Mass wasting Flashcards
Define weathering
Chemical and physical processes that produce soils, clays, sediments, and dissolved substances
Define erosion
removal and transport of particles produced by weathering from their source by wind, water, ice
Define mass wasting
movement of earth materials down a slope due to gravitational force
Mass wasting is influenced by three primary factors
material characteristics
water content
slope steepness
Define what material characteristics, water content, and slope steepness describe
Material characteristics: slopes may be composed of unconsolidated (regolith) or unconsolidated materials
Water content: affected by precipitation and material porosity
Slope steepness: influences how materials move under various climates
Out of the 3 factors of mass wasting, which ones are more strongly influenced by human activity
slope steepness and water content
Are consolidated or unconsolidated materials stronger
consolidated
Define angle of repose
Maximum angle of unconsolidated materials
The angle of repose is greater for ________ and less _______ materials
courser and less rounded materials
Does fine sand or angular pebbles assume a shallower angle of repose
fine sand
particles dropped in a pile create an angle of repose based on their ______ and ______
size and angularity
unconsolidated sand and silt have what for a maximum angle of repose
35 degrees
steeper slopes will collapse
unconsolidated materials include what kind of materials
sand, silt, clay, soil, and rock fragments
They can moderate to steep slopes
What are types of consolidated materials
rock, lithified sediments, vegetated soils, and cohesive particles
they often form more stable slopes
Mass movement of consolidated materials are usually linked to increasing _______ _______
water content
Does water content affect the stability of consolidated and unconsolidated material
sure does
Why do saturated materials lose strength
water reduces frictional forces between particles
What happens if water content increases enough to allow materials to flow as a fluid
liquefaction
List these from most cohesive to least: dry sand, damp sand, water-saturated sand
Damp sand, dry sand, water-saturated sand
Describe the water content and unconsolidated sediment cohesion of damp sand
dampness binds sand particles so that they resist movement
Describe the water content and unconsolidated sediment cohesion of dry sand
dry particles are bound only by their size and friction with one another
Describe the water content and unconsolidated sediment cohesion of water-saturated sand
saturated particles are separated by water, which keeps the grains apart and also acts as a lubricant, allowing them to flow
Surface tension: Water molecules in a liquids interior are _________ in all directions. Surface molecules have a net _______ attraction that results in surface tension allowing objects to _______.
attracted
inward
float
Stability of slopes depend on
physical characteristics of soil, rock and other slope materials, including water.
Component of gravitational force parallel to slope(shear force) ___________ with slope steepness
increases
If shear ______ exceeds sheer _______, slopes can fail
force
Strength
Shear strength is a _________ force to moving downslope
Shear force is a _________ force to moving downslope
frictional
gravitational
So frictional reduces the movement downslope, and gravitational wants to move down the slope
What are the 4 natural processes that cause mass wasting
earthquakes, rainfall, chemical/mineralogical changes, frost wedging/thawing
What are 4 human activities that cause mass wasting
adding weight, slope steepening, increasing moisture, and removing vegetation
What are the 3 characteristics used to classify mass movements
type of material that fails
Rate of movement
mechanism of failure
Are all mass movements landslides
no
Define a creep
A gradual downslope movement of soil or regolith
When and where do terracettes form
they form during a soil creep and are typically combined with a freeze-thaw cycle or cycles of soil saturation and drying
Define solifluction
Freeze-thaw activity generated mass movement
thawed water saturated soil flows over frozen layer underneath
What does solifluction typically form
lobes and sheets on slopes
Define a curved rupture surface shape and where we would see it
rotational slope failure
slump
define a flat rupture surface and where we would see it
translational slope failure
rock slide
What kind of mass movement forms stair step pattern of displaced blocks and hummocky ridges near the toe
slumping
Why do slump occurs
erosion or undercutting at base of slope
define slumping
concave and cliff-like scarp ( steep slope)
block moves coherently along the failure plane
Rock slides occurs when
frost wedging has loosened jointed bedrock layers which move downhill as a unit
rock fall occurs when
ice wedging often breaks rocks along joints, preparing them to loosen and fall away
Which mass wasting event is it when individual blocks free-fall down a slope
rock fall
What is the type of material, rate of movement and mechanism of a rock fall?
rock
fast
fall
What are the characteristics and processes of a mud flow
characteristics: water permeable soil and water impermeable rocks
Process: Rain has soaked fine grained permeable rocks which loosen quickly and flow downhill over impermeable rocks at moderate speeds
The 2014 Oso landslide was what kind of mass movement
mud flow
4 reasons why some areas are particularly prone to mass wasting
Steep mountainous terrains, high precipitation, abundance of unconsolidated glacial sediments,
geographic position
What is the type of material, type of motion and rate of motion for rock fall
rock fragments
vertical or near vertical fall
very fast
What is the type of material, type of motion and rate of motion for rock slide
a large rock body
translational sliding
typically very slow, sometimes can be fast
What is the type of material, type of motion and rate of motion for creep or solifluction
soil or soil mixed with ice
flow
very slow
What is the type of material, type of motion and rate of motion for slump
thick deposits of unconsolidated sediment
rotational sliding
slow
What is the type of material, type of motion and rate of motion for mudflow
loose sediments with a significant component of silt and clay
flow
moderate to fast
What is the type of material, type of motion and rate of motion for debris flow
sand, gravel, and larger fragments
flow
fast
What is the largest recorded slide in Canadian history
The Hope slide
What is the deadliest slide in Canadian history
The Frank Slide
Why did the Frank slide happen
folded sedimentary rock with vertical joints and bedding planes
weathering, erosion decreased rock strength
What type of slide was the saint-Jude slide
clay - quickclay
It took the house down because the surface underneath became like quicksand
How does quick clay come to be
Groundwater flowing though the clay removes ions left behind by the seawater, this makes the clay weaker over time
leda (quick) clay slides, describe why liquefaction and slides occur
glaciomarine clays: deposited in sea
water. The clay deposits contain up
to 80% water, held together by
surface tension.
* Clays lose shear strength due to
long-term fresh water flushing that
removes ions in the clay
liquefaction and slides can occur due to high rainfall or seismic events
What are ways we can prevent mass wasting
vegetation (stabilizes slope and improves slope stability of slope for water run-off)
Regrading slopes (fill and cut)
Preventing undercutting (placing riprap to prevent erosion at base of slope)
Decrease weight on slope
decrease water infiltration (directing runoff using drainage)
rock bolts, netting, water drainage
frequent monitoring and inspection
