Mass movement

Question 1

1) Which of the following locations would be most likely to see large-scale, rapid mass wasting?
A) Florida Everglades
B) Central Illinois
C) Mojave Desert
D) The Rocky Mountains

Answer 1

The Rocky Mountains
Mass wasting (the downslope movement of soil and rock due to gravity) is most likely in areas with steep slopes, loose material, and significant weathering. The Rocky Mountains have steep slopes, high elevation, and various weather conditions (like freeze-thaw cycles), which contribute to large-scale and rapid mass wasting events such as landslides and rockfalls.

Question 2

2) A ________ is not the sole cause of a mass wasting event, but the last of many causes that
initiate the downslope movement of materials.
A) debris flow
B) slide
C) repose angle
D) trigger

Answer 2

D) trigger
A trigger is the final event or factor that initiates mass wasting. While mass wasting is influenced by many factors (such as slope angle, material composition, and water content), a trigger is the last contributing factor that sets the movement into motion. Common triggers include heavy rainfall, earthquakes, volcanic activity, or human disturbances like construction.

Question 3

3) Which sediment size has the steepest angle of repose?
A) Gravel
B) Sand
C) Silt
D) Clay

Answer 3

Gravel: Larger, angular particles interlock more effectively, resulting in a steeper angle of repose (typically 35-45 degrees).
Gravel has the steepest angle of repose due to its coarse, angular nature.

Question 4

4) A stream is flowing over a hill covered in thick soil. The stream is eventually blocked to create
a small pond in order to free land downhill for construction. What will ultimately happen to the
strength and cohesion of the soil in the area around this pond?
A) Strength and cohesion will decrease.
B) Strength and cohesion will increase.
C) Strength will decrease and cohesion will increase.
D) Neither will be affected

Answer 4

A) Strength and cohesion will decrease.
The formation of a pond increases the water content in the surrounding soil. Water can significantly impact soil strength and cohesion through the following mechanisms: Reduced Strength, Reduced Cohesion
Thus, the soil around the pond becomes weaker and less cohesive over time, increasing the risk of slope failure or other forms of instability.

Question 5

) Which type of motion will supply material to and maintain talus slopes?
A) Flow
B) Fall
C) Slide
D) Slump

Answer 5

B) Fall.
Talus slopes are accumulations of rock debris at the base of steep cliffs or slopes. These slopes are formed and maintained primarily by rockfall, where individual rocks or blocks of rock break off from the cliff face and fall freely or bounce down to the base due to gravity.

Question 6

6) A ________ is an example of a rotational slide.
A) rockslide
B) fall
C) mudflow
D) slump

Answer 6

D) slump.
A slump is a type of rotational slide where a mass of material moves downslope along a concave, curved surface. As the material moves, it typically rotates backward, creating a characteristic scarp or step-like appearance at the top of the slope.

Question 7

8) True/False: Mass wasting is possible only with the aid of a transportation agent such as
water, wind, or ice.

Answer 7

False.
Mass wasting is the downslope movement of soil, rock, and debris under the influence of gravity alone. While transportation agents like water, wind, or ice can contribute to or accelerate erosion and sediment transport, mass wasting does not require their involvement

Question 8

9) Imagine you are at the beach, building a sandcastle. Dry sand cannot hold a form, so the
addition of water is necessary to build the castle. However, too much water will destroy the
sandcastle and cause the sand to flow away in slurry. This is similar to the role pore water has
on sediments in a slope. What role does water play to maintain a slope? What role does water
play to cause mass wasting of the slope?

Answer 8

Water helps maintain a slope by increasing cohesion between sediment grains through surface tension, much like how damp sand holds a sandcastle together. However, too much water saturates the sediment, reducing friction and increasing pore pressure, which destabilizes the slope. This excess water can lead to mass wasting as the weight of the saturated material and reduced shear strength cause it to flow downslope.