SLOPE. What does slope measure? Slope measures the steepness of a line.
Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G...
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Transcript of Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G...
![Page 1: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/1.jpg)
Mass Wasting and HillslopesMass Wasting and Hillslopes
Steep slopeGd > F
Gentle slopeGd< F
Gp
Gp
Gp
ModerateslopeGd= F
Boulderon vergeof moving
Boulder isstable
BouldermovesdownslopeF
F
F
Gd
Gd
Gd
W
W
W
• Gravity overcomes Friction
W = mgF0 = Gd
![Page 2: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/2.jpg)
Sliding Threshold when Sliding Threshold when gravity componentgravity component = = friction componentfriction component, both parallel to slope, both parallel to slope
• Shear Forces are parallel to 2 touching surfaces.• If the slab is about to move, then the
downhill force = resisting force pointing uphill
Downhill force = mass x gravity x sine of dip
FF00 = mg sin (dip) = mg sin (dip) (1)(1) is the same as the dip
F0 = mg sin(α)
αmg
h
dip
![Page 3: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/3.jpg)
Your book uses mg = weight "w"Your book uses mg = weight "w"
Downhill force = mass x gravity x sine of dip
FF00 = w sin (dip) = w sin (dip) (1)(1) is the same as the dip
Shear ForceShear Force = F0 = w sin(α)
αw
h
dip
Aside: Bloom confuses shear force with shear stress.Stress = Force / unit areaStress units are, e.g. Newtons/m2
or pounds force/ inch2 aka psi
That said, we will skip the issue by staying with Forces
![Page 4: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/4.jpg)
Role of water for slabs Role of water for slabs
• Friction ForceFriction Force is proportional to Normal ForceNormal Force• It is the amount of Force needed to lift the
surfaces apart• Increased water pressure between the surfaces
lifts the upper slab, and it will slip at a lower dip angle.
• Proportionality constant c
αmg
h
dip
N
![Page 5: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/5.jpg)
Friction Coefficient c?Friction Coefficient c?
• Ff uphill = N x constant “c”
• Notice N = mg cos
When it slips, F0 = Ff = N x constant
Then
• F0 = mg sine mg cos x c
• so c = sine cos
![Page 6: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/6.jpg)
ExampleExample
• Suppose the rock slips at = 30o
• sine 30o = 0.5
• Cosine 30o = 0.866
• c = Sine 30o /cosine 30o
• c = 0.5/0.866 = 0.577
αmg
h
dip
N
![Page 7: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/7.jpg)
Water's role for slabs: Water's role for slabs:
Before FallBefore Fall
![Page 8: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/8.jpg)
Water's role for slabs: Water's role for slabs:
After FallAfter Fall
Of course, in ourarea, winter freezingcauses frost wedging,breaks loose any remaining bonds
![Page 9: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/9.jpg)
Classification of slope movementsClassification of slope movements
Slides
FallsSlumps
Flows
(note rotation)
![Page 10: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/10.jpg)
Slow mass movement indicatorsSlow mass movement indicators
Example: Soil Slump
![Page 11: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/11.jpg)
Scarp
Scarp
Scarp
CD
CD
Lobe
LobeDF
Soil CreepSoil Creep
![Page 12: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/12.jpg)
Signs of Soil CreepSigns of Soil Creep
Vertical featuresexposed in new roadcut
Vertical features (if available) curved near surfaceVertical features (if available) curved near surface
![Page 13: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/13.jpg)
Creep Typical FeaturesCreep Typical Features
““Drunken forest”Drunken forest”
![Page 14: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/14.jpg)
SolifluctionSolifluction
Soil saturated with water, soggy mass flows downhill
When soil moisture cannot flow deeper, trapped in soil
![Page 15: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/15.jpg)
Gelifluction: Freezing lifts particles, Gelifluction: Freezing lifts particles, thaw drops them further downhillthaw drops them further downhill
![Page 16: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/16.jpg)
Gelifluction: ThawGelifluction: Thaw
![Page 17: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/17.jpg)
Rapid Mass MovementRapid Mass Movement
• Flows: mixture moves downslope as a Flows: mixture moves downslope as a viscous fluidviscous fluid
• Slumps: move downslope along a concave Slumps: move downslope along a concave slip surfaceslip surface
• Slides: move downslope along preexisting Slides: move downslope along preexisting plane of weakness as a single, intact mass plane of weakness as a single, intact mass
• Falls: rock drops from steep slopeFalls: rock drops from steep slope
http://geology.com/news/2008/spectacular-yosemite-rockfall-and-debris-avalanche-photos.shtml
![Page 18: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/18.jpg)
Rapid Mass MovementRapid Mass Movement
![Page 19: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/19.jpg)
FlowsFlows
• Flows with a high water content are less viscous, faster and more dangerous– Debris avalanches- rain- regolith detaches 200
kilometers per hour– Lahars– Liquefaction- Quick Sand due earthquake -
increased pore water pressure - grains separate - liquefies instantaneously
– Mudflow swift slurry- heavy rains – Earthflows dry masses of clayey regolith
• 1-2 meters per hour
Mixture moves downslope as a viscous fluidMixture moves downslope as a viscous fluid
![Page 20: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/20.jpg)
Yungay AvalancheSource: Lloyd S. Cluff
Debris Avalanche
Town in PeruEarthquake dislodgedSlab ice => landslide25000 killed
May 31, 1970 Ancash Earthquake
![Page 21: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/21.jpg)
![Page 22: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/22.jpg)
LaharLahar
http://www.massey.ac.nz/~trauma/http://www.massey.ac.nz/~trauma/issues/2004-1/galley.htmissues/2004-1/galley.htm
![Page 23: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/23.jpg)
Liquefaction - Quick Clay or SandLiquefaction - Quick Clay or Sand
Asphalt Parking Lot
Caused by EarthquakesCaused by EarthquakesSediment not compacted is like “pick-up-sticksSediment not compacted is like “pick-up-sticksSeismic waves increase fluid pressure, force grains Seismic waves increase fluid pressure, force grains apart, structures above resting on water, they sink in. apart, structures above resting on water, they sink in.
![Page 24: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/24.jpg)
Mudflow in Sarno, Italy, 1998Mudflow in Sarno, Italy, 1998
![Page 25: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/25.jpg)
Slumgullion Slumgullion EarthflowEarthflow
• San Juan Mtns, CO
• Volcanics• Dams
Lake Fork of the Gunnison
Earthflows dry masses of clayey regolith1-2 meters per hour
![Page 26: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/26.jpg)
SlidesSlides
• Slumps: special case, weakness is curved
• Mudslides
• Rock Slides
• Avalanche and Debris Slides
www.pdc.org/.../2007/Rio-de-Janeiro/rio.htm
Slides: move downslope along preexisting plane of weakness as a single, intact mass Slides: move downslope along preexisting plane of weakness as a single, intact mass
![Page 27: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/27.jpg)
Slumping Slumping with visible with visible Scarps in Scarps in Dorset, Dorset, EnglandEngland
These are These are rotationalrotational
SlumpSlump
![Page 28: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/28.jpg)
Little Hat Mountain Slump, CALittle Hat Mountain Slump, CA
scarpscarp
Toe, Toe, no veg.no veg.
![Page 29: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/29.jpg)
La Conchita La Conchita SlumpSlump
• Typical urban landslide, after heavy rains– Preexisting slide
masses– Development to the
edge of existing– Lawsuits– 9 houses destroyed– Property values down
![Page 30: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/30.jpg)
slump scar
Snow Avalanche
![Page 31: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/31.jpg)
Turtle Mountain Debris SlideTurtle Mountain Debris Slide
![Page 32: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/32.jpg)
http://blogs.agu.org/mountainbeltway/2012/08/17/turtle-mountain-and-the-infamous-frank-slide/
East limb limestones at steep angle
Locals mining coal seamunder thrust fault
April 1903
![Page 33: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/33.jpg)
Frost heave, Yosemite NP.Frost heave, Yosemite NP.Glacier Point climbing area.Glacier Point climbing area.1996 Rockfall1996 Rockfall162,000-ton granite slab.162,000-ton granite slab.160 mph speed.160 mph speed.Killed several people.Killed several people.
Falls: Falls: RockfallRockfall
![Page 34: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/34.jpg)
Angle of ReposeAngle of Repose• For loose materials, the angle of repose
dictates the maximum steepness a material can be arranged before it will move downslope
• Bloom claims: p 189 lower right to 190 “The angle of the talus is a function of fragment size and angularity ….”
http://www.quanterra.org/guide/guide1_5.htm
Rockfall Talus Slope
![Page 35: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/35.jpg)
An ExampleAn Example
• These talus cones illustrate the characteristic steep slopes. Talus, due to its large grain size, has a steep angle of repose.
Talus cones from Glacier National Park in Canada.
http://capone.mtsu.edu/cdharris/GEOL100/erosion/talus-creep.htm
![Page 36: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/36.jpg)
Angle of Repose depends on particle size and shape?Angle of Repose depends on particle size and shape?
Is this right? Should we believe this? Do an experiment.What is your null hypothesis?
![Page 37: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/37.jpg)
Slope StabilitySlope Stability
• Slope characteristics such as composition, vegetation, and water content also influence slope stability.
• Haiti is plagued by slides after many trees were cut down.
![Page 38: Mass Wasting and Hillslopes Steep slope G d > F Gentle slope G d < F GpGp GpGp GpGp Moderate slope G d = F Boulder on verge of moving Boulder is stable.](https://reader030.fdocuments.in/reader030/viewer/2022032517/56649c895503460f94941d63/html5/thumbnails/38.jpg)
Natural TriggersNatural Triggers
• Natural triggers such as:Natural triggers such as:
– torrential rainstorms 1967 central Braziltorrential rainstorms 1967 central Brazil– Earthquakes 1812 New Madrid, MissouriEarthquakes 1812 New Madrid, Missouri– volcanic eruptions 1980 Mount St. Helensvolcanic eruptions 1980 Mount St. Helens
produce damaging mass movementsproduce damaging mass movements
http://www.terradaily.com/reports/At_least_26_dead_in_China_mudslide_999.html
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Human TriggersHuman Triggers
• excessive irrigationexcessive irrigation
• clear-cutting of steep slopesclear-cutting of steep slopes
• slope oversteepening or overloadingslope oversteepening or overloading
• mining practices mining practices
can also cause mass movement.can also cause mass movement.