Barchans are primarily crescent-shaped sand dunes that are likely to shift while facing the wind with intensity from one particular direction. They are most commonly found in sandy desert regions and are most commonly associated with regions where a single dominant wind direction impacts a limited supply of sand.
The concept of Barchans dunes represents the dune morphology, which is a prominent topic for students preparing for UPSC Prelims. Students aspiring to take the exam must prepare themselves to answer questions based on the topic.
Candidates must also read about What are the main features of the Indian desert? at the linked article.
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What Are Barchans? Are They Found In India?
Barchans are sand dunes in the shape of a crescent. When the wind flows dominantly in one single direction, it leads to the formation of one such barchan. Among the many types of dunes, barchans are the most commonly occurring dunes, and although it is common to find barchans in India, they can be spotted in desert areas all across the globe.
Think of barchans as a convex that faces the wind. Usually, the horns of the crescent can be seen pointing downwind, which also marks the advancing wind in the lateral direction. These dunes may appear asymmetrical in shape like a cross-section and have a gentle slope that faces the wind. The steeper slope faces away from the wind and is known as the slip face. A typical barchan may reach up to the height of 30 to 100 feet and width of 1200 feet when measured perpendicular to the wind.
On the windward side, they will gradually migrate with the wind due to erosion and subsequent deposition on the leeward side. The typical range of such migration ranges from about a meter to 100 meters in a year. Barchans can either occur as a group of isolated dunes or form a chain extending across a wide span of plains in the direction where the wind prevails. The name of the barchans originates from Turkistan, where they are characteristic of open and inland desert regions.
How Are Barchans Formed In The Desert?
The crescentic shape of barchans is a type of sand dune which is likely to form due to the merger of three different variables. The following ways show how sand can move in a desert setting.
Saltation is an event that occurs when the grains of sand jounce along with the direction of the wind. Incidentally, about 95% of the sand grains move in this typical manner.
A creep is an incident when the grains of sand clash with another type of grains, such as those of clay and gravel. About 4% of sand movement accounts for the formation of creep sand dunes.
In the case of suspension, the grains of sand blow high up in the air and eventually settle down depending on the movement of the wind. Nearly 1% of the sand usually travels in this way.
The result of these movements of sand in the desert region results in the formation of crescentic sand dunes. Barchans dunes are likely to form where there is not much sand cover on the plains. The face of a Barchan can be very steep. When the sand escapes from the top region of the sand dune, it is likely to form a trailing wall behind it, which is typically not very steep. It can extend further backwards to meet the floor of the desert.
The rounded shape of the trailing wall reaches from the ends of either side to the middle, which forms a crescent-like shape resembling the moon. This crescent shape is destroyed if there is a substantial change in the direction of the wind. Moreover, the movement of wind in one direction in such geography gives rise to the formation of barchans. The Grand Erg Oriental in the Sahara Desert is a classic example of barchans, and so are the White sand dunes in National Monument, New Mexico.
To Sum Up
It is important to understand barchans meaning if you are a student preparing for UPSC exam. The features of the barchans are quite unique. The fact that they can move and that they form of the windward slope, slip face and crest, make them a different type of geographical element, questions about which can be asked in the exam.