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Study Guide for Geo Exam 4

Study Guide for Geo Exam 4 - Study Guide for Geo Exam 4...

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Study Guide for Geo Exam 4: WINDS and DESERTS Chapter 19 Desert landscapes can appear so “foreign” – we might as well be on Mars •Focus on implications of lack of water •Wind as dominant agent of erosion and deposition •Underlying origin of deserts in climate zones patterns of wind flow Eolian or wind driven, processes shape the land surface in deserts where soil moisture is minimal and few plants live. Earth’s atmosphere circulates in wind belts created by solar input and Earth’s rotation Deserts are characterized by lack of rainfall (< 25 cm/yr) Subtropical Desert – beneath high pressure divergence zones of descending dry air masses – 30° N & S of equator •Rain shadow of coastal mountains •Cold ocean currents •Continental interior •Eolian deposition and dune migration Cross-bedded quartz sandstone is the hallmark of eolian deposition in dunes o Figure 19.11 •Dune form reflects sand supply and wind speed Scarce sand Barchan – unidirectional wind Plentiful Sand Transverse – moderate wind Blowout – strong wind Longitudinal – strong, steady wind Water plays decisive role in shaping landscape Physical weathering, little soil Cliff retreat by rockfall, talus slopes at base Debris flows carry sediment onto alluvial fans Chemical weathering thick soil Mass wasting by slump, earth flows Streams carry away sediment delivered to channel by mass wasting •Deserts characterized by Interior Drainage Ephemeral or “losing streams Playa Lakes – streams feed lakes which periodically dry up leaving salt deposits COASTLINES and OCEAN BASINS Chapter 20
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•Wind & Waves Waves generated by wind blowing across sea surface Height function of –Wind velocity, fetch – area over which wind blows, and duration Water moves in circular pattern that dies out with depth – –“wave passes but water stays in same place” wavelength (L) = distance between troughs or crests no motion below depth = L/2 called “wave base” Wave drags on bottom & breaks where water depth = wave base (=L/2) Beach is sand buffer between surf and land Width represents dynamic balance of erosion & deposition of sand by waves Reflects erosive power of surf Wide in summer, narrow in winter Width of beach reflects erosive power of surf Summer beach is wide –waves smaller, beach built outward, bar eroded Winter beach is narrow –waves larger, beach eroded, sand stored on offshore sand bar Waves approach shore at angle, drag on bottom refracts (bends) wave crests toward beach Wave energy focused on headlands, dispersed in embayments Accelerated erosion of headlands Sand spread on beaches in bays Longshore current transports longshore drift of sand Current of water + sand moves parallel to shore as result of waves striking shore at an angle Longshore drift erodes & deposits sand •150,000 - 350,000 yd 3 /yr (15,000 - 35,000 big dump truck loads / yr)
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