Sand dunes are mounds of sand built by the wind. They are found in many parts of the world, including deserts, beaches, and riverbeds.

Sand dunes are formed when the wind picks up sand and carries it away. The sand is deposited in mounds when the wind slows down or changes direction. The process of sand dune formation is called sand transport.

There are three main types of sand transport:

* Saltation is the process of sand grains bouncing along the ground. This is the most common type of sand transport.

* Suspension is the process of sand grains being carried by the wind. This occurs when the wind is strong enough to lift the sand grains off the ground.

* Creep is the process of sand grains rolling along the ground. This occurs when the wind is too weak to lift the sand grains off the ground.

The shape of a sand dune depends on the type of sand transport that is occurring. Sand dunes that are formed by saltation are typically rounded, while sand dunes that are formed by suspension are typically more elongated.

Sand dunes are constantly changing shape. The wind is always moving and changing direction, which means that the sand dunes are always being reworked. This process of change is called dune migration.

Dune migration can have a significant impact on the environment. Sand dunes can bury roads and houses, and they can also change the course of rivers. However, sand dunes can also be beneficial. They can help to protect coastal areas from storms, and they can also provide a habitat for plants and animals.

How to Stop Sand Dunes

Sand dunes can be a nuisance, especially if they're encroaching on your property. There are a few things you can do to stop sand dunes from forming or to reduce their size:

* Plant vegetation. Vegetation can help to hold the sand in place and prevent it from being blown away by the wind.

* Build a fence. A fence can help to block the wind and prevent it from picking up sand.

* Use sandbags. Sandbags can be used to create a barrier that will stop the sand from moving.

* Apply a chemical stabilizer. A chemical stabilizer can be applied to the sand to help hold it in place.

If you're concerned about sand dunes, you should contact your local conservation agency. They can help you determine the best way to stop sand dunes from forming or to reduce their size.