When there are perfect conditions for producing sand dunes, steady wind in one direction and just enough sand, a barchan sand dune forms. Barchans have a gentle slope on the wind side and a much steeper slope on the lee side where horns or a notch often forms. The whole dune may appear to move with the wind.
When ideal conditions exist for sand dune formation, steady wind blowing in one direction and sufficient sand, a barchan dune forms. Barchans have a gentle slope on the windward side and a steeper slope on the leeward side where horns or a notch may form. The entire dune might appear to move with the wind.