I. Deserts

II. Erosion by Wind

III. Deposition by Wind

IV. Morphology of Dunes

V. Landforms from Interior Drainage

VI. Possible Essay Questions

VII. Practice Questions

• Lack of moisture make deserts geologically different -
• A dry climate produces little vegetation; soil is not protected from erosion during rainfall.
• Lack of moisture leaves soil loose, rather than cohesive, so it is susceptible to erosion by both running water and the wind.

• Erosion by running water is more rapid than in humid climates -
• Running water is responsible for most desert erosion.
• Flash floods and mudflows are common because there is no vegetation to hold back the runoff.
• Slopes are steeper because, due to the lack of water in the soil, mass wasting is reduced in importance.

• Erosion by wind is much more common than in humid climates -
• Silt and clay are blown away as suspended load -
• Dust storms are an example.
• Distance of travel can be over 1,000 miles.
• Sand is bounced along the ground as bed load -
• Distance of travel is short and confined to the immediate desert area.
• Gravel is not moved at all -
• Result of the above size-sorting process is a wind-lag layer on the desert surface called desert pavement.

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• Process of blowing away loose, weathered material is called deflation, which produces:
• Depressions in the land surface called blowouts.
• Bushes growing on mounds of soil because the intervening soil has been blown away from around the roots.
• Deflation will continue until:
• Water table is reached; soil is cohesive here, so will not blow away. The result of deflation to the water table is an oasis.
• A layer of lag gravel called desert pavement is left behind; the soil is then protected from further erosion by the wind.

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• Silt and clay -
• Thick piles of windblown dust which accumulate downwind from deserts are called loess.
• Loess deposits also form downwind from continental glaciers because the cold air over a glacier produces high pressure and strong off-glacier winds that, in turn, pick up the fine glacial meltwater deposits and blow them into distant areas.
• Sand -
• Piles of sand which accumulate in deserts or near beaches are called dunes.

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• Windward side of a dune (faces into the wind) -
• A gentle slope with a compact and rippled surface.
• Sand is eroded from this side of the dune.
• Leeward side of a dune (faces away from the wind) -
• A moderately steep slope (at angle of repose) with a loose and smooth surface.
• Sand is deposited on this side of the dune.
• Erosion on the windward surface and deposition on the leeward surface as dunes migrate and climb over one another produces a feature in sedimentary rocks called cross bedding.

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• Alluvial fans - Form where mountain streams enter a valley.
• Bajada - A broad, sloping depositional surface formed by the merging of several alluvial fans.
• Playa - A flat, clay or salt surface formed at the center of the basin toward which all the surrounding streams flow.
• After rains the playa may contain a playa lake.
• Inselberg - The last stage of an eroding mountain top that is slowly being covered by alluvium.

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• Why are flash floods and mudflows more common in the desert than in humid climates?
• Why are slopes steeper in the desert than in humid climates?
• Describe the load that is transported by the wind.
• Describe and illustrate the origin of deflation mounds.
• Describe and illustrate the origin of an oasis.
• Describe and illustrate the origin of desert pavement.
• Describe and illustrate the characteristics and morphology (shape) of a sand dune.
• Describe and illustrate the origin of an alluvial fan.
• Describe and illustrate the origin of a playa.
• Describe and illustrate the origin of an inselberg.

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VII. Practice Questions

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