While talking about sand dunes, a spectacular image of small hill ranges of sand in a desert appears before our eyes, although sand dunes may be seen in other locations like sea-beaches as well.
Basically, sand dunes are mounds of sand, formed by wind. Have you noticed that on a windy day, small waves are created in a pond or river? Similarly, sand dunes are also formed by wind.
Let’s try to explain. In dry weather, a sudden heavy wind, carrying dust along with it, may disturb you sometimes. In the same way, in a sandy area, like the desert or sea beach, when wind blows, it carries sand grains along with it and transports the sand grains from one place to another. Now, if there are any obstacles, in the way of blowing wind, such as rocks, wood or trees, then wind speed becomes weak and sand grains are deposited there. When the process of depositing sand is continued for long period of time, then a heap or mound of sand is formed. These are called sand dunes.
Each sand dune has two sides. One is the windward side – the side of the sand dunes, facing the side from which wind is coming. And the opposite side is called the slip-face. See the picture below.
Let’s discuss the different types of sand dunes.
Crescent dune or barchan dune
Its shape is like crescent moon, as shown in the picture. It is usually created when the wind is blowing from only one direction. Generally, its pointed tips are in downward direction of the wind and concave side or semi-circular inner side is the slip face, i.e. opposite side of the direction of the wind.
Generally linear dunes are formed parallel to the wind direction and the pressure of the wind is similar on both sides of the dune. It is shaped in long straight ridges. Sometimes it takes a zigzag shape.
A parabolic dune is a U-shaped dune, like a crescent dune. Contrary to the Crescent dune, in the Parabolic dune, the inner side is the windward side, while the outer side is the slip face.
When the wind blows from three or more different directions, a star dune is formed. Star dunes have several arms and have at least three slip faces.
Sand dunes are natural barrier to stormy winds or waves and are also a beautiful creation of nature. They also function as shelters for animals and plants that exist in this habitat. So, human intervention should not destroy this beautiful gift of nature.