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41 terms

Geology Ch 8 Mass Movements

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internal heat builds mountains
vs. gravity which pulls mountains down
mass wasting (movements)
gravity pulling geological materials downward
landslide
rapid mass movements
shearing stress is counteracted by shear strength (aka friction)
...
angle of repose
maximum slope angle at which material is stable (not going to slide); angle varies with material
steepness of the slope
affects the equilibrium between the forces: the steeper the slope, the greater the component of gravity parallel to the slope
water and clay can weaken rocks and make them prone to landslides. give an example
ex. Montmorillonite, a mineral of the clay group, has the property of absorbing twenty times its own weight in water, dramatically increasing the weight of the material (and therefore the component of gravity parallel to the slope), exacerbating potential for movement.
quick clays
clay sediments of glacial origin deposited under the sea; they acquired a honeycomb structure caused by the dissolution of the sodium chloride. The honeycomb structure is easily broken by vibrations, so slopes containing quick clays are prone to collapse.
sensitive clays
behave the same way as quick clays, but they have a different origin.
creep
a slow, downward movement of unstable surface material
rockfalls
fast movements where the material falls through the air off a very steep slope
talus
The accumulation of rubble at the bottom of the slope
slumps
movements of rocks or unconsolidated materials that occur along a curved surface over a short distance; there is a rotational component to the movement.
flows
mass movements that occur in a chaotic fashion; different kinds: avalanches of snow or debris, mudflows and lahars, nuées ardentes (pyroclastic flows), and earthflows. All but the earthflows are fast.
prevention methods:
bridges
removing and re-grading the angle
retention structures (low walls)
fluid removal techniques
hardened with heat
injected with cement
diverting mudflows
The stability of a slope is increased when
A) its slope angle is increased during construction of a roadway
B) a building is constructed upon it
C) water is drained from the slope
D) vegetation is removed from the slope
C
Sandy soil has greatest strength when it is
A) dry
B) moist
C) saturated
D) quick
B
What process is mainly a result of soil expansion and contraction?
A) soil creep
B) landslide
C) mudflow
D) soil flowage
A
The angle of repose indicates the strength of soil when it has which moisture condition?
A) saturated
B) dry
C) quick
D) moist
B
Clay has no strength when it is
A) dry
B) moist
C) saturated
D) quick
D
Which mass movement involves material with the highest water content?
A) slump
B) rockfall
C) earthflow
D) mudflow
D
Which is the fastest moving mass movement?
A) slump
B) soil creep
C) avalanche
D) solifluction
C
he form of mass movement in which materials move in a disorganized, chaotic fashion is
A) slide
B) flow
C) rock fall
D) slump
B
Talus forms a steep slope because it is
A) coarse grained and angular
B) subject to soil creep
C) fine grained and rounded
D) usually saturated
A
solifluction
is a type of mass wasting where waterlogged sediment moves slowly downslope, over impermeable material
Which is the slowest moving mass movement?
A) slump
B) soil creep
C) avalanche
D) solifluction
B
When soil freezes, it can
A) slump
B) flow
C) liquefy
D) heave
D
Rockfalls produce
A) mudflows
B) heaves
C) slumps
D) talus
D
The type of mass wasting that involves a rotational failure along a curved surface:
A) solifluction
B) slump
C) debris flow
D) debris avalanche
B
In granular soils, soil strength
A) is best when the soil is moist
B) is best when the soil is saturated
C) is best when the soil is dry
D) is not related to moisture content.
A
Which mass movement consists of the coarsest particles?
A) debris avalanche
B) earthflow
C) soil creep
D) mudflow
A
Rock bolts
A) are used to stabilize soil slopes
B) were tried once with disastrous consequences
C) are used to stabilize potential rock slides
D) are placed into rock beneath soil to prevent the soil from sliding.
C
In which type of mass wasting movement does the moving material retain its original shape?
A) heave
B) slide
C) creep
D) flow
B
A head scarp and hummocky toe are characteristics of a(n)
A) slump
B) heave
C) talus
D) rockfall
A
Clays that are deposited in a marine environment
A) are susceptible to quick conditions
B) are never susceptible to quick conditions
C) are the strongest, most stable type of clay deposit
D) are stronger when wet than when dry
A
Which change can lead to slope failure?
A) rise of water table in slope material
B) decline of water table in slope material
C) removal of material from the top of a slope
D) addition of material to the base of a slope
A
Landslides can also cause
A) earthquakes.
B) volcanic eruptions.
C) flooding.
D) seismic gaps.
C
Vegetation tends to increase slope stability by
A) adding water to the soil.
B) removing weight from the slope.
C) holding rainwater on the surface.
D) holding soil in place with roots.
D
One factor that influences slope stability but which humans can't alter is
A) vegetation cover.
B) geologic structure.
C) slope angle.
D) water content.
B
A slope that looks stable but has bent trees, tilted fence posts, and cracked walls may actually have
A) soil creep.
B) occasional mudflows.
C) modest landslides.
D) frequent rock fall.
A
A 1960 flood in the Italian Vaiont River Valley came from a landslide that
A) filled the valley.
B) splashed into a reservoir.
C) hit a dam and broke it.
D) filled a nearby wetland.
B