Aeolian Processes Flashcards
What is wind as a geomorphological agent?
Weathering + Erosion + Transport + Deposition = Denudation
What is wind as a geomorphological agent?
Erosion, Transport, Deposition
Erodes rocks and sediment
Transport available sediment
Deposits transported sediment
Examples of hot arid zones
Sahara Desert - North Africa
Gobi Desert - East Asia
Antarctica - The entire continent
Patagonian desert - South America
What is the distribution of arid zones linked to?
Large atmospheric cells
Why are arid zones linked to large atmospheric cells?
Airflow in response to gradients in
- Heat
- Pressure
What is the Coriolis force?
An apparent force that acts in moving objects in a rotating reference frame, such as the Earth
Caused by the rotation of the Earth
It deflects the path of moving objects, including wind
What does the wind direct result from?
The combined action of the pressure gradient and Coriolis force
What are large-scale climate influences?
Hadley cell
Maritime vs. continental
Cold ocean currents
What are seasonal large-scale climate influences?
- ITCZ
- Monsoons
What are daily large-scale climate influences?
Breezes
What are Aeolian processes?
Sediment transported by fluid - air can be considered a fluid in this context
Random molecular motion and no fixed shape or volume
The viscosity of air?
Lower viscosity 1.8x10-5 Nsm-2
The density of air?
Lower density 1.3kg m-3
Does air have efficient sediment transportation?
No
What is the viscosity of water?
High - 1x10-3 Nsm-2
What is the density of water?
1000kg m-3
Does water have efficient sediment transport?
Yes
What is sediment movement a function of?
Erosivity and Erodibility
+ complicating factors
What is erosivity?
A function of gravity
lift and drag components
When does sediment transport occur?
When the force exceeds a threshold value, commonly determined by the particle size of sediment
What is erosivity?
Wind field
Contact area/ morphology
Impact from other grains
What is sediment movement a function of?
Of erosivity and erodibility and complicating factors
What is erodibility?
The susceptibility to wind erosion
- Particle size of surface sediments
- Plant cover
- Surface crusting
- Soil moisture
What are the factors contributing to Aeolian landforms?
Wind strength (velocity and time), direction and directional variability (eg seasonal)
- Sediment - source, grain size
- Moisture/ adhesion agent
- Vegetation
- Obstacles/ geomorphology
- Humans
Sand sediment size?
2 - 0.063mm
or
2000 - 63 um
What is the typical wavelength of sand dunes?
<1m to several 10s km, h: 10s cm to >150m
What are the major regional controls of sand dunes?
wind regime and sediment supply
What are the different types of sand dunes?
- Transverse dunes
- Linear Dunes
- Star dunes
What are the most common sand dunes?
Linear dunes are most common globally
c. 50% all dunes
What are the wavelengths of ripples?
<1 cm to c. 25cm, h: <h to c. 5cm
Dimensions controlled by grain size and wind speed
What is the size of silt sediment?
0.063 - 0.004 mm
or
63 - 4 um
Silt landforms
- Loess
What is loess?
Typically silt size particles but some sand and clay too
Alternating layers if silt and soils
What are Yardangs?
Bedrock carved by the wind abrasion (dust and sand)
What are ventifacts?
Rock abraded (and pitted) by wind-driven sand
What are pavements?
Or lag gravel
- the material left behind as the finer material has been eroded away
Why is dust a critical component of Earth Systems?
- Surface-atmosphere feedback, radiation balance & climate modulation
- Ocean fertilization and CO2 breakdown
- Long-distance nutrient transport & vegetation fertilization
- HUman health & land use
The dust cycle interacts with the ocean’s biological pump and reduces atmospheric CO2 through biological processes
