Textbook Notes (368,449)
Canada (161,886)
Geography (106)
GG231 (31)
Rob Milne (27)
Chapter 5

Chapter 5 - Mass Wasting/Landslides

5 Pages
121 Views
Unlock Document

Department
Geography
Course
GG231
Professor
Rob Milne
Semester
Winter

Description
Risks and Disasters – Chapter 5  The Frank Slide o Turtle Mountain (mountain that moves) o April 29, 900m*650m*150m slab crashed into valley o Formed a small lake, buried approx. 2km of Canadian pacific railway and 3km of Frank and Grassy Mountain Railway o Frank was fully evacuated, but people moved back o 1911, people were evacuated, today, has about 300 people o Another large landslide could occur on the south peak of mountain o Contributing Factors  Cause – internal/external factor that reduces stability of slope and brings it to point of failure  Trigger – event that sets off landslide  Geology  Water infiltrates the mountain and over time decreases stability of the slope  Glaciations  Erosion eroded shales on lower slope, steepened overall slope of mountain reducing strength  Mining  Coal mining created large openings in the mountain  Weather  Heavy rain falls and increase in water exerts pressure on rocks o Lessons learned  Large landslides cannot be prevented  Geology is important  Human activity can trigger landslides  Introduction to Landslides o Mass wasting/landslides – down slope movements of rock or sediment due to gravity o Can be slow/fast and involve small/large sediment or rock o Types of landslides  Four variables to classify  Mechanism of movement (flow, slide, fall, topple, complex movement)  Type of material (rock, consolidated sediment, organic soil)  Amount of water  Rate of movement  Fall – bouncing of rock or blocks of sediment from face of a cliff  Slide – down slope movement of coherent block of rock or sediment along discrete failure plan  Slump – type of slide in which failure plane is curved upward  Flow – slow to rapid down slope movement of sediment in which particles move semi- independently of one another, common with aid of water  Debris flows – mixture of mud, debris and water, range in consistency  Creep – very slow rock flow, mm to dozens of cm per year  Sacking – special type of creep involving movement of large rock masses, up to many billions of cubic metres along ill-defined, deep failure planes  Topple – slow creep-like movement in which rock mass pivots about a point  Rock avalanches – high-velocity flows of fragmented rock  Subaqueous landslides – underwater landslides, slump or slide on submerged slope of delta or edge of continental shelf o Forces on slopes  Driving forces – moves rock or sediment down a slope  Largest driving force – weight of slope material and amount of water  Resisting forces – opposes movements 1 Risks and Disasters – Chapter 5  Shear strength – resistance to failure by sliding or flow along potential slip planes o Potential slip planes- surfaces of weakness in slope material  Slope stability evaluated by computing factor of safety (FS)  Ratio of resisting factors to driving forces o If <1 then stable o If =1 then failure can be expected  Role of material type  Material can affect type and frequency o Mineral composition o Degree of cementation or consolidation o Presence of planes of weakness  Planes of weakness can be dangerous if they are inclined more than 15 degrees and intersect/parallel to slope of hill or mountain  Slides have two basic movement patterns o Rotational – curved slip surfaces  Produces small topographic benches that tilt upslope o Translational – planar slip surfaces  Common type is debris avalanche  Failure plane generally at base or in colluviums o Mixture of weathered rock and other debris below soil  Role of slope and topography  Influenced by slope steepness and topographic relief o Steeper – greater the driving forces  Topographic relief – height of hill or mountain above the land below  Role of climate  Weather characteristics of a region over years or decades  Influences amount and timing of water that erodes hill slopes and the type/abundance of hillside vegetation  Arid and semi arid climates o Sparse vegetation, thin soil, exposed bare rock o Mass movements include rock falls, debris flows and shallow soil slips  Subhumid and humid climates o Abundant vegetation, thick soil cover slopes o Deep complex landslides, soil creep, rockslides, slumps and debris flows  Role of vegetation  Provides protective cover reducing impact from rain  Plant roods add strength and cohesion  Adds weight to slope, increasing slope failure  Role of water  Soil slips and debris flows happen during rainstorms  Slumps develop months following deep water infiltration  Erosion of slope toe reduces mass of resisting material, increasing slope failure  Contributes to liquefaction, causing granular sediments to lose strength and flow as liquid  Thaw flow slides – occur during warm spells in summer when seasonal melted layer is thickest  Role of time  Forces acting on slope change with time  Weathering of rocks reduces cohesion and strength 2 Risks and Disasters – Chapter 5  Soil water acidic because it reacts with carbon dioxide, creating carbonic acid  Geographic regions at risk from landslides o Landslides occur wherever there are significant slopes o Mountainous areas have higher risk for landslides o
More Less

Related notes for GG231

Log In


OR

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


OR

By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.


Submit