1
11
Mass WastingMass Wasting
Presentation Modified from Instructor Resource Center on CD-ROM, Foundations of Earth Science, 4th Edition, Lutgens & Tarbuck
22Mass WastingMass Wasting
�� DownDown--slope movement of rock, loose material & soil slope movement of rock, loose material & soil
under direct influence of gravity.under direct influence of gravity.
33
EarthEarth’’s External Processess External Processes
�� Weathering, mass wasting, and erosion are all Weathering, mass wasting, and erosion are all
called external processes because they occur at called external processes because they occur at
or near Earthor near Earth’’s surfaces surface
�� Internal processes, such as mountain building Internal processes, such as mountain building
and volcanic activity, derive their energy from and volcanic activity, derive their energy from
EarthEarth’’s interiors interior
2
44
Mass Wasting: The Mass Wasting: The
Work of GravityWork of Gravity
�� Mass wastingMass wasting is the downslope movement of is the downslope movement of
rock and soil due to gravityrock and soil due to gravity
�� Controls and triggers of mass wastingControls and triggers of mass wasting
�� WaterWater——Reduces the internal resistance of materials Reduces the internal resistance of materials
and adds weight to a slopeand adds weight to a slope
�� Oversteepening of slopesOversteepening of slopes
55List factors that will affect how easily List factors that will affect how easily
mass wasting occurs.mass wasting occurs.
�� Steepness of slopeSteepness of slope
�� WaterWater
�� Adds weightAdds weight
�� ““lubricateslubricates”” failure surfacesfailure surfaces
�� VegetationVegetation
�� Roots hold soilRoots hold soil
�� Absorb waterAbsorb water
�� TriggersTriggers
�� EarthquakesEarthquakes
�� ThunderThunder
66
Mass Wasting: The Mass Wasting: The
Work of GravityWork of Gravity
�� Controls and triggers of mass wastingControls and triggers of mass wasting
�� Removal of vegetationRemoval of vegetation
•• Root systems bind soil and regolith togetherRoot systems bind soil and regolith together
�� EarthquakesEarthquakes
•• Earthquakes and aftershocks can dislodge large volumes of Earthquakes and aftershocks can dislodge large volumes of
rock and unconsolidated materialrock and unconsolidated material
�� ThunderThunder
3
77Mass WastingMass Wasting
�� DownDown--slope movement of rock, loose material & slope movement of rock, loose material &
soil under direct influence of gravity.soil under direct influence of gravity.
88List factors that will affect how easily List factors that will affect how easily
mass wasting occurs.mass wasting occurs.�� Steepness of slopeSteepness of slope
�� WaterWater
�� Adds weightAdds weight
�� ““lubricateslubricates”” failure surfacesfailure surfaces
�� VegetationVegetation
�� Roots hold soilRoots hold soil
�� Absorb waterAbsorb water
�� TriggersTriggers
�� EarthquakesEarthquakes
�� ThunderThunder
99
Types of Mass WastingTypes of Mass Wasting
Figure 3.3
4
1010
Mass WastingMass Wasting
�� Classified asClassified as……
Amount of WaterAmount of Water
Falls(Rock falls)
Slides(Rock slides)
Flows(Debris Flows,
Mud flows)
Slumps
Creep(Slow down-slope movement of soil or regolith)
1111
Steepness of Slope Steepness of Slope –– The Angle of ReposeThe Angle of Repose
Angle of ReposeAngle of Repose
Angle of Repose: The steepest angle at which Angle of Repose: The steepest angle at which
loose material remains stationary without loose material remains stationary without
sliding sliding downslopedownslope. .
1212
Mass WastingMass Wasting
�� Classified asClassified as……
Amount of WaterAmount of Water
Falls(Rock falls)
Slides(Rock slides)
Flows(Debris Flows,
Mud flows)
Slumps
Creep(Slow down-slope movement of soil or regolith)
5
1313
CreepCreep�� Slow, downSlow, down--slope slope
movement of soil or movement of soil or
sediment.sediment.
�� Responsible for building Responsible for building
and road damage.and road damage.
http://www.structures.ucsd.edu/Taiwaneq/geotechnical.html
1414
Mass WastingMass Wasting
�� Classified asClassified as……
Amount of WaterAmount of Water
Falls(Rock falls)
Slides(Rock slides)
Flows(Debris Flows,
Mud flows)
Slumps
Creep(Slow down-slope movement of soil or regolith)
15151999 Yosemite 1999 Yosemite
RockfallRockfall
Talus Cone
Curry Village
Exfoliation Cracks
6
1616
Mass WastingMass Wasting
�� Classified asClassified as……
Amount of WaterAmount of Water
Falls(Rock falls)
Slides(Rock slides)
Flows(Debris Flows,
Mud flows)
Slumps
Creep(Slow down-slope movement of soil or regolith)
1717SlumpsSlumps
�� Sliding ofSliding of
�� Unconsolidated materialUnconsolidated material
�� As an intact unitAs an intact unit
�� Curved failure surface(s)Curved failure surface(s)
�� Often after Often after
rainfallrainfall
Figure 3.3
1818
Slumping at DevilSlumping at Devil’’s Slides Slide
�� Highway 1 south of SFHighway 1 south of SF
7
1919
DevilDevil’’s Slides Slide
2020What are some of the factors that cause What are some of the factors that cause
DevilDevil’’s Slide to slide?s Slide to slide?
Cross Section
JeepJeep
TrailTrail
SpringSpring
(water seep)(water seep)
Hard SandstoneHard Sandstone
Shale,Shale,
Siltstone &Siltstone &
SandstoneSandstone
2121
Mass WastingMass Wasting
�� Classified asClassified as……
Amount of WaterAmount of Water
Falls(Rock falls)
Slides(Rock slides)
Flows(Debris Flows,
Mud flows)
Slumps
Creep(Slow down-slope movement of soil or regolith)
8
2222SlidesSlides
�� Rapid downRapid down--slope movementslope movement
�� Sediment, soil & Sediment, soil & regolithregolith break loosebreak loose
�� Mountainous areasMountainous areas
�� Rapid and destructiveRapid and destructive
�� Often after Often after
rainfallrainfall
Figure 3.3
23231997 Highway 50 Landslide1997 Highway 50 Landslide
�� ““Mill Creek SlideMill Creek Slide””
�� January 24, 1997January 24, 1997
�� Closed Hwy 50Closed Hwy 50
�� Destroyed 3 cabinsDestroyed 3 cabins
�� Dammed South Dammed South Fork of American Fork of American River for 5 hoursRiver for 5 hours
�� Many cabins Many cabins destroyed in destroyed in flooding after Am. flooding after Am. River breeched damRiver breeched dam
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
2424
Mill Creek LandslideMill Creek Landslide
�� Hwy 50 closed Hwy 50 closed
4 weeks4 weeks
�� 35,000 truck 35,000 truck
loads of earth loads of earth
materialmaterial
�� $4.5 million$4.5 million
�� + >$1M/day + >$1M/day
relatedrelated
costscosts
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
9
2525
CrossCross--Sectional ViewSectional View
Joints Joints
GraniteGranite
(actually (actually granodioritegranodiorite))
GabbroGabbro(actually (actually pyroxenitepyroxenite))
Burned Burned
vegitationvegitation
From R.H. Syndor, Calif. Geology, May/June 1997
2626ObservationsObservations�� Parent rock has composition Parent rock has composition
similar to similar to gabbrogabbro
�� PyroxenitePyroxenite
�� A forest fire burned this area A forest fire burned this area
in 1992.in 1992.
�� There are distinct sets of There are distinct sets of
joints in the rock.joints in the rock.
�� Early snow fell in Dec. 1996.Early snow fell in Dec. 1996.
�� Unusual tropical rains fell Unusual tropical rains fell
after the snow.after the snow.�� Jan. 1997 received a record 19 inches of rain.Jan. 1997 received a record 19 inches of rain.
Explain how each of these observations contributed to the Mill Creek landslide.
2727
Upper section Upper section ““SlideSlide””
Lower section Lower section ““FlowFlow””SlideSlide
FlowFlow
Open cracksOpen cracks
observed in 1996observed in 1996
Moved 50 feetMoved 50 feet
upup--slopeslope
10
2828Hwy 50 Now Completely Mapped for Hwy 50 Now Completely Mapped for
Landslide HazardsLandslide Hazards
Mill Creek Mill Creek
LandslideLandslide
Cleveland Corral Cleveland Corral
LandslideLandslide
From T.E. Spitter and D.L. Wagner, Calif. Geol., May/June 1998
2929
Cleveland Corral SlideCleveland Corral Slide
�� Near Mill Creek SlideNear Mill Creek Slide
�� Actively Monitored by USGSActively Monitored by USGS
�� Potential for Potential for
blockingblocking
Hwy 50Hwy 50
�� Potential forPotential for
damming damming
American American
RiverRiver
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
3030
Monitoring SystemMonitoring System
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
11
3131
Monitoring MovementMonitoring Movement
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
3232Slide HistorySlide History
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html