With mechanics as they are now? I expect creeper will bulge away from the gorge near the shield, and pour into the gorge at either end. With pressure (depth) greater in the gorge, it'll probably force itself closer to the shield in the gorge than it will on the plateau.
As for pushing creeper up a terrain level? As it compresses (makes deeper) creeper against a cliffside, I expect the creeper will flood out. Whether there is a point at which it will force ALL creeeper out, I couldn't say, but evaporation would take care of scraps.