  The motion of glaciers over their bedrock or drops of fluid along a solid
surface can vary dramatically when these substrates are lubricated. We
investigate the coupled flow of a gravity current (GC) of strain-rate softening
fluid that is lubricated by a denser, lower-viscosity Newtonian fluid. We
present a set of experiments in which such GCs are discharged axisymmetrically
and at constant flux over a flat surface. Using imaging techniques we follow
the front evolution of each fluid and their thickness field. We find that the
two fronts of our lubricated GCs evolve faster than non-lubricated GCs, though
with similar time exponents. In addition, the thickness of the non-Newtonian
fluid is nearly uniform while that of the lubricating fluid is nonmonotonic
with localised spikes. Nevertheless, lubricated GCs remain axisymmetric as long
as the flux of the lubricating fluid is sufficiently smaller than the
non-Newtonian fluid flux.
