Floating Extensional Flows

The centres of glacial ice sheets are grounded to the underlying bed and dominated by shear flow. As the ice deforms under gravity it can become sufficiently thin to float over surrounding oceans. These floating regions of ice (ice shelves) are characterised by extensional flows. The dynamical differences between the two regions can result in substantial differences in the flow patterns, owing to the non-Newtonian ice rheology.

In this video (high/low resolution) we model the flow of an ice sheet into a denser ocean with a viscous gravity current that intrudes into a denser salt solution. To emphasise the important role of rheology in the floating extensional region, we compare and contrast a Newtonian flow to a non-Newtonian flow in two parts. First, we present a viscous gravity current on a flat plane released from a point source at a constant flux. Both the Newtonian and non-Newtonian fluids demonstrate an axisymmetric front. In the Second part, the viscous gravity currents intrude a denser ocean and a floating region forms. The Newtonian fluid maintains axisymmetric flow in the floating region. In contrast, axisymmetry breaks down in the non-Newtonian extensional region, which ruptures into a set of finger-like protrusions. These observations may relate to the mechanism underlying the break-up of large ice shelves.

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