Chapter 19 Deserts and Winds

Chapter 19 Deserts and Winds Earth: An Introduction to Physical Geology

M 1 Which one of the following statemen ts is true? Desert landscapes are monotonous, relatively flat areas covered to various depths with sand. Deserts and dry lands are concentrated in areas of ascending air masses and relatively low atmospheric pressures. Despite infrequent rainfalls, erosional and depositional features of running water are important in desert landscapes. Rainshadow deserts occur where air masses descend after first having risen to cross a mountain range. A C

2 ______have rainfall amounts and soil moisture contents between those of true deserts and humid lands. Tundras Steppes Sundras Sabkhas A B

3 Most dry lands lie between ______degrees north and south of the equator. 40 and 50 20 and 30 5 and 10 0 and 5 A B

4 Which one of the following statemen ts concerni ng rock weatheri ng is true? Warm temperatures and high soil moisture contents accelerate chemical weathering. Low temperatures and high soil moisture contents accelerate chemical weathering but inhibit mechanical weathering. Warm temperatures and low soil moisture contents both promote rapid rates of mechanical weathering. Temperature has no effect on rock weathering. A A A ______is an intermitt ent stream channel in the dry land areas of the western United States. rivulet playa rill wash A D

6 ______refers to the "bouncin g" mode of sand transport in a windstor m or stream. Saltation Ventifaction Siltation Deflation A A

7 Which one of the following will effectivel y limit further deflation in a given area? sea level desert pavement a hanging valley the repose level A B

8 Which one of the following statemen ts is correct? Alluvial fans typically rim desert valleys; playas form in the lowest, interior parts of the valleys. Inselbergs are low, circular depressions on gently sloping pediments and bajadas. Playas are typically covered with gravel-sized desert pavement and loess deposits. Saline sediments and evaporites are common in inselbergs and pediments of desert landscapes. A A

9 In which area would surface water most effectivel y infiltrate into the local groundw ater system? a stream in a steep-sided, bedrock canyon in the mountains streams flowing in the numerous channels of an alluvial fan a playa lake with a thick mud bottom All of the above would promote infiltration. A B Which of the following character istics would suggest geologica lly recent, fault uplift of a desert mountain range? flat, upland surfaces, steep slopes and small alluvial fans extensive pediments and bajadas and small, deep playas inselbergs, extensive pediments and flat valley floors steep playas with extensive, bedrock alluvial fans and numerous sand dunes A A

11) How is desert pavemen t formed? Deflation removes the coarse fragments leaving behind a layer of loess. Alluvial fans are eroded to form inselbergs with rocky surfaces. Groundwater in an alluvial fan evaporates, leaving behind a surface layer of hard-baked mud. Runoff and deflation carry off the silt and clay, leaving coarser particles behind. A D

12) Which one of the following is determin ed by the angle of repose for dry sand? longitudinal dune gradient angle slope of an alluvial fan a vertical cut bank in loess inclination angle of a dune slip face A D

13) Which one of the following statemen ts about sand dunes is correct? A dune migrates in the direction of inclination of the slip face. The more gently sloping surface is the leeward slope of the dune. Sand is blown up the slip face and rolls down the more gently sloping flank of the dune. In a sand dune, the more gently inclined strata lie parallel to the slip face. A A

14) Depositio n of glacial rock flour from blowing winds is responsib le for ______. deflation ventifacts blowout pavement star steppes loess deposits A D Which one of the following is the one best measure of the wetness or dryness of a region? total annual precipitation mean annual temperature difference between annual precipitation and evaporation potential percentage of precipitation that falls during the summer months A C

16) Which one of the following concerni ng desert lands is false? Less than 30 percent is covered with dunes and drifting sand. Wind erosion and deposition are important processes. Running water has little effect on shaping the landscape. Most desert areas are characterized by descending wind patterns. A C

17) Desertific ation has been particula rly well documen ted over the past 50 years in ______. the Empty Quarter of the Arabian Peninsula the Sahel along the southern margin of the Sahara Desert the Dust Bowl states of the Great Plains the steppe lands of southern Russia, Ukraine, and Kazakhstan A B

18) Which of the following statemen ts concerni ng dry lands is not true? Precipitation totals are low; dew points are lower in the summer than winter. Evaporation potential exceeds actual precipitation. Storms are infrequent and rainfall amounts are highly variable. Wind is the dominant agent of erosion and sediment transport. A D

19) How are sand grains transport ed by the wind? high in the moving air column as suspended load by saltation in the first few meters above the land surface by deflation of abraded desert pavement by being picked up in swirling dust clouds and carried to distant blowouts A B

20) Which of the following best describes the climatic factors that cause low latitude deserts like the Sahara in Africa? Cool, dry air aloft is descending; surface winds are blowing toward the equator. Warm, humid air aloft is descending; surface winds blow away from the equator. Warm, humid air is rising; surface winds are calm. Cool, dry air at the surface is rising causing winds to blow away from the equator. A A

21) How is desert pavemen t formed? Deflation and sheet wash remove fine- sized materials leaving coarse, weathered, rock fragments concentrated at the surface. Blowing wind removes fine- size soil particles; coarser particles abrades to sand size. Running water deposits gravel and sand over the finer-sized soil particles. Intense chemical weathering removes the sand- and silt- sized particles, leaving coarse rock debris covering the land surface. A A

22) Loess deposits in the central United States ______. blew in from the dry areas in the Great Plains and southwestern desert areas originated as rock flour in Pleistocene glacial streams and rivers accumulated from flooding of the Mississippi River were originally deposited as barchanoid dunes and later redeposited by glaciers A B

23) Assume that the central slip face of a barchan dune slopes downhill toward the east. What is the direction of the prevailin g wind? east to west north to south south to north west to east A D

24) Desert and steppe lands cover about what percenta ge of Earth's land area? 10% 66% 30% 3% A C

25) Inselberg s are ______. insulated icebergs floating in a hot spring blowouts cut from bedrock in mountainous areas lithified rock formed by cementation of wind- deposited, dune sands bedrock hills in a highly eroded desert landscape A D A ______is formed by abrasion of rocks by windblo wn sand. playa ventifact pediment desert pavement A B

27) Which one of the following would probably not affect the size and depth of a blowout? a rise in sea level the near surface water table type and density of vegetation areas of desert pavement A A

28) What mature, desert landscap e feature consists of coalesced alluvial fans? balda bajada bahia baja A B

29) A ______is a crescent- shaped dune whose tips point downwin d. parabarcal transverse barchan star A C

30) During a typical sandstor m, saltating sand grains reach a maximu m height of ______above the land surface. 1 inch 2 meters 10 centimeters 40 feet A B

31) Rainshad ow deserts are common in ______. vast, dry, steppe lands like the Great Plains north central Africa the dry valleys of eastern California and Nevada Europe north of the Alps A C

32) ______are both dry land, erosional features cut from bedrock. Inselbergs and barcanoids Pediments and playas Bajadas and blowouts Pediments and inselbergs A D

33) ______dunes result from persisten t, onshore winds in certain coastal areas. Diabolic Barchanoid Parabolic Staroid A C

34) ______dunes are long, high, sand dunes parallel with the prevailin g wind direction. Transducinal Longitudinal Latitudinal Transversal A B

35) Which one of the following is a low- latitude desert character ized by high atmosph eric pressures and descendi ng air masses (not rain shadow deserts). Sahara Desert; northern Africa Atacama Desert in Chile, South America Gobi Desert, China and Mongolia desert valleys of the Great Basin, U.S. A A

36) ______complexl y shaped dunes formed in response to different, seasonal, wind direction s A A

37) ______linear sand ridges at right angles to the prevailin g wind direction A E

38) ______linear sand ridges parallel to the prevailin g wind direction A F

39) ______multiple, connecte d, crescent- shaped coastal dunes with the tips pointing toward the beach A D

40) ______sand ridges at right angles to prevailin g winds with crescent- shaped slip faces pointing downwin d A D

41) ______single, crescent- shaped dune with the tips pointing downwin d A B

1 W E 1 A) pothole

B) glacial striation

C) ventifact

D) steppe stone A s

2 A) arroyo

B) wadi

C) inselberg

D) nullah A i

3 A) ventifact

B) alluvial fan

C) playa

D) inselberg A v

4 A) sand dune

B) deflation

C) blowout

D) desert pavemen t A s

5 A) barchan dune

B) star dune

C) transvers e dune

D) parabolic dune A s

1 T 1 Running water is an importan t erosional agent in many arid lands despite infrequen t rainfalls. A T

2 Sand dunes cover more than 50 percent of most desert lands. A F Deserts between 30 and 45 degrees of latitude are more extensive in the southern hemisph ere than in the northern hemisph ere. A F

4 The loess in western China was derived from windblo wn, glacial rock flour. A F

5 Bajadas develop from coalescen ce of alluvial fans along fronts of mountain ranges in arid lands. A T

6 About one-third of the Earth's land areas have arid to semiarid climates. A T

7 The Basin and Range Province of the southeast ern United States is well known for its numerou s and diverse arid region landform s. A T

8 A playa is an intermitt ent lake on the floor of a desert valley. A T

9 Steppes are the driest of the true desert lands. A F

10) Intermitt ent streams in dry areas of the western United States are called washes. A T

11) Windblo wn loess, like sand, typically accumula tes as mound- like dunes. A F

12) In North America, loess deposits are found mainly in the dry to semiarid lands of southwes tern United States and northern Mexico. A F

13) Sand is transport ed by saltation in running water and blowing winds. A T Blowouts are broad, shallow depressio ns excavate d by deflation. A T

15) Ventifact s are wind- abraded blowouts exceedin g one kilometer in diameter. A F

16) The steeper, lee slope of a sand dune is called the slip face. A T

17) Loess consists mainly of silt-sized particles. A T

18) Saltation refers to evaporati on of shallow, muddy waters from a playa lake. A F

19) Desert pavemen t accelerat es deflation of bedrock pediment s in alluvial fans. A T

20) Inselberg s and small, steep, alluvial fans are character istic of recently faulted, basin and range terrain in dry lands. A T

21) Wind turbines 10 meters above the ground surface are subjected to relatively little abrasion by blowing sand. A T

1 S 1 ______dunes are long, sand ridges that develop at right angles to the prevailin g wind direction. A T

2 A ______is an intermitt ent lake on the floor of a desert basin. A p

3 ______is the skipping and bouncing transport of sand in blowing wind and running water. A S

4 In dry lands, ______is the covering of coarse particles left on the surface after the finer particles are carried away by wind and running water. A d

5 ______are rocks with one or more flat surfaces abraded by windblo wn sand. A V

6 The leeward slope of a sand dune is also known as the ______. A s

7 ______are solitary, crescent- shaped dunes whose tips face downwin d. A B

8 ______describes the complex, internal stratificat ion or bedding in a sand dune. A C

9 Deposits of windblo wn silt are called ______. A l

10) ______dunes form in areas where the prevailin g wind direction s change with the seasons. A S

11) The low, bedrock ridges and peaks of a highly eroded, basin and range, desert landscap e are called ______. A i

1 C U 1 Wind is 2) included along with gravity, water, and ice as an agent of erosion. In many national parks and other areas of natural beauty, statemen ts are often made that credit wind as having sculpted the landscap e. Briefly discuss the importan ce of wind as an agent of erosion and explain why such statemen ts are probably geologica lly inaccurat e.

What 1 features or character istics would distingui sh a Paleozoic sandston e formatio n as being eolian (wind- blown) in origin rather than having formed from an ancient stream or coastal environ ment? V 1 Label the alluvial fans and playa lakes on the diagram below.

2 Label the bajadas and playa on the diagram below.

On the blank spaces provided beside each illustratio n, write the name of the c) ______type of dunes shown in the illustratio n.

a) ______

b) ______

d) ______

e) ______

f) ______