Hillslopes - moving mass: creep,slides and flows 1. Force balance - driving vs resisting forces 2....
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Transcript of Hillslopes - moving mass: creep,slides and flows 1. Force balance - driving vs resisting forces 2....
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Hillslopes - moving mass: creep,slides and flows
1. Force balance - driving vs resisting forces
2. Soil creep - slope dependent, diffusive processes
3. Mass movements - landslides and rock falls
4. Flows - of debris and mud
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FORCE BALANCE
GRAVITY
SHEAR STRENGTH (FRICTION
AND COHESION or VISCOSITY)
DRIVING VERSUS RESISTING
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http://ees.as.uky.edu/sites/default/files/elearning/module11swf.swf
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Processes that move mass on slopes
first consider infiltration rate
Rainsplash (bare soil only)Rainsplash (bare soil only) Channels (ephemeral, permanent) Channels (ephemeral, permanent) Creep (grab-bag, many processes)Creep (grab-bag, many processes) Mass movement (landsliding = translational, Mass movement (landsliding = translational,
rotational and rockfall)rotational and rockfall) Flowage (debris and mud)Flowage (debris and mud)
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Slope types – connect to process
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Rain splashRainsplash - splatering, downslope component
2
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Where flow is thin, rainsplash disturbance prevents channelization
Incision begins when shear stress exceeds
strength
2
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Critical Distance from drainage divide = channelization2
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Soil Creep - evidence
Marathon Basin, west Texas. J.S. Aber.Marathon Basin, west Texas. J.S. Aber.
3
Which way is soil moving?
Rate is a function of slope Q= ks
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Other biotic effects - vary by climate and location
3
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Mammals (gophers here)3
NET DOWNSLOPE TRANSPORT
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Rotational failure - clay, silt, homogeneous material
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Rotational Failures
Bishop method of slices
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Importance of unique events/thresholds
Discrete vs. continuous processesStorms
DisturbanceLandslides
Debris Flows
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2000
2600
5900680082009400
The Ritterbush Record 50 cm
Cal
end
ar Y
ears
BP
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AMS 14C Analysis
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Storm Frequency
• 4 maxima; currently increasing—observed?
0 2 4 6 8 10 12
Calendar kyr BP
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NorthAtlanticClimate
GISP2 nssK
GISP2 ssNa
Coolings
Storm
Freq.
StormsFloods
0 2 4 6 8 10 12Calendar kyr BP
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Hillslope- channel transition, colluvial hollows
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Bank erosion?