Dynamics of the folds of the McMurdo Ice Shelf, Scott Base, Antarctica

Abstract

The McMurdo Ice Shelf flows obliquely onto the coastline northeast of Pram Point, Ross Island, Antarctica. Ground penetrating radar (GPR) imaging charted the detailed structure of the associated enigmatic pressure ridges and the deformation due to compressive forces. Two perpendicular GPR antenna orientations improved the positioning of subsurface features. Surface measurements of fold wavelengths and interlimb fold angles complemented GPR imaging. Stratigraphic reflections showed the folding style; GPR profiles revealed fold train complexities with no surface expression. Brine layer defects were easily recognized; firn layer defects were more difficult to detect. Three-dimensional brine layer imaging highlighted a diapiric feature. GPR did not penetrate the brine layer, except possibly beneath the tops of folds; results suggest sinusoidal folding continues to the base of the ice shelf. Synclinal thrust faults may be secondary features, altering the sinusoidal shelf shape to approximate the equilibrium profile that buoyancy forces require. Time-lapse GPR showed subsurface deformation, including: brine layer defects; subsurface changes near the transition, likely due to summer melt; and a fold between two crevasses identified from subsurface discontinuities. Time-lapse photographs complemented GPR profiling, allowing longer timescale analysis of pressure ridge deformation, and tracking years of fold emergence and break-up.