Desert and Wind Action
A desert is a place with low rainfall 10" inches or (25 cm)
Distribution of deserts
1.Areas with sinking wind ~ 30E N/S
2.Rain shadow
3.Great distance from the ocean e.g. China
4.Cold ocean currents
Characteristics of Deserts
1. Lack of through-flowing streams, intermittent lakes and drainage
2. Flash flood
3. Mud flows
4. Desert channels have big sizes of features in SW USA
5. Plateaus - flat-top area elevated above the surrounding surface
6. Mesa - a broad flat top hill banded by cliffs
7. Butte - a narrow pinnacle of resistant rock with flat top and very steep sides
8. Monoclines erosion give rise to - hogback (equal shape), cuesta (unequal shape)
9. Playa lake - very flat dry lake bed of hard and cracked clay
A good agent of erosion and deposition
Velocity is important - Velocity is due to temperature differences.
Winds in the desert could be up to 60 miles per hour
Wind erosion and transportation
(Dust bowl of the 1930's)
Wind picks up sediments- fine grains are carried up and heavier sand grains are moved close to the ground in leaping pattern (e.g. saltation in sandstorm)
Yardangs (Streamlined parallel ridges aligned with the direction of a strong prevailing wind ~ 10 m high and approximately 100 m long
Wind-blown sand can sculptor isolated pebbles, cobbles or boulders into artifacts (ventifacts) (rocks with flat wind abraded surfaces)
Deflaction-- the removal of clay, silt, and sand by wind erosion
Blowout is in a depression on land surface caused by wind erosion
Desert pavement(pebble armor) - the pebble layer prevents the
wind from removing sediments usually after the wind has removed the
fine
grained material
Loess - wind blows silt and clay with porosity - 60% - fertile
Sand dunes - mounds of loose sand grains heaped up by wind composition of sand dune - feldspar, quartz, limestone, and rocks
Wind ripple - sand moves perpendicular to the long dimension
of
the ripples
Type of sand dune is determined by the amount of sand, direction, duration, and strength of wind
1. Barchan - hot sandy area, crescent shape, Tips point to wind direction (downwind)
2. Transverse dune - relatively straight, elongated and oriented perpendicular to the wind. Occurs where wind direction is steady, a lot of sand, little vegetation
3. Parabolic dune - common in blowout particularly near a beach; is deeply curved
4. Longitudinal - (Seif)- large symmetrical ridge of sand parallel to the wind direction (up to 200 m high, 120 km in length as in Sahara)
5. Star dunes - isolated hills of sand creating complex form of dune field
Dune field
