An Investigation of the Gravity Signature of the Windmill Islands, East Antarctica

Abstract

Gravity and GPS surveys were conducted on the Windmill Islands, East Antarctica, during the 2004/05 summer season. The aims of the study were to investigate the subsurface geology of the area and to deduce the changes in gravity and rock surface heights since the first surveys of the area were conducted almost five decades earlier, caused by glacial isostatic readjustment. The area became ice free following the end of the Last Glacial Maximum (LGM) 5,500 to 8,000 years ago and is thought to contain signals as to the state of nearby Law Dome. G-model Lacoste and Romberg gravity meters were used to make precise gravity measurements, std ±0.04 milligal. Two calibrated hand held single frequency Garmin GPS receivers were used to determine position including elevation, the standard deviation of the elevation being 2.7 m. Ninety three gravity stations were established. Additionally, forty three observations from a survey in 1993-94 were re-reduced and merged with the 2004-05 data to allow a complex three-dimensional subsurface model to be constructed. The Windmill Islands are at the rock/ice interface and thus this work has given an insight into the likely underlying bedrock structures and variability below Law Dome. This survey has set the foundation for future time-series gravity work in the Windmill Islands.