OUTLINE

1. OUTLINE • Introduction • How Wind Transports Sediment • How Wind Erodes Landforms • Types of Wind Deposits • Air-Pressure Belts and Global Wind Patterns • Location of Deserts • Characteristics of Deserts • GEO-FOCUS 15.1:Radioactive Waste Disposal—Safe or Sorry? • Types of Landforms in Desert • Geo-Recap

2. OBJECTIVES 1 Wind transports sediment and modifies the landscape through the processes of abrasion and deflation. 2 Dunes and loess are the results of wind depositing material. 3 Dunes form when wind flows over and around an obstruction. 4 The four major dune types are barchan, longitudinal, transverse, and parabolic. 5 Loess is formed from wind-blown silt and clay and is derived from three main sources: deserts, Pleistocene glacial outwash deposits, and floodplains of rivers in semiarid regions. 6 The global pattern of air-pressure belts and winds is responsible for Earth’s atmospheric circulation patterns. 7 Deserts are dry and receive less than 25 cm of rain per year, have high evaporation rates, typically have poorly developed soils, and are mostly or completely devoid of vegetation. 8 The majority of deserts are in the dry climates of the low and middle latitudes. 9 Deserts have distinctive landforms produced by both wind and running water.

3. Fig. 15-CO, p. 346

4. Fig. 15-1, p. 348

5. Fig. 15-2, p. 348

6. Fig. 15-3, p. 349

7. Fig. 15-4, p. 350

8. Fig. 15-4a, p. 350

9. Fig. 15-4b, p. 350

10. Fig. 15-5, p. 350

11. Fig. 15-6, p. 351

12. Fig. 15-7, p. 351

13. Fig. 15-7a, p. 351

14. Fig. 15-7b, p. 351

15. Fig. 15-7c, p. 351

16. Fig. 15-8a, p. 352

17. Fig. 15-8b, p. 352

18. Fig. 15-8c, p. 352

19. Fig. 15-9, p. 352

20. Fig. 15-9a, p. 352

21. Fig. 15-9b, p. 352

22. Fig. 15-10, p. 353

23. Fig. 15-10a, p. 353

24. Fig. 15-10b, p. 353

25. Fig. 15-11, p. 353

26. Fig. 15-11a, p. 353

27. Fig. 15-11b, p. 353

28. Fig. 15-12, p. 354

29. Fig. 15-12a, p. 354

30. Fig. 15-12b, p. 354

31. Fig. 15-13, p. 355

32. Fig. 15-14, p. 355

33. Fig. 15-15, p. 356

34. Fig. 15-16, p. 357

35. Fig. 15-17, p. 357

36. Figure 1, p. 359

37. Fig. 15-18, p. 361

38. Fig. 15-19, p. 361

39. Fig. 15-20, p. 362

40. Fig. 15-20a, p. 362

41. Fig. 15-20b, p. 362

42. Fig. 15-21a, p. 363

43. Fig. 15-21b, p. 363

44. CHAPTER SUMMARY • Wind transports sediment in suspension or as bed load, which involves saltation and surface creep. • Wind erodes material by either abrasion or deflation. Abrasion is a near-surface effect caused by the impact of saltating sand grains. Ventifacts are common wind-abraded features. • Deflation is the removal of loose surface material by wind. Deflation hollows resulting from differential erosion of surface material are common features of many deserts, as is desert pavement, which effectively protects the underlying surface from additional deflation. • The two major wind deposits are dunes and loess. Dunes are mounds or ridges of wind-deposited sand, and loess is wind-deposited silt and clay. • The four major dune types are barchan, longitudinal, transverse, and parabolic. The amount of sand available, the prevailing wind direction, the wind velocity, and the amount of vegetation present determine which type will form. • Loess is derived from deserts, Pleistocene glacial outwash deposits, and river floodplains in semiarid regions. Loess covers approximately 10% of Earth’s land surface and weathers to a rich and productive soil.

45. CHAPTER SUMMARY • The winds of the major air-pressure belts, oriented east–west, resulting from rising and cooling air, are deflected by the Coriolis effect. These belts help control the world’s climate. • Deserts are very dry (averaging less than 25 cm of rain per year), have high evaporation rates, have poorly developed soils, and are mostly or completely devoid of vegetation. • Dry climates are located in the low and middle latitudes where the potential loss of water by evaporation exceeds the yearly precipitation. Dry climates cover 30% of Earth’s land surface and are subdivided into semiarid and arid regions. • The majority of the world’s deserts are in the lowlatitude dry-climate zone between 20 and 30 degrees north and south latitudes. Their dry climate results from a high-pressure belt of descending dry air. The remaining deserts are in the middle latitudes where their distribution is related to the rainshadow effect and in the dry polar regions. • Mechanical weathering is the dominant form of weathering in deserts. The sparse precipitation and slow rates of chemical weathering result in poorly developed soils.

46. CHAPTER SUMMARY • Desert rainfall is unpredictable and, when it does occur, tends to be intense and of short duration. As a consequence of such aridity, desert vegetation and animals are scarce. • Running water is the dominant agent of erosion in deserts and was even more important during the Pleistocene, when wetter climates resulted in humid conditions. • Wind is an erosional agent in deserts and is very effective in transporting and depositing unconsolidated fine-grained sediments. • Important desert landforms include playas, which are dry lakebeds; when temporarily filled with water, they form playa lakes. Alluvial fans are fanshaped sedimentary deposits that may coalesce to form bajadas. • Pediments are erosional bedrock surfaces of lowrelief gently sloping away from mountain bases. • Inselbergs are isolated, steep-sided erosional remnants that rise above the surrounding desert plains. Buttes and mesas are, respectively, pinnacle-like and flat-topped erosional remnants with steep sides.