INTRO
-A. DESERTS receive less than 10 inches of rain per yrB. STEPPES1. Receive 10-25 inches of rain per yr2. Gernerally separate deserts from more humid enviromentsC. DESERTIFICATION-in some areas, deserts are expanding due to human actions
Types of Deserts
A. POLAR DESERTS1. Intensely cold, perpetual snow cover, no liquid water2. Antartica, interior of GreenlandB. SUBTROPICAL DESERTS1. Form at 30 degrees North or South of equator in zones of subsiding air2. Large daily temp variation3. Sahara desert, Great Australian desertC. MID-LATITUDE DESERTS1. Rain shadow desertsa. Form where mountain ranges create a barrier to moist airi.Humid air rises and rainfall occurs on windward side, air warms when descends on opposit side of mountains, clouds dont formb. Great Basin, North America2. Interior desertsa. Form in interiors of continents far frm moisture of oceansb. Hot summers, cold wintersc. Gobi desert in central Asia
Characterisitcs of Deserts
A.RUNNING water most important erosional agent in desrtsB.MECHANICAL weathering dominantC. THIN, poorly developed solisD. EPHERMERAL streams- streams that flow only response to rainfallE. FLASH floods common-a desert may receive most or all its yearly rainfall at one timeF. SPARSE but well adapted vegetation
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 floorB.BAJADA-broad apron of sediment formed by coalescing alluvial fanC.PLAYA LAKE-temp lake in a desertD.PLAYA-dry, flat lake bed may be encrusted with saltsE. INSELBERG-isolated , steep sided erosional remnant of mountainsF.BASIN and range1.Extends from southerin Oregon through Arizona into Mexico2. Consists of about two hundred small mountain ranges separated by valleys3.In southern Oregon and northern Nevada, the mountains are just beginning to erodea.Alluvial fans and play lakes common4.In southern Nevada and northern Arizona, mountains are in a later stage of erosiona. Valleys are begninning to fill in with material deposited from eroding mountainsi. Bajadas common5. In southern Arizona, the mountains are in a late stage of erosiona. Inselbergs are all that remain of eroded mountains
WIND EROSION
A. DEFLATION1.Lifting and removal of loose material2. Deflation lowers the surface of the land3. Blowouts-shallow depressions created by deflation4.Desert pavementa.Layer of coarse particles left behind as deflation removes the finer sand and siltb.As long as desert pavement is undisturbed, prevents further deflationB. ABRASION1. Windblown sand cuts and polishes surfaces2.Ventifacts-rocks with flat sides that have been planed by windblown sand
Wind Deposits
A. LOESS1.Windblown silt and clay; tan to yellow color2. Sourcesa. Desertsb. Glaciers-stratified driftB.SAND DUNES1.Mounds or ridges of sand2. Commonly have an asymmetrical profilea. Sand moves by altation (bouncing and skipping)up the windward sideb. Cross beds-inclined layers of sand form of the leeward side3. Types of Sand Dunesa. Barchan dunesb.Longitudinal dunesc. Transverse dunesd. Prabolic dunese. Star dunes