Module 6 Flashcards
Can You DIG IT?
distinguish between mechanical and chemical weathering
describe the factors that affect the shear strength of materials; link to weathering processes
define the Factor of Safety
define the term “mass movement”
distinguish between the various types of mass movement processes
identify on a map of Canada the locations of the most damaging landslides; relate these events to the nature of the surface materials
list the measures that can be undertaken to reduce landslide hazards
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Landslides are most susceptible In Canada where?
Least Ssuceptible in Canada?
Western Canada
Canadian Shield
Landslides are most susceptible In Canada where?
Least Ssuceptible in Canada?
Western Canada(sedimentary rock locations)
Canadian Shield
Weathering
2 types
weathering: processes at or near the Earth’s surface that result in the breakdown of exposed rocks to form regolith
driven by solar radiation: an exogenic process
- physical weathering: mechanical break-up of bedrock into small particles through the action of physical forces acting at or near Earth’s surface
- chemical weathering: chemical changes in rock-forming minerals in the presence of water
Weathering is a _______ process because it is driven by solar radiation
exogenic
Soil vs. Regolith
Soil supports plant life
regolith(dirt) does not
The most common rock type at the earths surface is
sedimentary rock 52%
The frequency of primary rock-forming minerals at the Earth`s surface.
2 most common:
- Feldspar - 30% Quartz - 28% (aluminosilicate minerals)
- Mica - 18% Pyroxene, Amphibole – 1% (ferromagnesian minerals)
Global Weathering Patterns are based on ______ and ______
describe Cold/dry climates, Midlatitudes, and Arctic
temperature and humidity
Cold/dry climates are dominated by mechanical weathering like frost shattering
Midlatitudes: abundance of moisture means promotion of chemical weathering and greater production of regolith, frost action in winter season
-deeper weathering profile
Arctic: mostly mechanical as there isn’t much moisture
-shallow weathering profile
Depth of Weathering Profile:
humid climates – ______
arid climates - _______
deep
shallow
effectiveness of physical weathering processes influenced by:3
rock structure – size and abundance of fractures; effective porosity and permeability
degree of saturation of pore space by fluids
frequency of freeze-thaw cycles, wet-dry cycles
hydration
hydration involves the adsorption of water into or onto the crystal structure of minerals
e. g., evaporite minerals, clay minerals, iron oxides
- expandable clays
Involves water but is still physical weathering because
- works best with evaporite minerals and hydroxides
- adsorption, hydrating minerals causing them to expand which is what makes it physical weathering
Why is hydration a physical weathering process?
Involves water but is still physical weathering because
- works best with evaporite minerals and hydroxides
- adsorption, hydrating minerals causing them to expand which is what makes it physical weathering
Effectiveness of chemical weathering processes affected by: 5
rock structure – size and abundance of fractures; effective porosity and permeability
rock composition – silicate vs. carbonate minerals
supply of water and carbon dioxide
degree of saturation of pore space by fluids
ambient temperatures
-when its colder rate of weathering decreases
CHEMICAL WEATHERING REQUIRES _______ CONTENT(at least as a medium)
water
Hydrolisis
in hydrolysis, H+ displaces metallic cations and silica, forming secondary clay minerals
silica combines with OH- to form soluble minerals
-silica released aids in lithification
Core stone(still being weatherd solid rocks) –> Sacrolite –> Regolith(all the small pieces around)
Carbonation
acidic surface waters penetrate carbonate rocks along fractures and bedding planes and dissolve the rock
carbonation, the dissolution of limestone (CaCO3)and dolomite (CaMg(CO3)2), creates karst landscapes
1.By dissolving carbon dioxide in water to make carbonic acid
2. Carbonic acid breaks down the limestone
.NO solid phase in this one
Other Notes:
- Bicarbonate: also can contribute to lithification and the creation of sedimentary rock
- Dolomite, because of magnesium content, would delay the second step of the chemical weathering
Karst Landscapes are created by ______
carbonation
Dolleens
Dolleens/sink holes
Surface features in this are referred as Dolleens/sink holes
-linked to subterranean cave systems
-water trying to traverse a karst terrain is usually directed underground, sub surface.
bedrock:
regolith:
soil:
colluvium :
bedrock: unweathered rock
regolith: surface layer of rock particles
soil: surface layer containing living organisms and capable of supporting plants
colluvium : transported regolith and soil on hillslopes
WHENEVER THE MAGNITUDE OF THE ______ STRESS IS HIGHER THEN THAT OF THE ______ STRESS MATERIALS WILL LIKELY MOVE DOWN SLOPE
SHEAR
normal
Mass Movement
defined as the spontaneous, gravity-driven, downslope movement of materials on hillslopes
as the slope angle increases, the force of gravity exerts a greater downslope force
shear stress > normal stress
movement may occur when internal cohesion and frictional resistance, collectively referred to as shear strength, are overcome by shear stress
movement may occur when internal ______ and ______ resistance, collectively referred to as shear strength, are overcome by shear stress
cohesion
frictional
shear strength = _______ and _______
internal cohesion and fricrtional resistance
Factor of Safety=
shear strength/shear stress
F < 1; slope is unstable and mass movement may occur
F > 1; slope is stable
When is a slope stable in terms of Factor of safety?
F < 1; slope is unstable and mass movement may occur
F > 1; slope is stable
Slope stability is affected by:4
slope angle
nature of surficial materials
nature and extent of vegetation cover
pore water pressure
Topographic Relief
Slope Angle
Topographic relief
refers to the height of a hill or mountain above the land below
landslides occur more frequently in areas of high relief
Slope angle
the steeper the slope, the greater the driving force
steep slopes are associated with falls and topples
moderate slopes are associated with slides and flows
gentle slopes are associated with creep
steep slopes are associated with ____ and _____
moderate slopes are associated with _____ and _____
gentle slopes are associated with ____
steep slopes are associated with falls and topples
moderate slopes are associated with slides and flows
gentle slopes are associated with creep
Role of Material type determines:
planes of weakness
bedding planes in sedimentary rocks, foliation planes in metamorphic rocks, joints in igneous rocks, or zones along which Earth has moved before
degree of consolidation
creep, slumps and flows are common in unconsolidated materials
shape of slip surface
rotational slides or slumps are curved
translational slides are planar
_______ shape/slip surface is common in SK and can be described as
Rotational: rotates out of the face as it moves down slope
-common here on prairie rivers
Was is the Schmidt Hammer Test Used for?
SCHMIDT HAMMER TEST IS HOW WE MEASURE: ROCK MASS STRENGTH
Rock Mass Strength: Levels
Very Strong: Strong: Moderately strong: weak: very weak:
very strong: quartzite, gabbro, basalt
-Canadian sheield
strong: marble, granite, gneiss
- matamorphic
moderately strong: sandstone, shale, slate
-sedimentaary
weak: coal, siltstone, schist
very weak: chalk, rock salt
-evaporite rocks
Role of Climate in rock stability:
compare arid regions and humid regions
influences the amount and timing of precipitation that infiltrates rock and soil or flows across the surface as overland flow
water saturates soil, lubricating planes of weakness and increasing pore water pressures
water erodes bases of slopes which decreases stability
arid regions are prone to rock falls, debris flows, and soil creep
humid and sub-humid regions are prone to creep, slides, slumps, and debris flows
Positive Pore Water Pressure
In periods of the year where there is an abundance of water it can move through the rock system to create POSITIVE PORE WATER PRESSURE
-makes rocks more susceptible on slopes
cohesion _______ with vegetation
increases
Factor of safety:
.If _________ is greater than the ______: Nothing should happen
- as you approach a balance then it gets sketchy
- if it is reversed with shear _______ being larger than shear _______ then something should happen
.If numerator is greater than the denominator: Nothing should happen
- as you approach a balance then it gets sketchy
- if it is reversed with shear stress being larger than shear strength then something should happen
Two Pieces of information for each mass movement proceess
Two pieces of information for each process: Nature of movement and type of material
