Geological works by Wind

What is Air?

Air is the mixture of gases that forms the Earth's atmosphere.

It consists primarily of:

Nitrogen (~78%)

Oxygen (~21%)

Small amounts of other gases like argon, carbon dioxide, and trace gases.

Air is essential for life on Earth, providing oxygen for breathing and carbon dioxide for photosynthesis.

What is Wind?

Wind is the movement of air in the Earth's atmosphere, typically caused by differences in atmospheric pressure due to variation in the temperature at different latitudes.

How it forms:

When the Sun heats the Earth's surface unevenly, it creates areas of high and low pressure.

Air moves from high-pressure areas to low-pressure areas, creating wind. Its velocity depends on the degree of temperature differences.

Wind plays a crucial role in weather patterns, climate, and even geological processes like erosion and sediment transport.

In simple terms: Air is what we breathe, and wind is moving air.

Wind Erosion

Wind erosion refers to the process where wind removes loose particles of sand, silt, and clay from the Earth's surface and transports them to other locations. It is most active in arid and semi-arid regions due to the following factors:

1. Sparse vegetation: Lack of plants means the soil is less bound and easily blown away.

2. Dry climate: Dry soil particles are lighter and easier to move.

3. Loose sediments: Desert environments often have an abundance of loose particles that are easily picked up by wind.

Processes of Wind Erosion

1. Deflation:

The removal (sweeping out) of loose particles (like sand and silt) from the surface, leaving behind coarser materials such as gravel and pebbles.

Results in the formation of:

Deflation hollows (blowouts): Shallow depressions or basins.

Desert pavement: A surface covered with coarse, compacted particles.

Oasis: Basin filled with Groundwater.

2. Abrasion:

Wind-driven particles hit rock surfaces, wearing them down over time. This is like sandblasting, where wind-carried sediments act as tools to sculpt rocks.

Abrasion occurs closer to the ground, where particle concentration is higher.

3. Attrition: The wind driven loose particles collide among each other forming smaller particles of sediments. This process of collision of particles and forming further finer  particle is called Attrition.

Erosional Landforms by Winds

1. Deflation Hollows (Blowouts):

These are shallow depressions or basins formed by the removal of fine, loose materials through deflation.

They can vary in size from a few meters to several kilometers.

Example: Some desert basins in the Sahara.

2. Oasis: It is similar to Blowout but in this case the basin touches the Water table and the Groundwater fills the basin. Thus some vegetation also germinated peripherally.

3. Desert Pavement:

A layer of closely packed gravel, pebbles, or larger rocks left behind after wind removes finer particles.

Over time, deflation clears the finer sediments, leaving a compact surface that protects the underlying soil from further erosion.

4. Yardangs:

Streamlined, elongated ridges of rock sculpted by wind erosion.

Formation:

Occurs where layers of soft and hard rock alternate. Wind erodes the softer rock more quickly, leaving behind the harder rock as ridges.

Appearance: Long, sharp ridges parallel to the prevailing wind direction.

5. Ventifacts:

Rocks shaped and polished by wind-driven sand and particles.

Formation:

Wind erodes one side of a rock, creating smooth or faceted surfaces.

If the wind direction changes over time, multiple facets can form on the same rock.

There are 3 types of Ventifacts 

Einkanters: One face polished.

Zweikanter:  Two faces polished.

Dreikanter. Three faces polished.

6. Rock Pedestals (Mushroom Rocks):

Rocks with a narrower base and a broader top, resembling a mushroom.

Formation:

Wind abrasion is more intense near the ground because sand particles are concentrated at lower heights. Over time, the base erodes faster than the upper portion.

7. Zeugen:

Tabular, flat-topped rock formations with a resistant upper layer and a softer lower layer.

Formation:

Wind abrasion erodes the softer lower layers more quickly, leaving the upper hard layer intact. This differential erosion creates mushroom-like or flat-topped shapes.

8. Inselbergs:

Isolated, steep-sided hills or ridges standing prominently above flat surroundings.

Formation:

Result from long-term erosion, where wind and water strip away the surrounding softer material, leaving behind more resistant rock formations.

Transportation by Wind and Its Types

Wind plays a vital role in transporting sediments, especially in arid, semi-arid, and coastal regions. This process, also known as aeolian transportation, involves the movement of particles through different mechanisms depending on their size, weight, and wind velocity. The main types of transportation by wind are suspension, saltation, and creep.

1. Suspension

Definition: Suspension involves the transportation of fine particles, such as dust or silt, which are lifted and carried in the air over long distances.

Mechanism:

Fine particles (less than 0.2 mm in diameter) are light enough to remain airborne.

Wind lifts these particles into the atmosphere and carries them horizontally over large areas.

The distance traveled depends on wind speed and particle size.

Examples:

Dust storms in deserts where particles are transported over thousands of kilometers.

Loess deposits, such as those in China and Europe, are formed when suspended particles settle.

Characteristics:

Particles can remain suspended for hours or days. Common in regions with sparse vegetation and dry, loose soils.

2. Saltation

Definition: Saltation is the bouncing or hopping movement of medium-sized particles (0.2 mm to 0.5 mm in diameter) along the ground.

Mechanism:

Wind lifts particles a short distance into the air.

As the particles fall back to the ground, they collide with other particles, causing them to bounce and move forward.

This process continues in a chain reaction, transporting sediments across the surface.

Examples:

Movement of sand grains in deserts and along beaches.

Formation of ripples and dunes through the accumulation of transported sand.

Characteristics:

Saltation accounts for about 70–80% of wind-transported material.

Particles typically move in low arcs, less than 1 meter above the ground.

It is the most effective mechanism for sand transport in deserts.

3. Surface Creep (Traction)

Surface creep, also called traction, involves the rolling or sliding of larger particles (greater than 0.5 mm in diameter) along the ground.

Mechanism:

Larger, heavier particles cannot be lifted by wind. These particles are moved by the force of wind or by the impact of other particles in saltation.

The rolling motion is often gradual and occurs in a step-by-step manner.

Examples:

Pebbles or coarse sand grains moving in desert pavements.

Larger grains found at the base of sand dunes, transported by surface creep.

Characteristics:

Accounts for about 20–25% of wind-transported material.

The movement is slower compared to suspension and saltation.

These particles play a role in stabilizing desert pavements.

Factors Affecting Wind Transportation

1. Wind Velocity:

Higher wind speeds can lift heavier and larger particles.

Low velocities primarily transport finer particles.

2. Particle Size and Weight:

Lighter, finer particles are transported via suspension.

Medium-sized particles move via saltation, while heavy particles undergo creep.

3. Surface Conditions:

Dry, loose sediments are more prone to wind transportation.

Vegetation and moisture reduce wind activity by binding particles.

4. Topography:

Flat, open landscapes like deserts or beaches enhance wind transportation.

Depositional landforms by Wind:

Wind is a powerful geological agent in arid and semi-arid regions, capable of transporting and depositing sediments to create distinct landforms.

I. Sand Dunes

Sand dunes are the most recognizable wind-deposited landforms, formed when sand grains accumulate in areas where the wind's velocity decreases. Dunes vary in shape and size based on wind direction, sand supply, and vegetation cover.

Types of Sand Dunes:

1. Barchan Dunes:

Crescent-shaped dunes with their horns (wings) pointing downwind.

Form in areas with a unidirectional wind and limited sand supply.

Common in deserts like the Sahara.

Height: Ranges from a few meters to 30 meters.

Formation: Sand accumulates on the windward side and slides down the steep slip face on the leeward side.

2. Seif: These are similar to Barchan but of of the wings is missing due to Changes in direction of of wind.

3. Transverse Dunes:

Long ridges perpendicular to the prevailing wind direction.

Form in areas with abundant sand supply and consistent wind.

These dunes can stretch over hundreds of kilometers.

4. Linear (or Longitudinal) Dunes:

Long, narrow dunes aligned parallel to the wind direction.

Form in areas with limited sand supply and bidirectional winds.

Found in deserts like the Australian Outback.

5. Parabolic Dunes:

U-shaped dunes with their horns pointing upwind.

Often stabilized by vegetation and found near coastal regions.

Formed by deflation and blowouts in semi-arid areas.

6. Star Dunes:

Star-shaped dunes with multiple arms radiating from a central peak.

Form in areas with multidirectional wind regimes.

These are the tallest dunes, reaching heights of over 100 meters.

II. Loess

Description: Loess is a fine-grained, wind-deposited sediment composed primarily of silt-sized particles.

Formation: Wind picks up and deposits silt from deserts, glacial outwash plains, or river valleys.

Characteristics:

Loess deposits are highly fertile due to their high mineral content.

The deposits are loose but can maintain steep slopes due to their cohesive nature.

Distribution:

Found in areas like northern China (Loess Plateau), central Europe, and the central United States (Mississippi River Valley).

3. Sand Sheets

Description: Sand sheets are extensive, flat areas covered with coarse sand grains and minimal vegetation.

Formation:

Occur when wind lacks the energy to form dunes or when sand supply is insufficient.

Sand grains are too coarse to be transported further, leading to their accumulation.

Characteristics:

Feature low relief and gentle undulations.

Common in arid and semi-arid regions near dune fields.

4. Playa Deposits

Description: Playas are flat-bottomed desert basins where fine sediments and salts are deposited by wind.

Formation:

These deposits accumulate in ephemeral lakebeds in deserts.

When the water evaporates, wind picks up the lighter materials and redistributes them, leaving behind fine particles.

Example:

Found in basins like Death Valley in the USA.

5. Lag Deposits (Desert Pavements)

Description: Lag deposits, also called desert pavements, are surfaces covered with coarse pebbles and gravel.

Formation:

Wind removes finer particles through deflation, leaving behind heavier materials.

Characteristics:

These surfaces are compacted and protect underlying sediments from further erosion.

6. Ventifacts (Associated with Deposition)

Although ventifacts are primarily shaped by wind erosion, deposition often occurs around them:

Finer particles can accumulate around ventifacts or in wind shadows behind these rocks.

These features help in stabilizing localized sediment deposits.

7. Dune Fields and Ergs

Dune Fields:

Large areas covered predominantly by sand dunes.

Ergs:

Extensive sand seas found in deserts like the Rub' al Khali (Empty Quarter) in Arabia.

Formed when wind deposits vast quantities of sand over time.

Factors Affecting Aeolian Deposition

1. Wind Velocity: Slower wind leads to sediment deposition.

2. Sand Supply: Abundant sand allows the formation of larger dunes.

3. Vegetation: Stabilizes dunes and influences dune shape.

4. Topography: Landforms like valleys and cliffs affect wind patterns and deposition.