Koettlitz Glacier), 12 mgals (Radian Glacier) and 16 mgals (Hobbs Glacier) so that the error in the estimate of thickness should not exceed 20 per cent.

The three profiles are given in Figure 2. At the position of the profile the Hobbs is a noticeably underfit glacier flowing from a deep valley into a lowland region. In the profile of the Radian Glacier there is some suggestion that the valley is a pair of parallel troughs. Since the glacier is fed by two approximately equal size tributaries this is not completely unexpected, but it is unusual for the two tributaries to maintain their identity so far down the glacier. A similar feature has been observed on a Norwegian glacier by the writer, but only within a short distance of the confluence of the two tributaries (C. Bull and J. R. Hardy, loc. cit.). The southern arm of the Koettlitz Glacier, between Heald Island and the Pyramid area, is a slow-moving or dead relic of a much larger glacier fed from the inland ice of eastern Antarctica. However, at the position of the traverse its thickness exceeds 1,100 feet and the sub-glacial surface is below sea level. The glacier volley is appreciably deeper on the northern side, the outer side of the curve of the arm of the glacier as it swings northward.

These profiles of the glaciers and their significance will be discussed further in the Report on the Glaciological work of the Expedition.

Note: The calculations of the values of gravity and all the attendant corrections have not yet been checked. These preliminary results and considerations may not remain unaltered in the light of recalculations and more mature judgement.

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