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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
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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
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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
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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
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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
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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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