DESERTS GEO 3

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DESERTS GEO 3
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2010-06-27 23:22:59
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DESERTS GEO
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DESERTS GEO 3
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  1. INTRO
    • -A. DESERTS receive less than 10 inches of rain per yr
    • B. STEPPES
    • 1. Receive 10-25 inches of rain per yr
    • 2. Gernerally separate deserts from more humid enviroments
    • C. DESERTIFICATION-in some areas, deserts are expanding due to human actions
  2. Types of Deserts
    • A. POLAR DESERTS
    • 1. Intensely cold, perpetual snow cover, no liquid water
    • 2. Antartica, interior of Greenland
    • B. SUBTROPICAL DESERTS
    • 1. Form at 30 degrees North or South of equator in zones of subsiding air
    • 2. Large daily temp variation
    • 3. Sahara desert, Great Australian desert
    • C. MID-LATITUDE DESERTS
    • 1. Rain shadow deserts
    • a. Form where mountain ranges create a barrier to moist air
    • i.Humid air rises and rainfall occurs on windward side, air warms when descends on opposit side of mountains, clouds dont form
    • b. Great Basin, North America
    • 2. Interior deserts
    • a. Form in interiors of continents far frm moisture of oceans
    • b. Hot summers, cold winters
    • c. Gobi desert in central Asia
  3. Characterisitcs of Deserts
    • A.RUNNING water most important erosional agent in desrts
    • B.MECHANICAL weathering dominant
    • C. THIN, poorly developed solis
    • D. EPHERMERAL streams- streams that flow only response to rainfall
    • E. FLASH floods common-a desert may receive most or all its yearly rainfall at one time
    • F. SPARSE but well adapted vegetation
  4. Landforms developed in dry mountainous areas
    • A.ALLUIVIAL fan-cone of debris deposited at mouth of a canyon where streams flow out onto the flat desert floor
    • B.BAJADA-broad apron of sediment formed by coalescing alluvial fan
    • C.PLAYA LAKE-temp lake in a desert
    • D.PLAYA-dry, flat lake bed may be encrusted with salts
    • E. INSELBERG-isolated , steep sided erosional remnant of mountains
    • F.BASIN and range
    • 1.Extends from southerin Oregon through Arizona into Mexico
    • 2. Consists of about two hundred small mountain ranges separated by valleys
    • 3.In southern Oregon and northern Nevada, the mountains are just beginning to erode
    • a.Alluvial fans and play lakes common
    • 4.In southern Nevada and northern Arizona, mountains are in a later stage of erosion
    • a. Valleys are begninning to fill in with material deposited from eroding mountains
    • i. Bajadas common
    • 5. In southern Arizona, the mountains are in a late stage of erosion
    • a. Inselbergs are all that remain of eroded mountains
  5. WIND EROSION
    • A. DEFLATION
    • 1.Lifting and removal of loose material
    • 2. Deflation lowers the surface of the land
    • 3. Blowouts-shallow depressions created by deflation
    • 4.Desert pavement
    • a.Layer of coarse particles left behind as deflation removes the finer sand and silt
    • b.As long as desert pavement is undisturbed, prevents further deflation
    • B. ABRASION
    • 1. Windblown sand cuts and polishes surfaces
    • 2.Ventifacts-rocks with flat sides that have been planed by windblown sand
  6. Wind Deposits
    • A. LOESS
    • 1.Windblown silt and clay; tan to yellow color
    • 2. Sources
    • a. Deserts
    • b. Glaciers-stratified drift
    • B.SAND DUNES
    • 1.Mounds or ridges of sand
    • 2. Commonly have an asymmetrical profile
    • a. Sand moves by altation (bouncing and skipping)up the windward side
    • b. Cross beds-inclined layers of sand form of the leeward side
    • 3. Types of Sand Dunes
    • a. Barchan dunes
    • b.Longitudinal dunes
    • c. Transverse dunes
    • d. Prabolic dunes
    • e. Star dunes

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