a long, long time
Sand dunes that are at right angles to the wind are called Transverse Dunes. They form with weak winds and an abundant supply of sand.
Wind and waves form sand dunes on the beach
specify sand dunes range it the time they were created
barchan dunes
weathering
Large piles of sand are called dunes.
barchan dunes
Wind erosion and deposition may form sand dunes and loess deposits. When the wind strikes an obstacle, the result is usually a sand dune!
sand dunes
a sand dune that goes on in a long line
Sand Dunes. Aeroflot
they form to stop the beach over loading with sand