Chapter 15 Mass Wasting

Earth: An Introduction to Physical Geology 15.1

Multiple-Choice Questions1)

Which one of the following materials has the maximum, sustainable, slope angle, as determined by the angle of repose?

A)

dry silt B)

moist, sandy soil with a clay-rich matrix C)

dry sand D)

moist, clay-rich shale layers Answer :

C

2)

________ denotes the exposed, crescent-shaped rupture surface at the head of a slump. A)

Scoop B)

Sole C)

Toe D)

Scarp Answer :

D

3)

Consider a weathered rock or soil particle lying on a slope. How will the gravitational force pulling the particle downward along the land surface vary with the inclination of the slope?

A)

It will increase as the slope angle is lessened. B)

It will decrease as the slope angle is lessened. C)

It is not affected by the slope angle. D)

It will possibly increase or decrease as slope angle is lessened, depending upon other factors.

Answer :

B

4)

How do the strength and cohesion of clay-rich regolith or soil change with the addition of water?

A)

Water does not affect the cohesion but lowers the strength. B)

Water reduces the strength of clays but raises the cohesion of the soil. C)

Water increases the strength and cohesion. D)

Water lowers the strength and cohesion. Answer :

D

5)

________ involves movement on a zone of compressed air. A)

A slump B)

A mudflow C)

A rock avalanche D)

Soil creep Answer :

C

6)

Of the following, which one would most likely be triggered by an earthquake? A)

solifluction B)

soil creep C)

slump D)

rock avalanche Answer :

D

7)

Which one of the following operates primarily in areas of permafrost? A)

rock avalanche B)

solifluction C)

soil creep D)

mudflow Answer :

B

8)

Consider a steep highway cut made by removing slightly weathered to fresh, fractured, granite bedrock. Which of the following situations is most stable against rockslides?

A)

one set of widely spaced, sub-horizontal fractures B)

two sets of fractures, one inclined toward the road cut and the other away C)

two sets of fractures, one widely spaced and sub-horizontal, the other inclined away from the highway cut

D)

one set of widely spaced fractures inclined towards the road cut Answer :

A

9)

Which of the following was a major factor leading to the Gros Ventre, WY slide? A)

Erosion by the river had undercut the slope-forming shale and exposed the underlying sandstone.

B)

Soils and shallow bedrock were very wet and locally saturated. C)

A strong earthquake caused the unstable rock layers to move. D)

Dry weather caused the clay-rich strata to compact, allowing the overlying sandstone to slide into the valley.

Answer :

B

10)

What caused the mudflows (1985) on the Nevado del Ruiz volcano? A)

Hot ash fell onto snow near the summit. B)

A crater lake was broken during an eruption. C)

Warm weather caused rapid melting of snow and ice near the summit. D)

all of the above Answer :

A

11)

Why was the Alaskan pipeline built above ground and insulated? A)

to protect the pipeline against damage due to thawing ground and to keep the crude oil hot and fluid

B)

to keep the crude oil cool and highly fluid C)

to protect against damage from herds of elk and deer D)

to protect against damage from roots of large trees uprooted in windstorms Answer :

A

12)

A geologist wants to locate a horizontal coal bed on a soil-covered slope where soil creep is active. A distinctive sandstone bed underlies the coal bed. On the basis of weathered sandstone fragments in the soil, where is the coal bed?

A)

just below the lowest piece of sandstone seen in the soil B)

just above the highest piece of sandstone seen in the soil C)

just below the highest piece of sandstone seen in the soil D)

just above the lowest piece of sandstone seen in the soil Answer :

B

13)

Which disaster was triggered by a huge mass of soil and rock that suddenly slid into a water-filled reservoir?

A)

Nevado del Ruiz, Colombia, 1985 B)

Vaiont Canyon, Italy, 1963 C)

Sherman Glacier rock avalanche, AK, 1964 D)

Yungay-Ranrahirca, Peru, 1970 Answer :

B

14)

Which statement best describes slumping, a mass wasting process? A)

A block or blocks of unconsolidated regolith slide downhill along a curved slip surface. B)

Blocks of hard bedrock rapidly slide downhill along fracture surfaces. C)

The soil and regolith move downhill very slowly. D)

A mass of soil or regolith becomes saturated with water and suddenly flows downhill to the base of the slope.

Answer :

A

15)

Which mass wasting process has the slowest rate of movement? A)

slump B)

rock avalanche C)

solifluction D)

creep Answer :

D

16)

All of the following are factors affecting mass wasting except for ________. A)

gravity B)

water C)

slope angle D)

geologic age Answer :

D

17)

The most rapid type of mass movement is a ________. A)

slump B)

lahar C)

rock avalanche D)

debris flow Answer :

C

18)

As an erosional process, how is mass wasting unique from wind, water, and ice? A)

Mass wasting affects particles of all sizes whereas the others affect only smaller particles. B)

Mass wasting does not require a transporting medium. C)

Mass wasting affects much larger geographic areas than does wind, water, and ice. D)

All of the above make mass wasting unique compared to wind, water, and ice. Answer :

B

19)

Which of the following mass movements is most likely to occur in a geologic setting where the rock strata are inclined?

A)

debris flow B)

slump C)

creep D)

rockslide Answer :

D

20)

Which of the following statements concerning mudflows is not true? A)

Mudflows may be caused by heavy rains or melting snow. B)

In hilly areas, mudflows move down the canyons and stream valleys. C)

Mudflows deposit talus slopes. D)

Mudflows can move and carry very large boulders and other coarse debris. Answer :

C

21)

During wet weather or times when snow is melting, sometimes the downhill toe of a slump ________.

A)

turns into a rock avalanche B)

becomes an earthflow C)

stops moving because water makes the clay sticky D)

collapses and is deposited as talus at the base of the slope Answer :

B

22)

How do freezing, thawing, wetting, and drying contribute to soil creep? A)

The soil becomes much weaker when dry and frozen. B)

Gravity exerts a much stronger force when the soil is wet and thawed. C)

The soil expands and contracts, lifting particles and dropping them a slight distance downslope.

D)

Eventually, these cause the soil and regolith to suddenly slide down the slope. Answer :

C

23)

All of the following are possible indicators that creep is occurring except for ________. A)

tilted fences or power line poles B)

an extremely thick soil profile C)

curved tree trunks D)

cracks in roads or sidewalks Answer :

B

15.2

Word Analysis QuestionsExamine the words and/or phrases for each question below and determine the relationship among the majority of words/phrases. Choose the option which does not fit the pattern.

1)

A) wind B) water C) mass wasting D) ice Answer :

mass wasting

2)

A) slope angle B) water C) vegetation D) earthquake Answer :

earthquake

3)

A) rockslide B) debris flow C) creep D) slump Answer :

creep

4)

A) solifluction B) fall C) slide D) flow Answer :

solifluction

5)

A) earthquake B) lahar C) liquefaction D) landslide Answer :

lahar

15.3

True/False Questions1)

.Slump describes the very slow, downhill movement of soil and regolith. Answer :

FALSE

2)

The steepest, stable, slope angle possible in unconsolidated, granular materials like sand and gravel is called the angle of retention.

Answer :

FALSE

3)

Solifluction occurs during the warmer summer months. Answer :

TRUE

4)

The Gros Ventre slide of 1925 was actually a mudflow triggered by an earthquake. Answer :

FALSE

5)

Repeated freezing and thawing can be important in soil creep movements. Answer :

TRUE

6)

Lahars are essentially mudflows associated with volcanoes and volcanism. Answer :

TRUE

7)

Solifluction is an important mass wasting process in areas of permafrost. Answer :

TRUE

8)

A triggering mechanism, such as heavy rains or an earthquake, are necessary for mass wasting to occur.

Answer :

FALSE

9)

A scarp is the exposed portion of the rupture surface beneath a slump block. Answer :

TRUE

10)

Earthflows and slumps generally involve movement of unconsolidated or weakly consolidated soil and regolith.

Answer :

TRUE

11)

Bedding planes and fractures can both act as slip surfaces for rockslides. Answer :

TRUE

12)

The very destructive, mass wasting event that wiped out Yungay and Ranrahirca, Peru was caused by hot, volcanic ash falling on deep snow in the summit region of a volcano.

Answer :

FALSE

13)

Submarine landslides are generally much smaller than similar mass wasting events on land.

Answer :

FALSE

15.4

Short Answer Questions1)

________ denotes the downslope movement of soils and regolith. Answer :

Mass wasting

2)

________ is the basic force that moves or accelerates soil and regolith down a slope. Answer :

Gravity

3)

What is another name for volcanic mudflows, like those formed during the Mount St. Helens and Nevado del Ruiz eruptions?

Answer :

lahars

4)

Which process of mass wasting occurs primarily in permafrost regions? Answer :

solifluction

5)

Talus blocks or piles are associated with what of motiona fall, a slide, or a flow? Answer :

fall

6)

________ involves the downslope movement of a block or blocks of unconsolidated soil and regolith along a curved, slip surface.

Answer :

Slump

7)

What is the fastest moving of the mass wasting processes? Answer :

rock avalanche

8)

Unconsolidated, granular materials such as gravel and sand will support maximum slope angles of about 33 to 35 degrees. What is the name for this maximum slope angle?

Answer :

angle of repose

9)

________ denotes the exposed portion of the slip surface beneath a slump block. Answer :

Scarp

10)

________ is the fan-shaped pile of broken rock fragments at the base of a steep, bedrock slope or cliff.

Answer :

Talus

15.5

Critical Thinking QuestionsUse complete sentences, correct spelling, and the information presented in Chapter 15 to answer the questions below

1)

As a geologist working in a foreign country for the first time, you are asked to assess the potential for mass wasting in a particular region. What aspects or characteristics (geologic, geographic, biologic, etc.) of the region are you interested in for your assessment? Also, how could you possibly determine if mass wasting has been active in the recent geologic past (100's or 1000's of years)?

2)

Although it was not discussed in Chapter 15, what are some preventive measures that can be done to reduce or lessen the impact of mass wasting? (Hint: Think about the controls and triggers of mass wasting.)

3)

Based on the examples and discussion in Chapter 15, what is the relationship of climate to mass wasting? Also, are certain climates more susceptible to mass wasting? Why?

15.6

Visualization Questions1)

In the diagram below, match the letter of each illustration to the correct form of mass wasting.

a) debris flow b) slump c) earthflow d) rockslide

Answer :

A = b B = d C = a D = c

2)

What process of mass wasting is illustrated in the diagram below?

Answer :

creep

3)

Examine the block diagram below. Identify the labeled features a) and b).

Answer :

a) scarp b) earthflow