Deposits of Sand: Ripples Versus Dunes

Abstract

We have seen that sediment can form mounds on the surface and that these mounds can grow through the instability associated with the saturation length. However, several effects lead to more complex structures—the recirculation bubble of airflow, the avalanching slip face of the dune, and the possibility that multiple particle sizes or densities may be present. These lead to some distinct types of structures—ripples rather than dunes. The way sediment is deposited can also leave traces in the dune (or in a sandstone if the dune becomes lithified), or on the surface on which the dune sits.