In some areas, winds tend to blow in roughly the same general direction all year. The Grand Erg Oriental, a sprawling sea of sand dunes in the Saharan Desert, is not one of them.

The winds in northeastern Algeria tend to be complex and changing. Easterly summer winds shift in the winter, becoming westerly. Meanwhile, passing storms and local geographical features further muddle the picture. If winds came consistently from one direction, crescent-shaped barchan dunes would reign. But the dominant dune type along the southern edge of Grand Erg Oriental (shown above) are large, pyramid-shaped star dunes, which only form in areas where winds blow from multiple directions.

The image was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite on October 27, 2012. Read more

NASA image courtesy NASA/GSFC/METI/ERSDAC/JAROS, and U.S./Japan ASTER Science Team. Caption by Adam Voiland.