Ch. 16: Wind Erosion and Landforms

Question 1

Describe how wind erodes, transports and deposits sediment. Which grain size is moved most easily by wind? Why?

Answer 1

-Suspension - how wind transports finer-grained sediment usually less than 0.2 mm ; they’re lifted in the air much higher or suspended in air for longer and travel furthest
-Saltation - how wind transports sediment larger than 0.2 mm; they drag along by the skipping and bouncing action and hit other grains, knocking them into air; tend to be the most easily moved by wind because larger and lighter sediment need stronger winds that carry weight of the larger and can overcome frictional pull of the lighter caused by their aerodynamic surface
-Surface creep - how wind transports coarser sediments; particles are too large for saltation and just end up rolling around the ground surface

Question 2

Describe the two principal wind-erosion processes as well as the main erosional landforms that result.

Answer 2

1.) Deflation - removing and lifting loose particles
2.) Abrasion - grinding rock surface by the “sandblasting” action of particles captured in the air

wind-erosion landforms:
-Deflation hollows (“blowouts”) - depressions in the landscape caused by wind deflation
-Desert pavement - a hard, stony surface covering land surfaces in arid regions
-Ventifacts - rocks that are pitted, grooved, or polished from eolian abrasion
-Yardangs - large-scaled streamlined rock structures (formed by deflation and abrasion) that are aligned parallel to most effective wind direction

Question 3

Why is disruption of desert pavement surfaces an important issue in arid regions? You may need
to consult your textbook for more information on this one.

Answer 3

-Because desert pavement surfaces when formed becomes almost like a shield against wind and water to prevent soil erosion, so if it’s disrupted, erosion could increase, leading to loss in soil fertility, and ecosystem destabilization

Question 4

Explain how dune formation initiates, and name the parts of a dune with respect to wind direction and slope. Be able to sketch a simple dune and label these parts.

Answer 4

How dune formation initiates:
-When saltating sand encounter small patches of sand their motion is dissipated as the accumulate
-Once accumulation reaches 30 cm, a slipface forms. After that, the following dune features follow: Stoss side - gentle sloping slipface in downwind side of dune feature. sand moves over that slope, crests then falls down the leeward slope

Question 5

List the three main dune forms, as well as the sub-types discussed in the lecture. Be able to list
the dune shapes as well as wind strength, direction and sand supply associated with each.

Answer 5

3 main dune forms:
1.) crescentic
2.) Linear
3.) Star

Crescentic dunes (curved shaped):
-Barchan - horns point downwind
-Constant strong winds
- Consistent wind direction
-limited sand supply
-Barchanoid ridges - form when barchan dunes align and join into long wave ridges
-constant strong winds
-consistent wind direction
- Increased sand supply
-Transverse dunes - long, sinuous, asymmetrical ridge formed from barchanoid
- constant weaker winds
- consistent wind direction
- high sand supply
- Parabolic dunes
-Horns point upwind
-constant strong winds
-consistent wind direction
- vegetation stabilizes arms

-Linear dunes (straight line shaped):
-Longitudinal dunes
-linear ridge, may be slightly
sinuous
-constant strong winds
- Multiple consistent wind
directions
-High sand supply

-Star dunes (radiating ridges)
-has largest scale
-Pyramidal shape
-constant weaker winds
-multiple wind directions
-lower sand supply

Question 6

What is loess? When did most loess form? Why is it important for agriculture and slope stability?

Answer 6

-Loess - clays and silts blown great distances by wind and deposited in unstratified, homogenous deposits
-The clays and silt sediments were left behind on outwash plains by the retreating Pleistocene glaciers 15 000 yrs ago
-It’s important because it can be beneficial and problematic. Due to its cohesive nature and good moisture retention, it can help stabilize slopes and form fertile soils, making good agricultural land and prevention of landslides. However if it gets saturated w/ water, it can become unstable and make the slope fail, especially in steep terrain.