Person:

Platt, John

Flow of glacial ice in the West Antarctic Ice Sheet localizes in narrow bands of fast-flowing ice streams bordered by ridges of nearly stagnant ice, but our understanding of the physical processes that generate this morphology is incomplete. Here we study the thermal and mechanical properties of ice-stream margins, where flow transitions from rapid to stagnant over a few kilometers. Our goal is to explore under which conditions the intense shear deformation in the margin may lead to deformation-induced melting. We propose a 2-D model that represents a cross section through the ice stream margin perpendicular to the downstream flow direction. We limit temperature to the melting point to estimate melt rates based on latent heat. Using rheology parameters as constrained by laboratory data and observations, we conclude that a zone of temperate ice is likely to form in active shear margins.

Flow of the Western Antarctic Ice Sheet is distinctly heterogeneous in a vast region bordering the Ross Sea. Broad streaks of ice, ~1 km thick, called "ice streams", having horizontal width of several 10s of km, slide over their bed (of soil-like matter, which was seafloor in the last inter-glacial period) at > 100 m/yr, whereas they are bordered laterally by stagnant ridges flowing at < 10 m/yr. Major issues are those of why this morphology forms and what it means for the overall rate of ice loss. Our recent studies show how shear heating of the ice, consequent formation of temperate ice zones producing melt as they deform, and subglacial hydrological processes associated with Rothlisberger drainage channels, can naturally form a non-singular Barenblatt ending of a tens of km long shear crack between ice and till at the bed.