Transcript Desert 2 - sabresocials.com

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