CEE 1030 1nd Edition Lecture 19 Deserts and Winds Outline of Last Lecture I Glaciers II Features of glaciers and glacial movement III Review IV Glaciers in relation to landforms a Glacial erosion b Glacial landforms c Glacial deposits V Glaciation effects VI Review cont Outline of Current Lecture I Distribution of land II Key questions in deserts a What is a dry climate b Where are deserts located c How does erosion occur III Types of deserts IV Wind deposits V Types of sand dunes VI Review Current Lecture I II Distribution of land a Dry regions cover 30 of Earth s land surface b Deserts are not measured by temperature but by dryness Key questions in deserts a What is a dry climate i Dry climate where annual precipitation is less than water loss by evaporation ii Desert arid driest of dry climate zones iii Steppe semi arid marginal zone b Where are deserts located i Low latitude deserts ii Bands of semi arid climate at Tropics of Cancer and Capricorn iii Mid latitude deserts occur in areas sheltered by mountains These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute iv Continental interior deserts form on inland of large land masses 1 Wind moving onto continent loses most of its moisture by precipitation c How does erosion occur i Weathering in arid climates 1 Most weathered debris in deserts consists of unaltered rock and mineral fragments from mechanical weathering ii Most desert erosion is a result of running water iii Deserts characterized by dry washes dry channels of ephemeral streams that contain water only during heavy rainfall iv Precipitation is rare in the desert usually only through very heavy rain v Sparse vegetation and poorly integrated drainage systems contribute to runoff vi Flash floods common vii Desert rivers 1 Most permanent rivers in the desert originate outside of the desert 2 Infiltration and evaporation deplete streams viii Interior drainage system 1 Most arid regions have streams that don t flow to ocean but to a basin ix Early landscape evolution 1 Landscape evolution driven by tectonic uplif 2 Running water erodes 3 Streams transport and deposit large amounts of sediment 4 Playa lakes form in flat central area of undrained desert basins 5 Bajada apron of sediment along a mountain front 6 Inselbergs isolated mountain remnants x Wind in the desert 1 Wind also works to erode transport deposit sediments 2 Differences between water and air a Wind less capable of picking up coarse particles b Wind is not confined can spread sediment over a large area 3 Wind transport a Suspended load fine particles transported within the air b Saltation transport of particles through a series of bounces c Bedload particles moved across a ground surface also called a creep xi Wind erodes by abrasion 1 Yardangs wind sculpted ridges III IV V VI 2 Ventifacts stones with flat faces Types of deserts a Hot and dry warm all year very hot in summer precipitation evaporates in the air b Semiarid summers moderately long and dry winters with low precipitation c Coastal cool winters followed by moderately long warm summers d Cold short moderately warm summers long cold winters with snowfall Wind deposits a Types of wind deposits i Dunes mounds and ridges of sand from the wind s bedload ii Loess extreme blankets of silt from the wind s suspension load b Sand dune hill or ridge of wind deposited sand i Most dunes have asymmetrical profile ii Bedload accumulates in wind shadow iii Sand moves up windward slope by saltation accumulation at the crest iv When leeward side of dune becomes steeper than the angle of repose of sand crest collapses down the slipface Types of sand dunes a Shapes and sizes vary according to i Wind direction ii Wind velocity iii Availability of sand iv Amount of vegetation b Transverse dunes long ridges oriented perpendicular to the prevailing wind c Longitudinal dunes long ridges of sand oriented parallel to prevailing wind d Barchan dunes sand dunes shaped like crescents with tips pointing downwind e Parabolic dunes crescent shaped dune similar in shape to barchans but tips point in to wind Review a Wind lifs fine loose particles from the desert floor and leaves behind larger particles This process is called deflation