Physical Geology Exploring the Earth 6th Edition By James S. Monroe – Test Bank

Physical Geology Exploring the Earth 6th Edition By James S. Monroe – Test Bank

CHAPTER 15 ‑ TEST QUESTIONS

TRUE OR FALSE

1. By percentage volume most of the hydrologic cycle is limited to ocean-atmosphere transference.

ANSWER: true

2. Streamflow is generally laminar.

ANSWER: false

3. Runoff occurs when the rate of rainfall is greater than the infiltration capacity of the soil on which it is falling.

ANSWER: true

4. The gradient of a stream does not change over the length of the stream.

ANSWER: false

5. Streams with broad, shallow channels and narrow, deep channels have a higher flow velocity than do those with semi-circular channels.

ANSWER: false

6. Erosion occurs through hydraulic action and abrasion.

ANSWER: true

7. The total load of a sediment a stream can carry consists of suspended load and bed load.

ANSWER: false

8. Flow at all but the slowest velocities is turbulent.

ANSWER: true

9. A dry surface has a higher infiltration capacity than a moist surface.

ANSWER: false

10. The Mississippi River is an example of channel flow.

ANSWER: true

11. A stream’s velocity varies only along its length.

ANSWER: false

12. The average channel velocity increases downstream where the gradient is lower.

ANSWER: true

13. Most of a stream’s kinetic energy is involved in eroding and transporting sediment.

ANSWER: false

14. Mass wasting can be an important source of sediment carried in a stream.

ANSWER: true

15. A large stream will tend to have a great competency but little capacity.

ANSWER: false

16. Competence of a stream is defined by the largest particle that a stream can carry.

ANSWER: true

17. Meandering streams have semi-circular cross-sections along most of their length.

ANSWER: false

18. Alluvial fans are formed where running water flows into another body of water.

ANSWER: false

19. A 10 year-flood occurs every ten years.

ANSWER: false

20. A 10-year flood could occur in two consecutive years or it could occur once in a 20 year period.

ANSWER: true

21. Artificial levees may actually increase the possibility of flooding downstream.

ANSWER: true

22. A dendritic drainage pattern develops when more sediment is supplied to a stream than can be transported by it.

ANSWER: false

23. Streams and stream valleys are the result of erosion of the stream along its length to base level.

ANSWER: false

24. Along a graded stream, no sediment is eroded, transported, or deposited.

ANSWER: false

25. A v-shaped cross section and an irregular profile characterize a well-developed or “old” valley.

ANSWER: false

MULTIPLE CHOICE

26. Flooding in Johnstown, PA, in 1889 was disastrous and deadly because
27. the town was built on a floodplain
28. the flood wave traveled at velocities as high as 60 km/hr
29. 20-25 cm of rain fell over a 24 hour period
30. an upstream dam failed

* E. all of the above

27. The primary purpose of the Tennessee Valley Authority is to
28. oversee river development
29. control flooding

* C. generate electricity

1. provide recreation

28. The type of flow, laminar or turbulent, is controlled by
29. flow discharge
30. water temperature

* C. flow velocity

1. water viscosity
2. mud content

29. Sheet flow is most likely to occur in areas with
30. dense vegetation

* B. low infiltration capacity

1. climates with high rainfall
2. large depressions
3. laminar flow

30. Assuming constant discharge, stream velocity increases as
31. roughness increases
32. depth decreases

* C. roughness decreases

1. slope decreases
2. width increases

31. In a downstream direction, which of the following trends occurs?
32. roughness increases
33. velocity decreases
34. slope increases
35. discharge decreases

* E. depth increases

32. Velocity increases downstream because
33. roughness decreases
34. discharge increases
35. width and depth increases
36. B and C

* E. all of the above

33. Erosion of the streambed occurs by
34. hydraulic action
35. abrasion
36. dissolution

* D. all of the above

34. A small, slow-flowing stream would generally have

* A. low competence and low capacity

1. low competence and high capacity
2. high competence and low capacity
3. high competence and high capacity

35. Streamflow and sediment deposition on the floodplain is

* A. a common event

1. relatively uncommon
2. occurs only on large river systems
3. something that should be prevented if possible
4. Which of the following drainage patterns would be expected to develop in flat-lying sedimentary rocks?
5. trellis

* B. dendritic

1. rectangular
2. radial
3. meandering

37. A graded stream represents a balance between which of the following variables?
38. gradient and channel characteristics
39. flow velocity
40. sediment load
41. A and B

* E. all of the above

38. If vegetation decreases in a watershed such that sediment supply to the stream is increased, which of the following changes might you expect?

* A. slope will increase

1. velocity will increase
2. the stream pattern might become more meandering
3. discharge will decrease
4. roughness will decrease

39. Graded streams tend to be characterized by
40. a smooth, concave longitudinal profile
41. insignificant erosion along its bed
42. insignificant deposition along its bed
43. B and C

* E. all of the above

40. Stream terraces will develop if
41. sediment supply to the stream increases

* B. base level is lowered

1. the capacity of the stream decreases
2. discharge decreases
3. a dam is built downstream

41. Which of the following describes a well-developed or “old” stream valley?
42. valleys are v-shaped and narrow with an irregular profile
43. streams meander with a narrow floodplain and relatively smooth profile

* C. a broad, flat floodplain with a meandering stream, oxbow lakes, and a graded profile

1. none of the above

FILL-IN

42. Water enters the atmosphere by ______ from the ocean surface. Most of this water condenses and returns to the ocean as __________.

ANSWER: evaporation, precipitation

43. The total area that provides runoff to a stream is called its __________ __________.

ANSWER: drainage basin

44. The gradient of streams tends to be (steeper, gentler) __________ in their upper reaches, and (steeper, gentler) __________ in their lower reaches.

ANSWER: steeper, gentler

45. The __________ ___________ is the maximum rate at which the soil or other surface materials can absorb water.

ANSWER: infiltration capacity

46. When infiltration capacity is exceeded and water begins to move rapidly downslope, a continuous film of water known as __________ flow develops. This type of flow can cause __________ __________.

ANSWER: sheet, sheet erosion

47. When flow is restricted to long, trough-like depressions, the flow is known as __________ flow.

ANSWER: channel flow

48. The outer bank of a meander in a meandering stream is called the __________ __________, where (erosion, deposition) __________ takes place. The inner side of the channel meander is called the __________ __________, which is where (erosion, deposition) __________ occurs.

ANSWER: cut bank, erosion, point bar, deposition

49. The renewal of erosion which results in creation of stream terraces is generally attributed to a change in __________ level, or, a change in climate resulting in greater __________ , and thus, discharge.

ANSWER: base, runoff

50. A change in base level leading to formation of stream terraces can come about by __________ of the land over which the stream flows, or a __________ of sea level.

ANSWER: uplift, lowering

51. The process by which water vapor reenters the atmosphere by evaporation from plants is known as __________.

ANSWER: transpiration

52. That there is no mixing between parallel layers in the water is characteristic of ___________ flow.

ANSWER: laminar

53. A ___________ stream cuts directly through a ridge or series of ridges instead of going around them.

ANSWER: superposed

MATCHING

54. Match the characteristics of the various types of streams below with the appropriate stream type:

____ dividing and rejoining channels A. Braided streams

____ oxbow lakes B. Meandering streams

____ meander scars C. Deltaic rivers systems

____ common in semi-arid and arid regions

____ bottomset, foreset and topset beds

____ common where vegetation is sparse

____ common where melting glaciers are the primary water source

____ bird’s foot distributary channels

____ peat deposits

ANSWER: A, B, B, A, C, A, A, C, C

55. Match the drainage patterns with the topographic features with which they are associated.

____ gently sloping surfaces A. Dendritic drainage

____ areas of flat-lying sedimentary rocks B. Rectangular drainage

____ channels with right angle bends C. Trellis drainage

____ a tree branch-like pattern of streams D. Radial drainage

____ swamps and poorly drained soils E. Deranged drainage

ANSWER: A, A, B, A, E

56. Match the drainage patterns with the topographic features with which they are associated.

____ isolated volcanic peaks A. Dendritic drainage

____ a region of intersecting joint systems B. Rectangular drainage

____ glaciated regions C. Trellis drainage

____ mountainous folds with main streams within synclines D. Radial drainage

____ tributaries joining main streams at right angles E. Deranged drainage

ANSWER: D, B, E, C, B/C

57. Match the following variables with the characteristic stream pattern with which it is associated.

____ excessive sediment A. braided

____ fine-grained sediment B. meandering

____ suspended load transport

____ bedload transport

____ easily-erodible banks

____ low slope

ANSWER: A, B, A, A, A, B

58. Match the following phenomena with the change they might induce in a river system.

____ increase in sediment A. erosion or downcutting

____ upstream damming B. filling or deposition

____ deforested watershed

____ decreased sea level

____ upstream debris flows

____ increased base level

ANSWER: B, A, B, A, B, B

CRITICAL THINKING

59. Since levees can protect many areas during floods, why are they controversial?

ANSWER: In addition to being expensive, levees in many cases make problems worse, by restricting the flow of water that otherwise would have spread over a floodplain.

60. Is it possible to change the velocity of a stream but have it maintain the same discharge? Explain.

ANSWER: Yes. The discharge (Q) is a product of the velocity (V) and the cross-sectional area (A); that is, Q = V x A. To maintain the same discharge while changing the velocity, it is necessary to change the cross-sectional area at the same time, and in the opposite manner. For example, if the velocity is increased, the cross-sectional area would need to be decreased by an appropriate amount.

61. You are in charge of designing an artificial stream channel to move a certain amount of water which is carrying sediment. At one point along the channel, more water will be added from a side stream.

(a) Will the capacity of the main channel be affected? Explain.

(b) Can you design the channel so that the competence will not be affected? Explain.

ANSWER: (a) Yes. Capacity depends on discharge, which will be increased.

(b) Yes. The competence will stay the same if the velocity is kept constant (you can accommodate the increased discharge by increasing the width and/or depth and keeping the velocity the same).

62. Briefly explain the trade-offs that accompany any flood control project.

ANSWER: The obvious benefits of controlling flooding are offset by loss of sediment deposition area, loss of wetland habitat, loss of the natural evolution of a drainage basin (natural changes in the stream channel such as meandering), increased soil erosion, and decreased natural ability to moderate effects of floods.

63. Glen Canyon Dam, completed in 1963 near the Utah- Arizona border, controls the water in the Colorado River which flows through the Grand Canyon. Since 1963 several changes have occurred in, along, and near the river as a result of the damming.

(a) What are 2 changes that you would predict upstream from the dam?

(b) What are 2 changes that you would predict downstream from the dam?

ANSWER: (a) upstream, any two of: deposition/flooding of lands above the dam/loss of habitat/loss of some forms of recreation (white water, or stream fishing )/increased evaporation;

(b) downstream, any two of: increased erosion/decreased water supply/increased salinity/changed water temperatures/loss of habitat/loss of some forms of recreation (white water).

64. Using the concept of a graded stream, describe how a stream whose profile has been faulted will respond to the faulting. Assume it is a normal fault with the downthrown block on the downstream half of the profile.

ANSWER: The fault scarp itself is now part of the profile, and it has a steeper slope. Water running over the steeper slope will erode it. The sediment will be deposited downstream where the slope is lower because the “old” slope won’t provide sufficient velocity to transport the eroded sediment. This erosion and deposition will continue until the slope is smooth or graded again.

SHORT ANSWER

65. What is the most costly and destructive type of natural disaster?

ANSWER: flooding

66. What was the most important lesson learned from the Flood of ’93 in the Midwestern United States?

ANSWER: Despite the best efforts at flood control, some floods will occur anyway.

67. How does flood control actually exacerbate problems in many flood-prone areas?

ANSWER: When flood control projects are completed, the flood-prone areas tend to become more highly developed.

68. Why doesn’t Venus have surface water?

ANSWER: Its runaway greenhouse effect makes it too hot for water to exist.

69. What are four of the reasons running water is important to humans?

ANSWER: any four of the following: domestic uses, industry, agriculture, power, transportation corridors

70. Very briefly, what is the hydrologic cycle?

ANSWER: the transfer of water from the ocean to the atmosphere by evaporation, from the atmosphere back to the ocean or to the land by precipitation, and from the land back to the ocean by runoff, or back into the atmosphere from the land by evaporation and transpiration

71. Approximately what percentage of atmospheric water comes directly from the ocean?

ANSWER: 85%

72. Approximately what percentage of the hydrologic cycle precipitation falls on land as rain and snow?

ANSWER: 20%

73. In the hydrologic cycle, what happens to the precipitation which falls on the land?

ANSWER: It becomes runoff, it evaporates or is transpired, or it is absorbed (becomes groundwater).

74. What is meant by the term runoff?

ANSWER: water which returns to the oceans as surface flow, from streams

75. What powers the hydrologic cycle?

ANSWER: heat from solar radiation, and gravity

76. Briefly explain what property of water makes hydrologic cycling possible.

ANSWER: Water changes phase from liquid to solid to vapor all within the normal range of Earth surface temperatures.

77. What are four ways that water can be temporarily stored, from a few years to a few thousand years, on the land areas, before returning to the oceans?

ANSWER: Water can be stored in lakes, snow fields, glaciers, or as groundwater.

78. What characterizes turbulent flow?

ANSWER: The stream flowlines are complexly intertwined, with mixing between adjacent layers.

79. What is the primary factor that determines whether water moves by turbulent vs. laminar flow?

ANSWER: the velocity of the flow

80. On what factors does the infiltration capacity of a surface depend?

ANSWER: the existing degree of water saturation, the duration and intensity of rainfall, the degree of soil consolidation

81. Distinguish sheet flow from channel flow.

ANSWER: With sheet flow, water moves in a more-or-less continuous film over the surface. With channel flow, the runoff is confined to long, troughlike depressions.

82. What is the gradient of a stream?

ANSWER: the slope over which the stream flows/the vertical drop through which the stream moves, divided by the horizontal distance the water moves

83. In semi-straight channeled streams, where does the highest velocity of flow occurs? Explain why this is the case.

ANSWER: in the center, just below the surface. There is more friction to be overcome at the bed and banks of the stream than there is in the center.

84. In meandering streams, where does the water velocity tend to be greatest?

ANSWER: along the outer bank of a meander loop

85. Why does the velocity of a stream generally increase downstream even though the gradient decreases?

ANSWER: because of the acceleration caused by gravity, because channels are generally smoother downstream, and because stream volume tends to increase as more tributaries enter downstream

86. What is the difference between the velocity and the discharge of a stream?

ANSWER: The velocity is the rate at which the stream is moving; the discharge is the total volume of water in the stream moving past some point in a given period of time.

87. How is the gradient of a stream calculated?

ANSWER: by dividing the difference between the highest and lowest elevations by the horizontal distance over which the stream flows.

88. Briefly explain why a stream with a semi-circular channel has a higher average velocity than a stream with a rectangular or v-shaped channel, all other factors being equal.

ANSWER: A semi-circular channel has a higher volume to surface area ratio and so friction losses are smaller.

89. Approximately what percentage of a stream’s kinetic energy may be available to erode and transport sediment?

ANSWER: 5%

90. What is(are) the source(s) of the dissolved load in most streams?

ANSWER: solution of stream bed and banks, sheet flow, and groundwater flow into the stream

91. By what two processes can a stream erode material from its banks and bed?

ANSWER: hydraulic action, abrasion

92. What are the two categories of the solid load of a stream?

ANSWER: bed, suspended

93. How are the particles of the bed load moved along the bed of a stream?

ANSWER: by rolling, sliding, and saltation

94. What is the competence of a stream, and on what does it depend?

ANSWER: The competence is the measure of the maximum-sized particles that a stream can carry. Competence depends on a stream’s velocity.

95. Briefly explain how a streams’ capacity differs from its competency.

ANSWER: Capacity is the volume of material a stream can carry, and is dependent on stream discharge. Competency measures the maximum-sized particles that a stream can carry, and is dependent on stream velocity.

96. When do streams do most of their erosion, transportation of sediment, and deposition?

ANSWER: during flooding

97. Under what conditions will a braided stream develop?

ANSWER: when the stream is supplied with excessive sediment

98. What is the origin of oxbow lakes?

ANSWER: They are former meanders which have been cut off from the stream.

99. What are natural levees?

ANSWER: the ridges of alluvium left along a stream’s margins by repeated deposition during floods

100. What causes a delta to form?

ANSWER: The stream’s velocity decreases rapidly when it flows into another body of water, and deposition occurs.

101. What are the three types of marine deltas that are recognized, based on the relative importance of the processes involved in their formation?

ANSWER: stream-dominated, wave-dominated, and tide-dominated

102. A bird’s-foot delta, such as that of the Mississippi River, is typically formed as which of the three types of marine deltas?

ANSWER: a stream-dominated delta

103. In what climatic regions do alluvial fans form best?

ANSWER: semi-arid and arid regions

104. Briefly explain why braided streams are common in regions adjacent to glaciers.

ANSWER: Braided streams form when there is an excess of sediment load for the amount of water available and the depth of the stream channel. Glaciers provide a great deal of sediment in comparison to the amount of meltwater they release.

105. If the formation of an oxbow lake results in an increase in stream velocity, explain what causes a stream to meander.

ANSWER: A stream meanders when the volume and velocity of a stream is too great for its gradient. An increase in the distance travelled, by virtue of a meandering path, balances volume and velocity with a low gradient.

106. What is the probability of occurrence of a ten-year flood in any given year?

ANSWER: one out of ten, or 1/10

107. Why are predictions of the magnitudes of 50-year or 100-year floods unreliable for most of North America?

ANSWER: because knowledge of long-term behavior of most streams is limited by the short period of time during which records have been kept.

108. What is a drainage basin?

ANSWER: the total surface region which provides runoff to a stream system

109. What is meant by the term “divide” as in the Continental Divide along the Rocky Mountains?

ANSWER: It is the topographic boundary between adjacent drainage basins.

110. What is the base level of a stream?

ANSWER: the lower limit to which the stream can erode

111. What is ultimate base level for a stream?

ANSWER: sea level

112. Briefly explain how a stream can apparently have a valley which extends onto the continental shelf or to the shelf-slope break.

ANSWER: The stream valley must have been established when sea level was lower.

113. Briefly explain why a dam can create a temporary base level, and what effects this base level can have on the stream system both above and below the dam.

ANSWER: A dam decreases the velocity of stream water and results in the deposition of sediment above the dam. Below the dam, the stream will be sediment free but still having energy to transport sediment, so it may begin eroding.

114. Briefly explain what will happen to a stream’s behavior if one drains a lake which is a temporary base level for that stream.

ANSWER: Drainage of a lake which serves as a temporary base level will lower the base level for the part of the stream above the lake. The stream may respond by eroding, in an attempt to reach its new base level.

115. Briefly explain how a stream might adjust toward an equilibrium state following a heavy rain.

ANSWER: A heavy rain will increase stream volume and velocity. The channel and gradient will be temporarily too small and low, respectively, for the increased volume. Stretches of the stream with a low gradient will experience erosion, and stretches farther downstream which may experience deposition as the gradient of the upstream portion is adjusted (increased).

116. The ideal graded stream has a balance among what 5 factors?

ANSWER: its gradient, discharge, flow velocity, channel characteristics, and sediment load

117. Name three of the processes involved in the evolution of valleys

ANSWER: any three of: downcutting, lateral erosion, mass wasting, sheet wash, headward erosion

118. Lateral erosion creates conditions along a stream valley which can promote movement of material by what other geologic process?

ANSWER: mass wasting

119. How does an incised meander form?

ANSWER: A graded stream near baselevel may be uplifted so that the meander pattern is eroded into the bedrock of the uplifted block.

120. What is stream piracy?

ANSWER: The event which occurs when headward erosion cuts through a drainage divide and diverts part of the drainage of another stream.

121. Briefly explain what happens to the two stream systems when one stream pirates another.

ANSWER: The pirating stream has more water, greater discharge, and greater potential to erode and transport; these same properties are decreased in the pirated stream.

122. What is a superposed stream?

ANSWER: A superposed stream is one whose course was developed earlier, while flowing over a relatively flat surface, and which has maintained its course by downward erosion, as more resistant rock layers were uplifted into its path.

123. What is a stream terrace?

ANSWER: an uplifted erosional remnant of a floodplain that formed when a stream was flowing at a higher level

124. Briefly explain how a meandering stream can become incised in solid bedrock.

ANSWER: A stream with a previously established meandering pattern may become incised into solid bedrock which is uplifted, or the same stream may be responding to a relative lowering of its base level.