In collapsible stratifications a particular type of fracture can develop for which nucleation and propagation are governed by the transformation of gravitational energy into fracture energy. The associated nucleation problem is studied for a stratification consisting of an elastic surface layer, a collapsible intermediate layer and a rigid basal layer. An analytical model for fracture nucleation is obtained by calculating the energy ('crack energy') associated with a localized collapse of the intermediate layer. The size and energy of a critical crack are evaluated as functions of continuum properties of the strata. The theory is illustrated by an application to the case of whumpfs in collapsible snow stratifications.