Aeolian Deposition

Aeolian Deposition

Wind deposited landforms are good indicators of the wind direction at the time of formation, and also the intensity of the wind.
Wind deposited sand occurs as sand sheets, ripples and draas.
Sand Sheets are flat, gently undulating and sandy plots of sand surfaced by grains that are too large to be carried in saltation.
They form 40% of Aeolian depositional surfaces. A good example is the Selima Sand Sheet in Southern Egypt, and occupies 60,000 square kilometres.
Wind blowing over the sand surface cause the sand to ripple into crests and troughs where the long axes are perpendicular to the wind direction.
The average length of jumps during the saltation is relates to the wavelength, or distance between adjacent crests of the ripples.
The coarsest material is found at the crests. This is the opposite to dunes where the coarsest material is found in the troughs.

This shows the movement of the grains up the upwind slope and the slipface positioning.

Image courtesy of USGS

The wind moves the sand grains by saltation or creep up the upwind side of the dune/ripple. The sand accumulates at the top on the crest and when the build up has become too much it avalanches down the slipface (lee slope).
As this process of avalanching continues the dune/ripple migrates in the direction of the wind.