erosion and deposition by gravity

creep

Creep is the very slow movement of rock and soil down a hillside. Creep occurs so slowly you cant see it happening. You can only see the effects of creep after years of movement. This is illustrated in Figure 10.33. The slowly moving ground causes trees, fence posts, and other structures on the surface to tilt downhill. Creep usually takes place where the ground freezes and thaws frequently. Soil and rock particles are lifted up when the ground freezes. When the ground thaws, the particles settle down again. Each time they settle down, they move a tiny bit farther down the slope because of gravity.

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slump

Slump is the sudden movement of large blocks of rock and soil down a slope. You can see how it happens in Figure 10.32. All the material moves together in big chunks. Slump may be caused by a layer of slippery, wet clay underneath the rock and soil on a hillside. Or it may occur when a river undercuts a slope. Slump leaves behind crescent-shaped scars on the hillside.

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other types of mass movement

Two other types of mass movement are slump and creep. Both may move a lot of soil and rock. However, they usually arent as destructive as landslides and mudslides.

mudslides

A mudslide is the sudden flow of mud down a slope because of gravity. Mudslides occur where the soil is mostly clay. Like landslides, mudslides usually occur when the soil is wet. Wet clay forms very slippery mud that slides easily. You can see an example of a mudslide in Figure 10.31.

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landslides and mudslides

The most destructive types of mass movement are landslides and mudslides. Both occur suddenly.

landslides

A landslide happens when a large amount of soil and rock suddenly falls down a slope because of gravity. You can see an example in Figure 10.30. A landslide can be very destructive. It may bury or carry away entire villages. A landslide is more likely if the soil has become wet from heavy rains. The wet soil becomes slippery and heavy. Earthquakes often trigger landslides. The shaking ground causes soil and rocks to break loose and start sliding. If a landslide flows into a body of water, it may cause a huge wave called a tsunami.

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instructional diagrams

No diagram descriptions associated with this lesson

questions

Gravity causes erosion by all of the following except

a. glaciers.

-->  b. moving air.

c. flowing water.

d. mass movement.

The rate of erosion by gravity

a. is sudden and dramatic

b. is very slow over long periods of time

c. neither of these

-->  d. both of these

Factors that increase the risk of landslides include

a. dry soils.

b. lack of rain.

-->  c. earthquakes.

d. two of the above

When a rock falls from a cliff face, the agent of erosion is usually

a. wind

b. water

-->  c. gravity

d. glaciers

Downhill creep

-->  a. results in curved tree trunks

b. falls as a whole unit

c. leaves large scars in the hillside

d. cannot be noticed because it is so slow

Mass movement can occur

a. suddenly.

b. very slowly.

c. only on sloping land.

-->  d. all of the above

Slump may be caused by

a. wet clay.

b. water erosion.

c. scars on a hillside.

-->  d. two of the above

A slump is the sudden

a. fall of rock and soil down slope

b. flow of mud down slope

-->  c. movement of a large block of rock and soil down slope

d. flow of volcanic ash and water down slope

Creep usually takes place where the ground

a. is level.

b. is prevented from moving.

-->  c. freezes and thaws frequently.

d. is always saturated with water.

Mass movement may be caused when

a. droughts dry out the ground

-->  b. a river undercuts a slope

c. the gravitational polarity reverses

d. none of these

Evidence that creep has occurred include

-->  a. cracked pavement.

b. crescent-shaped holes.

c. huge piles of mud.

d. large chunks of rock.

Gravity pulls soil and rocks downhill.

-->  a. true

b. false

Mass movement is always a very slow process.

a. true

-->  b. false

A landslide may carry away an entire village.

-->  a. true

b. false

Mudslides occur where soil consists mostly of sand.

a. true

-->  b. false

Slump occurs more slowly that creep.

a. true

-->  b. false

Curved tree trunks are a sign of land creep.

-->  a. true

b. false

Slump is more destructive than a landslide.

a. true

-->  b. false

Undercutting can cause the ground to become unstable.

-->  a. true

b. false

Soil is lifted up when the ground freezes.

-->  a. true

b. false

Heavy rainfall makes ground more susceptible to landslides.

-->  a. true

b. false

Landslides can cause earthquakes.

a. true

-->  b. false

An earthquake is a type of mass movement.

a. true

-->  b. false

Landslides rarely cause much damage.

a. true

-->  b. false

Trees tilting downhill are evidence for slump.

a. true

-->  b. false

During creep, soil moves downhill when it thaws.

-->  a. true

b. false

sudden movement of a large block of rock and soil down a slope

a. creep

b. landslide

c. mass movement

d. mudslide

-->  e. slump

f. gravity

force that indirectly causes erosion by moving water or ice

a. creep

b. landslide

c. mass movement

d. mudslide

e. slump

-->  f. gravity

sudden movement of a large amount of soil and loose rocks down a slope

a. creep

-->  b. landslide

c. mass movement

d. mudslide

e. slump

f. gravity

gradual movement of rock and soil down a hillside

-->  a. creep

b. landslide

c. mass movement

d. mudslide

e. slump

f. gravity

any type of erosion and deposition caused directly by gravity

a. creep

b. landslide

-->  c. mass movement

d. mudslide

e. slump

f. gravity

sudden flow of a large amount of wet, slippery clay down a slope

a. creep

b. landslide

c. mass movement

-->  d. mudslide

e. slump

f. gravity

diagram questions

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