Unraveling the Mysteries of Barchans

Barchans are crescent-shaped sand dunes that are primarily formed when the wind blows predominantly from one direction. These dunes are a common sight in desert landscapes worldwide, including India.

The unique structure of barchans is such that they have a convex side facing the wind, and the horns of the crescent point in the direction of the wind. These dunes are usually asymmetrical in shape, with a gentle slope facing the wind and a steeper slope, known as the slip face, facing away from the wind. The size of a barchan can vary significantly, with heights ranging from 30 to 100 feet and widths up to 1200 feet, measured perpendicular to the wind.

Over time, barchans tend to move with the wind due to erosion on the windward side and deposition on the leeward side. This movement can range from a few meters to up to 100 meters per year. Barchans can be found as isolated dunes or in extensive chains stretching across plains in the direction of the prevailing wind. The term barchan originates from Turkistan, where these dunes are a common feature of open desert regions.

To further understand how wind influences the formation of barchans, you might want to read about:

How Are Barchans Formed?

The formation of barchans involves a combination of three different variables that determine how sand moves in a desert setting.

Saltation

Saltation refers to the process where sand grains bounce along the direction of the wind. This process accounts for about 95% of sand movement.

Creep

Creep is the phenomenon where sand grains collide with other types of grains, such as clay and gravel. This process accounts for approximately 4% of sand movement.

Suspension

Suspension is when sand grains are lifted into the air and settle down as the wind moves. This process accounts for about 1% of sand movement.

The combination of these movements results in the formation of barchans , which are commonly found in areas with a sparse sand cover. The steep face of a barchan is formed when sand escapes from the top region of the dune and forms a trailing wall, which is typically less steep and extends to meet the desert floor.

The trailing wall's rounded shape extends from both ends to the middle, forming a crescent shape. This shape can be disrupted if there is a significant change in wind direction. For instance, the Grand Erg Oriental in the Sahara Desert and the White Sand Dunes in New Mexico are notable examples of barchans .

In Conclusion

Understanding the meaning and formation of barchans is crucial for students preparing for the UPSC exam . The unique features and movement of barchans make them an interesting subject for geographical studies and a potential topic for examination questions.