  We investigate ice polyamorphism in the context of the two-dimensional
Mercedes-Benz model of water. We find a first-order phase transition between a
crystalline phase and a high-density amorphous phase. Furthermore we find a
reversible transformation between two amorphous structures of high and low
density; however we find this to be a continuous and not an abrupt transition,
as the low-density amorphous phase does not show structural stability. We
discuss the origin of this behavior and its implications with regard to the
minimal generic modeling of polyamorphism.
