Barchans [Crescent-Sand Dunes]

By : Neha Dhyani

Updated : Sep 8, 2022, 15:54

Barchans are crescent-shaped sand dunes 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. Barchans are located in sandy deserts all over the world.

Barchan Landforms and Examples

A Barchan dune, also known as a crescent-shaped dune of a U-shape consisting of horns pointing below or opposite the wind. Barchans have abundant sand supply, stony ground, and a steady wind movement.

  • Barchans can be discovered around shrubs and bigger rocks as these act as anchors to keep the major dune area in place, whereas the tips are blown away by the wind.
  • Barchan dunes can reach upto a height of 100 feet.
  • The word Barchan arrives from “Barkhan", a Russian word.

Examples of Barchans:

  • Nebraska Sand Hills, Nebraska
  • Indiana Dunes National Lakeshore, Lake Michigan
  • Great Sand Dune National Park, Southern Colorado
  • Grand Erg Oriental, Sahara Desert.

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.

  • Crescent shaped sand dunes are also called barchan dunes.
  • 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.

  • Barkhan is a feature of 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.
  • Barchans migration could threaten 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.

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 worldwide.
  • The Sahara desert in Egypt and the Gobi desert in Asia are their most well-known.
  • Strong winds generated Barchans on Mars' surface, according to photos acquired by orbiting probes.

Barchans in India

  • The barchans or barkhans are discovered in the Rajasthan desert.
  • Barchans are circles of different sizes with a surface that curves towards the outside, facing the prevailing winds.
  • These can be located in Rajasthan in Jaisalmer city.
  • The Thar Desert, or the Great Indian Desert, also displays barchans, which rank 17 in terms the world’s largest desert.

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FAQs on the Barchans

Q1. What are Barchans in the desert?

Barchans are a unique feature found in crescent-shaped dunes, and they are primarily exposed to one direction of the wind.

Q2. What is the approximate size of Barchans?

Barkhan is a feature that 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 is Barchan formed?

Barchans can form when there is a lot of sand in the desert. It is necessary to have a consistent airflow from one direction, and a barchan's surface is exceptionally steep.

As sand departs from the top of the dune, it produces a low-rise trailing wall that extends backward to reach the desert bottom.

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

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

Q5. In which physiographic division of India you will find barchans?

We will find barchans in the Rajasthan desert. These are concentric in shape and have curved sides facing prevalent winds, as seen in Jaisalmer city.

Q6. What is the shape of the Barchans?

Crescent shaped sand dunes are called Barchan dunes. They form in arid parts with unidirectional wind and limited sand supply.

Q7. What is the difference between barchan and seif dunes?

Barchan is a crescent-shaped dune, whereas Seif dune is a long-type crescent-shaped dune. Barchan or Barkhan is feature of an area where the amount of sand is moderate, and the wind blows only in one direction, while seif dunes are formed when the branch dune moves in more than one direction.

Q8. What are barchans meaning in Geography?

Barchans meaning in Geography is a crescent-shaped dune. It was introduced in 1881 by Alexander von Middendorf and other inland desert regions. They are a typical landform in sandy deserts worldwide and are arc-shaped, asymmetrically marked in cross-section.

Q9. Where would you see the group of barchans?

The Barchans is a group of small snow-capped islands observed at the end of west of the Argentine Islands, in the Wilhelm Archipelago.