rare, some dark sand is found on Hawaii which also has many volcanoes discharging basalt. Barchan is a Russian term because this type of dune was first seen in the desert regions of Turkistan. Some of the wind on Mars is created when the dry ice at the poles is heated in the spring. At that time, the solid carbon dioxide (dry ice) sublimates or changes directly to a gas and rushes away at high speeds. Each Martian year 30% of the carbon dioxide in the atmosphere freezes out and covers the pole that is experiencing winter, so there is a great potential for strong winds. Some places in Terra Sabaea show dunes, as in the images below. Erosional features in Terra Sabaea Concentric crater fill A concentric crater fill is a landform where the floor of a crater is mostly covered with a large number of parallel ridges. It is common in the mid-latitudes of Mars, and is widely believed to be caused by glacial movement. Layers in craters Layers along slopes, especially along crater walls are believed to be the remains of a once wide spread material that has mostly been eroded away. Layers Many places on Mars show rocks arranged in layers. Rock can form layers in a variety of ways. Volcanoes, wind, or water can produce layers. Groundwater may have been involved in the formation of layers in some places. , Linear Ridge Networks Linear ridge networks are found in various places on Mars in and around craters. Ridges often appear as mostly straight segments that intersect in a lattice-like manner. They are hundreds of meters long, tens of meters high, and several meters wide. It is thought that impacts created fractures in the surface, these fractures later acted as channels for fluids. Fluids cemented the structures. With the passage of time, surrounding material was eroded away, thereby leaving hard ridges behind. Since the ridges occur in locations with clay, these formations could serve as a marker for clay which requires water for its formation. Other features Interactive Mars map See also Barchan Glacier Glaciers on Mars Groundwater on Mars List of terrae on Mars References Recommended reading Grotzinger, J. and R. Milliken (eds.). 2012. Sedimentary Geology of Mars. SEPM. Lorenz, R. 2014. The Dune Whisperers. The Planetary Report: 34, 1, 8-14 Lorenz, R., J. Zimbelman. 2014. Dune Worlds: How Windblown Sand Shapes Planetary Landscapes. Springer