Explain the formation and movement of sand dunes.

weathering my cause the dunes to form

Formed by piling up of sand

Sand dunes move when bedrock is broken down

Explanation:

Sand dunes are formed when the sand pile up one over the other. In general in a sand dune, the sand is stacked on top of another dune. This happens majorly during the dry climate.  

These sand dunes move when the bedrock is broken down. As the bed rock breaks down, large blocks are broken down into sand sized grains which are eventually deposited along the sides of streams, in lakes, or in the ocean.