Rutford Ice Stream, Antarctica

Rutford Ice Stream is in many ways a typical Antarctic outlet glacier. Constrained by a subglacial-bed trough to the east of the Ellsworth Mountains, it drains an area of 49,000 km2 of the West Antarctic Ice Sheet. Varying in width from 20 to 30 km, flowing fast (up to 400 m/a) for more than 150 km before it starts to float, and over 2000 m thick along most of its length, it discharges 18.5±2 Gt of ice per year across its grounding line. It has an average driving stress of 40 kPa, which is resisted by lateral shear stresses at the margins in boundary layers up to about 10 km wide, and by basal shear stress in the middle third of the ice stream. Seismic studies of the base reveal varied conditions, with soft deformable till and more competent sediments. Stresses in the margins of up to 160 kPa lead to fracturing and crevassing, highlighted as bright bands in satellite synthetic aperture radar (SAR) images. Shallow seismic refraction and radar measurements indicate that fracture is initiated at depths around 10–20 m, consistent with the SAR penetration depths. Indications of change come from SAR interferometry of the upstream shear margin, where decadal fluctuations in the velocity profile suggest the effective width of the ice stream is varying. The limit of tidal flexing has been accurately located with SAR interferometry and shows no change in position between 1992 and 1996. Downstream of the grounding line there is a strong pattern of ice thickness variation advecting with the flow. We do not have a good explanation for the pattern, but it could have been caused by fluctuations in the position of the grounding line as a consequence of changes in ice thickness advecting downstream. The extent of the pattern suggests that the changes were occurring between 100 and 400 years ago.

Details