Slopes

Question 1

What is Hillslope?

Answer 1

The elevated land between valley bottoms

Question 2

What are hillslope processes?

Answer 2

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

Question 3

Characteristics of bedrock slopes?

Answer 3

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

Question 4

Characteristics of soil-mantled slopes?

Answer 4

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

Question 5

What are bedrock hillslopes?

Answer 5

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

Question 6

Where are bedrock hillslopes found?

Answer 6

Arid climates
Common in humid areas with low weathering rates

Question 7

What are the processes of bedrock hillslopes?

Answer 7

• Falls and slides

Question 8

What are the physical characteristics of bedrock hillslopes?

Answer 8

Parallel retreat at threshold angles

Question 9

What are soil-mantled hillslopes?

Answer 9

Transport-limited
With thick soil mantle

Question 10

Where are soil-mantled hillslopes found?

Answer 10

Humid climates

Question 11

What are processes of soil-mantled hillslopes?

Answer 11

Soil creep and slides

Question 12

what are the physical characteristics of soil-mantled slopes?

Answer 12

Convex profiles
Typically parabolic

Question 13

What does surface erosion impact?

Answer 13

Individual grains, detached separately and transported over the slope surface

Question 14

What are some examples of surface erosion?

Answer 14

• Rain-splash
• Overland flow
• Rills
• Gully
• Reactivated ancient gullies

Question 15

What are the types of overland flow?

Answer 15

Horton Overland flow
Slope foot saturation - termed saturation overland flow

Question 16

What is the Horton Overland Flow?

Answer 16

Rainfall rate excess of infiltration capacity

Question 17

What is overland flow?

Answer 17

Water flowing over the soil surface

Question 18

What infiltration rate?

Answer 18

The rate that’s actually taking place

Question 19

What is the infiltration capacity?

Answer 19

A hypothetical maximum rate

Question 20

What does the Horton Overland Flow depend on?

Answer 20

Rainfall rate and surface

Question 21

What does the saturation overland flow depend on?

Answer 21

Rainfall amount

Question 22

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

Answer 22

Damage increase with gradient

Question 23

What are the four major styles of mass wasting?

Answer 23

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

Question 24

Where are rock falls most common?

Answer 24

Arid and semi-arid lands
and along shorelines

Question 25

What can trigger rock falls?

Answer 25

Earthquakes

Question 26

Factors of a rock fall?

Answer 26

Rapid and observable

Question 27

What happened on Monday 7th Jan 2020?

Answer 27

5.8 magnitude earthquake destroying Punta Ventana Puerto Rico

Question 28

What is rock fall?

Answer 28

Downward motion of rock or soil through the air

Question 29

On what kind of slope does rock fall occur?

Answer 29

Very steep faces or cliffs

Question 30

What is slide/ slumps?

Answer 30

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

Question 31

What happened to the A625?

Answer 31

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

Question 32

What are debris flows?

Answer 32

- 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.

Question 33

Where does water-logged material moving slowly typically occur?

Answer 33

Fine-grained soil or rock

Question 34

What can bedrock slides limit?

Answer 34

The relief of mountain ranges

Question 35

What happened to Mt. Cook, New Zealand?

Answer 35

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

Question 36

What does soil creep impact?

Answer 36

Whole soil mass rather than individual grains

Question 37

What is soil creep?

Answer 37

Continuous gravity driven process with no discrete boundaries

Question 38

What is soil creep?

Answer 38

The continuous gravity-driven process with no discrete boundaries

Question 39

What is soil creep caused by?

Answer 39

- Seasonal processes such as thermal- or moisture-driven expansion/contraction - Bioturbation

Question 40

What is bioturbation?

Answer 40

The disturbance of the mixing of sediment by living organisms

Question 41

What is solifluction?

Answer 41

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

Question 42

What is stress?

Answer 42

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

Question 43

What is normal stress?

Answer 43

Force acting perpendicular to the principle plane within a mass

Question 44

What is shear stress

Answer 44

The force acts perpendicular to normal stress = slippage

Question 45

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

Answer 45

slope failure

Question 46

What factors influence the balance between stress and strength?

Answer 46

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

Question 47

When do failures occur?

Answer 47

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

Question 48

What is the role of water?

Answer 48

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

Question 49

How does water impact the angle of repose>

Answer 49

- 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

Question 50

What is the role of vegetation on a slope?

Answer 50

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

Question 51

What are the triggers for failure

Answer 51

- Shocks eg earthquakes - Slope modification (removal of vegetation) - Undercutting - Changes in hydrology - Volcanic eruptions

Question 52

How can earthquakes impact slopes?

Answer 52

- They have destructive potential A secondary effect of earthquakes

Question 53

What happened on 12th January 2001 in El Salvador?

Answer 53

Las Colinas slide claimed the lives of more than 500 people

Question 54

What happened in the Regolith landslides?

Answer 54

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