DESERTS

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Deserts : 

Deserts Occurrence Landscapes, Landforms and Processes Desertification – Climate Change

Importance of deserts : 

Importance of deserts Cover significant area of continents (30% of land area) Surface processes are active and exposed Provide clues to climate change They’re pretty

Occurrence : 

Occurrence

Occurrence – global circulation : 

Occurrence – global circulation Direction of atmosphere circulation varies with latitude Vertical circulation – creates zones of high and low pressure High = dry

Regional circulation : 

Regional circulation The Basin and Range is an area of high pressure  sinking air The western Basin and Range is in a rain shadow

Effects of topography : 

Effects of topography Orographic effects of mountains – intercept moisture Leeward locations are “low and dry” – rain shadow

Occurrence : 

Occurrence Western Americas – lots of rain shadows

Climate : 

Climate Desert climate  arid, less than 250 mm precipitation/year Steppe climate  semi-arid, less than 500 mm precipitation/year

Occurrence : 

Occurrence

Landscapes : 

Landscapes Sand sea or erg (e.g., Sahara, Namib deserts)

Landscapes : 

Landscapes Desert pavement – layer of coarse sediment protects surface from erosion

Landscapes : 

Landscapes Desert basins (or bolson) – Basin and Range

Landforms and processes : 

Landforms and processes Importance of wind AND water Wind – sediment transport by saltation and suspension Water – wetter climates of the geologic past

Wind erosion : 

Wind erosion Sand-blasting and percussion

Slide 15: 

Desert pavement – forms by deflation and blowouts

Deflation or blowout : 

Deflation or blowout Loose sediment is removed (deflated) from the landscape by wind erosion Vegetation holds soil particles in place – forms pedestals www.nps.gov

Slide 17: 

Ventifacts – wind-abraded rocks

Slide 18: 

Yardangs in Iran

Slide 19: 

Yardangs in Iran (a little closer)

Deposition – sand dunes : 

Deposition – sand dunes Sand deposited on undulating surfaces Dune type is determined by prevailing wind direction and sand supply

Slide 21: 

Barchan Dunes

Slide 24: 

Parabolic dunes – corners are anchored by vegetation

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