Calculate the expected deflection of the lithosphere beneath a thick icesheet. Say the icesheet is 4000 m thick, and ice has a density of 917 kg/m³. (The Antarctican icesheet is roughly this thick at its maximum thickness.) The thickness of the crust (of density 2700 kg/m³) beneath the center of the icesheet and the region outside of it is the same. The density of the upper mantle that gooshes out of the way to allow this deflection of the surface is 3300 kg/m³. What I want to know is how far down the rock is depressed beneath the load of the ice.