3.3. Slope processes and development Flashcards Preview

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Flashcards in 3.3. Slope processes and development Deck (23)
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1
Q

Define slopes

A

Refers to an inclined surface or hill slope. Generally, it is the area between a watershed (or drainage basin divide) and the base of the slope

2
Q

Define slope form

A

The shape of the slope in cross section

3
Q

Define slope evolution

A

Development of slopes over time

4
Q

Define slope processes

A

Activities acting on the slope

5
Q

Define regolith

A

The superficial and unconsolidated material found at the Earth’s surface. It includes soil, scree, weathered bedrock and deposited material

6
Q

Why is slope an open system?

A
  • Inputs to the system = Energy from the sun, mass (water and sediment)
  • Outputs from the system = Energy (re-radiated heat), and mass (water and regolith)
  • Some factors occur on the outside of the slope (exogenetic)
  • Some factors occur on the inside of the slope (endogenetic)
7
Q

Factors affecting slopes

A
  • Climate
  • Aspect, the direction it faces
  • Vegetation
  • Geology
  • Regolith and soil
8
Q

How does climate affect slope?

A
  • Humid areas - slopes are rounder due to chemical weathering
  • Arid areas - slopes are more jagged due to more mechanical weathering
9
Q

How does geology affect slope?

A
  • Faults create lines of weaknesses and therefore instability in a slope can create steep valley sides
  • Rock types can affect slopes vulnerability to weathering
  • Vulcanicity can cause igneous intrusions (batholiths) which when exposed can create steep slopes
10
Q

How does regolith and soil affect slope?

A
  • Deep regolith can mean slope instability
  • Regolith with high % of sand can cause slope failures
11
Q

How does aspect affect slope?

A
  • In northern hemisphere: North facing slopes receive very little heat from the sun in mid winter. Conversely, south facing slopes receive much more heat. Therefore, a north facing slopes will usually develop a dramatically different snowpack than a south facing slope.
  • In southern hemisphere: South facing slopes tend to be warmer and often develop thin ice crusts. Because these crusts tend to grow weak layers around them from near-surface faceting
12
Q

How does vegetation affect slope?

A
  • Vegetation can decrease overland runoff and reduce erosion or binds the soil together
  • However, biological weathering can occur, deepening regolith and increase slope failure
13
Q

Define mass movement

A

Any large scale movement of the earth’s surface that are not accompanied by a moving agent such as a river, glacier, or ocean wave

14
Q

Why does mass movement occur?

A

Due to slope failure, when gravity acts to move the material downwards and the resistance of the slope is not strong enough

15
Q

2 factors that cause slope failure

A
  • A reduction in shear strength
  • An increase in shear stress
16
Q

Factors increasing shear stress

A
  • Removal of lateral support through undercutting or slope steepening - erosion by rivers, wave action, faulting
  • Removal of underlying support - undercutting by waves
  • Loading of slope - weight of water, vegetation and accumulation of debris
  • Lateral pressure - water in cracks, pressure release
  • Transient stress - earthquakes
17
Q

Factors reducing shear strength

A
  • Weathering
  • Change in pore water pressure - saturation, softening of material
  • Changes of structure - creation of cracks
  • Organic effects - burrowing of animals, decay of tree roots
18
Q

What are the types of mass movements?

A
  • Flow
  • Slide
  • Falls
  • Slumps
  • Avalanches
19
Q

Define heave and how does it occur?

A
  • Heaves/creeps are slow movements of materials up to the surface of the slope and down slopes
  • Very slow and small scale process.
  • Occurs mainly in winter
  • Individual soil particles are pushed to the surface by wetting, heating or freezing of water
20
Q

Define flows and how does it occur?

A
  • Are movements of a mass of a soil or rock that contain significant amount of water
  • Slumps occur on weaker rocks , especially clay.
  • This is often rotational along a curved slip plane
  • Clay absorbs water and becomes saturated and exceeds its liquid limit
  • It then flows along a slip plane.
  • This can be due to the undercutting at the base of a cliff
21
Q

Define slides and how does it occur?

A
  • Are an entire mass of material moving along the slip plane
  • They occur where there is a combination of weak rocks, and steep slope and undercutting
  • As the slide moves along the slip plane, it tends to retain its shape and structure until it hits the bottom of the slope
  • Slip planes occur at fault lines, along a bedding plane and at the junction of two layers
  • Rock slides are when a huge volume of rock moves together
  • Landslides include rock, stones and soil
22
Q

Define falls and how does it occur?

A
  • Are movements of rock/debris under the effect of gravity
  • Falls occur on steep slopes (greater than 700)
  • On bare rock faces where joints are exposed they are more common
  • Normally caused by weathering, and once the rocks are detached they fall under the influence of gravity.
  • If the fall is short it produces straight scree, if it is long it forms a concave slope
23
Q

Define avalanch and how does it occur?

A
  • Avalanches are rapid movements of snow down a slope
  • They are common in mountainous areas
  • New snow can fall of older snow ( a dry avalanche)
  • Or partially melted snow moves ( a wet avalanche)
  • They occur most frequently on slopes over 22o
  • They also occur on north facing slopes where the lack of snow limits snow stability (doesn’t have time to cohese with partial melting)