INTRODUCTION:

As a guest of the Victoria University of Wellington Antarctic Expedition, 1962-3, the writer made a series of measurements of the acceleration due to gravity along the Taylor Valley, south Victoria Land, between McMurdo Sound and the terminus of the Taylor Glacier.

The limited value of gravity measurements along a single line is appreciated, but these measurements add to the regional gravity coverage of the area, a significate part of which has been made by earlier Victoria University of Wellington Antarctic Expeditions (1959-9 in the Wright Valley and 1960-1 in the area north of the Koettlitz Glacier.)

METHODS:

The instrument used was a Worden Master Geodetic Gravity Meter operated without thermostating, because power supplies were not readily available. The temperature calibration of the instrument is known but the results here reported have not been corrected for the small variations in instrument temperature. The corrections involved are negligible compared with errors arising from other sources.

Values of gravity were measured at 17 points along the valley, at approximately 2 km intervals. (Fig. 1) The value of gravity at the Base Station near the end of the Taylor Glacier was determined by two linkages (by U.S. Navy helicopter) with the established gravity stations at the U.S. McMurdo Station 13, and Scott Base Gravity Station 2. The traverse along the valley was made on foot, the interval between the two readings at the base station being 25 hours.

Gravity stations were located at geographic features which are easily recognizable on the existing aerial photographs and on the 1:50,000 planimetric and 1:100,000 topographic maps of the area produced by the United States Geological Survey, Special Maps Division, Washington.

The altitudes for the gravity stations given in this report were obtained with a small temperature-compensated hand altimeter. As given here they are probably not reliable to better than 50 feet, and at stations 10 to 16 inclusive the error may be larger. However the altitudes of the stations were measured again later in the season with better altimeters. Further, most of the stations are on the edges of lakes, the altitudes of which have been calculated by aerial triangulation methods during the process of map construction, by the U.S. Geological Survey. Final values for these altitudes should be correct to about 20 feet.

In reducing the data it has been assumed that all of the rock between the gravity stations and sea-level is of density 2.67 gm.cm.⁻³. No allowance has been made for the lesser density of the glacial deposits at the mouth of the valley, but the errors arising from this should not exceed 5 milligals. Terrain corrections have not-yet beep applied. These may amount to 10 milligals (1 milligal = 0.001 cm. sec⁻².) at stations 11 to 16 inclusive, but elsewhere they should be smaller and the application of the correction will not appreciably alter the overall picture presented by the results.

RESULTS:

Values of the Bouguer anomaly decrease westward from −55 milligals at the mouth of the valley to −137 milligals near the end of the Taylor Glacier. (Table 1) At the eastern end of the valley the gradient of the anomaly is approximately 3 milligals/kilometre, which is comparable with the gradients of 5 milligals/kilometre observed near the coast in the Wright Valley area, (C. Bull, "Gravity observations in the Wright Valley area of South Victoria Land", New Zealand Journal of Geology and Geophysics) and at the eastern end of the ice-free area north of the Koettlitz Glacier. (C. Bull, "Gravity page 2 observations in the Koettlitz Glacier area, South Victoria Land", New Zealand Journal of Geology and Geophysics).

Such gradients are consistent with the existence of a north-south fault line along the coast, the eastern side being down-thrown. It has been considered that the Victoria Land mountain range, bounding the inland ice of eastern Antarctica from latitude 70°S to 85°S, is a horst structure and that the coastal north-south fault line is one limit of the horst. However, geophysical studies on the inland ice west of the Victoria Land mountain range have not provided good evidence for the existence of the fault which should mark the western limit of the horst structure.

The gradients of gravity along the Taylor Valley are also consistent with an abrupt increase in thickness of the crustal material of the earth from a value of about 17 kilometres in the Ross Sea area to about 40 kilometres under the western part of the Victoria Land range. Further geophysical considerations must await the integration of these results with the others previous obtained in the area.