THE 'WHALEBACK' DUNES OF VICTORIA VALLEY, ANTARCTICA: A GROUND PENETRATING RADAR PERSPECTIVE

The Lower Victoria Valley is one of the McMurdo Dry Valleys and has the largest concentration of aeolian sand dunes on the continent of Antarctica. The aeolian bedforms include elongate slipfaceless dunes which have been called 'whaleback' dunes. The dunes are composed of coarse sand and are capped by granule ripples. In December 2006, a high resolution ground penetrating radar (GPR) study was undertaken to image the internal stratigraphy of a “whaleback” dune. A pulseEKKO 1000 GPR system with an automated odometer was used to collect 450 and 900 MHz data. The GPR profiles across the dune reveal low-angle sigmoid concavo-convex reflections that are interpreted as sets of cross-stratification which record the migration of the whaleback dune. An 800m profile along the axis of the dune reveals low angle dips from west to east showing that the dune has accreted towards the east. Profiles at 100m intervals transverse to the dune axis reveal sets of cross stratification dipping towards the south and locally towards the north. These apparent dips are resolved to show that the dune has migrated up valley from west to east driven by Katabatic winds blowing down valley from the Polar ice cap. At the same time it has been building obliquely towards the south. Local accretion towards the north is attributed to reworking of the dune by easterly winds blowing inland from the Wilson Piedmont Glacier and Ross Ice Shelf. The slipfaceless 'whaleback' dunes of Antarctica are not sand mantles as previously described but are actively migrating, long-wavelength, low-amplitude bedforms.