How did these sand dunes form? At one time, a river ran through this area. When it dried, the sandy bottom formed the dunes.

Gravity caused the grains of sand to fall from a mountain, forming the dunes.

Wind carried the sandy soil from far away and deposited it where it formed huge hills of sand.

A glacier traveled over the land creating the different hills of sand.

White Sands National Monument

How does the sand dunes form?

Sand dunes are created when wind deposits sand on top of each other until a small mound starts to form. Once that first mound forms, sand piles up on the windward side more and more until the edge of the dune collapses under its own weight. ... As more barchan dunes are formed, they can move together and line up.

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the 4th option is the answer