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ENVS165 - Theory and Laboratory Experiments in Earth Surfaces Processes > Slopes > Flashcards

Slopes Flashcards

1
Q

What is Hillslope?

A

The elevated land between valley bottoms

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2
Q

What are hillslope processes?

A

Movement of rock and soil by mass wasting, rain splash and overland flow

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3
Q

Characteristics of bedrock slopes?

A

Soil production < erosion
Little to no soil cover with bedrock at surface
Sediment transport is weathering limited
Slope form controlled by rock properties

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4
Q

Characteristics of soil-mantled slopes?

A

Soil production > erosion
A surficial layer of soil covers the bedrock
Sediment transport is transported limited
Slope form controlled by soil properties, production & transport rates

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5
Q

What are bedrock hillslopes?

A

WEATHERING LIMITED
- With steep slopes
- Thin to absent soil mantle

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6
Q

Where are bedrock hillslopes found?

A

Arid climates
Common in humid areas with low weathering rates

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7
Q

What are the processes of bedrock hillslopes?

A
  • Falls and slides
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8
Q

What are the physical characteristics of bedrock hillslopes?

A

Parallel retreat at threshold angles

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9
Q

What are soil-mantled hillslopes?

A

Transport-limited
With thick soil mantle

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10
Q

Where are soil-mantled hillslopes found?

A

Humid climates

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11
Q

What are processes of soil-mantled hillslopes?

A

Soil creep and slides

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12
Q

what are the physical characteristics of soil-mantled slopes?

A

Convex profiles
Typically parabolic

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13
Q

What does surface erosion impact?

A

Individual grains, detached separately and transported over the slope surface

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14
Q

What are some examples of surface erosion?

A
  • Rain-splash
  • Overland flow
  • Rills
  • Gully
  • Reactivated ancient gullies
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15
Q

What are the types of overland flow?

A

Horton Overland flow
Slope foot saturation - termed saturation overland flow

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16
Q

What is the Horton Overland Flow?

A

Rainfall rate excess of infiltration capacity

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17
Q

What is overland flow?

A

Water flowing over the soil surface

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18
Q

What infiltration rate?

A

The rate that’s actually taking place

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19
Q

What is the infiltration capacity?

A

A hypothetical maximum rate

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20
Q

What does the Horton Overland Flow depend on?

A

Rainfall rate and surface

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21
Q

What does the saturation overland flow depend on?

A

Rainfall amount

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22
Q

What increases in both Horton Overland Flow and Saturation overland flow?

A

Damage increase with gradient

23
Q

What are the four major styles of mass wasting?

A

1/ Fall
2/ Slide
3/ Flow
4/ Creep

24
Q

Where are rock falls most common?

A

Arid and semi-arid lands
and along shorelines

25
Q

What can trigger rock falls?

A

Earthquakes

26
Q

Factors of a rock fall?

A

Rapid and observable

27
Q

What happened on Monday 7th Jan 2020?

A

5.8 magnitude earthquake destroying Punta Ventana
Puerto Rico

28
Q

What is rock fall?

A

Downward motion of rock or soil through the air

29
Q

On what kind of slope does rock fall occur?

A

Very steep faces or cliffs

30
Q

What is slide/ slumps?

A

Slipping of coherent roc or soil units often with a backwards rotation

31
Q

What happened to the A625?

A

Large parts were removed during a large landslide in 1977 (following the dry summer of 1976 and heavy rain in the winter of 1976/77) the road developed large steps in the carriageway. The road finally closed in 1979

32
Q

What are debris flows?

A
  • Slow to the very rapid flow
  • Saturated soil & rock debris down distinct channels
  • Typically coarse-grained materials
  • Lots of internal deformation
  • Relatively high water content/ fluid-like flow
  • Failure typically along a well-defined shear plane at the soil-bedrock interface.
33
Q

Where does water-logged material moving slowly typically occur?

A

Fine-grained soil or rock

34
Q

What can bedrock slides limit?

A

The relief of mountain ranges

35
Q

What happened to Mt. Cook, New Zealand?

A

Top 10 meters of summit fell away in a massive debris avalanche on December 14, 1991

36
Q

What does soil creep impact?

A

Whole soil mass rather than individual grains

37
Q

What is soil creep?

A

Continuous gravity driven process with no discrete boundaries

38
Q

What is soil creep?

A

The continuous gravity-driven process with no discrete boundaries

39
Q

What is soil creep caused by?

A
  • Seasonal processes such as thermal- or moisture-driven expansion/contraction
  • Bioturbation
40
Q

What is bioturbation?

A

The disturbance of the mixing of sediment by living organisms

41
Q

What is solifluction?

A

A type of creep particularly associated with periglacial conditions and freeze-thaw cycles
- Faster than most other forms of creep

42
Q

What is stress?

A

The force acting over a cross-sectional area within a solid or liquid

43
Q

What is normal stress?

A

Force acting perpendicular to the principle plane within a mass

44
Q

What is shear stress

A

The force acts perpendicular to normal stress = slippage

45
Q

What happens if the two stress exceed the strength or resistance of the slope material?

A

slope failure

46
Q

What factors influence the balance between stress and strength?

A

Angle of the slope, cohesion of the materials, presence of water, and geological characteristics

47
Q

When do failures occur?

A

When the gravitational force exceeds the resistance offered by the slope materials, causing movement and deformation

48
Q

What is the role of water?

A

Adds weight to the slope: air in pore space is replaced by water

49
Q

How does water impact the angle of repose>

A
  • Low amounts of water causes cohesion
  • Saturation causes buoyancy, reduction N and thus friction
  • Over pressuring can cause liquefaction
  • Angle of repose maximal with least water
  • Angle of repose strongly reduced
  • Generally initiated by shock
50
Q

What is the role of vegetation on a slope?

A
  • Plant roots, trees in particular, substantially increase slope strength, reducing shallow slides and slumps
    Planting is an effective tool in slope stabilisation
51
Q

What are the triggers for failure

A
  • Shocks eg earthquakes
  • Slope modification (removal of vegetation)
  • Undercutting
  • Changes in hydrology
  • Volcanic eruptions
52
Q

How can earthquakes impact slopes?

A
  • They have destructive potential
    A secondary effect of earthquakes
53
Q

What happened on 12th January 2001 in El Salvador?

A

Las Colinas slide claimed the lives of more than 500 people

54
Q

What happened in the Regolith landslides?

A

The upper layer of soil slipped due to heavy rainfall
Striking Manawatu, New Zealand In Feb 2004
Compared to the area of steep pasture with the scrub-covered gullies (upper right), where protective vegetation reduced the number of slips

ENVS165 - Theory and Laboratory Experiments in Earth Surfaces Processes (6 decks)

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