The diagram illustrates how sand dunes are gradually formed in deserts or on coast.
Overall, sand dunes are formed under the influence of wind and the geographical locations of wet sand.
Firstly, the small sand particles on dry ground in deserts or on coast are blown and lifted up by wind. If these particles happen to land on the nearby area full of wet sand, a tiny sand dune will occur. Following this, the sand dune becomes larger in size as the wind continues to blow.
What’s more, this sand dune can create other sand dune by migrating its sand particles through the force of wind. Once the original dune reaches a certain volume, the sand particles on its surface can be blown away by the wind and migrate to a new place with wet sand, forming a new sand dune. The final volume of the sand dunes are determined by the size of wet sand area, which means a bigger sand dune usually has a larger area of wet sand as its foundation.