Oct 14 Lecture: Mass Wasting

Question 1

mass wasting=

Answer 1

movement of earth material down slope via gravity

Question 2

mass wasting can occur in ____ materials or ___

Answer 2

unconsolidated (sediment/ soil/ debris)

consolidated (rocks)

Question 3

why do more landslides occur in wet season?

Answer 3

water acts as a lubricant, decreases friction, and adds weight

Question 4

describe the air cushion model

Answer 4

• compressed air trapped beneath the debris reduces friction b/w debris and the slip plane
• this air cushion allows even large boulders to travel great distances

Question 5

types of mass movements are characterized by: (3)

Answer 5

• material
• nature of movement
• speed of the movement

Question 6

what are the 11 types of mass movements

Answer 6

1. rock falls
2. rockslide
3. rock avalanche
4. soil creep
5. earth flow
6. debris flow
7. mudflow
8. debris avalanche
9. slump
10. debris slide
11. solifluction

Question 7

rockfalls

Answer 7

• steep slopes
• newly detached blocks plummet in free-fall from a steep cliffside
• evidence= talus/ colluvium

Question 8

talus/ colluvium =

Answer 8

rocky accumulations at the bottom of a cliff

- evidence of a rockfall

Question 9

rockslide

Answer 9

gently sloping weak planes

- rocks don’t fall freely, but slide down the slope

Question 10

anatomy of a landslide:

Answer 10

1. zone of depletion (scarp): at top
2. zone of accumulation: middle/ bottom
3. toe: very bottom (looks like toes)

Question 11

rock avalanche

Answer 11

• large quantities of material flow (not slide or fall)

- typically triggered by EQ, can travel at 100s of km/hr

Question 12

in a rock avalanche, the ___ __ b/w rocks allows them to move very fast

Answer 12

compressed air
(keeps the rocks apart= less friction)

Question 13

soil creep=

Answer 13

slowest, unconsolidated mass movement

• regolith occurs
• slower moving= can contain more volume

Question 14

2 mechanisms of soil creep

Answer 14

1. freeze (expand)- thaw cycle

2. dry-wet cycle

Question 15

regolith =

Answer 15

very slow deformation of surface debris- the upper layers move down the slope faster than those underneath
- soil creep

Question 16

3 hallmarks of soil creep

Answer 16

1. bent tree trunks
2. bent rock layers
   - fence zigzagging

Question 17

T/F

soil creep is never a hazard because it is so slow

Answer 17

false

can still be a hazard to water/ gas lines, telephone poles, etc

Question 18

earth flow

Answer 18

fluid movements of fine grained materials (soils, weathered shale, clay)

Question 19

debris flow

Answer 19

• fluid movements of rock fragments supported by a muddy matrix

Question 20

mudflow

Answer 20

• flowing masses of material finer than sand + some rock debris w/ lots of water
• water= less resistance= moves very fast

Question 21

debris avalanche

Answer 21

• fast, downhill movement of soil, rocks, and trees
• typical in humid, mountainous regions
• fast (high water content, steep slopes)

Question 22

slump=

Answer 22

• slow slides of unconsolidated material that travels as a unit
• scarp usually forms at top
• creates “steps”

Question 23

debris slide=

Answer 23

• fast version of a slump

- debris move largely as a unit along planes of weakness (eg waterlogged clay zone)

Question 24

solifluction=

Answer 24

• occurs in cold climates: water in surface layer freezes/ thaws
• when the surface thaws, soil becomes waterlogged, but water cannot seep downwards
• so, saturated soil oozes downhill, carrying rocks/ debris with it

Question 25

what happened in the vajont dam disaster

Answer 25

massive amount of rock broke off the top of Monte Toc & fell into the Vajont dam, producing a tsunami-like wave. The wave overtopped the dam and rushed downstream, destroying villages

Question 26

Explain the events of the Frank Slide

Answer 26

in Frank, Alberta

• rockslide buried the coal mine (people in the mine survived, people above ground died)
• caused by collapse of the unstable turtle mtn face

Question 27

fold hinge fractures=

Answer 27

fractures commonly develop in rock @ fold hinges

• fractures oriented roughly perpendicular to the rock layering
• can allow ground water etc in, makes more unstable