Landslides Flashcards
What are ‘translational’ slides?
Rapid translational movement of a relatively coherent mass of rock or sediments along well-defined inclined surfaces
What are ‘rotational’ slides or slumps?
rotate along curved interfaces
What forces govern slides?
gravity and shear stress along the interface
what forces govern falls?
gravity
what forces govern topples?
gravity
What is the most common landslide trigger?
heavy rain
What are common characteristics at the foot of a slide?
(where material has been deposited)
transverse ridges and radial cracks
Does the same source region of landslides periodically fail?
No
Are landslides an expression of a self-organised critical system?
What is the constant loading and
Yes (powerlaw behaviour with constant slope)
What scale is used in landslide hazard mapping?
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)
Name 4 factors that increase the driving force on a layer on a slope
- steepening topography (could be caused by tectonics, erosion or human activity)
- temporary earthquake shaking
- deposition of soil or rock increasing the mass of the potential slide
- addition of water
Name 2 things that can modify cohesion
water content and vegetation
What is ‘liquefaction’?
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
What is the Safety Factor (F) a ratio of?
resisting forces to active forces
where: resisting forces = tauarea
and: acting forces = mgsin(alpha)
For what values of F is the slope stable?
1 - 1.5 = marginally stable
>1.5 =stable
For what values of F is the slope unstable?
< 1
When is infinite slope analysis used?
for shallow slopes where the thickness of the potentially unstable layer is small relative to the length scale of the slope
What are ‘Distributed Physically-based Models’?
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
What are the advantages of ‘physically-based’ models?
based on underlying processes and can be improved as more data becomes available and can be used to model time-dependent hazard
What is the difference between slurry flows and granular flows with an example of each
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
What do high values of H/L indicate?
low mobility
What has the decrease of H/L with increased volume been linked to?
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
What is a good approximation for the cohesion of compacted sandy silt?
50kPa
Which impact parameter is best to describe fall impact?
KE
Which impact parameter is best to describe slide impact?
Velocity
Which impact parameter is best to describe flow impact?
Velocity and thickness
What are the potential secondary hazards of landslides?
Floods
Tsumamis
Dam building
Changes to coastal sedimentation
How to submarine landslides differ from subaerial?
Much larger
Up to 30,000km^3 as opposed to 100s km^3
Extremely common & widespread eg continental shelf
Why are submarine landslides a hazard?
Tsunami
Damage to pipelines
Damage to drilling platforms
