How does a sand dunes change earths surface

They act as barriers whereby wind deposits its load to come up with major land forms in the desert.

Explanation:

Sand dunes retain the load that arises as a result of erosion processes, and disposition.

Wind deposits con form hills and sand sheets.

An example of this is in California, whereby Sand dunes make up to 25 % of the land-forms in the arid areas.

Sand dunes can also influence the formation of oases, as a result of wind action.