Deserts

Arid Climates In an arid climate rainfall is 400mm (15.6 in) per year. Evaporation rate _______ precipitation. Thus, both deserts and the extreme North and South poles of the Earth are both arid climates.

13.06.b Unusual shift in wind direction Persistent high pressure Temporary change in ocean currents Some Causes of Drought

Desert Formation Dry Air descending in atmosphere causes zones of arid climate. Can sometimes be caused by rain shadow effect of mountain areas.

13.08.a Observe locations of deserts and other arid lands Mojave Desert Sonoran Desert

13.08.c Subtropical deserts: descending air and high pressure Continental desertRain shadow desert Coastal desert Subtropical deserts Polar deserts Continental deserts Rain shadow desert Settings of Deserts and Other Arid Lands

Basin and Range Uplifted crustal blocks Interior drainage into basins produces _____________ and ________ _______ and _____ lakes Erosion of mountain mass causes local relief to continually diminish Eventually mountains are reduced to a few large bedrock knobs called ___________ projecting above a sediment filled basin

Landscape evolution in a mountainous desert – early stage

Landscape evolution in a mountainous desert – middle stage

_______: dry flat lake bed in a desert region. Common in the Basin and Range.

Landscape evolution in a mountainous desert – late stage

Weathering in Deserts Not as effective as in humid regions Mechanical weathering forms unaltered rock and mineral fragments Some chemical weathering does occur Clay forms Thin soil forms

Water in Arid climates Streams are ____ most of the time Desert streams are said to be _________ Flow only during periods of rainfall Different names are used for desert streams including wash, arroyo, wadi, donga, and nullah

Rainfall Desert rainfall Rain often occurs as heavy showers Causes _______ floods Poorly integrated drainage Most erosional work in a desert is done by ______________

Wind Actions in Deserts Erodes and deposits sediments _________ Lifting of loose material Produces ________ __________________ ________

13.02.b Dust Storms and Whirlwinds Whirlwind in Peru Sand and dust storm originating from North Africa Dust storm in Southwest U.S.

Formation of a desert blowout

Formation of desert pavement

Wind Deposits ______: typically silt and clay sized particles. Extensive blanket deposits Primary sources are _______ and _______ stratified drift _____: sand sized particles moved by _________.

Sites Where Wind-Blown Material Is Deposited c Sand Dunes Loess: Windblown Silt

Dunes Mounds and ridges of sand formed from the wind's bed load Characteristic features _________ – the leeward slope of the dune __________ – sloping layers of sand in the dune

Formation of sand dunes