Slopes and Mass Wasting 2 Flashcards
(29 cards)
The Varnes classification of slope movements classifies them based on 3 things:
- rate of movement
- implied water content
- morphology of resulting debris and failure planes
List the 6 main types of slope movements:
- fall
- topple
- rotational slide
- translational slide
- flow
- slope deformation
flows tend to have ___ water content, which ___ shear strength
higher water= decreases shear strength
T/F (each sentence)
- flows behave like fluids
- deformation in flows is usually reversible
- in flows, there is movement throughout the whole falling body, not just along a discrete plane
- usually, there is only one big fall when something fails
- true
- false- flow deformation is IRREVERSIBLE
- true
- false, usually there are some small initial falls, then the whole thing might fall
falls=
what commonly causes them?
= rapid dropping or rolling through the air
common due to structural controls and undercutting by rivers, waves, or human impacts
Topples=
Common where?
similar to falls, but the movement is focused along a hinge point
common where structures are oriented INTO the slope
Slides=
movement of large slabs/ blocks of material, moving along one or more failure planes
What’s a characteristic of slides that makes them easy to spot?
usually there are some largely intact surfaces remaining after the failure (eg a big block of intact vegetation)
Failure planes of slides could be along: (give 2-3 examples)
- lithological contacts
- a thin bed of weaker sediment (eg clay beds)
- structural feature like faults or joints
Crown cracks (ie “tension cracks”)=
form behind the scarp of a slide- indicate a possible slide in the future b/c it’s unstable
What feature divides the disturbed and undisturbed area of a glacier?
the toe
T/F
the foot of a slide generally displays a mix of slide and flow processes because there is less water down there
false
this does happen, because there is MORE water down there
In a translational slide, the failure plane is ___ to the surface
eg:
parallel
eg. active layer detachment slide
(think about the caramel chocolate: caramel= failure plane, so slides down the caramel)
In a rotational slide (or slump), the failure plane is ____.
What is a noticeable characteristic of these?
curved
- slope is steeper higher up, and then shallower lower down towards the foot/ toe
t/f
in flows, material flows downslope in an irreversible way (similar to a viscous fluid)
true
t/f
flows cannot occur in dried materials
false!
they TYPICALLY involve water, but are also known in dried materials
Debris flows=
rapid moving mass of debris, rock, sand, vegetation, air, water, etc that are able to keep flowing, even at low gradients
debris flows are commonly initiated in ___ (steeper/ shallower) terrain –> eroded debris gets added to the mass –> deposition in a ____ runout zone
steeper
shallower runout zone (quite shallow, because they can keep flowing at very low gradients)
Levees=
raised ridges of coarse debris along the margins of debris flow paths (left behind by debris flows)
T/F
debris flows can have coarser, big boulders on top of finer sediment
true! even though this is not typical of physics
Quick-clay failures=
flows/ slides of disturbed glaciomarine clays (which were deposited when sea level was locally higher during the last glaciation/ deglaciation)
Where in Canada are quick-clay failures very common?
Quebec!
eg. deposits of the Champlain sea
also norway
Explain the role of water content and cations in quick-clay failures
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
Rock avalanche=
very rapid, very large flow-like motion of fragmented rock
