What Are Sand Dunes and How Are They Formed?


Sand dunes are accumulations of sand formed by the action of the wind. Their formation is associated with the transport of grains of sand which are deposited in large amounts when they encounter certain obstacles. There are different types of dunes, often defined by their shape and direction in which they are structured. The ecosystems which contain sand dunes are often much more biodiverse than we may think, since sand is associated with only certain types of life. thedailyECO helps you to learn more by asking what are sand dunes and how are they formed?
What are sand dunes?
Also known simply as dunes, sand dunes are large accumulations of sand formed and shaped by the action of the wind. They can cover areas which measures hundreds of thousands of square miles. Those that cover large areas are known as ergs or sand seas. While many dunes may appear very large, they are often a range of dunes connected together. This is known as dune system or a dune complex.
There are different environments with the presence of dunes such as deserts, coastlines and coastal plains. Dunes are very dynamic ecosystems. Unfortunately, they are also relatively vulnerable, one of the reasons they are of such great scientific interest.
Learn about another sand phenomenon with our article on the formation of sandstorms.

How are dunes formed?
The initial source of sand for dunes to form is the sand deposited on water currents. This could be ocean water currents on beaches, as well as by lakes and rivers in the case of inland dunes. When beach sand is exposed to the air for a certain period of time, it dries out and loses mass. This makes it mor susceptible to being carried by the wind, giving rise to the formation of coastal dunes.
Although sand dunes come in many sizes and shapes, they are all generated through the same process by the action of the wind. The factors that influence the formation of dunes are:
- Contribution of sediments
- Size of the sediment
- Speed of the wind
- Presence of obstacles
To better understand the formation of sand dunes, we look at how these factors come together to form their structure:
- Once the sediments have been dried out, the formation of a dune begins when the wind speed is sufficient to lift the sand grains. When the wind blows, the grains are picked up. The higher the wind speed, the greater the distance the sand grains travel.
- After being lifted into the air, the clouds of sand grains will travel in the same direction as the wind, until the wind slows down and the grains are deposited. The presence of obstacles will modify the speed of the wind. A dune begins to form when the wind encounters an obstacle. For example, a plant, a rock or a fallen tree trunk.
- As this happens, sand is deposited until a mound of sand forms around said obstacle. This mound represents an even greater obstacle to the wind, accumulating more and more sand as the sediment-heav wind passes over it. Plants are the most effective obstacle, as they are able to grow as the sand accumulates. The height of the vegetation plays a very important role in the formation of dunes. The higher they grow, the slower the wind speed over the sand. In addition, the movement of the sand is affected by the amount of plants and the surface they cover.

Types of sand dunes
As we have already referenced, the two main types of dunes are coastal dunes and inland dunes. Coastal dunes are found on coastlines and inland dunes are mainly found in deserts. Both types can be large in size and share characteristics such as scarcity of nutrients and water, as well as mobility of the substrate. Coastal dunes have a strong marine influence of salinity and storms. Dunes can be classified according to the shape of their base into:
- Barchan: a C-shaped or crescent-shaped dune that forms in areas where the sand supply is limited. Its surface is hard, flat and devoid of vegetation.
- Longitudinal dune: an elongated, but straight dune that forms parallel to the prevailing wind. The quantity of sand grains present is limited.
- Transverse dune: long ridges separated by depressions oriented at right angles to the wind in a constant direction. They occur in places where sand accumulates abundantly and covers the ground completely.
- Parabolic dune: these are U-shaped dunes with their ends facing away from the wind (i.e. the opposite of the barchan dune). They are typical of coastal areas where vegetation partially covers the land.
- Star or pyramid dune: an isolated hill with several ridges extending from the summit. They form when there are large concentrations of sand and the wind direction is variable.
- Barchanoid dune: constitutes an intermediate form between isolated barchans and transverse dune extensions.
Discover more about how wind can shape shorelines with our article asking what is coastal erosion?
Why are dunes so important?
Sand dunes are very important for their respective ecosystems. This is because dunes:
- Protect the coasts from erosion by acting as natural defenses and preventing the sea advancing inland through waves, currents and swells. Learn more about the types of erosion in geography with our related guide.
- Constitute a large sand filter capable of absorbing rainwater and storing it deep down.
- Provide sand, helping to maintain wide beaches.
- Provide a habitat conducive to the development of native flora and fauna .
- Are beautiful landmarks that promote tourism, education, research and cultural enrichment.

Examples of dunes
Here are some examples of famous dunes from around the world:
- Federico Kirbus Dune: located in the Fiambalá Basin, in the province of Catamarca, in the Argentine Republic. It is the largest dune on the planet.
- Duna Grande or Cerro Marcha: it is the highest dune in Peru and the second highest in the world.
- Duna la Reyna: present in the Sonoran Desert, Mexico, in the El Pinacate and Gran Desierto de Altar Biosphere Reserve.
- Sossusvlei Dune: found in Namibia in the Namib-Naukluft National Park.
- Dunes of the Sahara Desert: famous dune system in North Africa.
Now that you know what dunes are and how they are formed, you may want to check out our article on the different types of deserts where sand dune systems can be found.
If you want to read similar articles to What Are Sand Dunes and How Are They Formed?, we recommend you visit our Ecosystems category.
- Jiménez-Orocio, O., Hesp, P., Martínez, M., Espejel, I., & Moreno-Casasola, P. (2014). Dune types. A general diagnosis of coastal dunes in Mexico (pp. 27-40). Conafor.
- Celsi, E., & Iannamico R. (2013). Dunes and marine beaches. Wave-proof ecosystems. Buenos Aires coasts project.