Slopes and Mass Wasting 2

Question 1

The Varnes classification of slope movements classifies them based on 3 things:

Answer 1

1. rate of movement
2. implied water content
3. morphology of resulting debris and failure planes

Question 2

List the 6 main types of slope movements:

Answer 2

1. fall
2. topple
3. rotational slide
4. translational slide
5. flow
6. slope deformation

Question 3

flows tend to have ___ water content, which ___ shear strength

Answer 3

higher water= decreases shear strength

Question 4

T/F (each sentence)

1. flows behave like fluids
2. deformation in flows is usually reversible
3. in flows, there is movement throughout the whole falling body, not just along a discrete plane
4. usually, there is only one big fall when something fails

Answer 4

1. true
2. false- flow deformation is IRREVERSIBLE
3. true
4. false, usually there are some small initial falls, then the whole thing might fall

Question 5

falls=

what commonly causes them?

Answer 5

= rapid dropping or rolling through the air

common due to structural controls and undercutting by rivers, waves, or human impacts

Question 6

Topples=

Common where?

Answer 6

similar to falls, but the movement is focused along a hinge point

common where structures are oriented INTO the slope

Question 7

Slides=

Answer 7

movement of large slabs/ blocks of material, moving along one or more failure planes

Question 8

What’s a characteristic of slides that makes them easy to spot?

Answer 8

usually there are some largely intact surfaces remaining after the failure (eg a big block of intact vegetation)

Question 9

Failure planes of slides could be along: (give 2-3 examples)

Answer 9

• lithological contacts
• a thin bed of weaker sediment (eg clay beds)
• structural feature like faults or joints

Question 10

Crown cracks (ie “tension cracks”)=

Answer 10

form behind the scarp of a slide- indicate a possible slide in the future b/c it’s unstable

Question 11

What feature divides the disturbed and undisturbed area of a glacier?

Answer 11

the toe

Question 12

T/F
the foot of a slide generally displays a mix of slide and flow processes because there is less water down there

Answer 12

false

this does happen, because there is MORE water down there

Question 13

In a translational slide, the failure plane is ___ to the surface
eg:

Answer 13

parallel

eg. active layer detachment slide

(think about the caramel chocolate: caramel= failure plane, so slides down the caramel)

Question 14

In a rotational slide (or slump), the failure plane is ____.
What is a noticeable characteristic of these?

Answer 14

curved

• slope is steeper higher up, and then shallower lower down towards the foot/ toe

Question 15

t/f
in flows, material flows downslope in an irreversible way (similar to a viscous fluid)

Answer 15

true

Question 16

t/f
flows cannot occur in dried materials

Answer 16

false!

they TYPICALLY involve water, but are also known in dried materials

Question 17

Debris flows=

Answer 17

rapid moving mass of debris, rock, sand, vegetation, air, water, etc that are able to keep flowing, even at low gradients

Question 18

debris flows are commonly initiated in ___ (steeper/ shallower) terrain –> eroded debris gets added to the mass –> deposition in a ____ runout zone

Answer 18

steeper

shallower runout zone (quite shallow, because they can keep flowing at very low gradients)

Question 19

Levees=

Answer 19

raised ridges of coarse debris along the margins of debris flow paths (left behind by debris flows)

Question 20

T/F
debris flows can have coarser, big boulders on top of finer sediment

Answer 20

true! even though this is not typical of physics

Question 21

Quick-clay failures=

Answer 21

flows/ slides of disturbed glaciomarine clays (which were deposited when sea level was locally higher during the last glaciation/ deglaciation)

Question 22

Where in Canada are quick-clay failures very common?

Answer 22

Quebec!
eg. deposits of the Champlain sea
also norway

Question 23

Explain the role of water content and cations in quick-clay failures

Answer 23

these can have very high water content

• salts (cations) can increase cohesion but can be liable to fail due to the leaching of salts or land disturbance

Question 24

Rock avalanche=

Answer 24

very rapid, very large flow-like motion of fragmented rock

Question 25

why can rock avalanches move like a flow?

Answer 25

sometimes there is water added by glacier ice or snow
- lots of air in there= allows it to move quickly

Question 26

What impact did the rock avalanche have on the Mt. St. Helens eruption?

Answer 26

earthquake –> caused a rock avalanche which removed 1/3 of the mountain and decompressed the magma body
= the eruption was huge and was able to blast out the side

Question 27

Why might there be so much mass wasting in Canada?

Answer 27

There were glaciers here not long ago! Our slopes are still adjusting to the loss of ice (post glacial conditions)

Question 28

what is the approx cost of mass movements in canada per year?

Answer 28

about $1 billion! and many deaths