2D and 3D Geophysical Imaging of Polygonal Patterned Ground in the McMurdo Dry Valleys, Antarctica

The PPG found in the Dry Valleys is some of the oldest on the planet with ages of up to 8 million years assigned to them. The activity of some of these Antarctic PPG areas has come into question with the proposal that they may be the result of sublimation processes rather than actively re-working freeze and thaw processes. Near surface geophysical methods of ground penetrating radar (GPR), resistivity tomography and electromagnetism have been applied to four Antarctic Dry Valleys polygonal patterned ground (PPG) areas; two in Victoria Valley and two in Beacon Valley. The aim was to resolve subsurface structure and activity of the PPG without disturbing the delicate permafrost soils. Multiple techniques were used so that there could be greater reliability on the interpretations of this data without the need for damaging subsurface geological calibration of the geophysics by obtaining direct subsurface data through methods such as trenching or drilling. Subsurface structure of the PPG was resolved; active layer depth, deformation of permafrost in the vicinity of contraction cracks and zones of attenuation were identified. Significant deformation in the subsurface horizons of the permafrost and associated with thermal contraction crack wedge growth was identified over PPG suggested to be formed only by sublimation in Beacon Valley, thus calling into question this interpretation of the PPG activity. The most reliable identification of subsurface features occurred with correlation between GPR and resistivity tomography results