Barchans - Crescent-Sand Dune

By : Neha Dhyani

Updated : May 18, 2022, 4:57

Barchans are dunes formed in a crescent-shaped and are also known as barkhan dunes. Barchans are mostly formed by the wind from one direction and appear convex. They are arc-shaped, significantly asymmetrical in cross-section, with a gradual slope towards the wind sand ridge, and made out of well-sorted sand. They are located in sandy deserts all over the world.

Formation of Barchans

Barchans can be easily formed when there is a lot of sand in the desert. It is necessary to have a consistent airflow from one direction. A barchan's front is extremely steep.

As sand departs from the top of the dune, it produces a low-rise trailing wall that extends backwards to reach the desert bottom. From the extremities on each side toward the centre, the trailing wall takes on the shape of a crescent moon when it is one-quarter full.

The crescent form can be disrupted if the wind direction changes significantly.

Features of Barchans

Live dunes in the shape of a crescent or moon progress gradually in the direction of the prevailing winds. Barchans are probably started by a random sand buildup over an obstruction, such as a patch of grass or a pile of boulders.

Their horns thin down and get lower towards the direction of the wind as they occur transversely to the wind. The lower frictional retardation of the winds near the edges is the major reason for its shape.

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The windward side is convex and moderately sloping, but the protected leeward side is concave and steep. As additional sand is deposited by the prevailing wind, the crest of the dunes advances.

The sand is propelled up the windward side and then slips down the leeward side when it reaches the peak, causing the dune to progress. Barchan migration could pose a threat to desert life by encroaching on an oasis and burying palm trees and houses. To prevent portions of the productive land from being destroyed, long-rooted sand-holding plants and grasses are planted to impede the expansion of the dunes.

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Structure of Barchans

The steeper slope faces away from the wind, and the angle of repose of the sand is typically 30 - 35 degrees for medium-fine dry sand. The wind packs the upwind side, which is around 15 degrees.

Barchans may reach heights of 9 - 30 m (30 - 98 ft) and widths of 370 m (1,210 ft) when measured perpendicular to the wind.

Dunes such as Barchan dunes may be found in deserts all over the world. The Sahara desert in Egypt and the Gobi desert in Asia are the most well-known of them. Strong winds generated Barchans on Mars' surface, according to photos acquired by orbiting probes.

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FAQs on the Barchans

Q1. What is meant by Barchans?

Ans. A crescent-shaped moving dune is known as a barchan. Barchans are primarily exposed to one direction of the wind.

Q2. What is the approximate size of Barchans?

Ans. Barchans may reach heights of 9 - 30 m (30 - 98 ft) and widths of 370 m (1,210 ft) when measured perpendicular to the wind.

Q3. How do the Barchans get their shape?

Ans. When there is a lot of sand in the desert, Barchans can form. It is necessary to have a consistent airflow from one direction. A barchan's surface is extremely steep. As sand departs from the top of the dune, it produces a low-rise trailing wall that extends backwards to reach the desert bottom.

Q4. What is the difference between longitudinal dunes and Barchans?

Ans. The primary distinction between Barchans and longitudinal dunes is their shape and size. Barchans are crescent-shaped dunes created mostly by wind movement in one direction. The longitudinal dunes, on the other hand, appear to have symmetrical cross-sections.