Deck 10: Landslides and Slope Failure

Question 1

What would you likely observe if you saw a debris flow?

A) Material moving as a unit down a slope.
B) Material moving chaotically down a slope.
C) Material moving slowly down a slope.

Answer 1

Material moving chaotically down a slope.

Question 2

How and why does saturation change the risk associated with mass wasting of unconsolidated material?

A) Increases risk by decreasing weight and increasing grain cohesion.
B) Decreases risk by increasing weight and decreasing grain cohesion.
C) Decreases risk by decreasing weight and increasing grain cohesion.
D) Increases risk by increasing weight and decreasing grain cohesion.

Answer 2

Increases risk by increasing weight and decreasing grain cohesion.

Question 3

Which of the three labeled locations on the topographic map above has the highest risk of mass wasting?
(Numbers represent elevation in meters above sea level.)

A) A
B) B
C) C
D) All three locations are equal.

Answer 3

A

Question 4

-Complete the concept map for number 1.

A) Wind
B) Water
C) Slope
D) Gravity

Question 5

-Complete the concept map for number 2.

A) Material
B) Regolith
C) Slide
D) Slump
E) Slope

Question 6

-Complete the concept map for number 3.

A) Slide
B) Slump
C) Slope

Question 7

-Complete the concept map for number 4.

A) Material
B) Regolith
C) Slide
D) Slope

Question 8

-Complete the concept map for number 5.

A) Material
B) Regolith
C) Slide
D) Slump
E) Slope

Question 9

-Complete the concept map for number 6.

A) Material
B) Regolith
C) Slump
D) Slope

Question 10

Use the following information to answer the following questions. There are two main approaches to reducing the risk from landslides; hard and soft. Hard approaches involve construction of retaining walls, slope reduction, and drainage improvements. Soft approaches include zoning restrictions and land use regulations. Read the following mass wasting scenarios to determine if the event involved hard, soft, or both approaches.

-A homeowner has the foundation of his house reinforced to lessen the effects of liquefaction.

A) Hard
B) Soft
C) Both

Question 11

Use the following information to answer the following questions. There are two main approaches to reducing the risk from landslides; hard and soft. Hard approaches involve construction of retaining walls, slope reduction, and drainage improvements. Soft approaches include zoning restrictions and land use regulations. Read the following mass wasting scenarios to determine if the event involved hard, soft, or both approaches.

-City council passes an ordinance preventing a development from building on a historical landslide.

A) Hard
B) Soft
C) Both

Question 12

Use the following information to answer the following questions. There are two main approaches to reducing the risk from landslides; hard and soft. Hard approaches involve construction of retaining walls, slope reduction, and drainage improvements. Soft approaches include zoning restrictions and land use regulations. Read the following mass wasting scenarios to determine if the event involved hard, soft, or both approaches.

-Ditches along a road are cleaned to remove vegetation and debris.

A) Hard
B) Soft
C) Both

Question 13

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What hypothesis is presented to explain the landslide?

A) An earthquake triggered it
B) A recent heavy rain triggered it
C) Rising groundwater triggered it

Question 14

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What prediction do scientists make in this scenario?

A) Rainfall percolates through the soil.
B) Other areas may fail.
C) Future earthquakes may cause landslides.

Question 15

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What empirical data are mentioned here as a cause for the mass wasting?

A) Rainfall
B) Rising groundwater levels
C) Earthquake levels

Question 16

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What force must be overcome in order for mass wasting to occur in most cases?

A) Slope
B) Friction
C) Saturation

Question 17

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-Which of the following slopes would be at greatest risk for mass wasting?

A) 10° slope
B) 20° slope
C) 30° slope

Question 18

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What direction is the force of friction compared to the surface of a slope?

A) Parallel
B) Perpendicular
C) Oblique

Question 19

Read the following USGS statement and answer this question.
USGS Statement on Bluebird Canyon Landslide in Laguna Beach, California
In the early morning of June 1, 2005, a landslide began moving in the Bluebird Canyon area of Laguna Beach, California. No rainfall or earthquake activity occurred during or immediately before the landslide movement. This movement is almost certainly related to the extremely heavy winter rains that occurred from December through February. Rainfall from the winter season has been slowly percolating downward through the soil and is gradually raising ground-water levels. As ground water rises, slopes can become unstable and begin to move, even if no rain is presently occurring. The current landslide might enlarge to include areas upslope or other adjacent areas within the next few days and weeks.
The continuing infiltration of water from the winter rainy season could trigger other deep landslides in the southern California region over the next few weeks and months. (from www.usgs.gov/homepage/ landslide_laguna.asp)

-What factor triggered (caused the start of) the December, 1991, debris flows at Caraballeda, Venezuela?

A) Steep slopes
B) Urban development
C) Excessive rains

Question 20

-What type of mass wasting is pictured above (photo courtesy USGS)?

A) Rock fall
B) Slump
C) Creep
D) Debris flow

Question 21

-What common rockfall feature is pictured at the base of this cliff at Devil's Tower National Park in the image shown above?

A) Alluvial fan
B) Talus slope
C) Rockslide
D) Debris flow

Question 22

-Which form of mass wasting would be most likely after heavy rains on a recently active volcano with significant ash deposits?

A) Mudflow
B) Slump
C) Rockslide
D) Debris flow

Question 23

-What criteria are primarily used to classify mass wasting?

A) Land use and velocity of movement
B) Volume of water and velocity of movement
C) Type of material and type of movement
D) Slope angle and volume of precipitation

Question 24

-What set of conditions would result in the greatest chance of mass wasting at a location?

A) High precipitation, low slope, consolidated materials
B) Low precipitation, high slope, consolidated materials
C) High precipitation, high slope, unconsolidated materials
D) Low precipitation, low slope, unconsolidated materials

Question 25

The term "landslide"
applies to several forms of mass wasting.

Question 26

Rockfalls happen when boulders on rocky cliffs dislodge and fall.

Question 27

Rockslides occur when large sheets of rock break free along preexisting, structurally weak surfaces and move down a slope.

Question 28

Slumps occur when soils slowly move down a linear slope.

Question 29

Mudflows and debris flows occur when water and loose materials move down a slope like a thick liquid.

Question 30

Creep is the rapid movement of material down a slope.