GEOG 1400 Lecture Notes - Lecture 36: Abrasive Blasting, Grand Erg Oriental, Silt

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9 Aug 2016
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GEOG 1400 – (Jan. 19th)
11. Aeolian Geomorphology (the work of the wind)
(Map)
- Major sand seas and dune fields in low latitude (after Lancaster 1994)
- Tend to be around the subtropics or the latitudes between 25-35 degrees N or S.
- These are the zones where you tend to have the largest deserts.
(Image)
- Geometric features, very defined crests.
- Ripples, tiny undulations.
- Dunes
Wind Action
- Wind erodes, transports, and deposits material.
- Finer sediment (dust), larger sediment (sand).
- Lot of erosion.
- Areas where there is large supplies of loose dry material at the surface. This limits the
effectiveness of the wind action.
- Effective wind action in coastal areas, no obstacles.
Wind Erosion
- Deflation: The action of particles removed from the surface.
oLifting and transporting, and the distance it is transported depends on the material.
oOnce lifted it can be very easily transported, even thousands of km (long distances
and high altitudes above the ground).
oSand and clay usually a few meters (1-2 m) above the ground and doesn’t move
that far. By strong winds.
- Abrasion: Imagine clouds of sand moving. Equivalent to “sandblasting”.
oDriven into the ground by their movement.
Dust Storms
- Created by strong, turbulent winds.
- Big cloud of dust, fine sediment. Travels long distances. Near the ground it creates a
darker cloud.
- Has to be the right wind conditions.
(Image)
- Difficult conditions, nearly impossible to be outside.
- Sometimes can be carried over to continents to another continent.
Transport of Sand
- Volume of sand increases with wind speed. But not a linear increase.
- Wind speed generates and transports. Wind speed is very significant when it become of
40-45 km.
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- Saltation
Saltation
- Saltating grains have great erosive power.
- Increases usually with the wind speed.
- The impact transfer of energy, which facilitates the ground??? (look into recording).
- Feed back created by the impact of moving grains.
- Height or the jumps increase with wind speed.
(Image)
Great Sand Dunes – Colorado
(Image)
- One of the or the largest dune field in North America
- Stuck between two mountain ranges?
- Huge sand source from one of the mountain ranges.
Great Sand Dunes – Colorado
(Image)
Sand Dunes
- Spectacular shape in geometry
- A hill of loose sand shaped by the wind.
- Developed where there is source of sand.
- Made of quartz. Quartz is one of the two dominant minerals. Pure sand is quartz. When
you take a sample of the sand from these dunes, the dunes are made of sand and a fairly
narrow range of size. (size is very similar). Due to the wind transportation.
(Image)
- Ripples
(Image)
- Dunes
(Image)
- Steep face is always on the downward direction.
- Ripples along the downward face.
Sand Dune Development
- Sand grain is blown up the gentle slope and over the crest to fall down the slip face.
- Dune is created by the wind direction.
- Maximum angle (30-35 degrees), the equilibrium angle. Angle of repose, most natural
face of a downward dune.
- Material moves along the dune and falls.
- Whole thing keeps its shape and moves along. Just going downwind through the process
of saltation.
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