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
·
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
·
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
·
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
·
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
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