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Geohazards > Landslides > Flashcards

Landslides Flashcards

1
Q

What are ‘translational’ slides?

A

Rapid translational movement of a relatively coherent mass of rock or sediments along well-defined inclined surfaces

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2
Q

What are ‘rotational’ slides or slumps?

A

rotate along curved interfaces

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3
Q

What forces govern slides?

A

gravity and shear stress along the interface

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4
Q

what forces govern falls?

A

gravity

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5
Q

what forces govern topples?

A

gravity

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6
Q

What is the most common landslide trigger?

A

heavy rain

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7
Q

What are common characteristics at the foot of a slide?

A

(where material has been deposited)

transverse ridges and radial cracks

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8
Q

Does the same source region of landslides periodically fail?

A

No

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9
Q

Are landslides an expression of a self-organised critical system?
What is the constant loading and

A

Yes (powerlaw behaviour with constant slope)

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10
Q

What scale is used in landslide hazard mapping?

A

a scale of landslide intensity that takes into account different landslide styles. (Intensities should give a measure of the consequences that correlate with the resulting damage)

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11
Q

Name 4 factors that increase the driving force on a layer on a slope

A
  1. steepening topography (could be caused by tectonics, erosion or human activity)
  2. temporary earthquake shaking
  3. deposition of soil or rock increasing the mass of the potential slide
  4. addition of water
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12
Q

Name 2 things that can modify cohesion

A

water content and vegetation

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13
Q

What is ‘liquefaction’?

A

loosely packed sands and soils can when saturated lose all coherency leading to a sudden transition from behaviour as a solid (grains touch) to behaviour as a liquid

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14
Q

What is the Safety Factor (F) a ratio of?

A

resisting forces to active forces

where: resisting forces = tauarea
and: acting forces = mgsin(alpha)

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15
Q

For what values of F is the slope stable?

A

1 - 1.5 = marginally stable

>1.5 =stable

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16
Q

For what values of F is the slope unstable?

A

< 1

17
Q

When is infinite slope analysis used?

A

for shallow slopes where the thickness of the potentially unstable layer is small relative to the length scale of the slope

18
Q

What are ‘Distributed Physically-based Models’?

A

models that use a combination of landslide physics and empirical relations to describe stability of a region rather than just a single slope or site

19
Q

What are the advantages of ‘physically-based’ models?

A

based on underlying processes and can be improved as more data becomes available and can be used to model time-dependent hazard

20
Q

What is the difference between slurry flows and granular flows with an example of each

A

slurry flow- water controls internal resistance (saturated) and contain 20-40% water e.g mudslide

granular flow- unsaturated, interaction between the rocks and soil fragments in the flow is important e.g a debris avalanche

21
Q

What do high values of H/L indicate?

A

low mobility

22
Q

What has the decrease of H/L with increased volume been linked to?

A

The fact that slides and flows travel from regions of steep to less steep topography, so that as L increases, H/L on average will decrease as well.
(?) Problem sheet 5- 1a

23
Q

What is a good approximation for the cohesion of compacted sandy silt?

A

50kPa

24
Q

Which impact parameter is best to describe fall impact?

A

KE

25
Q

Which impact parameter is best to describe slide impact?

A

Velocity

26
Q

Which impact parameter is best to describe flow impact?

A

Velocity and thickness

27
Q

What are the potential secondary hazards of landslides?

A

Floods
Tsumamis
Dam building
Changes to coastal sedimentation

28
Q

How to submarine landslides differ from subaerial?

A

Much larger
Up to 30,000km^3 as opposed to 100s km^3
Extremely common & widespread eg continental shelf

29
Q

Why are submarine landslides a hazard?

A

Tsunami
Damage to pipelines
Damage to drilling platforms

Geohazards (4 decks)

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