Deserts Deserts: definition • A region which has an arid climate or where evaporation exceeds precipitation • Steppe: region often adjacent to a desert • Semiarid climate: irregular precipitation, enough to generate minimal plant growth Desert and Steppe areas around the world: Deserts: • Cover a fifth of the earth’s surface • Can be found at all altitudes and latitudes • Four physical factors cause deserts : all are influenced by prevailing winds a. Continentality b. Lee side of mountains c. Cold ocean currents d. Prevailing winds Prevailing Winds: • Found 30 n and s latitude due to the global wind circulation system • Descending air masses are compressed, warm and absorb moisture Lee Side: Coastal Location: Desert Erosion: Water • Seldom rains in desert regions • When it does massive DOWNPOUR or it’s called a FLASHFLOOD • Dry weathered soil, and minimal vegetation to anchor the soil causes rapid erosion • Rainwater carries sediment away and deposits it on the valley floor • Within 10 to 20 minutes the rain is gone and the water has evaporated Wind erosion processes: • Deflation ; is the removal of rock waste from the land by wind – Blowout or deflation hollow ; depression caused by deflation due to lack of vegetation to hold material down Landforms: created by water • Alluvial Fan: • Fan shaped delta formed at the foot of mountains in a desert valley • A Bajada is an apron of sediment resulting from a coalescence of alluvial fans Landforms : water • Playa Lake: – A temporary shallow lake formed in the central basin of a desert during a rare downpour – A Playa is the dry flat lake bed that remains Wind erosion processes: • Deflation: removal of rock waste from the land by the wind • Abrasion : “sandblasting” effect on materials caused by the impact with particles carried by the wind • Bedload: – Saltation – Suspension – Particles are bounced along the ground or suspended in the air; both these process erode rock surfaces and carry material Sand Dunes: • Many different types but learn these: • Barchan: crescent shaped with convex portion facing the wind • Formed with a constant wind and limited sand supply • Longitudinal or seif • Elongated in general direction of wind • Formed with slightly different wind directions and limited sand supply Inactive or stable dune: • Parabolic Dune: • Formed along coastlines or large lakes • Winds cause blowouts in sand resulting in a crescent shape with convex side facing the wind Reg Deserts: little sand