Depositional Landforms of Wind - Barchan, Seif, Sand Dunes, Loess - Geography Notes

Depositional landforms caused by wind are sand dunes, loess, barchan, seif, parabolic, transverse dunes, longitudinal dunes, etc. Wind-blown sediments are deposited as a result of a significant reduction in wind speed and obstruction caused by bushes, forests, marshes and swamps, lakes, large river walls, and so on. Sand is deposited on both the windward and leeward sides of fixed obstacles. This article explains the depositional landforms of the wind which is an important part of the geomorphology syllabus for the UPSC IAS Exam.

What are Depositional Landforms of Wind?

• Depositional landforms of wind are the result of wind carrying and depositing various materials, such as sand, silt, and clay, in specific patterns.
• These landforms are often characterized by their unique shapes and compositions.
• Wind-formed deposits are primarily found in arid and semi-arid regions.
• Depositional landforms include sand dunes, loess deposits, and playas.
• Wind-driven particles can travel vast distances before settling, contributing to the creation of these landforms.

Depositional Landforms of Wind

Sand Dunes

• A dune is a landform created by the movement of sand by wind or water.
• It's usually shaped like a mound, ridge, or hill.
• Sand dune formation is best in dry, hot deserts.
• Sand dune forms include Barchans, Seifs, and others, depending on the shape of the dune.
• They might be active or live dunes that are constantly moving, or they can be inert permanent dunes that are anchored in vegetation.

Barchan

• A crescent-shaped dune is known as a barchan or barkhan dune.
• Barchans face the wind, appear convex, and are primarily formed by the wind from one direction.
• They are arc-shaped, significantly asymmetrical in cross-section, with a gradual slope facing the wind sand ridge, and made out of well-sorted sand.
• They are found in sandy deserts all over the world.
• Two "horns" face downwind on this type of dune, with the steeper slope known as the slip face facing away from the wind.

Seif

• A seif is a long, narrow sand dune or a chain of dunes that is generally directed parallel to the prevailing wind or in a direction formed by two or more winds blowing at sharp angles to one another.
• The dune crest is made up of a sequence of peaks and gaps, and the steep, or slip.
• The majority of seif dunes are found in the open desert, resting on a coarse sand sheet.
• In Libya and southern Iran, seifs are very common.
• Crosswinds cause them to grow in height and width, whereas winds parallel to their axis cause them to grow in length.

Loess

• Loess is a crustal, primarily silt-sized deposit that is created by wind-blown dust deposition.
• Loess or related deposits nearly cover ten percent of the Earth's land surface.
• It's a yellow, friable substance that is usually quite fertile.
• Loess is a fine loam that is high in lime, very cohesive, and porous.
• Water rapidly sinks into the surface, ensuring that it is always dry.
• Streams have cut deep valleys through the thick mantle of soft loess and badland topography may develop.
• It is so soft that roads constructed through a loess region soon sink and their walls rise steeply.
• The most extensive deposit of loess is found in northwest China in the loess plateau of the Hwang-Ho basin.

Parabolic Dunes

• Parabolic dunes are U-shaped sand mounds with convex noses and prolonged arms.
• These dunes are also known as U-shaped, blowout, or hairpin dunes and can be seen in coastal deserts.
• Their crests, unlike crescentic dunes, point windward.
• Since the extended arms of parabolic dunes have been fixed by vegetation, they follow rather than lead, although the majority of the sand in the dune migrates forward.
• The trailing arm of the world's longest known parabolic dune is 12 kilometers long.

Transverse Dunes

• Long sand dunes with a wavy ridge running along their length are known as transverse dunes.
• These sand dunes are arranged in parallel or side-by-side rows.
• Winds carrying a lot of sand create them.
• The ridges found here are perpendicular to the wind's direction.

Longitudinal Dunes

• Longitudinal dunes extend parallel to the direction of the prevailing wind, forming parallel ridges of dunes.
• Longitudinal dunes can emerge when sand supply increases to the point where barchans (which require little sand) can change into longitudinal dunes by elongating one of its limbs.

Conclusion

Mountainous regions adjacent to deserts receive large quantities of dust, though most of it soon finds its way into the streams unless the region is covered with forests. Accumulations of wind-blown sediment are particularly conspicuous in the world’s drylands and along sandy coasts. These wind deposits are of two distinct types viz. mounds and ridges of sand from the wind’s bedload called dunes and extensive blankets of silt called loess which was carried in suspension.

FAQs

MCQs

1. What is the primary characteristic of a barchan dune?

A. Its alignment with wind direction
B. Its crescent shape with horns pointing downwind
C. Its steep leeward side
D. Its composition of loess

2. Which type of dune is formed parallel to the prevailing wind direction?

A. Barchan
B. Transverse dune
C. Seif dune
D. Star dune

3. Loess deposits are primarily composed of which type of sediment?

A. Sand
B. Clay
C. Gravel
D. Silt

4. Which of the following landforms is formed by wind deposition?

A. Glacial moraines
B. Loess
C. Alluvial fan
D. Drumlin

5. Where can large deposits of loess be found?

A. Antarctica
B. Central Asia
C. Amazon Basin
D. Saharan Desert

GS Mains Questions and Model Answers

1. Discuss the formation and characteristics of depositional landforms created by wind in arid regions.

Answer: Depositional landforms created by wind are prominent in arid and semi-arid regions where wind is the dominant agent of erosion and deposition. These landforms, including barchans, seif dunes, sand dunes, and loess, result from the accumulation of wind-blown sediments.
Barchans are crescent-shaped dunes that form in areas with unidirectional winds, while seif dunes are long, narrow ridges that form parallel to the wind direction. Sand dunes vary in shape and size based on wind conditions and sand availability. Loess deposits are fine-grained wind-deposited sediments found far from their source, known for their fertility. The formation of these landforms depends on factors such as wind velocity, sand supply, and obstructions that influence wind patterns.

2. Analyze the significance of loess deposits in agricultural productivity and soil fertility.

Answer: Loess deposits are fine-grained wind-deposited sediments primarily composed of silt. They are highly fertile and support extensive agricultural activities in regions where they are found, such as the Loess Plateau in China, Central Asia, and parts of North America.
The fine texture of loess makes it easy to cultivate, and its high mineral content contributes to soil fertility. Loess plains are often used for the cultivation of cereals, wheat, and other crops. However, loess is also prone to erosion if not managed properly, leading to soil degradation. Therefore, sustainable agricultural practices are essential to maintain the productivity of loess deposits.

3. Evaluate the role of wind as a geomorphic agent in shaping desert landscapes.

Answer: Wind plays a crucial role as a geomorphic agent in shaping desert landscapes through the processes of erosion, transportation, and deposition. In arid and semi-arid regions, where vegetation cover is sparse, wind is responsible for creating a variety of landforms such as sand dunes, barchans, and seif dunes.
Wind erodes loose materials from one location, transports them, and deposits them in another, creating dynamic features that constantly change shape and size. Wind erosion can lead to the formation of deflation hollows and yardangs, while wind deposition results in the creation of dunes and loess deposits. The impact of wind as a geomorphic agent is particularly significant in desert environments, where it continuously modifies the landscape.

Previous Year Questions on Wind Depositional Landforms

1. UPSC CSE Prelims 2020

Question: Which of the following is a depositional landform created by wind?
A. Cirque
B. Loess
C. Moraine
D. Drumlin

Answer: B

Explanation: Loess is a depositional landform created by wind, consisting of fine silt and clay particles. The other options are landforms associated with glacial activity.

2. UPSC CSE Mains 2018 (GS Paper 1)

Question: "Wind is a significant geomorphic agent in arid regions, responsible for both erosional and depositional landforms." Discuss with examples.

Answer: In arid regions, wind acts as a significant geomorphic agent, shaping the landscape through processes of erosion and deposition. Wind erosion leads to the formation of deflation hollows, yardangs , and ventifacts, while wind deposition creates landforms like barchans, seif dunes, sand dunes, and loess deposits.
For example, in the Sahara Desert, large barchan dunes are formed by unidirectional winds, while in parts of Central Asia, extensive loess plains have developed from the deposition of wind-blown silt. These landforms demonstrate the transformative power of wind in shaping desert landscapes.