As wind blows it carries sand other dust particles along it. As the speed of the wind slows down the sand and dust particles settle on the surface of the earth and forms pile. This phenomenon is responsible for the formation of sand dunes. Sand dunes are formed mostly in desert areas where sand is found is found in abundance. When wind blows in these areas, it lifts and transports sand from one place to another. When the wind stops blowing or reduces its speed, the heavier sand particles fall and get deposited in low hill-like structures. These are called the sand dunes.
A sand dunes is a mount ,hill, or ridge of sand that lies behind the part of the beach affected by tides