||Tifernine Dune Field, Algeria |
The Tifernine Dune Field is located at the southernmost tip of the Grand Erg Oriental, a "dune sea" that occupies a large portion of the Sahara Desert in eastern Algeria. This astronaut photograph illustrates the interface between the yellow-orange sand dunes of the field and dark brown consolidated rocks of the Tinrhert Plateau to the south and east (image right). Three distinct landforms are visible in the image, each providing information about past and present climate in the area.
The oldest landform is represented by the rocks of the Tinrhert Plateau, where numerous channels incise the bedrock; these channels were eroded during a wet and cool climate period, most probably by glacial meltwater streams. As the dry and hot climate that characterizes the Sahara today became established, water ceased to flow in these channels. Winds eroded and moved large amounts of drying sediment (sand, silt, and clay), which piled up in large, linear dunes that roughly parallel the direction of the prevailing winds of the time (image center).
The present climate is still hot and dry, but current wind directions are more variable. The variable winds are modifying the older, linear dunes, creating star dunes, recognizable by a starfish-like pattern when seen from above. White to grey regions within the dune field are exposed deposits of silt and clay, together with evaporite minerals (such as halite, or common table salt) formed by evaporation of water that collected in small basins between the dunes.