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EAS 205 > landslides > Flashcards

landslides Flashcards

1
Q

what is mass wasting?

A

movement of earth material down slope under influence of gravity

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2
Q

mass wasting can involve unconsolidated material or consolidated material; what are they and give an example of each

A

unconsolidated: loosely arranged or unstratified, whose particles are not cemented together
ex. sediment / soil

consolidated: materials of sufficient hardness or ability to resist weathering / erosion
unconsolidated
ex. rocks

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3
Q

what type of landslide occurred in Hope, BC on January 9th

A

rock avalanche

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4
Q

why / how do mass movements occur?

A

gravity, shear force, and normal force

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5
Q

what is shear force?

A

one pulling the block down parallel to the slope

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6
Q

what is normal force

A

pulling the block directly into (i.e., perpendicular) to the slope

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7
Q

how do shear and normal force work together to cause a landslide?

A

The shear force pulls the block down the slope, but the block doesn’t move unless the shear force overcomes the strength of the bond between the block and the slope.

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8
Q

mass movements are classified based on several characteristics

A

nature of material
nature of movement
speed of movement (1mm/year to 5m/sec)

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9
Q

what are the common systems for classification of landslides?

A

cruden and varnes

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10
Q

what are the types of landslides as classified by cruden and varnes?

A

falls
flows
lateral speeds
topples
slides
complex

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11
Q

what is a fall as stated by cruden and varnes?

A

rapid, free fall, rolling, bouncing, metres/min to metres/sec

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12
Q

what is a flow as stated by cruden and varnes?

A

viscous fluid movement, range from slow to fast

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13
Q

what is a lateral speed as stated by cruden and varnes?

A

lateral movement of the ground, usually accompanied by subsidence

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14
Q

what is a topple as stated by cruden and varnes?

A

rapid rotation of a mass about a point

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15
Q

what is a slide as stated by cruden and varnes?

A

movement of large slabs / blocks / consolidated material along one or more distinct surfaces
- rotational
- translational

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16
Q

what is a complex as stated by cruden and varnes?

A

2+ types

17
Q

what is a translational landslide?

A

can contain loose sediments or large slabs of bedrock

18
Q

what is a rotational (slump) landslide

A

landslides that occur along a curved or spoon-shaped surface

19
Q

how are ways we have further weakened the slope to cause a landslide?

A
  1. coal mining
  2. dump garbage into cracks formed by slope failure (adds weight)
  3. constructing structures at crest (adds weight)
  4. building storm sewers that discharge water onto the slope
20
Q

how do rock avalanches form?

A

triggered by an earthquake, a large quantities of material flow

21
Q

how fast can rock avalanches move?

A

velocities of hundreds of km/hr

22
Q

what happened at Mount Huascan in Peru?

A

rock and snow / glacial ice avalanche

23
Q

what is the difference between a rockfall and debris avalanche?

A

Rockfalls involve the detachment and freefall, bouncing, or rolling of individual blocks of rock from a cliff face (loose boulders roll down due to low gravity)

debris avalanche is a rapid and turbulent flow of a large mass of debris mixed with water and air. Its movement is more fluid-like and affects a larger area (great deal of loose surface material appears to have slid down toward lower elevations)

24
Q

what is a soil creep?

A

slowest unconsolidated mass movement (1 - 10mm.yr)

25
Q

what is regolith (soil creep)?

A

a very slow deformation of the surface debris where upper layers move down the slope faster

26
Q

the mechanism of creep can follow two cycles, these are?

A

freeze-thaw
dry-wet

27
Q

what are two hallmarks of a soil creep?

A
  1. bent tree trunks / rock layers / power poles / fences / gravestones
  2. building foundations / roads crack
28
Q

what is solifluction?

A

cold climates when water in the surface layers of the soil freeze and thaw; when surface thaws, soil becomes saturated and oozes downhill carrying rock and broken debris

29
Q

at what place do fractures commonly develop?

A

fold hinges

30
Q

what is the air cushion model?

A

compressed air trapped beneath the debris greatly reduces friction between the debris and slip plane. allows large boulder to travel great distances

31
Q

mega landslides that occur underwater create?

A

mega tsunamis

32
Q

how can we prevent landslides?

A
  1. reduce slope angle, place support at base, and reduce weight on slope
  2. build retention structures
  3. leave stabilizing vegetation
  4. decrease water / pore pressure of rock / soil
  5. other stabilizing techniques, like support walls, rock bolts, driving tunnels, chain-link fence over rocks by road
33
Q

how do water forces on soil affect slopes?

A

water fills voids and increase weight
exerts pore pressure to decrease stress and strength

EAS 205 (17 decks)

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