Dunes are not simply larger ripples (although they are sometimes called "megaripples"), even though they share the same basic morphology as ripples. In general, dunes form by the migration of sediment up the stoss slope and down the lee slope, forming cross beds that are homologous to cross laminations. Eddies on the lee side form a distinctly scoured trough.
Dunes range in height from 5 cm to over 10 m and form in fine to very coarse sand and gravel. Straight crested dunes produce planar cross beds. Sinuous and lenticular dunes produce trough cross beds.