Barchan Dunes from Space
March 15, 2004
The Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), onboard NASA's Terra satellite, captured the above image on August 20, 2000. Looking somewhat like the scales on a fish, these scale-like features are actually shifting sand dunes flowing across the huge, sandy desert known as the Registan, located in southern Afghanistan. As winds in this arid region blow from the prevailing southwesterly quadrant over relatively flat terrain, sand piles up, forming crescent-moon shaped dunes. The tapered tips of these dunes, called barchan dunes, point in the direction of the wind flow. Barchan dunes migrate across the desert surface as sand grains on the crest of the dune are toppled by the wind and spill down the leeward face (protected from the wind). The mound of sand on the leeward side continues to grow until, eventually, gravity topples the growing pile, moving the dune’s leading edge slowly forward.