Antarctica's Sub-Ice Geology Surveyed

Press, Volume CIII, Issue 30339, 15 January 1964, Page 15

Antarctica's Sub-Ice Geology Surveyed

McMURDO STATION. Two University of Wisconsin scientists recently completed 27,500 miles of flights over Antarctica's ice cap, trailing a plastic “bird” that tells much about that which lies hidden beneath the thick blanket of snow. They flew a combined distance greater than the circumference of the earth —more than any other scientists here this year—to map variationsin the strength of Antarctica’s magnetic field. They made more than the total of all previous aeromagnetic measurements in West Antartica, the area of great American research concentration. Many of their flights were over little-known or even completely unknown territory. The magnetic variations they studied, or “anomalies” in geophysical language, are caused by sub-ice geological features such as mountains. The bird, an electronic device, “sees” these features by sensing the increase they generate in the earth’s magnetic field.

Mr Per Gjelsvik, of Bergen, Norway, flew 13 trips out of McMurdo Station on the coast and covered 16,500 miles. Mr R. E. Wanous, of St. Petersburg, Florida, flew eight trips out of Byrd Station on the ice cap and covered 11,000 miles. All were at an average height of 2500 ft above the surface. Messrs Gjelsvik and Wanous are project assistants and also electrical engineering students with the University of Wisconsin Geophysical and Polar Research Centre, where they work under the direction of Dr. C. R. Bentley and Dr. J. C. Behrendt.

Computer Used

The data they gathered must first be translated by computer into useable form for a map of the Antarctic’s magnetic terrain, and then interpreted by geophysicists into a description of the subglacial land. The process will take several months.

However, strong anomalies found in a line parallel with the Prince Albert mountains of Victoria Land may indicate a mountain ridge buried under the ice, according to the scientists.

The University of Wisconsin has been conducting a long-term aeromagnetic project in Antarctica for several years as part of the United States Antarctic Research Programme, which is financed and co-ordinated by the National Science Foundation, an independent agency of the United States Government.

Air transport was provided by the Navy’s VX-6 Squadron. The two men, who flew in Dakotas, credit much of their success to excellent assistance from the squadron. Tire long flights were free from serious trouble, according to the scientists. Wanous was involved in two forced landings on the ice cap, once to help another plane downed by engine failure, and another time because of engine failure on his own plane. No damage resulted in either case, and help arrived within a few hours. Discrepancies The plane crews and scientists frequently found great discrepancies between sketchy maps of relatively little-explored Antarctica and their own observations. Careful comparison of their records with previous records will be made when maps of the area of their flights are revised. Aeromagnetic measure-' ments are primarily useful for discovering contours of; basement rock, the geological; layer underlying the sedimen-1 tary layer on the surface.'

They operate on the principle that basement rock has a fairly uniform distribution of magnetic materials called magnetite within it, so that large magnetic anomalies can be attributed to large masses of basement rock.

The dispersal of magnetite is not perfectly uniform, however, and large concentrations of magnetite ore complicate the raw data. Gross temporary fluctuations in the earth’s magnetic field also complicate the data, so analysts must correlate it with records of permanent ground stations. To construct a complete and accurate picture of ice thickness and file shape and nature of the land beneath the snow, magnetic data must be combined with seismic and gravity data. No method alone is sufficient, according to the scientists.

The instrument they use is known as a nuclear precession magnetometer. It uses the fact that the rate at which the axis of the spinning nucleus of an atom precesses (swings in an arc) is a measure of the strength of the earth’s magnetic field in the immediate vicinity. The precession can be measured electronically. The sensor is encased in a 2ft long bomb-shaped “bird,” which is trailed on a 100 ft line to avoid interference by the metal of the aircraft. Cables lead into the plane from the “bird” and connect to the recording instrument, about the shape and size of a floormodel television set. It is designed to code the time and incoming signals directly on computer tape.