Mass Wasting - csus.edu · Mass wasting is the downslope movement of rock and soil due to gravity ... soil under direct influence of gravity. List factors that will affect how easily

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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.

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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

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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

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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


•• Earthquakes and aftershocks can dislodge large volumes of Earthquakes and aftershocks can dislodge large volumes of

rock and unconsolidated materialrock and unconsolidated material


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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



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Types of Mass WastingTypes of Mass Wasting

Figure 3.3

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�� 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)

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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. .

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Falls(Rock falls)

Slides(Rock slides)

Flows(Debris Flows,

Mud flows)

Slumps


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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

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Falls(Rock falls)

Slides(Rock slides)

Flows(Debris Flows,

Mud flows)

Slumps


15151999 Yosemite 1999 Yosemite

RockfallRockfall

Talus Cone

Curry Village

Exfoliation Cracks

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Falls(Rock falls)

Slides(Rock slides)

Flows(Debris Flows,

Mud flows)

Slumps


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

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Slumping at DevilSlumping at Devil’’s Slides Slide

�� Highway 1 south of SFHighway 1 south of SF

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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

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Falls(Rock falls)

Slides(Rock slides)

Flows(Debris Flows,

Mud flows)

Slumps


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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

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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


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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.

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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

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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

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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


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Monitoring SystemMonitoring System


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Monitoring MovementMonitoring Movement


3232Slide HistorySlide History


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Mass Wasting - csus.edu · Mass wasting is the downslope movement of rock and soil due to gravity ... soil under direct influence of gravity. List factors that will affect how easily