1. A view overlooking Death Valley, California. A view overlooking Death Valley, California. Fig. 14-CO, p.333

2. Why do deserts exist? Why do deserts exist? Falling air creates deserts at 30 degrees north and south latitudes. The red arrows inside the globe show surface winds; the blue arrows (right) show air flow on the surface and at higher elevations. Falling air creates deserts at 30 degrees north and south latitudes. The red arrows inside the globe show surface winds; the blue arrows (right) show air flow on the surface and at higher elevations. Fig. 14-1, p.335

3. The major deserts of the world. Where are they concentrated? The major deserts of the world. Where are they concentrated? Deserts cover 25% of the Earth’s land surface where 13% of the world’s population lives. A desert is any region that receives less than _______ inches of rain per year. Deserts cover 25% of the Earth’s land surface where 13% of the world’s population lives. A desert is any region that receives less than _______ inches of rain per year. Fig. 14-2, p.335

4. Rain-shadow deserts form where warm, moist air from the ocean rises as it flows over mountains. As it rises, it cools and water vapor condenses to form rain. The dry descending air on the lee side absorbs moisture, forming a desert. Rain-shadow deserts form where warm, moist air from the ocean rises as it flows over mountains. As it rises, it cools and water vapor condenses to form rain. The dry descending air on the lee side absorbs moisture, forming a desert. Fig. 14-3, p.335

5. Rainfall patterns in the State of California, where prevailing winds carry moist Pacific air eastward over the mountains. Note that rain-shadow deserts lie east of the mountain ranges. Rainfall patterns in the State of California, where prevailing winds carry moist Pacific air eastward over the mountains. Note that rain-shadow deserts lie east of the mountain ranges. What about the Atacama and Gobi deserts? What about the Atacama and Gobi deserts? Rainfall given in cm/year. Rainfall given in cm/year. Fig. 14-4, p.336

6. Water and Deserts. Water reaches the desert from three sources: streams (from wetter regions), groundwater and rain/snowfall. The Colorado River (above) flows from the Rockies through the arid SW United States and empties (where?). Water and Deserts. Water reaches the desert from three sources: streams (from wetter regions), groundwater and rain/snowfall. The Colorado River (above) flows from the Rockies through the arid SW United States and empties (where?). Fig. 14-5, p.337

7. Desert Streams: Courthouse Wash, Utah. In the spring, when rain and melting snow fill the channel with water… Desert Streams: Courthouse Wash, Utah. In the spring, when rain and melting snow fill the channel with water… Fig. 14-6a, p.337

8. …same wash, in the summer, when the creek bed is dry… …same wash, in the summer, when the creek bed is dry… A stream bed that is dry for most of the year is called a wash (or arroyo)… A stream bed that is dry for most of the year is called a wash (or arroyo)… where does the water go? what is a “water table” and where is it in this photo? where does the water go? what is a “water table” and where is it in this photo? Fig. 14-6b, p.337

9. Desert Lakes: Desert Lakes: Mud cracks pattern the floor of a playa in Utah. Mud cracks pattern the floor of a playa in Utah. An intermittent desert lake is called a playa…how does it form? An intermittent desert lake is called a playa…how does it form? Is the Salton Sea a playa lake? Is the Salton Sea a playa lake? Fig. 14-7, p.338

10. When lakes evaporate, ions precipitate to deposit salts on the playa. Economically valuable mineral deposits can accumulate over the years. Here, a mule team is hauling valuable mineral deposits from Death Valley during the 1800s. When lakes evaporate, ions precipitate to deposit salts on the playa. Economically valuable mineral deposits can accumulate over the years. Here, a mule team is hauling valuable mineral deposits from Death Valley during the 1800s. Fig. 14-8, p.338

11. Flash Floods: Flash Floods: In August 1997, 11 hikers perished when a flash flood filled a slot canyon similar to this one in the Utah desert. The steep walls made escape impossible. In August 1997, 11 hikers perished when a flash flood filled a slot canyon similar to this one in the Utah desert. The steep walls made escape impossible. Fig. 14-9, p.338

12. Pediments and Bajadas: An alluvial fan in Death Valley forms where a steep mountain stream deposits sediment where is enters a valley. A Bajada is a depositional surface. Pediments and Bajadas: An alluvial fan in Death Valley forms where a steep mountain stream deposits sediment where is enters a valley. A Bajada is a depositional surface. Fig. 14-10, p.339

13. The Bajada in the foreground merges with a gently sloping pediment to form a continuous surface in front of mountains in Mongolia. The basin has no external drainage. A pediment is an erosional surface where sediment is transported from the mountains to the bajada. The Bajada in the foreground merges with a gently sloping pediment to form a continuous surface in front of mountains in Mongolia. The basin has no external drainage. A pediment is an erosional surface where sediment is transported from the mountains to the bajada. Fig. 14-11, p.339

14. Two American Deserts: The Colorado Plateau; Death Valley and the Great Basin Two American Deserts: The Colorado Plateau; Death Valley and the Great Basin Features of the Colorado Plateau include spires and buttes formed when streams reach a temporary base level and erode laterally. The streams transport the eroded sediment away from the region. Bottom photo is spires and buttes in Monument Valley, Az. A plateau is a large elevated area of fairly flat land. It is a larger area than mesas and buttes. Features of the Colorado Plateau include spires and buttes formed when streams reach a temporary base level and erode laterally. The streams transport the eroded sediment away from the region. Bottom photo is spires and buttes in Monument Valley, Az. A plateau is a large elevated area of fairly flat land. It is a larger area than mesas and buttes. Fig. 14-12, p.340

15. Location of Great Basin shown in red…Colorado Plateau is to the right of the great basin and takes in parts of Utah, Colorado, Arizona and New Mexico. Location of Great Basin shown in red…Colorado Plateau is to the right of the great basin and takes in parts of Utah, Colorado, Arizona and New Mexico. Fig. 14-13b, p.341

16. Fig. 14-12a, p.340

17. Fig. 14-12b, p.340

18. Death Valley and the Great Basin: sediment eroded from surrounding mountains is slowly filling Death Valley, in the rain shadow of the Sierra Nevadas. DV has no external drainage, unlike the Colorado Plateau which drains to the Gulf of California. Death Valley and the Great Basin: sediment eroded from surrounding mountains is slowly filling Death Valley, in the rain shadow of the Sierra Nevadas. DV has no external drainage, unlike the Colorado Plateau which drains to the Gulf of California. Fig. 14-13, p.341

19. Fig. 14-13a, p.341

20. Bajadas and pediments are common features of the Great Basin. The form from a combination of tectonic, erosional and depositional processes. Mountains a valleys commonly form by block faulting (horst and graben or basin and range topography). Mountains slowly drown in their own sediment… Bajadas and pediments are common features of the Great Basin. The form from a combination of tectonic, erosional and depositional processes. Mountains a valleys commonly form by block faulting (horst and graben or basin and range topography). Mountains slowly drown in their own sediment… Fig. 14-14, p.341

21. Fig. 14-14a, p.341

22. Fig. 14-14b, p.341

23. Fig. 14-14c, p.341

24. Wind: it blows across and erodes bare, unprotected desert soil and forms features such as dunes, desert pavement and loess. Wind: it blows across and erodes bare, unprotected desert soil and forms features such as dunes, desert pavement and loess. To right, wind erodes silt and sand (called deflation) but leaves larger rocks behind to form desert pavement. This is a continuous cover of stones that protects the desert surface from further erosion. To right, wind erodes silt and sand (called deflation) but leaves larger rocks behind to form desert pavement. This is a continuous cover of stones that protects the desert surface from further erosion. Fig. 14-15, p.342

25. Fig. 14-15a, p.342

26. Fig. 14-15b, p.342

27. Wind also moves sand grains by saltation (usually not lifted more than 1 meter off the ground) which can carve features by abrasion such as the pinnacle to right in the Grand Canyon. Wind also moves sand grains by saltation (usually not lifted more than 1 meter off the ground) which can carve features by abrasion such as the pinnacle to right in the Grand Canyon. Fig. 14-16, p.343

28. Dunes: a mound or ridge of wind- deposited sand. They form when wind erodes sand from one location and deposits it in another. Dunes: a mound or ridge of wind- deposited sand. They form when wind erodes sand from one location and deposits it in another. To right, dunes near Lago Poopo, Bolivia. To right, dunes near Lago Poopo, Bolivia. Fig. 14-17, p.343

29. Blowouts can form (saucer or trough-shaped depression). They can very large, such as the Qattara Depression in Egypt (100 meters deep, 10 km in diameter). Blowouts can form (saucer or trough-shaped depression). They can very large, such as the Qattara Depression in Egypt (100 meters deep, 10 km in diameter). Fig. 14-18, p.343

30. Most dunes are assymetrical; wind erodes sand from the windward side of a dune, carries it up to the dune crest and the sand slides down on the sheltered leeward side (slip face) at the angle of repose for sand (approx. 35 degrees). Most dunes are assymetrical; wind erodes sand from the windward side of a dune, carries it up to the dune crest and the sand slides down on the sheltered leeward side (slip face) at the angle of repose for sand (approx. 35 degrees). Fig. 14-19, p.343

31. What’s this? When dunes become buried by younger sediment and lithified over geologic time, the sandstone retains the original sedimentary structures of the dunes. Steeply dipping layers of the dune face are preserved here as cross-bedding (Zion National Park). What’s this? When dunes become buried by younger sediment and lithified over geologic time, the sandstone retains the original sedimentary structures of the dunes. Steeply dipping layers of the dune face are preserved here as cross-bedding (Zion National Park). Fig. 14-20, p.344

32. Types of Dunes: When sand supply is limited (rocky deserts), the tips of Barchan dunes travel faster than the center and point downwind. Barchans migrate independently. Types of Dunes: When sand supply is limited (rocky deserts), the tips of Barchan dunes travel faster than the center and point downwind. Barchans migrate independently. Fig. 14-21, p.344

33. Fig. 14-21ab, p.344

34. Fig. 14-21c, p.344

35. If sand is plentiful and evenly dispersed, it accumulates in long ridges called transverse dunes aligned perpendicular to the prevailing wind. If sand is plentiful and evenly dispersed, it accumulates in long ridges called transverse dunes aligned perpendicular to the prevailing wind. Fig. 14-22, p.346

36. Fig. 14-22a, p.345

37. Fig. 14-22b, p.345

38. If sparse desert vegetation is present, like along a seacoast or semiarid desert, a blowout might form at bare areas between vegetation as sand is eroded while the tips are anchored by plants surrounding the blowout. A parabolic dune is similar to a barchan, except that the tips of a parabolic dune point into the wind. If sparse desert vegetation is present, like along a seacoast or semiarid desert, a blowout might form at bare areas between vegetation as sand is eroded while the tips are anchored by plants surrounding the blowout. A parabolic dune is similar to a barchan, except that the tips of a parabolic dune point into the wind. Fig. 14-23, p.346

39. Fig. 14-23a, p.346

40. Fig. 14-23b, p.345

41. If the wind direction is erratic but prevails from the same general compass direction and sand supply is limited, then long, straight longitudinal dunes form parallel to the prevailing wind direction. In the Sahara Desert, they can reach 100 km long. If the wind direction is erratic but prevails from the same general compass direction and sand supply is limited, then long, straight longitudinal dunes form parallel to the prevailing wind direction. In the Sahara Desert, they can reach 100 km long. Fig. 14-24, p.346

42. Fig. 14-24a, p.346

43. Fig. 14-24b, p.346

44. Loess: wind can carry silt for hundreds or thousands of miles and deposit it as silt. Silt is porous, uniform and typically lacks layering, and particles can interlock. It’s not cemented, but can form vertical cliffs and bluffs. The largest deposits in China, more than 300 meters thick, were used as dwellings. In 1920, a great earthquake collapsed the cave system and killed an estimated 100,000 people. Above are loess caves in Pakistan. Loess: wind can carry silt for hundreds or thousands of miles and deposit it as silt. Silt is porous, uniform and typically lacks layering, and particles can interlock. It’s not cemented, but can form vertical cliffs and bluffs. The largest deposits in China, more than 300 meters thick, were used as dwellings. In 1920, a great earthquake collapsed the cave system and killed an estimated 100,000 people. Above are loess caves in Pakistan. Fig. 14-25, p.346

45. Loess deposits in the United States. Soils formed on Loess are generally fertile and make good farmland. Loess deposits in the United States. Soils formed on Loess are generally fertile and make good farmland. Fig. 14-26, p.347

46. Desertification: What is it? Desertification: What is it? Fig. 14-27, p.348

47. p.349