No. 74: Mar-Apr 1991
Anomalies in the measurement of gravity in Australian mines have stimulated an experiment in one of the very deep holes drilled in the Greenland ice cap. The hole at location Dye-3 is 2 kilometers deep. Gravity measurements were made at 183-meter intervals between depths of 213 and 1673 meters. Elaborate precautions were taken to assure that proper corrections were made for ice density and the nature of the rock below the ice. Ice-penetrating radar sketched the topography of the icerock surface, and surface-gravity measurements assessed density variations in surrounding ice and rock. The results of this finely tuned experiment are found in the final two sentences of the report's Abstract:
"An anomalous variation in gravity totaling 3.87 mGal (3.87 x 10- 5 m/s 2 ) in a depth interval of 1460 m was observed. This may be attributed either to a breakdown of Newtonian gravity or to unexpected density variations in the rock below the ice."
(Zumberge, Mark A., et al; "The Greenland Gravitational Constant Experiment," Journal of Geophysical Research, 95:15483, 1990.)