After these objects exceed a certain critical angle, they form avalanche strata. These features are shaped by processes called surface creep and suspension. Abnormally large versions of these features, occasionally hundreds of miles across, are known as draa. When these features form in large groups, the aggregation is called an erg. A slipface with horns on either side is a technical description of the (*) crescent type of these entities, which are also known as barchans. The parabolic type of these features is formed in areas of unidirectiona
After these objects exceed a certain critical angle, they form avalanche strata. These features are shaped by processes called surface creep and suspension. Abnormally large versions of these features, occasionally hundreds of miles across, are known as draa. When these features form in large groups, the aggregation is called an erg. A slipface with horns on either side is a technical description of the (*) crescent type of these entities, which are also known as barchans. The parabolic type of these features is formed in areas of unidirectional wind, while the Seif variety is very common in the Rub al Khali and Sahara deserts. A namesake "grass" is planted on these features to protect them when they occur at beaches. For 10 points, name these wind-built mounds of sand.
After these objects exceed a certain critical angle, they form avalanche strata.
sand dunes