landslides

Question 1

what is mass wasting?

Answer 1

movement of earth material down slope under influence of gravity

Question 2

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

Answer 2

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

Question 3

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

Answer 3

rock avalanche

Question 4

why / how do mass movements occur?

Answer 4

gravity, shear force, and normal force

Question 5

what is shear force?

Answer 5

one pulling the block down parallel to the slope

Question 6

what is normal force

Answer 6

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

Question 7

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

Answer 7

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.

Question 8

mass movements are classified based on several characteristics

Answer 8

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

Question 9

what are the common systems for classification of landslides?

Answer 9

cruden and varnes

Question 10

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

Answer 10

falls
flows
lateral speeds
topples
slides
complex

Question 11

what is a fall as stated by cruden and varnes?

Answer 11

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

Question 12

what is a flow as stated by cruden and varnes?

Answer 12

viscous fluid movement, range from slow to fast

Question 13

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

Answer 13

lateral movement of the ground, usually accompanied by subsidence

Question 14

what is a topple as stated by cruden and varnes?

Answer 14

rapid rotation of a mass about a point

Question 15

what is a slide as stated by cruden and varnes?

Answer 15

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

Question 16

what is a complex as stated by cruden and varnes?

Answer 16

2+ types

Question 17

what is a translational landslide?

Answer 17

can contain loose sediments or large slabs of bedrock

Question 18

what is a rotational (slump) landslide

Answer 18

landslides that occur along a curved or spoon-shaped surface

Question 19

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

Answer 19

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

Question 20

how do rock avalanches form?

Answer 20

triggered by an earthquake, a large quantities of material flow

Question 21

how fast can rock avalanches move?

Answer 21

velocities of hundreds of km/hr

Question 22

what happened at Mount Huascan in Peru?

Answer 22

rock and snow / glacial ice avalanche

Question 23

what is the difference between a rockfall and debris avalanche?

Answer 23

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)

Question 24

what is a soil creep?

Answer 24

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

Question 25

what is regolith (soil creep)?

Answer 25

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

Question 26

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

Answer 26

freeze-thaw dry-wet

Question 27

what are two hallmarks of a soil creep?

Answer 27

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

Question 28

what is solifluction?

Answer 28

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

Question 29

at what place do fractures commonly develop?

Answer 29

fold hinges

Question 30

what is the air cushion model?

Answer 30

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

Question 31

mega landslides that occur underwater create?

Answer 31

mega tsunamis

Question 32

how can we prevent landslides?

Answer 32

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 3. other stabilizing techniques, like support walls, rock bolts, driving tunnels, chain-link fence over rocks by road

Question 33

how do water forces on soil affect slopes?

Answer 33

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