Last Updated on August 4, 2022
Sand dunes are among the world’s most beautiful and dramatic landforms. Dunes entice people of all ages to climb up and then roll or slide down the gentle sand slopes, photographers can’t get enough of their elegant curves, undulating patterns, and shifting shadows.
Sand dunes also appear to have their own personality: they move and change frequently, generating formations like stars and crescents. As the wind blows, they all whisper, and a few of them even sing or boom as dry sand flows down the steep face.
How are sand dunes formed?
A dune is a hill of sand that forms when the combination of wind forces and/or water currents allows for the accumulation of sand: the wind lifts the accumulated sand from the sea and carries it inland, until it meets an obstacle that will force the sand to settle, with sand particles stacking on top of one another until a mound is formed. Dunes are then subject to continuous movement and resizing depending on the direction and strength of the wind.
In order for a dune to form, the following needs to occur:
- A large amount of sand (or dust or volcanic ashes) needs to be available;
- Strong wind and/or water currents transporting the sand to a given direction;
- Dry weather conditions cause the sand to dry up;
- An obstacle causes the sand movement to halt and the dune to form against it.
Types of Sand Dunes
The type of dune in geography is determined by its shape. Geologists have classified dune types into five main categories: barchan or crescent dunes, parabolic dunes, transverse dunes, linear dunes and star dunes.
Barchan / Crescent
Barchan Dunes / Crescent Dunes
This is the traditional dune form: when viewed from above, Barchan dunes resemble crescent moons, with convex (outward) backs and steep, concave (inward) faces. The crescent’s curving tips or wings point downwind, partially enclosing a single slip-face. Barchans arise when there is a limited quantity of sand, reasonably flat ground, and a consistent wind flow from one direction. A barchan dune can reach the height of a multi-story skyscraper. The most frequent are barchan dunes, which can be found in deserts all around the world.
A parabolic dune resembles a barchan in shape, however it is the exact opposite. The dune’s tips face the wind, while the dune’s main body moves with the wind, forming a depression between the tips. Blowing out dunes are sometimes called as parabolic dunes because of this structure. When vegetation stabilizes sediments and a U-shaped blowout forms between clusters of plants, these dunes arise.
Transverse dunes are long, asymmetrical dunes that grow at right angles to the direction of the wind. They form when there is a lot of sand and the winds aren’t too strong. These dunes have a single, steeply sloping slip face. On a broad scale, a group of transverse dunes resembles sand ripples.
A linear dune (or longitudinal dune) arises when there is plenty of sand and strong cross winds blow from at least two directions, forcing the sand into long lines or ridges. Linear dunes’ crests or summits are frequently straight or slightly curved, with slipfaces on both sides. Linear dunes can be as tall as 655 feet (200 meters) and as long as 62 miles (103 kilometers).
Three or more sinuous ridges radiate out from a central sand peak in what makes a pyramidal or star-shaped dune. Where there is enough of sand and strong breezes from all directions, a star dune forms. There are three or more slipfaces on this dune. It develops upwards rather than moving along the ground. The largest and highest dunes are star dunes.
Additional Sand Dune Classification
Dunes that are smooth and extended, resembling the back of a whale, and are generated by the passing of a series of longitudinal dunes along the same course. A sand levee is another name for it.
A barchanoid ridge consists of several joined barchan dunes and looks like a row of connected crescents. Each of the barchan dunes produces a wave in the barchanoid ridge. Occurs when the sand supply is greater than in the conditions that create a barchan dune.
Sub-type of longitudinal dunes that are shorter and feature a more sinuous ridge.
Dune formations that feature a circular or elliptical shape and no slip-faces. May be formed by the modification of stationary barchans.
Dunes that are in-between the shape of a star and a transverse dune. Their ridge is asymmetrical and features two slip-faces, caused by winds that reverse direction.
Sand dunes F.A.Q.
What causes sand dunes?
Dunes are the result of a combination of three natural movements: those of the earth, of the sea and of the wind. Brought to the coastal system by the waves of the sea, the sand is lifted by the wind that pushes it inland.
Any obstacle placed in the path of the wind can start the accumulation of sand that will originate the dune: the lines of wind flow, in correspondence of the obstacle, are disjointed and continue their path slightly deviated, creating on the leeward side (sheltered from the obstacle) an area where the wind speed becomes significantly lower and unable to continue the transport of grains that are thus deposited. If there is enough sand available and if the wind continues to blow in the same direction for a long period, the primitive accumulation will turn into a dune.
Are sand dunes constructive or destructive?
Sand dunes are constructive: they are built via deposition by the constructive force of wind which shifts rock particles on top of each other until a sandhill is formed. They can be formed in both coastal and inland areas, usually near strong currents, deserts, or volcanoes.
Are sand dunes formed by erosion or deposition?
Sand dunes are an example of deposition. They are formed by the shifting of sand particles by the wind, sea waves, or both, although in some areas they can be a sign of land degradation or desertification. Some sand dunes are also originated by volcanic activity, with ashes and lava particles being shifted rather than sand.
What are “singing” and “booming” sands?
In a few selected places in the world a phenomenon can occur that causes the shifting sands of a dune to produce an audible sound. These dunes are called singing dunes or booming dunes. The sound is the result of vibrating sand particles and can be heard easily under certain enviromental conditionss, usually under hot, dry and windy weather.
Why are sand dunes important?
The dunes that form a continuous belt along the coast serve as barriers from storm surges and swells. Another function is to serve as a sand reserve for the beach during the onslaught of stormy seas. The waves, on this occasion, erode the sand from the beach and the dunes in front of the sea, depositing it along a new coastal profile, which varies according to the energy of the waves themselves.
The integrity of the dune belt, with its characteristic wedge shape with the vertex stretching out towards the sea, is an indispensable condition to protect the innermost ecosystems, attenuating the force of the sea winds loaded with salt (and pollutants) and diverting them upwards: crossings create dangerous openings where the wind infiltrates, coming to expose the vegetation laboriously settled in this difficult environment, characterized by wind, aridity, inconsistency of the soil, in addition to the problems arising from the presence of man.
Where is the highest sand dune?
Duna Federico Kirbus in Argentina is the tallest sand dune in the world. It is 1234 meters (4048 feet) tall and was named after the researcher who first discovered its height and value.
Are sand dunes dangerous?
Sand dunes can pose a threat to human habitats, particularly to crops, buildings, and people living in desert areas. Dunes are always moving and changing, extreme weather conditions and trong winds can cause sand storms and sand avalanches and be quite destructive. Dune movements causing desertification in formerly vegetated areas is one of the most threatening negative effects of global warming and climate change that the world is currently facing.
Do all deserts have sand dunes?
Dunes can sometimes cover large areas of land, but they do not have to be necessarily associated with deserts. Despite the imagery of limitless oceans of sand that many people associate with the word “desert,” dunes cover just a small portion of the world’s deserts, less than 10%. There exist in fact many different types of desert environments ranging from sandy, to rocky, to ice frozen.
How many sand dunes are there in the world?
It is impossible to quantify how many sand dunes there are out there, because the number is always changing. Dunes are not static: they are costantly made, unmade and shifted by the wind. There are 24 deserts in the world (including cold deserts), as well as many pseudo-deserts, and sand dunes can also occur in coastal areas or near volcanoes.
What are the most popular sand dunes?
The are a few famous sand dunes all around the world, namely the dunes of the natural oasis in Huacachina and Cerro Blanco in Peru, the dunes of Sossuvlei and the Namib desert in Namibia, the singing dunes of Kazakhstan, the Coral Pink Sand Dunes in Utah and the White Sands of New Mexico.
Sources: Sand Dunes of the Southwest
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