 Presumably, irregular surface topography obstructs ice flow and locally creates atmospheric conditions suitable for the development of blue-ice areas.Irregular topography does not need to be exposed to the surface to generate blue-ice areas, although they must have an effect on the ice surface topography to induce the formation of blue-ice areas.Consequently, many blue-ice areas form when ice thicknesses decrease, which has been postulated to happen during interglacials although in general the past history of blue-ice areas is poorly known.