Deserts
Intro
• Deserts cover 25 % of Earth’s land surface
• 13 % of population live on deserts
• We have adapted irrigations systems to water
crops
Why deserts Exists
• Latitude
@ the equator – The air absorbs
moisture equatorial oceans and rises
because it is warmer and therefore is
less dense , than the surrounding air.
Rising air cools as pressure decreases.
But cool air cannot hold as much
water as warm air so the water vapor
condenses and falls as rain.
This equatorial air is drier because loos
of moisture and flows northward and
southward at high altitudes
Desserts
Mountains:
Rain-Shadow Mountains
Desert lakes and Desert Streams
Pediments and Bajadas
• Pediment is a broad, gently sloping surface eroded into
bedrock. The bedrock surface of a pediment is covered with a
thin veneer of gravel that is on the process of being
transported from the mountain across the mountain to the
bajada
The Colorado Plateau and Great Basin
Wind
• Wind Erosion
Wind erosion is called deflation is a selective
process. Air is much less then water, wind
Transport and Abrasion
To move sand-sized particles, wind first pushes them along the
surface. If the particle is too heavy to be lifted, it continues to
move forward along the ground in a movement called creep.
Smaller or lighter sediments are picked up into the wind flow
when the speed (or velocity) of the wind flow is great enough to
lift them up. But even after they're lifted, the particles are still
subjected to the pull of gravity, so after a short period of
suspension they fall back to the surface.
This type of particle motion is called saltation: The particle jumps
along the surface, being repeatedly lifted and dropped as it
moves in response to the force of the wind flow.
As the particles land, they bounce farther along and bump other
which may begin to sulfate or move forward in the same manner
In this way the bed load of a wind current is filled with sand-sized
sediment bouncing along in the direction of the wind flow. If the
surface is very hard, the bed load may extend up to 2 meters
(about 6.S feet) above the surface because objects bounce higher
off a more compact surface. For example, a marble onto grass, it
will not bounce or move very far. But if you same marble onto
pavement, it will bounce and move much farther
Dune
• Is a mound or ridge of wind –deposited sand
• Heights  30 to 100 m
• Some exceed 500 m
Creation bedding  Cross beds
Types of Sand Dunes
Types of Sand Dunes
Loess
Desertification