What Are Sand Dunes and How do They Form?

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Picture a desert. What do you see? Like most people, you probably imagined images of heatwaves sweltering off the tops of massive sand dunes. Have you ever stopped to think about how these large masses were formed? What exactly are sand dunes anyway?

What Are Sand Dunes?

Couple hiking at Great Sand Dunes National Park, Colorado
Credit: Andrew Repp/ Shutterstock

Sand dunes are simply mounds of sand. They form in desert regions that have a lack of vegetation and require some sort of natural force to move the sand particles from one place to another. In most cases, this force is the wind.

How Are Sand Dunes Formed?

Great Sand Dunes National Park Colorado at Sunset
Credit: Kris Wiktor/ Shutterstock 

The formation of sand dunes requires three things:

  • Lots of loose sand with little vegetation
  • Natural forces to move the sand particles
  • An obstacle to stop the sand from moving

As one might witness at the beach, wind is strong enough to pick up loose sand particles. In a very sandy desert, sand particles will blow around until they hit something to stop their momentum. In nature, this obstacle might be a tree or a small patch of grass. Trees and grass will continue to accumulate sand particles until they become completely covered. As the wind continues to blow, more and more particles will stack up and form a dune. If you sat very still at a windy beach long enough, you would become the obstacle that helps form a dune!

Parts of a Sand Dune

Sand dunes with sharp detailed lines running through slopes, Morocco
Credit: Mr_Karesuando/ Shutterstock

Sand dunes consist of a windward slope, crest, and what's known as a slip face. The windward slope is the face of the dune in the direction that the wind blows. In your mental image of a desert, this is the part of the sand dune with ripples. The crest, however, is at the very top of the dune and below the crest is the slip face. This is the part of the dune where the sand falls after it’s blown over the crest or when the crest becomes unstable and collapses. The slip face is the smooth face on the opposite side of the dune. The crest, of course, is the peak.

Where Are Sand Dunes Located?

Winding desert landscape showing tall sand dunes in the Namib Desert
Credit: Agatha Kadar/ Shutterstock

Sand dunes are located on every continent — even in Antarctica. They form in any region with lots of sand, high winds, and little vegetation. Sand dunes mostly form in deserts or along shorelines. Some of the most famous sand dunes are located in the Sahara Desert in Africa, which is probably the desert you were picturing earlier, but many deserts around the world have sand dunes. The Atacama Desert in Peru has some of the largest sand dunes in the world. The Cerro Blanco dune is over 3,800 feet tall!

In the United States, there are several places where you can find sand dunes. Out west, California, Oregon, Colorado, and New Mexico have numerous deserts with dunes to explore. You can also find sand dunes along North Carolina’s Outer Banks and up north along the Great Lakes.

Types of Sand Dunes

Sunrise at Great Sand Dunes National Park and Preserve located in San Luis Valley
Credit: Rosalie Kreulen/ Shutterstock

Depending on how the wind blows, sand dunes can take on several different shapes:

  • Crescentic Dunes: This is the most common type of sand dune. These dunes look like a “C.” The windward side is on the outside of the arc and the slip face is located in the smaller area inside of the arc.
  • Linear Dunes: These dunes form in a somewhat straight line. Linear dunes are created when the wind blows from a consistent direction.
  • Star Dunes: These dunes have sharp, pointed ridges. When the wind blows in from many different directions, star dunes develop several slip faces that meet at sharp angles.
  • Dome Dunes: This is the least common type of sand dune. Dome dunes are circular without a slip face. The wind blows from all directions to create a uniform mound of sand.
  • Parabolic Dunes: This type of dune is the opposite of a crescentic dune. Instead of the windward side located on the outside of the "C," the wind blows from inside the arc and pushes sand up and out. Parabolic dunes are also called blowouts.

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