The photo shows a group of active star dunes in the desert--blowing sand can etch windows and shifting sand dunes can interfere with buildings and airports in desert regions

I. Desert regions and wind erosion

A. Desert and adjacent regions

1. Deserts

·         are those regions on Earth which are categorized as having arid climates

2. Steppes

·         are those regions adjacent to deserts categorized as having semiarid climates--steppes separate arid and humid climates

·         click here to see the Earth climate zones or see page 289 in text

B. Wind erosion processes

1. Deflation

·         is the removal of rock waste from the land by the wind

·         a blowout or deflation hollow is a depression excavated by the wind in easily eroded materials such as sand or silt deposits with little or no moisture or vegetation content--vegetation present in materials at the surface impedes deflation

·         click here to see a blowout  or see page 297 in text

2. Abrasion

·         is the grinding and scraping of a rock surface by the friction and impact of rock particles carried by the wind--it results in a "sandblasting" effect of the rock causing the rock to be polished and smooth-see page 299 in text

C. Wind erosion loads

1. Suspended load

·         suspended materials in the wind consists primarily of silt or clay size particles and if highly concentration can result in dust storms--the deposition of the suspended load can form large deposits which lack layering called loess – see bottom of page 296 in text for a dust storm – see page 303 for a picture of loess

2. Bed load

·         refers to rock particles which are transported by a bouncing effect and consist primarily of sand size particles--the accumulation of this type of load forms the desert sand dunes (active dunes)

II. Active sand dunes

A. Nature of active (unstable) dunes

1. Dune profile

·         the dune slopes upward in the direction of the wind and is called the windward slope--the slope then breaks downward sharply to a much steeper slope called the leeward slope or slip face

·         click here to see the dune profile or see page 301 in text

2. Shifting dunes

·         active dunes can readily shift positions down wind and bury roads, airport runways, homes, etc.

B. Categories of active dunes--pictures shown on page 301

1. Barchan

·         is a crescent shaped dune with the convex portion facing the wind direction and formed when the wind direction is constant and the sand supply is limited

·         click here to see photo of barchans or see page 302 in text

2. Transverse

·         is a dune elongated perpendicular to the direction of the wind and formed when the wind is constant and there is a large supply of sand--see page 301B in text

3. Longitudinal or Seif

·         is a dune elongated in the general direction of the wind and formed from slightly different wind directions with a limited supply of sand

·         click here to see photo of longdunes

4. Star or complex

·         is a dune formed when the direction of the wind is variable

·         click here to see photo of star dune

·         click here to see and review the sand dune types

III. Evolution of a desert landscape

A. Alluvial fans

B. Playa lake and playa

click here to see a photo of a bajada and playa lake

C. Inselberg

click here to seethe stages of landscape evolution in mountainous desert regions (A=early stage, B=middle stage, C=late stage) or see page 294 in text

click here for more information on deserts

IV. Inactive or stable



page 307
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page 314
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page 318
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page 320
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barchan dunes
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bajada and playa lake
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page 322
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