Chapter 6: Mass Wasting
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Transcript of Chapter 6: Mass Wasting
Chapter 6: Mass WastingChapter 6: Mass Wasting
Palos Verdes Hills LandslidePalos Verdes Hills Landslide
Landslide is a general term for rapid downslope movement/failure
Mass Wasting is even more general and includes slow movements (creep, slow flows…)
Subsidence is a vertical failure usually closed depression
A Classification of Mass WastingA Classification of Mass Wasting Nature of materialNature of material
RockRock Unconsolidated material (debris, mud)Unconsolidated material (debris, mud)
VelocityVelocity Nature of movementNature of movement
A Classification of Mass WastingA Classification of Mass Wasting
A Classification of Mass WastingA Classification of Mass WastingRockRock DebrisDebris
FallFall
(rare)(rare)
A Classification of Mass WastingA Classification of Mass WastingRockRock DebrisDebris
AvalancheAvalanche
A Classification of Mass WastingA Classification of Mass WastingRockRock DebrisDebris
SlideSlide
A Classification of Mass WastingA Classification of Mass WastingEarthEarth Debris Debris Mud Mud
Flow Flow
A Classification of Mass WastingA Classification of Mass Wasting
Slump Slump CreepCreep
A Classification of Mass WastingA Classification of Mass Wasting
Solufluction Solufluction
Solufluction Solufluction
Angle of repose:Angle of repose: higher with coarser and more higher with coarser and more angular particlesangular particles
Slope stability:Slope stability: Driving forces:Driving forces:
MassMass GravityGravity
Resisting forces:Resisting forces: InertiaInertia FrictionFriction CohesionCohesion
Slope stability scenario: what are the problems Slope stability scenario: what are the problems here?here?
Consolidated material can slide or slump, Consolidated material can slide or slump,
Unconsolidated can slump or flowUnconsolidated can slump or flow
Role of Role of slopeslope Steeper Steeper less stable (incr DF and decr RF) less stable (incr DF and decr RF)
Role of Role of materialmaterial
Climate controls water and vegetationClimate controls water and vegetation Vegetation absorbs rain impact and roots incr cohesionVegetation absorbs rain impact and roots incr cohesion Vegetation adds weightVegetation adds weight LoggingLogging (clearcut): (clearcut):
Less transpiration Less transpiration more water to soil more water to soil Increased snowpack in clearingsIncreased snowpack in clearings Roots rot and lose cohesionRoots rot and lose cohesion Long vertical run for rill developmentLong vertical run for rill development Logging Logging roadsroads are perhaps worse than the cuts are perhaps worse than the cuts
themselvesthemselves
Role of Role of climateclimate and and vegetationvegetation
Role of Role of waterwater
Adds Adds weightweight (incr DF) (incr DF) Initially increases Initially increases cohesioncohesion, but decreases after , but decreases after
a point (decr RF)a point (decr RF) Often Often saturated zonesaturated zone at surface if above at surface if above
impermeable layer (frozen, clay, rock)impermeable layer (frozen, clay, rock) Promotes Promotes weatheringweathering ErodesErodes gullies and slope bases gullies and slope bases AvalanchesAvalanches are all water are all water
Role of Role of vibrationvibration Earthquakes, traffic, sonic boomsEarthquakes, traffic, sonic booms Can Can immediate immediate loss of cohesionloss of cohesion LiquefactionLiquefaction = shock + water saturation = shock + water saturation
Human Use and LandslidesHuman Use and LandslidesLandslides are a growing problem.Landslides are a growing problem.
1. Incr population in landslide-prone areas1. Incr population in landslide-prone areas
2. Human activity that affects magnitude and 2. Human activity that affects magnitude and frequency of landslidesfrequency of landslides
Vaiont Dam DisasterVaiont Dam Disaster
Vaiont Dam DisasterVaiont Dam Disaster
LoggingLogging
Swanson & Dryness (1975) Cascade studySwanson & Dryness (1975) Cascade study
Found logging and roads increase landslide Found logging and roads increase landslide erosion by several times if performed on erosion by several times if performed on weak unstable slopesweak unstable slopes
Roads interrupt surface drainage (culverts Roads interrupt surface drainage (culverts blocked), alter subsurface movement, blocked), alter subsurface movement, redistribute massredistribute mass
UrbanizationUrbanizationPerson A undercuts slope for garage while person Person A undercuts slope for garage while person
B builds house above. Who is responsible?B builds house above. Who is responsible?
S. CaliforniaS. California Wave-cut terraces oversteepenedWave-cut terraces oversteepened Now lots of building on lower mtn slopes Now lots of building on lower mtn slopes
(most = old landslide deposits!)(most = old landslide deposits!)
DrainageDrainageDivideDivide
Isaquah Delta
Seattle Seattle TopographyTopography
Slope Slope Stability Stability
Slope Slope Stability Stability
Slope Slope Stability Stability
MapsMaps
Minimizing the HazardMinimizing the Hazard Identify potential hazard. Identify potential hazard.
Map unstable areas Map unstable areas
Minimizing the HazardMinimizing the Hazard Identify potential hazard. Identify potential hazard.
Map unstable areasMap unstable areas Land developers and buyers (YOU) look Land developers and buyers (YOU) look
for what??for what??
Minimizing the HazardMinimizing the Hazard If suspect, hire a consulting geologist to evaluateIf suspect, hire a consulting geologist to evaluate
Don’t buildDon’t build Minimize load or sink foundation deep to stable materialMinimize load or sink foundation deep to stable material Drainage controlDrainage control
Divert surface waterDivert surface water Surface drainsSurface drains Soil cement, asphalt, plastic to coverSoil cement, asphalt, plastic to cover
Cut-off trench to divert groundwaterCut-off trench to divert groundwater Drain internal water at base or even pump (Tukwilla)Drain internal water at base or even pump (Tukwilla)
Minimizing the HazardMinimizing the Hazard If suspect, hire a consulting geologist to evaluateIf suspect, hire a consulting geologist to evaluate
Grade slopeGrade slope Cut-and-fill: remove top and fill in at base Cut-and-fill: remove top and fill in at base Must do with care, since this often Must do with care, since this often causescauses problems problems Benching: series of cut-and-fills with diversion drainsBenching: series of cut-and-fills with diversion drains
Slope supportsSlope supports Retaining walls (permeable and/or drained)Retaining walls (permeable and/or drained) Rock boltsRock bolts
Landslide warning systemsLandslide warning systems Periodic inspectionPeriodic inspection Tilt metersTilt meters Well monitoringWell monitoring
Minimizing the HazardMinimizing the Hazard
Landslide correction (very tough…better to prevent)
Snow AvalanchesSnow Avalanches
1. Loose-snow avalanches1. Loose-snow avalanches in fresh cohesionless in fresh cohesionless snowsnow
Snow AvalanchesSnow Avalanches
2. Slab avalanches2. Slab avalanches above above subsurface hoar zonessubsurface hoar zones
SubsidenceSubsidenceSlow to rapid vertical sinking or settling Slow to rapid vertical sinking or settling
1. 1. Withdrawal of fluidWithdrawal of fluid (oil, gas, water)(oil, gas, water)
SubsidenceSubsidence
Slow to rapid vertical sinking or settling Slow to rapid vertical sinking or settling
2. Sinkholes2. Sinkholes Limestone solution, caves and collapse Limestone solution, caves and collapse
(also with salt deposits)(also with salt deposits)
Sink hole- Winter Park, FloridaSink hole- Winter Park, Florida
SubsidenceSubsidence
Slow to rapid vertical sinking or settling Slow to rapid vertical sinking or settling
1. 1. Withdrawal of fluidWithdrawal of fluid (oil, gas, water)(oil, gas, water)
2. Sinkholes2. Sinkholes Limestone solution, caves and collapse Limestone solution, caves and collapse
(also with salt deposits)(also with salt deposits)
3. Mining3. Mining
What is wrong here?What is wrong here?