Wind/Aeolian landforms in arid environments

Case study: Namibia

Context:

• hyper-arid (<30mm ppt)
• very dry
• one of the oldest deserts 55Ma
• aridity maintained by the dry descending air of the Hadley Cell
• main source of ppt= Advection fog (contact of warm land air with cold sea air)

Landforms:

1) Ventifacts & Desert Pavements 

2) Yardangs

3) Sand dunes

1. Ventifacts & Desert Pavements (wind erosion)

Location: Walvis Bay

• Occurs in every desert
• Takes a while to form 
• Size and energy of the wind relationship

Desert Pavements= The wind removes the fine materials and deflation continues until an accumulation of stones virtually blankets the surface. 

Ventifacts= Are small stones that have been shaped by attrition and abrasion due to wind blown sediment (Saltation). Flat faces develop in the prevailing wind direction. They are separated from the lee side by a sharp edge. (If there are different flat surfaces (facets) developed, there is more than one wind direction prevailing. Ventifacts with 3 facets are called dreikanters.

2. Yardangs

Location: Mouth of the orange river

The trough is formed either from deflation of the softer rock (geology) or from the erosion of weaknesses and joints (Lithology). The abrasion of the sides goes up to the height of 0.5m as that is the highest that rocks are transported via saltation. Are formed where there is a uni-directional prevailing wind.

3. Sand dunes 

Location: Namib Sand Sea/Cunene Sand Sea

NEED:

1) Large amount of loose sand

2) A wind or breeze

3) An obstacle

Formation:

1) Friction stops sediment leading to deposition

2) Positive feedback loop

3) Migration

This is how a sand dune may actually move over time 100m/yr, rolls along maintaining its shape as it goes.

5 types:

1) Transverse

2) Barchans

3) Linear (longitudinal dune)

4) Star

5) Parabolic

Transverse and Barchans are the most common.