Deserts
Deserts: definition
• A region which has an arid climate or where evaporation exceeds precipitation
• Steppe: region often adjacent to a desert• Semiarid climate: irregular precipitation,
enough to generate minimal plant growth
Desert and Steppe areas around the world:
Deserts:
• Cover a fifth of the earth’s surface
• Can be found at all altitudes and latitudes
• Four physical factors cause deserts : all are influenced by prevailing winds
a. Continentality
b. Lee side of mountains
c. Cold ocean currents
d. Prevailing winds
Prevailing Winds:
• Found 30 n and s latitude due to the global wind circulation system
• Descending air masses are compressed, warm and absorb moisture
Lee Side:
Coastal Location:
Desert Erosion: Water
• Seldom rains in desert regions• When it does massive DOWNPOUR or it’s
called a FLASHFLOOD• Dry weathered soil, and minimal vegetation to
anchor the soil causes rapid erosion• Rainwater carries sediment away and
deposits it on the valley floor• Within 10 to 20 minutes the rain is gone and
the water has evaporated
Wind erosion processes:
• Deflation ; is the removal of rock waste from the land by wind– Blowout or deflation hollow ; depression
caused by deflation due to lack of vegetation to hold material down
Landforms: created by water
• Alluvial Fan: • Fan shaped delta
formed at the foot of mountains in a desert valley
• A Bajada is an apron of sediment resulting from a coalescence of alluvial fans
Landforms : water
• Playa Lake:– A temporary shallow
lake formed in the central basin of a desert during a rare downpour
– A Playa is the dry flat lake bed that remains
Wind erosion processes:
• Deflation: removal of rock waste from the land by the wind
• Abrasion : “sandblasting” effect on materials caused by the impact with particles carried by the wind
• Bedload: – Saltation– Suspension – Particles are bounced
along the ground or suspended in the air; both these process erode rock surfaces and carry material
Sand Dunes:
• Many different types but learn these:
• Barchan: crescent shaped with convex portion facing the wind
• Formed with a constant wind and limited sand supply
• Longitudinal or seif
• Elongated in general direction of wind
• Formed with slightly different wind directions and limited sand supply
Inactive or stable dune:
• Parabolic Dune:• Formed along
coastlines or large lakes
• Winds cause blowouts in sand resulting in a crescent shape with convex side facing the wind
Reg Deserts: little sand
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