Nilosyrtis Mensae

The floors of these craters contain very interesting and enigmatic materials which may contain shallow subsurface ground ice with varying amounts of a sediment covering (mantle). When ice is covered with a critical thickness of sediment it is actually insulated and can survive longer than cleaner exposed ice. The ablation (melting) and sublimation (vaporization) of the ice causes a chaotic topography to develop with high and low regions. This may explain the relief seen on the crater floors. The terrain outside of the craters appears muted because it is most likely mantled with a dusty icy covering. This region of Mars is located along the highland/lowland boundary dichotomy.