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